To Mars or Bust - Water on the Red Planet
POST EDIT (March 26, 2018): I've been asked to add a glossary to this, and to lighten up on place names, and some technical jargon to make this post more readable. So I'll be adding a glossary and going through and removing extra information and putting that extra information as end notes for those interested. This will take some time to do because of my busy schedule, but I'll be doing it slowly over time. So if you see an incomplete glossary, or end notes, know that I'm working on them! Thank you! - Rook
This post is part of my ongoing "To Mars or Bust" (TMorB) series. Today we'll look at the widespread belief that Mars was once a warm, wet planet. It may have been. It may not have been. We don't yet know. Yet statements on academic, professional, and governmental websites, as well as those made by popular scientists, seem to be in consensus that Mars had substantial volumes of liquid water and was somehow a “lush, green world” (according to Michio Kaku). However, contrary to popular belief, there is no consensus. There is no definitive evidence to support the claim that Mars was once warm, and host to large bodies of liquid water. This isn’t to say the planet has no water. Clearly it does, and it isn’t surprising given the fact water is the second most abundant molecule in the solar system. But the quantum leap to thinking Mars was once like Earth is, at this point, folly.
It's not the nature of science to conduct research with a preconceived conclusion. This applies to planetary science just as it does for any other field. To approach research of a planet's present environment with a preconceived idea of what its past environment was like is folly. This may come as a shock to some readers, but we don't yet know the climate and chemistry of our own planet's primordial atmosphere, much less that of Mars.
It's important that I start all of these TMorB posts with the same points I've held since day one: I am not a Mars "hater". I've been called that goofy term a few times over the years in jest, but skepticism in light of perplexing evidence is not tantamount to claiming something is wrong. Good skepticism, like the very nature of science itself is tentative; swayed by the consensus of strong evidence. Contrary to what seems to be popular belief, there is no consensus that Mars ever had an ocean or a warm climate.
I find Mars to be fascinating. I'd love very much to see Mars explored one day by humans, not just robots. Of course, unlike some popular names out there who are gung ho on getting humans to Mars ASAP, I prefer we take the time to research and develop the necessary equipment/technology to protect any pioneers we send to the Red Planet. Few things could undermine progress towards, and on Mars faster than a rushed mission that ends in fatalities.
That aside, I find Mars’ current popularity to be exciting and see it as a key driver behind funding for research, and perhaps even for human missions to Mars one day. This popularity, it seems, started to really gain momentum in the mid-1990s, when dubious claims were made about a Martian meteorite showing direct evidence of life from Mars.
Microfossils and bacteria were supposedly seen under an electron microscope, and despite widespread skepticism from academia, a paper was published for peer-review. It didn’t take long to disprove the findings, and that paper stands as a prime example of the flawed science of seeing-what-one-wants-to-see.
Though it was proven the meteorite showed zero signs of Martian lifeforms, the popularity of earlier claims that it did had spread. In fact, it was such big news that the POTUS, Bill Clinton gave big a speech about life on Mars that inspired millions. That speech (and news of that poorly-researched paper), sparked a level of public interest no planet beyond Earth had ever experienced before. Pluto should probably hire Mars' PR person.
At any rate, my points of critique aren't with Mars; they're with the attitudes towards Mars that directly or indirectly affect, or could affect, science, and human safety. Attitudes that seem to follow the same slippery slope way of thinking as that 1996 paper.
This post will focus on the apparent see-what-one-wants-to-see approach towards science when it comes to Mars, and the more obvious public conveyance that we know or are pretty sure we know what kind of environment Mars had billions of years ago.
In the spirit of altruism, I'll write this blog post in two parts. Part 1 will focus entirely on the major evidence and hypotheses for there having been substantial volumes of liquid water on Mars' surface. Part 2 will focus on the major conflicting evidence. I will add a glossary at the end of this post for those interested in place names, and meanings of certain key terms. I've been told having a glossary will help keep my posts from getting too wordy.
OUTFLOW CHANNELS - KASEI VALLES
In Mars' northern hemisphere exists a vast network of canyons that many scientists believe were carved by liquid water in Mars' deep past. Kasei Valles is one of the planet's largest outflow channels, with such notable features as deep-cut canyons, what some scientists believe are massive river cataracts, presumed streamlined river island features, and craters with what might be fluvial erosional features.
Many scientists believe volcanism, tectonics, collapse, and subsidence in the once volcanically-active Tharsis region to the south, led to several massive groundwater releases (1). It's believed by some scientists that volcanic heating from deep below ground melted frozen ground water, leading to terrain collapse and subsequent catastrophic floods. These massive flooding events are believed to have occurred about 3.4 to 3.6 billion years ago (Gya).
Volumetrically-significant amounts of released groundwater roared northward, then cut eastward and out onto a vast volcanic plain which some scientists believe formed a large lake, or contributed to a growing ocean (2).
Below are a series of images of the Kasei Valles region showing some of the major erosional features that are believed by some to be fluvial in nature. The first image shows the general paths taken by inferred released groundwater:
In addition to these features, some scientists claim there are three sets of enormous cataracts (large erosional scallops) in the area between an "island" feature in the southern channel (3) and Sharonov crater.
These cataracts appear to have be the result of one or more mega-flooding events. They have headwalls up to 400 m high (not shown) rivaled only by features found in the channeled scablands of Washington here on Earth. The channeled scablands of Washington being evidence of what may have been the biggest flooding event in Earth's history.
As for Mars' interpreted outflow channels wherein these possible cataracts are found, the Jet Propulsion Lab's (JPL's) website says they were "...carved by giant floods of water" (JPL/CalTech). Some of these photos look convincing, but the evidence isn't conclusive to say so succinctly that they were carved by giant floods. JPL should use verbiage such as, "may have", or "possibly", or "we think this", "this is strong evidence for", etc.
South of the Outflow Channels - VALLES MARINERIS
I include Valles Marineris because it is contains one of the most recognizeable features on Mars: Huge rifts in the crust.
To be clear, these rifts are not likely associated with any plate tectonics as is the case with major rifts on Earth, but by the apparent sinking of the massive Tharsis region into what must logically be a plastic-behaving mantle. As the region sinks, it causes stress fractures in the crust, and that's what we likely see in the rifts of Valles Marineris.
Toward the eastern end of the rifts appear to be outflow channels that appear to flow out onto the volcanic plain just as the interpreted outflow channels discussed above appear to do. The following color-enhanced image provides visual reference:
Just as is believed to be the case with Kasei Valles, volcanic heating beneath the Valles Marineris region (4) is believed to have caused frozen groundwater to melt en masse, leading to floods across the surface towards the low-lying volcanic plains of Chryse Planitia.
Here is another color-enhanced image from higher up to provide a wider perspective of the regions we've discussed so far:
Clay Knobs & Hydrated Silica Materials of ACIDALIA PLANITIA
Beyond Chryse Planitia, to the north, is Acidalia Planitia. It's where fictional astronaut/botonist, Mark Watney decided it was a good idea to dump buckets of dry, cytotoxic Martian "soil" in his HEPA-filter-free living quarters in order to grow a bunch of potatoes rooted in pathogen-laden human feces (euphemistically called "night soil" back in the so-called Medieval 'Dark Ages').
The crust that once covered Acidalia Planitia has eroded into localized knobs of iron/magnesium-rich phyllosilicates surrounded by hydrated silica materials.
Though I assume clay minerals are what are the focus, not necessarily phillosilicates as a whole, because phillosilicates are sheets that include mica, clays, chlorites, and serpentines. Mica forms from a subsurface melt, chlorites & serpentines are metamorphic products, but clays are weathering products formed at the surface, and at least on Earth, do so in the presence of water.
Given our understanding that clays form in water-rich environments, many scientists believe these clay-rich knobs are indicative of water having been a major feature of this region billions of years ago. Though not all scientists believe this can be interpreted as there having been a large body of standing water here.
Some believe that the fact these knobs are localized, and not widespread, indicates the region had smaller hot springs and steam vents, rather than a large standing body of surface water.
Massive Reservoir of Frozen Groundwater Detected below UTOPIA PLANITIA
Utopia Planitia is at the same latitude as Acidalia Planitia, and according to Ivanov et al. (2015), shows congruent ages in stratified geologic layers. In other words, this plain is the same age as the plain discussed above. In fact, if we look at a global image of Mars, we can see clearly that all the plains (denoted by the word "Planitia") are connected. Like oceans on Earth, these plains are technically all part of the same massive northern hemispheric basin hypothesized to have been created by a massive impact billions of years ago during the Late Heavy Bombardment.
Though not an official term (yet), the entire basin is sometimes referred to as the greater Vastitas Borealis Formation (VBP). It is believe that a large portion of this greater region was once submerged by a large ocean billions of years ago. So by discussing each plain (Planitia), we are technically discussing different parts of what is believed to be the same ocean floor. To be clear, this 'ocean floor' is hypothesized, not fact. At least, not yet.
Scientists at NASA have indirectly detected a ice reservoir beneath Utopia Planitia. This ice reservoir is believed to contain a volume of ice, that if melted, would be volumetrically equal to that of Michigan's Lake Superior. Some believe this could mean the plains are an ancient seafloor, and the water frozen beneath it is the frozen remnant of that ancient sea.
Evidence of Possible Tsunami - VASTITAS BOREALIS FORMATION
To add to the ocean hypothesis intrigue, some scientists claim to see evidence of there having been an ancient meteor-induced tsunami with an estimated wave height of around 75 meters or more, and having travelled about 150 kilometers. These numbers having been derived from numerical models.
This tsunami event, if proven true, would have happened sometime during either the late Hesperian or early Amazonian periods (Costard et al., 2017). (Though saying either late Hesperian or early Amazonian doesn't really narrow things down much, as there is still ongoing debate as to what delineates these two geologic periods... which varies by as much as a billion-and-a-half years.)
Obviously a tsunami means there was a substantial ocean. Costard et al. (2017) have pointed the finger at a large crater (5) as being the culprit inducing the hypothesized tsunami.
Below is an artist's rendition of Mars' northern hemisphere nearly entirely covered by an ocean. This image is displayed on NASA's website:
Possibly More Evidence of Massive Floods - NORTHWESTERN SLOPE VALLEYS
The Northwestern Slope Valley system (NSV) is ten times larger than the interpreted outflow channels of Kasei Valles described above.
It contains what is believed to be the largest system of flood channels in the solar system. As is the case with above-described outflow channels, this region's flood waters are hypothesized to have surface from melted ground water ice reservoirs due to volcanic heating deep below the surface of the Tharsis region.
Scientists have determined there must have been several subsurface magmatic heating-induced catastrophic flooding events. Water and volatiles stored as frozen ground ice beneath the surface were geothermally heated and released at the surface.
If proven true, this not only would have likely contributed to immense volumes of surface water, but quite possibly also to the greenhouse gas content of the Martian atmosphere due to carbon dioxide outgassing.
Though, as we'll discuss in Part 2, Martian melts are largely (if not entirely) basaltic, and basaltic melts have the lowest water and gas content of all melts. We'll get back to this later.
It has been inferred that the region may have experienced flooding events whose discharge rates (volumentric flow rates) were up to 50,000 times that of Earth's Amazon River (James M. Dohm formerly of the University of Arizona, Department of Hydrology and Water Resources).
Such flow rates, if sustained, could have filled the basin with 93-million-cubic-kilometers of water within a 2-month period (J.M. Dohm). Multiple floods of such magnitude could have easily filled the northern basin. And this is exactly what has been posited by some scientists to have happened.
Some scientists believe a "smaller" release of 14-million-cubic-kilometer of water happened in a mere 8 days. Numbers vary from paper to paper, but all are substantial.
Flooding events like these would have given the mythical flood depicted in the Epic of Gilgamesh a run for its money!
Possible Pack Ice Structures - ELYSIUM PLANITIA
So far we've discussed geomorphological features on Mars' surface suggestive of there having been copious amounts of liquid water in the deep past. But other than water ice locked up in the planet's polar caps, there doesn't seem to be any large frozen surface reservoirs anywhere else. Hydrogen atoms have been remotely observed by NASA's Odyssey spacecraft (in 2002) elsewhere, and this suggests the possibility of water ice just beneath the surface, but despite some over-zealous headlines at the time of discovery, this evidence remains inconclusive. Such a signal could come from minerals exposed to water in the past, and not from subsurface water ice.
But all is not lost. Enter Elysium Planitia. This region is located just 5 degrees north of Mars' equator. Let's keep this in mind as we continue forward with this post. In one region of this plain are craters that are too shallow given their diameters. Some scientists believe this is suggestive of ice having partially filled them in. Furthermore, these craters are found in an unusually flat area about 800 km by 900 km across, as if it were leveled by ice just beneath the surface. Or so is the claim, though I may have interpreted the claim wrong, as ice doesn't necessary level things. In permafrost on Earth, ice forms topographical features such as pingos, and solifluction lobes as examples.
If ice were exposed at the surface of Mars, particularly at just 5 degrees north of the planet's equator, then it would certainly sublimate away. However, this ice is protected by a layer of volcanic ash, effectively preventing it from sublimating.
The depth of the ice has been inferred to be about 45 meters. This is based off observations of the above-mentioned craters' depth-to-diameter ratios. To add to the evidence of this region being a massive reservoir of water ice, researchers point to broken up 'plate' features that are curiously similar to broken sheets of ice in Antarctica. Pack ice.
Crater frequency across the region has been used to infer an age of about 5 million years for these 'plates' of ice. Even more interesting is that the gaps between the ice are inferred to be about a million years younger, suggesting this area solidified too slowly to have been lava flows (Russell & Head, 2003). The large plates of ice may have floated about on an ancient sea or lake, and eventually covered by ash. Ice not protected by ash sublimated away, leaving behind the apparent pack ice we infer to exist beneath the surface today.
The Elysium Planitia has long been suspected of having experienced massive flooding events, and scientists believe they know where the source of water for all this ice came from; the northwest trending radial fossae on the flanks of the Elysium Rise. Specifically, from the Cerberus fossae about 2 to 10 million years ago, a date range within which fits with the inferred age of the pack ice discussed in the previous paragraph.
Elysium Rise is home to numerous fossae, all of which are believed to have formed from laterally propagating dikes that have intersected or approached the surface from within the Elysium Mons volcano (Ibid.). Earlier we discussed the region known as Utopia Planitia. It is believed the massive reservoir of subsurface water ice believed to be beneath Utopia Planitia, came from flooding event(s) sourced from the fossae fissures of which Cerberus fossae is a part.
Deep beneath the surface, Russell & Head (2003) hypothesize the existence of an interconnected network of groundwater, stabilized under hydrostatic equilibrium beneath a confining solid cryosphere. During volcanic activity, lava flows and/or pyroclastics can disrupt the confining cryosphere, and potentially allow the release of large amounts of groundwater at the surface. What appear to be flood channels can be traced from the Cerberus fossae to the region containing ash-covered pack ice.
Though I intend to save the topic of whether or not Mars may have supported life for a future blog post in the TMorB series, it is worth mentioning here that Elysium Planitia is one of the prime candidates for having possibly harbored subsurface extant life. This is to say, life that still exists today. I believe this is possible in other regions as well, including Gale Crater as we'll get to shortly.
There will be much more for us to discuss on this region in the coming years, as NASA's InSight Lander is scheduled for launch some time between early May to early June of this year (2018), expected to land in late November 2018 on Mars. Landing site: Planitia Elysium! I look forward to that mission with great anticipation, as it has been delayed since March 2016, and of course because it will drill an unprecedented ~5 meters beneath the surface to investigate Mars' interior structure in this region. Below is an artist's depiction of the lander, with callouts for each of its instruments.
Possible Massive Flood Plain - ARES VALLIS
Ares Vallis is in the Chryse Planitia region of Mars, and is an ancient outflow channel/flood plain fed by water that surged to the surface at Iani Chaos. You may be noticing a trend of outflow channels having been fed by floods originating from regions with "chaos" in their names. We'll be getting to that soon.
Scientists chose Ares Valles as the landing site for their Pathfinder mission largely because they wanted Pathfinder (and Sojourner) within the Ares Valles flood plain. The area was deemed a safe landing site, and one full of a wide variety of rocks that had been deposited by an ancient catastrophic flood. Even better, the landing site was near the junction between Ares Valles and Tiu Valles, the latter being a 1,720 km long outflow channel with a mouth described by scientists at the European Space Agency (ESA) as being "estuary-like". As we know, estuaries is the tidal mouth of a river valley, or the end that meets the ocean such that the freshwater outflow meets the salty ocean water.
CHAOS TERRAIN - Possible Source Regions of Epic Flood Waters
Throughout this blog post you've no doubt noticed place names containing the word "chaos"; Iani Chaos for example. That word is in reference for a type of terrain for which there is no analog here on Earth. It is an exotic terrain composed of a hodge-podge of otherwise familiar'ish geologic features. Mesas, hills, buttes, huge tilted blocks..
As you've probably already noticed by this point, chaos terrain is most commonly found in the same areas as large ancient river valleys. In fact, many large interpreted river channels appear to originate from chaos terrain. Therefore, many scientists believe chaos terrain indicate the precise locations from which voluminous amounts of groundwater had once surfaced and surged across the face of the planet as catastrophic floods.
More often than not, if you find chaos terrain on Mars, there'll likely be an outflow channel flowing from it and emptying out onto some vast, flat, low-lying plain in an alluvial-fan like feature. For instance, the Tiu Valles outflow channel mentioned above (under the Ares Valles sub-section), was fed from chaos terrain along the Mars' Dichotomy. (Anyone interested, can read more about Mars' dichotomy here.)
Chaos terrain has been found in over two dozen areas across Mars. In the highlands of Chryse Planitia, in Margaritifer Terra, and regions along the Martian dichtomy. How they formed is still up for debate, but most hypotheses agree that whatever formed them, voluminous amounts of water were most certainly involved, and that water came from below ground.
According to Wikipedia, "Many different theories have been advanced for how floods of water came to be released with the formation of chaotic terrain."
Most of those theories posit either the melting of subsurface groundwater ice due to heating from meteoritic impact, or some form of geothermal heating from volcanic activity for example, while others posit melting of subsurface water ice-rich layers that reach the surface and somehow survive sublimating in the near vacuum. Of course to avoid that dillemma, an extraordinarily thick atmosphere is invoked. As mentioned, whichever hypothesis proves true, huge volumes of water were involved.
A handful of minerals known to form in the presence of water have been remotely detected in chaos terrain. These minerals are said to further support hypotheses invoking catastrophic groundwater release of one sort or another. We'll discuss in Part 2 how it doesn't necessarily take a lot of water to produce these minerals.
Scientists have determined chaos terrain across Mars was formed between 2 and 3.8 billion years ago. They have done this by looking at impact crater density on Mars. Analyzing impact crater density on Mars (or any terrestrial planet surface) is the only known technique for remotely unveiling ages of geological features (Fassett, 2016). Cratering chronology is calibrated based on samples obtained during the American Apollo and Soviet Luna missions of the 60s and 70s (techincally 50s, 60s, & 70s for the Soviets).
From these calibrations, scientists have since developed planet-specific models for extrapolating age. We won't get too involved in how exactly ages are extrapolated, but I do want to at least mention what I have so far, with regard to crater chronology, because I intend to return to this method of Martian chronology in part 2 of this blog post.
SEDIMENTARY ROCK LAYERS
One geologic feature that has many scientists convinced Mars played host to lakes and shallow seas, is the widespread existence of sedimentary rock layers. Stratification of sediment layers is common on Earth, and are notably produced when sediment is transported and deposited by moving water.
Sedimentary rock layers form when sediments are deposited on the floor of lakes and shallow seas. Over time these sediments become compressed under the weight of subsequent overlying deposits (lithostatic pressure), eventually cementing into sedimentary rock (lithification).
To be clear, lithification needs groundwater to work, at least on Earth anyway. But it doesn't need liquid surface water in any amounts. Episodic deposition over time results in multiple layers, with some areas on Mars showing over 100 layers indicating liquid water may have been on the surface for millions of years.
Stratified beds of sedimentary rock are commonly found within craters and other depressions such as the numerous chasmata across Mars. Notable regions include chasmata in Valles Marineris, impact craters of western Arabia Terra, intercrater plains of northern Terra Meridiani, and portions of the Hellas Basin rim.
If the stratified layering isn't convincing enough for there having been liquid water, then perhaps the fact the mineral hematite has been detected in Candor Chasma of the Valles Marineris. Hematite is known to precipitate out of water, and collect at the bottom of lakes, and springs here on Earth.
THE LAFAYETTE METEORITE
The Lafayette meteorite was discovered, after it was found. That sounds odd, but the meteorite sat unrecognized in geological collections at Purdue University for years before it was realized what it was. Potassium-argon dating of a particular rock within the meteorite, along with analysis of noble gases within that rock, suggested the meteorite came from Mars. Those noble gases closely matched atmospheric measurements taken in the 1970s by the Viking landers.
The particular rock analyzed in the Lafayette meteorite is called iddingsite, and this is of key importance. Iddingsite forms in the presence of liquid water. It is the product of chemical weathering of the mineral, olivine. Olivine is very susceptible to chemical weathering. If exposed to atmospheric carbon dioxide, and water, it quickly weathers into a mixture of clay minerals, and iron hydroxide goethite; together known as iddingsite.
The iddingsite in the Lafayyete meteorite is not believed to be the product of weathering here on Earth, but instead formed while still on Mars some 670 million years ago, give or take 91 million years (Swindle et al., 2000). This was determined by potassium-argon dating of the noble gases incorporated into the meteorite while still on Mars.
Though this could be the age of the iddingsite formation, Swindle et al. warn that it could otherwise be the later age of the atmospheric argon altered or incorporated into the meteorite. Though in context of our discussion here, the age descrepancy is largely inconsequential, as either way, the presence of iddingsite supports the wet Mars hypothesis.
A THICKER ATMOSPHERE
Of course, to maintain water on Mars' surface would certainly require a much thicker atmosphere than what exists there today. According to Phillips (2001), the Tharsis region may have outgassed enough carbon dioxide gas (as well as other gases) to raise planet-wide surface pressure to 1.5 bars. For reference, average surface pressure on Earth at sea level is just a little over 1 bar. Such a thick, carbon dioxide-rich atmosphere might have sufficed in keeping Mars' surface water in their liquid phase for millions of years for reasons to do with temperature and pressure.
As for today's thin Martian atmosphere, as it turns out, it apparently contains evidence supportive of there having been a lot of liquid surface water. That evidence has been inferred from remotely sensed isotopic anomalies between water and semi-heavy water molecules (HDO).
"Normal" water molecules consist of two hydrogen atoms, and a single oxygen. Both hydrogens are simple protium atoms with a proton, but no neutron in their nuclei. HDO molecules differ in that one of the protium atoms is replaced by a heavier hydrogen isotope called deuterium. Deuterium, unlike protium, has 1 neutron in its nucleus. That neutron adds to the overall mass of the molecule, hence the "heavy water" nomenclature.
Since I'm unable to format text to show sub- and superscripts, I can't write the proper chemical formula for water (or carbon dioxide for that matter). Contrary to the ubiquitous use of H2O across the blogosphere, that chemical formula is more apt to describe a hydroperoxyl radical, than water. Last I checked, a water molecule is composed of 2 hydrogens, not 2 oxygens. I could write water as HOH I suppose, but I think that might lead to confusion, so I'll just say "water" when referring to one hydrogen, two oxgyen kind of water. Good ol' H two O.
Since semi-heavy water (hydrogen-deuterium oxide) can be written HDO without any formatting issues, I'll refer to it simply as HDO. I'll apply this standard of writing for all chemical formulas henceforth. Something I never used to do in older blog posts... shame on me.
Anyway, because HDO is more massive than 'normal' water, it is less likely to be stripped from the atmosphere and lost to space (atmospheric escape). Over time, as more and more less-massive 'normal' water is lost to space the ratio of HDO-to-water increases.
A paper by Villanueva et al. (2015) reported findings that the HDO-to-water ratio in Mars' current near-polar atmosphere, revealed a 7-fold HDO enrichment over that of Earth's Standard Mean Ocean Water (SMOW). So what does that mean? To understand what it could mean, we must first quickly look at where nearly all of the deuterium in the universe came from. The Big Bang.
Though nearly, if not all, deuterium in the universe synthesized out of the Big Bang, I suppose I should also mention it's created within the cores of stars. However, in those cores, deuterium is destroyed as fast or faster than it's produced, so we won't consider stellar cores as a source. Given this, scientists have been able to calculate the primordial ratio of deuterium-to-hydrogen across the universe at 26 deuterium atoms per 1 million hydrogen atoms. Not surprisingly, this ratio has been measured in our solar system's gas giants. But we don't find this the ratio in Earth's oceans.
Analyses of the comets Hyakutake, Halley, and Hale-Bopp, showed a higher concentration of deuterium than found across the universe. That higher concentration has been attributed to solar heating of cometary ices as they pass near the Sun, thus triggering natural isotopic separation processes that lead to enriched deuterium levels.
As it turns out, the deuterium ratio in these comets is higher than what is found in Earth's oceans (as a mean), which is about 156 atoms of deuterium for every million atoms of hydrogen (otherwise referred to as SMOW). It has also been determined the ratio is 10 times higher than protosolar H2. These inferences support the idea that Earth must have gained a substantial volume of its water from sources other than comets during the Late Heavy Bombardment. In fact, Morbidelli et al. (2000) concluded that planetary embryos were the primary source, but that's perhaps something for a future blog post.
Mars no doubt experienced the joys of the Late Heavy Bombardment too, though likely avoided any collisions with planetary embryos. But given the fact Mars experienced collisions with comets and asteroids, we'd expect the deuterium concentrations in Martian water to be the same as those comets and asteroids. However, as mentioned above, the deuterium concentrations on Mars have been inferred to be higher by a factor of 7. Villanueva et al. believe this suggests Mars must have had a lot more water in the past. To the tune of a global equivalent water layer at least 137 meters deep. Interestingly, deuterium-to-hydrogen (D/H) ratios are higher in regions with low elevations, and lower in higher elevation regions. This seems to suggest water had pooled up in the basins, much as they have here on Earth.
The reasoning behind the conclusion made by Villanueva et al., insofar as the estimated total amount of water Mars had, has to do with atmospheric stripping of lighter molecules. The less massive ("lighter"), 'normal' water molecules would have been lost to space over time due in part to Mars' relatively weak effect of gravity, and lack of a protective magnetosphere. Meanwhile, the more massive ("heavier") HDO molecules were left behind. As more water was lost to space, the HDO concentrations on Mars would have increased.
Villanueva et al. took the current deuterium ratio and extroplated back to arrive at a conclusion that Mars must have had about 6.5 times the volume of water currently locked up as ice in its polar caps. That's enough water to fill a 20-million cubic kilometer ocean, and if that ocean were in the northern hemisphere as one might expect given its vast low-lying areas, that ocean could cover ~19% of Mars' surface. That's about 2% more surface coverage than Earth's Atlantic.
So many readers may be convinced that Mars indeed had an ocean, and one should expect nothing else given all the information provided. Couple that with the absolute statements by some zealous folks at NASA/JPL, on YouTube, popular magazines, and elsewhere, and one would be hard pressed to be skeptical.
But there remains a considerable amount of conflicting evidence to the Wet Mars Hypothesis, and this evidence isn't often heard about beyond academic circles.
Mars is largely lacking carbonates. This is a big deal. These are conspicous minerals to be missing from a planet believed to have had a substantial ocean and all the ingredients to form carbonates en masse. To understand why their scarcity is so conspicuous, we must first discuss a few fundamental concepts.
For those who might have read my climate change blog, I spent some time discussing the carbonate pH curve when discussing oceanic acidity as it relates to carbon dioxide levels in Earth's troposphere. Let's revisit it here as it relates to Earth's carbon dioxide solubility pump, this latter phenomenon being a perfect example of just how dynamic an ocean (on any planet) can be.
Unlike most gases, carbon dioxide doesn't just dissolve in ocean water, it readily reacts with it. Once dissolved as an aqueous solution in ocean water, it reacts to produce a handful of important carbon-based species of dissolved inorganic carbon.
These species include of course, the dissolved carbon dioxide (in aqueous solution), but also carbonic acid, bicarbonate ion, and carbonate ion. Bicarbonate and carbonate ions are formed as carbonic acid dissociates, and these latter two species can freely change between each other depending on pH of the ocean water. To write more clearly, bicarbonate can produce carbonate as pH increases, and vice-versa within parameters shown in the pH curve below. We can also see the relationship of carbonic acid in this curve:
The average pH of Earth's oceans favor production of bicarbonates (red line), though there has been an alarming trend towards lower pH levels in recent decades which will and already has begun having a devastating effect on shell-bearing life in our oceans. Those reading this are welcome to read more about how even a slight trend towards lower pH can have catastrophic implications for life in my climate change post titled, "Climate Change: A response to Dr. Lindzen's letter to the POTUS" found here: https://www.rookandalus.com/blogs/earthsclimate
Species of dissolved inorganic compounds are circulated throughout our oceans via a natural solubility pump powered by the effects of gravity, but more specifically by water densities. Water density is affected by salinity levels, and temperature, where salinity and density are directly proportional, and temperature and density are indirectly proportional. In other words, as salinity goes up, so does density and vice versa, when temperature goes up however, density goes down, and vice versa.
Our oceans are not uniformly dense due to temperature & salinity fluctuations. This lends itself to ocean water mixing, along with all the dissolved inorganic solids in it. In very basic terms, denser water sinks, displacing less dense water as it does so. The same goes for air, which is often incorrectly assumed to mean heat rises. Hot air rises, or more accurately is displaced upward due to sinking cooler (denser) air, but heat goes from where it is to where it isn't in the direction of least resistance as it tries to find a temperature equilibrium with its surrounding environment, just like all energy does. But I'm divagating here a bit.
The solubility of carbon dioxide in ocean water is affected by water temperature. The lower the temperature, the higher the solubility and vice versa (an inverse proportion). At higher latitudes where sunlight is less direct on average, temperatures are lower and therefore high-latitude water is denser and capable of reacting with more carbon dioxide than surface water nearer the equator. This means more dissolved inorganic compounds could possibly be in solution of colder high-latitude water, and as that denser water sinks (thermohaline circulation), it takes this dissolved carbon with it to the bottom of the oceans, effectively acting as a carbon sink.
The pH of ocean water is affected by hydrogen ion concentration. Surface water can dissolve more ions because as currents migrate surface water to higher latitudes, that water becomes colder. This equates to the water becoming more dense, therefore it sinks, taking the dissolved ions with it.
As we discussed above, carbon dioxide readily reacts with water to form a weak carbonic acid, and so if a planet has carbon dioxide in its atmosphere and rain falls through it, then the pH of that rainwater will drop as carbonic acid is produced. That "acid rain" chemically weathers rocks on the planet's surface, and some of the stuff chemically weathered from those rocks are the ions listed above, among others.
Given the fact that an ocean is a dynamic system, we can reasonably expect it will leave behind chemical evidence of it having existed even long after it's gone. That evidence of course, would very obviously be seen as vast deposits of carbonate species.
I say obvious, because carbonates under UV light, of which Mars gets plenty of, flouresce. Billions of years ago on Earth, our oceans were saturated with calcium because there was no mechnism in place to cause that calcium to precipitate out. By saturated, we're talking about 50% saturated. Eventually a mechanism did develop and limestone could form. Eventually lifeforms (ie. foraminifera) evolved that could use calcium, and today calcium is a minor element in ocean water. The evidence of an ocean, if ever our global ocean were to up and disappear like a fart in the wind, would be found in limestone and other calcium deposits.
The Red Sea is a perfect example, in that around 13,000 years ago, half of it evaporated away, therefore it became saturated (50%) with calcium, and limestone formed. The Mediterranean completely evaporated away during the Miocene. Both left barren seafloors chalk (pun) full of limestone. We need more chemical analyses of Martian basalt, but on Earth, basalt has calcium. Mars has an abundance of basalt. So we must logically ask if it has an abundance of calcium as well?
As a side note, ions dissolve in water, not minerals. I read in a blog elsewhere that minerals dissolve in water. They don't. Chemistry doesn't work that way, and if Mars has rewritten the rules of chemistry, then we have bigger problems on our hands than to wonder if that planet ever had an ocean.
Hydration of basalt should give us calcium. If we add carbon dioxide, then we should get limestone when an ocean evaporates away, or to the point of calcium saturation (~50%). I could be wrong, but I'd imagine we might see salt deposits as well. Salts are a symphony of ionically-dissolved material that would precipitate out of a body of water that has evaporated away.
At any rate, we must also consider that a planet capable of maintaining a vast liquid ocean, probably also maintains a thick atmosphere. Thick atmospheres invariably experience weather patterns, and on a planet covered with water, those weather patterns would very likely include rain storms. Mars is covered with rocks that rainfall would have certainly weathered; dissolving their silicate & carbonate minerals and transporting bicarbonate ions, and a host of dissolved inorganic compounds to the ocean via rivers & streams. The ingredients are there for carbonate minerals to form, particularly if we're to believe a Martian ocean supported life.
Another thing a thicker Martian atmosphere would have had, is carbon dioxide. Given the fact the planet's current thin atmosphere is nearly 96% carbon dioxide, I think it's safe to suspect a thicker ancient atmosphere would have consisted of a substantial portion of carbon dioxide.
That carbon dioxide would have invariably reacted with any surface water, including falling rain. There's simply no way around that. Assuming a balance of dissolved inorganic compounds in the water, we'd expect Mars would be chalk full of carbonates (pun intended), as carbon dioxide reacts with positively-charged ions like magnesium and ferrous iron that have been shown to have been widely available.
Yet at the time of this writing, scientists have yet to find any caches of carbonates on Mars. What this suggests is either the planet's oceans were acidic, weren't water, or never existed. And as we look at the other evidence, it's most likely the latter.
It has been postulated that the lack of carbonates on Mars could be due to ultraviolet dissociation, and/or a widespread carbonic acid-fog weathering; but that may be invoking the powers of imagination beyond what is necessary. It certainly isn't in the spirit of Occam's razor to invoke some additional, unusual, long-dead process to explain a thing that can be described by known processes we see occurring now.
It could be that our instrumentation simply isn't up to the task of detecting carbonates on Mars. Many scientists thought that perhaps the Thermal Emission Spectrometer (TES) on the Mars Global Surveyor, used to detect carbonates (and other minerals) on the Mars, was too course in its observations. So engineers designed an upgrade to be equipped to the Mars Odyssey Orbiter. The upgrade was the Thermal Emission Imaging System (THEMIS). According to the NASA website, its purpose was to "...detect smaller carbonate deposits...". Something one of my former professors mentioned to me, is that carbonates fluoresce in UV, and UV reaches Mars' surface quite easily given the planet's thin atmosphere. The fluorescence is in visible wavelengths, and should be easy to detect, but I'm not aware of this having been looked at. I could be wrong.
But as mentioned above, finding carbonate deposits on a planet that had an ocean should be a relatively easy task. Carbonates might be found all over the place, and in large quantities; particularly across the low-lying regions of the northern hemisphere where oceans and lakes are hypothesized to have existed.
Upgrading to a sensor better capable of detecting smaller deposits is a good thing, but then again, there's something to be said about having to upgrade the sensitivity of a sensor to detect something that should nearly be detectable with a telescope from Earth. If there was an ocean, and it evaporated away, calcium carbonate would form as an evaporite. To be fair, magnesium carbonates could form this way too.
To be fair, I've written here that Mars is largely devoid of carbonate minerals, but this doesn't mean Mars is completely devoid of them. There is widespread but small concentrations of carbonates in the surface dust on Mars (with an average mass fraction of less than 5%). Carbonates have also been remotely sensed in a crater on the rim of Huygens Crater, as well as having been inferred to exist in the Columbia Hills of Gusev crater.
Unfortunately, these are largely magnesium-carbonate deposits, which can form under minimal carbon dioxide pressure conditions in which liquid water is unstable, and possibly present in merely a transient state (Bandfield, Glotch, & Christensen, 2003). In fact, there exists uncertainty whether or not any water is required for magnesium-carbonate formation to occur (Ibid.). The concentrations of carbonates detected in the Columbia Hills of Gusev crater are likewise, rich in magnesium-carbonate.
The localized carbonate species found on the rim of Huygen Crater, has been reported to be calcium carbonate, and this of course does indeed play in favor of there having been liquid surface water. However, this remains unconfirmed, as it may be an iron carbonate. Impactor hits can explain why we see carbonates at the rim of craters. They were obviously at the surface prior to impact, then pushed up to the rim upon impact. Certainly more data collection is needed before assumptions can be made here.
All is not lost, as it is possible for magnesium- and iron carbonates to precipitate out from hydrothermal vents and veins respectively (the latter occuring naturally in the mineral siderite), but neither vents nor veins are oceans, and this particular route of precipitation remains unconfirmed.
The case for a Martian ocean gets worse. I mentioned earlier that the lack of carbonate minerals on Mars suggests to me that either its ocean was acidic, not water, or never existed. On the option that Mars' oceans may simply have been too acidic to leave behind carbonates; The very fact the planet has minerals such as magnesium carbonate (magnetite) undermine that possibility, or at least cause it problems, because such minerals would have likely dissolved in acidic conditions.
I remember back in 2011 a slew of media headlines touting the Phillips et al. (2011) paper in which the conclusion was made that Mars' southern polar cap contains up to 30 times more frozen carbon dioxide than previously estimated. It was calculated that if the entire volume of dry ice were to sublimate, it would nearly double Mars' atmospheric pressure.
However, a doubling of Mars' atmospheric pressure is only 12 millibars (mb); About 1% Earth's average pressure at sea level. This isn't enough to warm the planet, nor sustain an ocean. If we couple this with the fact that the Sun was about 20% less luminous at the time Mars is hypothesized to have had an ocean, and it becomes clear that no one should be making blanket statements or assumptions about what kind of ancient climate Mars had.
On Earth, the Faint Young Sun Paradox has supposedly been resolved by proxy evidence of there having been considerably more carbon dioxide in the atmosphere. This paradox, however, is more profound when considering an ancient wet Mars, whose orbit is considerably further out from the Sun, and as such receives less solar energy.
The chance of there having been enough carbon dioxide in the deep past was further diminished when the Rover Curiosity's Mars Science Lab (MSL) was used to analyze certain minerals in Gale Crater; a site believed by some to have played host to a long-lived lake (on the order of a few million years). If so, then single-celled subsurface lifeforms could have evolved at this location. The purpose of the analyses were to estimate how much carbon dioxide was present in the ancient atmosphere, as that plays a major role in dictating temperature and pressure regimes capable of supporting surface liquid water for extended periods of time.
The solubility of iron-rich olivine minerals is restricted by the presencs of carbon, therefore determining the amount of this type of olivine allows for scientists to extrapolate a limit of how much carbon dioxide was present in the atmosphere. The results showed that the ancient Martian atmosphere had more carbon dioxide, but concluded that it wasn't enough to support a climate warm enough to sustain liquid surface water (Bristow et al., 2017).
We'll be getting to olivine shortly, because its presence poses another problem for the Wet Mars Hypothesis.
Researchers concluded that there must be something else that kept Mars' climate warm enough to support water. Either that, or water was able to flow for some other reason not entirely hinged on warm temperatures. I don't claim to know the answer, but I am curious as to why there aren't third, and fourth possibilities. Perhaps there never was water there in the first place, or that the fluid present wasn't water at all.
Earlier I mentioned that the Faint Young Sun Paradox was supposedly resolved by hypotheses based on proxy evidence that Earth's early atmosphere had much more carbon dioxide. But contrary to popular opinion, scientists are still at odds over how Earth was able to sustain liquid water. Some evidence seems to suggest Earth had a carbon dioxide partial pressure as high as 1,000 mb, whereas others suggest it could have been as low as 230 mb.
There are thousands of geologists on Earth, numerous remote sensing satellites, thousands of core samples hundreds of meters long, and ongoing in situ and lab research actively attempting to resolve Earth's ancient atmospheric composition, and we've yet to reach a consensus.
Mars has zero geologists, 4 rovers (2 inactive) that have covered a combined linear distance of less than 50 miles at the time of this writing, that have drilled a mere 5 cm into a few rocks, and a handful of orbiters. I seriously doubt there'll be any consensus on what kind of ancient atmosphere Mars had any time soon.
If Mars enthusiasts with the resources to send people to Mars ever get serious about how to actually protect those people, then we may actually be able to get geologists footslogging about on Mars taking in situ samples, and bringing samples back to Earth for further in-depth study. Until then, we shouldn't expect there to be enough evidence for anyone to be making claims and assumptions that Mars was once a warm, wet planet. In fact, there shouldn't be claims to the contrary either. There simply shouldn't be any claims being made at this point.
We simply don't yet know. That doesn't always make for exciting news, and government funding often requires some level of public enthusiasm to come through (military funding exempt). But that's the reality. And by the time anyone willing to read this post finishes, I think it will be abundantly clear that claims to any past Martian conditions are at best hopeful, and at worse, naive.
Olivine & Jarosite
While Mars lacks carbonate minerals, there is one mineral it seems to have an abundance of: olivine. Olivine chemically weathers quite easily when exposed to water and carbon dioxide; two ingredients that certainly exist en masse in the Wet Mars Hypothesis. Olivine is one of the first minerals to crystalize out of a magma, and it is the first to to weather. I should be specific, and say that it crystalizes out of average Earth crustal abundance, and I'm not sure if that is what we have on Mars. Bowen's Reaction Series relates only to Earth's average crustal composition, and we simply don't know if it is applicable to Mars. We may not get the same distribution on Mars that we see on Earth. Mars' reaction series might only involve a handful of the minerals we see on Earth, and this could have profound implications for what we observe (and don't observe). I don't see this possibility discussed among the folks at NASA, but then again, I'm just one schmoe, and haven't read every paper.
At any rate, there is an interesting corrolation between Bowen's Reaction Series, and the Goldich Dissolution Series. A quick recap on what those series are:
Bowen's Reaction Series - Minerals crystalize out of average Earth crustal magmas at different temperatures and pressures. As magma nears the surface, it cools and the lithostatic pressure decreases because less and less material is above it as it ascends. As the melt cools and pressures decrease, minerals begin to crystalize out of it. The first to do so is olivene and calcium plagioclase; this means it crystalizes out at the highest temperature and pressure of all the minerals (aside from calcium-rich plagioclase). As the magma continues to approach the surface, other minerals sequentially crystalize out such that each forms at lower and lower temperatures and pressures. Those other minerals aren't important here, but keep the fact olivene is first to crystalize out in mind.
Goldich Dissolution Series - Minerals that crystalize out of magmas first, that is to say, at high temperatures and pressures, are also the first to chemically weather away at the surface. They are the least stable mineral at the surface, being the most vulnerable to chemical weathering. If we recall from Bowen's Reaction Series, olivine is the first to crystalize out, making it the least stable, and therefore the most vulnerable mineral to chemical weathering at the surface.
Yet olivine-bearing exposures have been detected in several regions across Mars (Hoefen et al., 2003; Christensen et al., 2003, 2005; Mustard et al., 2005, etc.).
Regions including, but not limited to, Nili Fossae, where a 30,000 square kilometer olivine-rich area has been spectrally detected. Nili Fossae is thought to have had substantial liquid surface water in the past, evidenced in part by the presence of carbonates.
However, they're magnesium-rich carbonates, and that species can form under current Martian atmospheric conditions as discussed earlier. Olivine has magnesium as well, but less so by percentage weight.
In Part 1 we considered iddingsite on the Lafayette meteorite as evidence for liquid water on Mars. This was assumed because iddingsite is a mixture of products resulting from the chemical weathering of olivine, and that chemical weathering involves liquid water.
However, the involvement of liquid water in a process doesn't necessarily necessitate an ocean's worth of it. In fact, to invoke large bodies of water seems only to further complicate explanations for the widespread presence of olivine on Mars' surface.
It may be easier to explain scarce deposits of iddingsite in context of near-surface water ice at its triple point, than it is to invoke an entire ocean and all its necessary environmental conditions. This might also apply to the scarce deposits of minerals known to form in the presence of water.
And on this latter point, NASA announced in a press release dated March 3, 2004 that the mineral jarosite was discovered on Mars, "...a mineral that forms under water." However, in a peer-reviewed paper (Heinrich, 1965), it is established that jarosite also forms from hydrothermal solutions. As geologist Peter Ravenscroft has noted, it "...is not quite the same as saying this mineral forms, or only forms, under water."
This sort of haphazard conveyance of discoveries on Mars to the general public is misleading. The difference between a mineral "forming under water", and it forming from solution can be the difference between an ocean and a puddle.
Consider this quote from a paper by Madden et al. (2004) as an example:
"On Earth, jarosite has been found to form in acid mine drainage environments, during the oxidation of sulphide minerals, and during alteration of volcanic rocks by acidic, sulphur-rich fluids near volcanic vents. Jarosite formation is thus thought to require a wet, oxidizing and acidic environment."
For whatever reasons, some people interpret that to mean large bodies of liquid surface water, and a thick atmosphere. Yet that very same paper posits that the very presence of jarosite is indicative of water-limited chemical weathering on Mars. This is because jarosite chemically weathers to ferric oxyhydroxides in wet, humid conditions.
As far as I'm aware, magmas contain juvenile water in the form of hydroxyls and oxygen, and that water can become acidic liquid water at and/or near the surface, particularly in the vicinity of volcanic vents. We'll be discussing juvenile water (aka magmatic water) in more detail shortly, because of all the magma types, basaltic contains the least, and that's just the type of melt Mars exuded.
At any rate, localized pockets of near-surface water that has melted at its triple point may at least partially explain some of the mineralogy we see (and don't see) on Mars. And it could do so within the framework of current Martian conditions. I think it's hard to deny that liquid water may play a role in Martian geology, but perhaps not in the voluminous way many scientists and engineers think (or want). We'll discuss the triple point of water, and how near-surface water ice can melt under current conditions in the next sub-section below.
Bertrand Russell interpreted 14th century Franciscan friar, William of Ockham as having said, 'if one can explain a phenomenon without assuming this or that hypothetical entity, there is no ground for assuming it.' In other words, one should opt for an explanation in terms of the fewest possible causes, factors, or variables. Keep it simple, because the simplest, most eloquent answers to questions in nature, have often turned out to be the correct ones.
The Triple Point of Water
At this point, I think it's clear that no one is claiming Mars is devoid of water. It's well established that there's water locked up as ice in the polar caps, as well as below surface across various regions in the lower latitudes, with the largest radar-detected reservoir beneath Utopia Planitia.
But all this water ice doesn't necessarily equate to there having been voluminous liquid bodies at the surface. Nor does it necessarily equate to there having been catastrophic flooding events. It could be that this ice experiences episodic, or sporadic melting under certain conditions, and over time has a noticeable effect on the geology and geomorphology of the planet. A key reason why this might be the case has to do with the fact that surface and near surface environmental conditions on Mars, on average, is very near the triple point of water.
The triple point of water is the point at which pressure and temperature are such that water can exist in all three phases; solid, liquid, and/or gas. This is point is met at just over 611 Pascals (Pa), and about 273 Kelvin (K).
The average surface pressure on Mars is very close to 611 Pa, averaging about 600 Pa. A Mark Watney fart could make up that difference. Mars' surface temperatures range between 120 K to 293 K; this range easily crosses the triple point temperature of 273 K.
It's reasonable to suspect frozen water on and just beneath the surface of Mars could theoretically change to liquid phase with arbitrarily small fluctuations in temperature and/or pressure.
With regard to pressure, the fact Mars experiences planet-wide dust storms indicates its thin atmosphere has pressure rises and falls. They may be small by Earth's standards, but Martian pressure fluctuations don't have to be significant to reach the triple point pressure.
Also worth considering, is the fact that Martian dust storms transport literally tons of lithic material across the planet. This action alone provides an active, observable source for building lithostatic pressure on subsurface water ice over time.
Added lithostatic pressure coupled with the right temperature, and near-surface liquid water could be realized. It may take many dust storms to accumulate the pressure needed for water ice to liquify at some depth, but time and dust storms are two things Mars has a lot of. According to Zweck & Martin (1993), there is a one in three chance of there being a global dust storm on Mars in any given year. We'll come back to this ability of Mars to pile on the pressure for subsurface ices later, when we discuss frozen carbon dioxide (dry ice).
So given what we've discussed so far, what we have is a uniquely dynamic planet with all the presently-observable ingredients necessary for there to be localized instances of near-surface liquid water. Liquid water that could hypothetically explain some of the minerals we see, and don't see across Mars.
Obviously, "some" of the minerals on Mars isn't all of the minerals we see or infer to see across Mars. Clay minerals are widespread on Mars, and its nearly ubiquitous presence requires a more robust explanation than subterranean water reservoirs. In fact, even sand, silt, and clay-sized grains require an explanation in and of themselves.
Aeolian Processes - Dust in the wind
Many features we see on Mars today that some scientists believe were created by flowing water, could have likewise been formed by sedimentary transport, and deposition by wind. Before we get to these, we ought to distinguish wind from the dust it can carry.
If there is one thing Mars has a lot of, it's silt, and clay-sized regolith (dust). Regolith is the weathered remains of parent rock, and the terms boulder, cobble, sand, silt, and clay are used to reference grain diameters with boulders being the largest, and clays being the smallest.
These variously-sized grains make up Martian regolith, that is often referred to by planetary scientists as "soil". Regardless of what planetary scientists say, the regolith on Mars is not soil.
It's regolith. In fact, that is the well-defined scientific term for precisely what it is; Broken up parent rock with a mixture of various minerals. To call it soil, is not only misleading, but it's flat out wrong. It's like calling a pile of nuts and bolts on the ground a well-lubricated functioning machine.
It's unfortunate they've adopted the term "soil" when referring to Martian regolith, because such aggrandizing vernacular is quite literally tantamount to referring to an inorganic mixture of rocks as somehow being organic. More specifically, the organic remains plants and animals; including fecal matter from the latter.
Insofar as I'm aware, Mars doesn't have, and likely never had a large supply of plants and animals from which to make soil with. Even if Mark Watney from that movie, "The Martian", was out spreading his crew mates' bags of dehydrated feces around Acidalia Planitia as if he were Johnny Appleseed.
The smaller-diameter regolith on Mars (the sands, silts, and clays) is often mistakenly said to be the result of eons of wind breaking up parent rock into smaller and smaller pieces.
However, contrary to popular belief, wind is not a weathering agent. It's the fine particles within the winds that become agents of weathering. Wind can blow against a rock for billions of years and have no effect, but if it's blowing debris into that rock, we can be sure that rock will erode over time. This mechanical form of weathering is called rock abrasion. Wind erosion is not weathering, but removal of fine regolith.
Rock abrasion is simply the mechanical break up of rocks when they strike or are stricken by other rocks.
It may seem inconsequential to distinguish wind from what is actually doing the abrading, but that difference means there is simply no way wind can be responsible for the presence of sands, silts, and clays across Mars. We cannot break down parent rock into smaller grains by blasting it with smaller grains, because to do so means there is already smaller grains to begin with. It's circular reasoning to suggest "wind erosion" is responsible for all the dust on Mars.
Aeolian processes may be the primary shapers of landforms on Mars today, but they certainly weren't in the beginning. And as far as clay minerals go, they almost certainly require the presence of water to form. This fact alone has been inspiring for many Wet Mars advocates, particularly since clay minerals are widespread across Mars, and is found in terrains that date back 4.1 to 3.7 billion years ago.
But there are many ways water can be involved in mineral-forming processes without the need for oceans, lakes, ponds, or even puddles. Given the lack of carbonates, presence of olivine, and other reasons we'll discuss shortly, looking at other possibilities seems a reasonable course to take.
A recent paper has been published positing the hypothesis that steam, not water, is behind all the clay minerals found on Mars (Cannon et al., 2017). Magmas contain water in the form of hydroxyls and oxygen, which are outgassed these melts ascend and flow as lava at the surface. We'll be discussing more on in the sub-section, "Magmatic Water" below.
In Mars' earliest years after accretion, the planet surface may have been a magma ocean. The tremendous amount of energy to melt the surface of Mars would have come from the accretion process itself, as well as short-lived (high-output) radio-isotopes, and core formation, this according to respected geologist, G. Jeffrey Taylor at the Hawai'i Institute of Geophysics and Planetology.
The hypothesis suggests that as Mars' magma ocean cooled, it would have outgassed tremendous amounts of water, carbon dioxide, and other gases which possibly could have formed a hot, dense, near-surface atmosphere. Though, basaltic melts are low in water and gases; in fact lowest of the major melt types, but anyway... That hot, dense steam-filled atmosphere would have reacted with Mars' primary crust as the magma ocean cooled, creating clay minerals en masse.
Experimental evidence demonstrated that under similar simulated atmospheric conditions, clay formation would have been rapid. They even postulate the possibility of Mars having had a supercritical atmosphere of water and carbon dioxide near the surface, which wouldn't be out of the question if the surface were a cooling global or near-global magma ocean.
The surface of Mars would have been covered in clay minerals as a result of chemical reactions with the catalyzing atmosphere. Crustal evolution models show the clay mineral layer being buried with time. It would have been buried locally due to impact ejecta spread out from meteoric strikes, as well as regionally by lava flows from volcanic activity. Wind transport of dust in the billions of years since would have buried the rest. We'll get to wind later, because it seems a common misconception that wind is somehow an agent of weathering, but it's not.
What Cannon et al. surmise, is that there should be a generally cohesive layer of clay minerals at depth, with limited surface exposures as we see ("see" as in infer with remote sensing) today.
The key aspect of this hypothesis that I find very appealing, is that it can theoretically be proven true or false with direct evidence. All that's needed is a lander capable of drilling deep enough to tap the hypothesized layer of primordial clays. If they're there, then this steam hypothesis will, ahem, definitely pick up steam. Thank you, thank you... I'm here all night. :)
It may sound strange, but as mentioned above, magmas contain water. But it isn't liquid water, it's in the form of hydroxyls and oxygen within the magma. It is released as water vapor when magmas ascend and outgas as lava flows at the surface. Since that marks the first time the water has ever been exposed at the surface, either on the ground or in the atmosphere, geologists refer to it as juvenile water.
There are three major types of magmas (and their associated volcanoes):
a. Rhyolitic b. Andesitic c. Basaltic
Of the three magma types, basaltic has the lowest water & gas content, and all volcanoes on Mars are basaltic shields. This might be worth considering in the bigger picture of just how much water could have been outgassed from Mars. In fact, it should be considered in conjunction with where Mars might have gotten all its water in the first place.
On Earth, large amounts of water can be transported to the asthenosphere via subducting plates; structurally bound within rocks and minerals, as well as what's trapped in pore spaces. But this sort of transport only works on Earth, where there is plate tectonics and a global ocean. Mars lacks plate tectonics, and there is no conclusive evidence that it ever had an ocean. Earth may have originally gotten the bulk of its water from collisions with planetary embryos. We'll get back to this shortly, when we discuss why some hypotheses conclude that Mars did not get its water this way.
To figure out where Mars got its water, we have to go back about 4.6 billion years when it was accreting out of the circumstellar disk. There are likely three major agents of water delivery during the accretion process: comets, small asteroids, and planetary embryos. In what percentages these agents have brought water to Earth, Mars, and Venus is still debated, but one thing we can probably be sure of, is that Mars was not struck by a planetary embryo given the region in which it likely accreted.
Not that anyone reading this wants to read more, but I discuss Mars unique accretion rate in a previous TMorB post which can be read here. That post is MUCH shorter than this one!
Mars would have had to rely on the collisions of small asteroids and comets for its water supply. It certainly couldn't have avoided such collisions. Lunine et al. (2003) hypothesized about 100 Earth masses worth of cometary material in the region between Jupiter and Neptune, and about an Earth mass of asteroidal material between 2.5 to 4.0 astronomical units (AU). Early solar system gravitational disturbances would have certainly put many of those objects on collision courses with Mars.
Lunine et al. assumed comets contained 50% water ice by mass, and small asteroids contained 10%. They then ran calculations to determine how many collisions Mars might have endured, and in what proportions, as well as what percentage of water could have been retained during and after collisions. Retention efficiency varies depending on collider mass and velocity.
They concluded that Mars could have received 0.06 to 0.27 Earth Ocean Mass (EOM) worth of water from comets and asteroids. I don't use plural for Earth's ocean, because technically it's one ocean with five different regional names. At any rate, in addition to determining just how much water Mars could have accreted, Luline et al. also calculated resulting isotopic composition of the water; The deuterium-to-water ratio (D/H ratio) we discussed in Part 1.
For the dryer values towards 0.06 EOM, water delivery was shared 50/50 by comets and small asteroids. For the wetter values towards 0.27 EOM, delivery was predominately by small asteroids.
As for deuterium concentrations; For dryer values, the D/H ratio was higher, about 1.6 times Standard Mean Ocean Water (SMOW) which as discussed in Part 1, is 156 parts per million (ppm) deuterium to hydrogen (D/H). For the wetter values, the D/H ratio was lower, about 1.2 times SMOW.
We'll recall from Part 1 of this post, that the 2015 Villanueva et al. paper concluded Mars had a D/H ratio 7 times that that of the SMOW. This estimate has varied over the years, but all reveal a D/H ratio considerably higher than the terrestrial average (here on Earth).
Venus has a D/H ratio 100 to 120 times that of the SMOW. But before we can simply extrapolate the amount of water a planet might have had in the past from these D/H ratios, we must first try to determine its rate of escape from an atmosphere (its escape efficiency). It's also necessary to determine deuterium's fractionation efficiency, which is a temperature dependent separation of isotopes that occurs naturally during such processes as evaporation, condensation, melting, freezing, etc.
Deuterium enrichment could be attributed to either continuous outgassing from a highly-fractionated mantle source, or by Rayleigh fractionation after massive outgassing from catastrophic resurfacing of a planet (Grinspoon, 1993). And nowhere in the solar system do we see better evidence of there having been catastrophic resurfacing of a planet than on Mars.
Nearly the entire northern hemisphere of Mars has experienced catastrophic resurfacing either by endogenic processes (mantle processes), a singularly monstrous impact, or by multiple devastating impacts.
As for the possibility of there having been continuous outgassing from a highly-fractionated mantle source; That might have resulted from the severe dessication of Mars' mantle, or perhaps by massive hydrogen escape early on in the planet's history (Ibid.).
As far as hydrogen escape goes, it's possible that an ocean's worth of steam was consistently outgassed, then quickly exposed to high-energy UV penetrating an unprotected atmosphere, which then could have broken apart outgassed water molecules, allowing the newly-liberated hydrogen to be stripped away to space (possibly via Jeans escape), as Mars' early magma ocean cooled out of accretion. Whew, that was a run-on sentence. Anyway, there may never have been any bodies of liquid water at the surface.
There have been experiment-based studies that claim Martian parental magma had up to 1.8% water as weight percent (McSween et al., 2001). However, analyses of Martian meteorites show they contain very little water. However, mineral-chemical, experimental, and cosmochemical constraints in a study by Filiberto & Treiman (2010) showed that Martian magmas contained little water, but high levels of chlorine. Minerals in the Martian meteorites analyzed were chlorine rich, but water poor.
This is consistent with previous studies that show Martian basalts are 2.5 times more chlorine rich than Earth's basalts on average, which Filiberto & Treiman say is an observation consistent with Mars’ overall enrichment in volatile elements. The authors claim chlorine has similar effects as water on mineral crystallization (which is news to me), and concluded that large amounts of water is unnecessary to explain the mineralogy of Martian meteorites, and therefore volcanic regions of Mars by extension. Volcanic eruptions contributed to the acidity of Mars' surface, but contributed very little in the way of water. The study suggests that it was chlorine, not water, that acted as the dominant volatile species in ancient basalts.
If a lot of carbon dioxide was present in a steamy atmosphere, a carbonic acid-rich environment might have chemically weathered parent rock, which as we'll discuss shortly, is one avenue through which Martian winds have anything to transport in the first place.
Carbon Dioxide Revisited
Another hypothesis put forth by N. Hoffman (2000) suggests Mars was an icebox with average global surface temperatures around -78 degrees Celsius. That carbon dioxide clouds reflected away relatively weak incoming solar radiation from a distant Sun that was about 20% less luminous than it is now. Hoffman notes that even a carbon dioxide-rich atmosphere several times more dense than Earth's present atmosphere, there still wouldn't have been enough heat to support liquid water at the surface.
The idea of a cold, icy Mars is supported by recent modeling studies. In 2015, Woodsworth et al. ran computer simulations for a warm, wet scenarios, and cold, icy scenarios to see what environmental parameters the models would derive to support these systems. They used a three-dimensional climate model rather than previously used one-dimensional radiative-convective, or two-dimensional energy-balance models.
Warm, wet simulations put out scenarios that did not match observed valley network distributions across Mars. However, the cold, icy simulations closely matched these distributions, and matched between ice/snow accumulations.
Mars' obliquity is believed to trek between 10 and 40 degrees (as compared to Earth's 22.1 to 24.5 degrees). The simulations used different values to see how the Martian environment was affected. At obliquities below about 20 degrees, and pressures below around 0.5 bar, both atmospheric carbon dioxide, and water vapor collapse at the poles, with lower latitudes left too cold and dry to experience any significant melting or runoff. This, is precisely what we see today (although Mars' obliquity is 25 degrees, its average surface pressure is far lower than the 0.5 bar in the simulation).
The authors concluded that a vast liquid northern ocean is unnecessary to explain the water detected at Gale Crater. Indeed, it could be explained in a cold scneario for fluvial alteration consistent with in situ geochemical analyses (McLennan et al., 2014; Grotzinger et al., 2014).
Hoffman's paper suggests large quantities of frozen carbon dioxide, clathrate, and perhaps even liquid carbon dioxide existed beneath the surface in regions around Mars. Liquid carbon dioxide would have been deeper beneath the surface, as it requires a pressure of over 5 bars at 211 Kelvin to maintain that phase. Hoffman proposed a depth of several hundred meters.
In Part 1 we discussed chaotic terrain, and how outflow channels lead out of them. The hypothesis being that the chaotic terrain was created when groundwater was released en masse, and raged as a catastrophic flood (or multiple floods) down towards the basins, cutting deep chasmata and valley networks as they went.
Hoffman determined that the chaos terrain regions are far too small to account for the volumes of liquid water it would have taken to create the canyons and valleys we see today. He dubbed this descrepancy, the "volumetric paradox". He proposes that it was jets of carbon dioxide gas that were released, not water.
The Sun was about 20% less luminous during the Noachian, leaving Mars an icy world with subterranean reservoirs of frozen carbon dioxide (dry ice), clathrate, and perhaps some pockets of liquid carbon dioxide at its triple point. The latter being at greater depth where overlying lithic pressure is at or exceeds 5 bars.
Today, just as it may have been billions of years ago, atmospheric carbon dioxide is very close to its freezing point on average. We know it reaches this point near the surface as dry ice snowfall has been documented over the winter poles. At lower latitudes, dry ice snow could also fall within large dust storms, wherein sunlight is largely blocked at the base of the storms near the surface.
As is the case with all forms of precipitation, water or carbon dioxide must condense on a nucleus of dust or some other particulate in order to create a snowflake, or raindrop, etc. Australian geologist, Peter Ravenscroft pointed out that this is key to understanding how an unstable layer of subterranean dry ice can form.
He proposes that over eons of time, repeated dry ice snowfall accumulates and is buried. Each speck of dust entrained within that frozen carbon dioxide adds up over time to become a substantial layer of ice-supported sediments in suspension. As more and more lithic material builds from millions or billions of years of dust storms, overlying pressure increases on deeply-buried carbon dioxide ice-supported sediment layers.
When that pressure reaches 5.11 bars (at 211 K), that dry ice will melt, causing a catastrophic collapse and subsequent release of that liquid to the surface. Once at the surface, that liquid carbon dioxide would volumetrically expand ~500 times its liquid volume and flow katabatically down towards Mars' basins. Such events could be responsible for both the unique chaos terrains, and outflow channels we see on Mars today. And all of it without the need for liquid water.
Other energy inputs could cause such collapse as well; Volcanic activity, meteoritic impacts, and/or sudden surface exposure to a near vacuum by new fissures could have released explosive outbursts of carbon dioxide gas too (Hoffman, 2000). And it's probably worth noting that despite Mars' thin atmosphere, that planet certainly experiences seasons, which in turn can affect subsurface phases of water.
Mars' orbit is considerably more eccentric than Earth's. This coupled with its tilt, and we observe a planet with seasons of unequal length. Northern winters are warm and short, due to the fact that Mars moves faster near perhelion for reasons to do with conservation laws. Winters in the south, on the other hand, are colder and longer lasting. This is due to the fact Mars moves slower near aphelion. Summers are long and cool in the north, and summers are short and hot in the south. It's reasonable to assume such climatic fluctuations could have some sort of impact on near-surface water ice hovering near or along its triple point. Possibly even cause local collapse that might trigger a cascade of carbon dioxide releases. But I'm no expert.
Hoffman compares his proposed carbon dioxide flows to Earth's pyroclastic, and turbidity flows. In fact, he has dubbed them, "cryoclastic flows" in deference to their volcanic cousins here on Earth. These dense flows of carbon dioxide gas could theoretically continue for 100s of kilometers before dispersing across Mars' basins, due to low atmospheric pressures, and Mars' weak effect of gravity.
Below is an excellent example of a turbidity flow which occurs off coasts of continents around the world. These flows are considered analogous to Hoffman's cyroclastic flow model:
Hoffman believes such events would have become more common during the Hesperian, as the Sun's luminosity continued to increase with time (as it continues to do today). Cryoclastic flow events would have ceased once large reservoirs of subterranean carbon dioxide left over from the colder Noachian were exhausted.
And as mentioned in the Monterey Canyon photo caption above, such dense flows can create features like tear-drop islands. To further complicate things, such features can also be created by wind-driven processes, which we'll discuss shortly.
Water ice also populates the subsurfaces of Mars in many regions, and as mentioned, exists very near or at the triple point. This could potentially have chemical and petrological effects, as well as curious physical effects when Mars' surface is struck by meteorites.
We'll recall from Part 1 the "splosh" look around craters in and around Kasei Valles; an example of such an impact is shown below for reference:
The crater pictured above, may be evidence of saturated mud, but it doesn't necessarily mean that was the case. Heat energy released by such impacts could have temporarily melted subsurface water, and carbon dioxide ice creating this splosh look; Quickly refreezing thereafter.
As for canyon width and depth, these measures don't necessarily evidence catastrophic flooding events, whether water or carbon dioxide driven. Certainly some fluid cut them, but it could have done so in smaller, episodic events that gradually deepened, and widened the canyons over geologic time.
Canyons could have also been widened by wind-driven processes that could have acted unimpeded for billions of years. Something that I'll emphasize has no analog here on Earth.
Wind-driven Rock Abrasion
On Earth, wind-blown silts and sands can abrade rock for millions of years. But eventually other types of mechanical, as well as chemical weathering processes, and tectonic activity will in one way or another, erase the effects of wind-powered rock abrasion on a given landscape.
These other factors may never have had any significant impact on aeolian-shaped Martian landscapes. In fact, some of them may never have existed on Mars at all; like root wedging, or plate tectonics as examples.
Unlike Earth, the Martian environment allows for wind-blown material to abrade its landscapes over the course of billions of years, not just millions. That's a marked difference in time, and one to which there is no precedent here on Earth.
Though Martian winds are comparatively weak to Earth's due to Mars' thin atmosphere, we do know they're strong enough as an agents of material transport and erosion thanks to Mars' relatively weak gravitational effect. Also, thin air can easily (or more easily) move at high velocities with relatively less energy input than thicker air. We see this evidenced in our 250 mb level jet streams here on Earth.
Wind transport of sediments is clearly evidenced in Mars' barchan dunes, its regional & global dust storms, as well as its many aeolian features; some of which were once incorrectly claimed to have been formed by water... such as the following for example:
Previous Evidence of Water on Mars Now Identified as Grainflows
Could such realizations be foreshadowing more evidence against a Wet Mars Hypothesis to come? Time, and unbiased investigations will tell.
Basalt readily weathers to fine dust given proposed steam, and acidic environmental conditions discussed above. As mentioned, wind certainly didn't create the dust (that whole circular logic thing we covered).
Wind-blown basaltic dust is highly abrasive; A quality that becomes obvious when its effects are modeled over the course of billions of years. Remember, Mars lacks active plate tectonics, and a robust water-infused weather system.
That kind of unimpeded ultra-long-term effect of wind-blown abrasive material simply has no analog here on Earth. So it's no surprise that its potential effects on Martian landscapes is overlooked. Canyons cut by water, carbon dioxide, or whatever fluid folks want to come up with, can be made wider over the course of billions of years. They can also be decorated with all sorts of aeolian features that can be mistaken as being fluvial in nature.
There's no denying Mars' dust-laden winds are observable, active agents of erosion, transport, and deposition in full swing as I write this. Although the process is a slow one, it can still be easily recognized within a human lifetime.
Consider the famed "Martian face" of Cydonia. We've seen it erode over the past few decades right before our eyes. A perfect example of a planet with an active sedimentary erosional, transport, and deposition system. Either that or little green iconoclasts defaced it. I'm willing to bet my hat it's the former though.
For whatever reason, I, and many actual scientists, believe Mars' active, wind-driven sedimentary system of erosion, transport, and deposition has been, and continues to be egregiously overlooked.
Many features widely believed to be formed by flowing water, could just as easily have been formed by dusty winds. Layered wind-dune deposits here on Earth look suspiciously a lot like supposed water-laid layers on Mars. As geologist Peter Ravenscroft points out, fine dust and silt can create flow lines, tear-drop islands, eroded mesas, and depositional lobes, with simply katabatic flow, and related fluid-bed dynamics. And it can all happen within current atmospheric conditions.
But time is often underestimated when it comes to Martian landscapes. As we've discussed, stuff on Mars has billions of years to form, not mere millions as is the case here on Earth. Planetary scientists need to take off their biased Earth glasses, and look at Mars impartially. Impartiality, and a sense of tentativeness when it comes to conclusions, are hallmarks of true science.
Consider Ares Vallis. We discussed it in Part 1: It's widely believed to be a vast flood plain; An outflow channel out of Iani Chaos, and the landing site of the Mars Pathfinder (and accompanying Sojourner) back in 1997.
We might recall these photos taken smack dab in the middle of this, ahem, flood plain from Part 1, but here is a spectacular high definition image as reference:
That image (above) taken in Ares Vallis, may be a perfect example of scientists ignoring the obvious en lieu of belief. Belief, of course, is something that fills the void of a lack of understanding.
I'm no geologist, but even in the eyes of some respected geologists around the world, this looks nothing like any flood channel ever seen on Earth. I'm going to go out on a limb, and say these are definitely not river rocks. And I'm not the only one to recognized this. Actual geologists do too, of which I am not.
For one, these rocks are highly angular, and even first-year geology students learn that rocks transported in rivers become rounded as they bounced and smack into other rocks along the river bed. Basaltic and andesitic rocks round rather quickly, and if this were truly a flood plain, especially one created by catastrophic flow as is the current belief, then we need to rewrite some fundamental understandings in geology textbooks.
These angular rocks are also randomly scattered. We never see this in any rivers. As rocks are carried down rivers, they sort out based on mass and size because rivers gradually lose energy as they descend into areas with less dramatic slope. Boulders are the first to settle out, then cobbles, then sands, then silts, and finally clays. We don't see anything of the kind here.
Also, as pointed out by Peter Ravenscroft (a real geologist unlike me), when larger rock settles out on the riverbed, smaller debris tends to bunch up behind it; Blocked from further transport. Again, we see nothing of the kind in Ares Vallis. Not one rock shows such packing together of pebbles and such. We'd expect to see that, and the packing should be on the side of the rocks facing the flow. Ares Vallis? Nada.
Also, we see what appears to be faceting due to wind abrasion, and oriented (at least in this photo), in the same direction. I'd be curious to know if this facesting is elsewhere in this area, and if the faceting is equally oriented.
Randomly scattered, highly angular rocks, showing no sorting distribution, or packing is clearly not a flood channel landscape. Not even close. But I could be overlooking something. Point here is that these peculiarities need to be explained.
Finally, let's consider possible shoreline features on Mars, like the following:
What we see in images like the one above, and other such images from the Amazonis/Lycus Contact, are 'shorelines' that lack any tell-tale coastal features we'd expect an oceanic shoreline to have. No seaward still-sands, no linear arrangement of coastal dunes following the shore, no wave-cut cliffs, no barrier ridges/islands, beach ridges, spits, or looped barriers appear to exist. The wide flat expanse thought to be an ancient ocean floor, could just as easily been made flat from expected fine dust and silt deposition over the eons from katabatic winds losing their puff in the lowest basins. Such flow naturally flows downhill, and naturally loses the energy to carry dust and silt, thus depositing its material like a blanket across topographically low parts of Mars.
In Part 1 we discussed Worcester crater, pictured below for reference:
Note the interior of the crater has drifts on the bottom left side, but not the top right, which looks like the external deposits are aeolian deposits in the wind shadow of the crater. Noteworthy geology right before our eyes that seems to have been overlooked.
In Part 1 above, we discussed phyllosilicates in Acidalia Planitia as requiring a water-rich environment to form. Mica forms from a melt below surface. Clays as we discussed are weathered products formed at the surface. Chlorites and serpentines are metamorphic products. So not all phyllosilicates indicate surface water.
So after all we've covered (and there is so much more than what we have discussed), is it fair to say Mars once had an ocean, or any standing or flowing bodies of liquid water on its surface? Likewise, is it fair to say it didn't? The answer to both those questions remains "no". As I said earlier a couple times, remote sensing, landers, probes, rovers, spacecraft... they will never be able to conclusively reveal Mars' ancient past. The only way will be to have feet on the ground, footsloggin' about, taking in situ measurements, and bringing quarantined samples back to Earth for further study. And it will take decades of this sort of work, and I suspect hundreds of billions, if not trillions of dollars to do.
But as is the theme in previous TMorB posts, we should first figure out how to adequately protect those scientists before we rush to be the first on Mars. Putin, Musk, Zubrin, and others may not like to hear that, but if we truly want to become interplanetary, we need to learn to be morally responsible first. But what do I know.
So I already said it, but the conclusion as to whether Mars was once home to an ocean and warm climate is thoroughly INCONCLUSIVE.
No one should be making any claims about Mars' deep past, and those who do are doing so in folly. In fact, to make any claims, or to even say this or that is "likely", or "probable", really only serves to demonstrate a general lack of understanding, or lack of information, or just plain old wishful thinking.
Many scientists, most of whom seem to get the most media coverage (few of whom are actual geologists or planetary scientists), seem to me to have preconceived notions of what Mars is, was, and will be. As we started out discussing, such bias is not scientific, and misleads the public who is genuinely interested in Mars, and very trusting of what they're told by those with PhDs.
This blog post barely scratches the surface of all the complications scientists are faced with in trying to interpret its landscapes, and mineralogy. Some evidence looks good for water, some looks bad. Some alternate hypotheses make valid points and seem to solve problems that arise when invoking water, but then they have their own problems.
One thing all scientists agree on, is that there is definitely water on the Red Planet, and images such as the one from Aromatium Chaos (pictured above in Part 2) are very convincing for there having been flowing water at the surface. But for how long, and are we certain it was indeed water? The evidence on Mars is confusing, and in some cases outright paradoxical, often requiring spectacular invocations of thicker-than-Earth atmospheres, and flooding events that rival the channeled scablands of Washington (that's worth looking up if you're unfamiliar).
But this fact (that Mars has water) could have a myriad of implications, some of which we may not have even thought of yet, and none of which might support an ocean hypothesis. The thing to do is to approach this fact without an Earth-bound prejudice, or some internal bias, and do research as research was meant to be done. Mars is not Earth, and I would even go so far as to say it isn't even Earth-like. I know that goes against the popular grain, but other than photos of some features, I have read nothing of the Martian environment (including how features were formed) that make me think, "oh wow, that's a lot like Earth". But as I always say, what do I know.
We can't want the Wet Mars Hypothesis to be true, and then tailor our research to support that fact, especially when such research ignores some fundamental understandings that might actually conflict with the conclusion.
As mentioned earlier, I doubt we'll get definitive answers from landers, rovers, and orbiters on and around Mars. They will and have provided clues, but it will take actual scientists on the ground with the equipment (and PROTECTION) they need to do first-hand investigations. Until that day, and until evidence supports one hypothesis or another to a degree where there is actual consensus, the best answer to the question of whether Mars had a warm, wet past is, "We don't know." At the very least, language suggesting "there is strong evidence for", or "some evidence suggests" are more honest than outright claiming an ancient Martian ocean, or a lush, green world as fact. There is no doubt water on Mars, and as we've discussed, there is strong evidence water may have once flowed on Mars. Consider Kasei Valles for instance (discussed earlier). We must also recall that the chemical elements in water, hydrogen and oxygen, are some of the most abundant elements in the universe. The water molecule is a detected cosmic molecule in interstellar and circumstellar environments (Fraser et al., 2002).
It seems most likely that if Mars had flowing water on its surface, it had it very early on after its formation. Atmospheric pressure was extreme as compared to Earth, and the water was likely acidic. Not the cool, refreshing ocean some seem keen on believing in. Life can exist in such conditions, but I wouldn’t hold my breath for anything beyond single cellular form. But what do I know.
I leave you with this 10-second clip of well-known influential scientist, Michio Kaku, wherein he describes Mars' deep past to millions of trusting viewers. Imagine what you might have thought having seen this before reading this humble post, and what you might think now that you've read it. I think that distinction will prove profound. He could be more honest to his audience, by saying Mars may have once been host to large bodies of surface liquid water that may have harbored single-celled lifeforms. There is no evidence that the planet was once lush, and tropical, but the prospects are intriguing as our landers, rovers, and orbiters continue to gather more data in the years leading up to eventual human exploration of the Red Planet.
Thanks for reading.
Fluvial: Processes associated with rivers and streams, as well as the deposits and landforms created by them.
Aeolian: SImply, having to do with wind. Contrary to what Wikipedia says about "Aeolian Processes", wind itself is NOT erode material. It can transport, and deposit material.
Erosion: When rocks and sediments are picked up and moved to another place by ice, water, wind or gravity.
Weathering: Includes processes that either dissolve, wear away or otherwise break down rock into smaller and smaller pieces.
Cementing: The last stage of lithification, wherein ions carried in groundwater crystalize between sedimentary grains, filling in pore spaces and interconnecting grains into a single bound rock.
Fossae: The plural of fossa, which is a descriptive term for long, narrow depressions on the surface of planets, dwarf planets, moons, and other extraterrestrial bodies, whose geology and geomorphology are yet unknown, or largely unknown with certainty.
Rise: Insofar as I'm aware, a rise (at least on Earth), is in reference to an underwater feature found between the continental slope and the abyssal plain at the bottom of oceans. It is the slope between continents and the deepest part of the ocean. It seems this is being alluded to in place names on Mars, in particular the region dubbed Elysium Rise, which transitions down into the Utopia Planitia in the same, interpreted way, as a continental rise on Earth transitioning into an abyssal plain.
Planitia: Latin word for 'plain'.
Chaos: When used in a place name on Mars, it is referring to the chaotic terrain described in this post (above). This type of terrain consists of jumbled ridges, cracks, and plains enmeshed with one another. Earth has no such terrain, though it has been observed on Mercury, Europa, and Pluto.
1. Groundwater release events are believed to have emanated from Echus Chasma in the Lunae Planum high plateau north of the Valles Marineris canyon system.
2. The volcanic plain referred to is Chryse Planitia.
3. The "island" feature being referred to in the southern channel is Lunae Mensae.
4. Valles Marineris begins at Noctis Labyrinthus and cuts east as a series of chasmata (the plural form of chasma, a planetary geology term for deep, elongated, steep-sided depressions), then emptying out as an apparent outflow channel across Chryse Planitia.
5. If a tsunami event did occur, scientists believe Lomonosov crater might have caused it.