List of evidence for water on Mars Options

[pumpkinpie]

Does there exist a list of all the evidence of water on Mars, listed by spacecraft?

Ideally, it would be a list with a short description and a link to a story or news release. For example:

Mars Global Surveyor: NASA Images Suggest Water Still Flows in Brief Spurts on Mars http://www.nasa.gov/mission_pages/mars/new...s-20061206.html
Phoenix: NASA Spacecraft Confirms Martian Water, Mission Extended http://www.nasa.gov/mission_pages/phoenix/...x-20080731.html
Opportunity: NASA Mars Rover Finds Mineral Vein Deposited by Water http://www.nasa.gov/mission_pages/mer/news/mer20111207.html

I know I could spend some time and extend the list that I've started above, but if someone or some organization has already done it I'd hate to reinvent the wheel!

Thank you.

[elakdawalla]

It would be a long list. Don't look for press releases, look for scientific papers. An easy way to do that is the NASA ADS abstract service.

Here is a link to a NASA ADS abstract service search for papers whose titles contain "water" and "Mars." The database contains 2004 entries that satisfy those criteria. Only 200 titles are displayed in response to any one search.

[pumpkinpie]

Thanks for the reply!

I think I should have been a little more specific in my post. Sometimes I forget that people can't read everything I think about when I am typing.

I work in a planetarium, so I do shows on Mars for the public and for schools. I would love to have just a highlights list--what scientists and/or NASA E/PO think are the (for example) 10, 20, 50 "best" discoveries of evidence of water on Mars. Every month it seems there is a new release saying "best evidence yet!" so that makes me think, ok, what was the last "best evidence yet!" and the one before, and the one before, etc.

I would use it a number of ways. For my own background information, so I am ready to answer the question from a student or general public "how do we know there is/was water there?" in 30 seconds or less. That applies for my student employees, too. They wouldn't have the same time to dedicate to learning about this topic as I do, so I would want to give them a simple list. It would also be great to include in handouts I give to teachers.

I may be asking a lot, with the only answer being "do it yourself and use your best judgement."

[elakdawalla]

This sounds like a pitch for a magazine article. I don't know of anything like this that currently exists. It would take a lot of research and would be outdated as soon as it was posted. You might try reading about water in Fredric Taylor's Water on Mars; that would be a good summary of the current state of the science, up to date as of 2009.

[JRehling]

There are a few different parts of the answer, broken down by ice/liquid/vapor, and past/present. And past includes many past eras.

Phoenix took a photo of the ice like a hockey rink in the polar subsurface, so that's about as direct evidence as you could ask for regarding the ice/present combination. That was no great surprise after Mars Odyssey showed the extent of subsurface ice by detecting where neutrons were absorbed by hydrogen (which is a component of virtually no other mineral than water ice).

Pointers to other key evidence are:

MGS and MRO: Orbital observation of gullies formed in the present.

MRO: Orbital detection of minerals that are likely formed only in water.

Opportunity: In situ detection of minerals and geomorphology that indicates standing (acidic) water.

This is far from exhaustive, but if you only have 30 seconds, you can only say so much.

[pumpkinpie]

Simple, but very helpful! Thanks!

[mcaplinger]

This is far from exhaustive, but if you only have 30 seconds, you can only say so much.

Water vapor was detected and globally mapped by the Viking Orbiter MAWD instrument, and the residual north polar cap was confirmed to be water ice by Viking as well.

There was some Earth-based spectroscopy in the 1950s that suggested the polar caps were water ice, but I'm not sure how definitive those were.

[nprev]

IIRC, they did the same around the same time for the clouds.

[mwolff]

Water vapor was detected and globally mapped by the Viking Orbiter MAWD instrument, and the residual north polar cap was confirmed to be water ice by Viking as well.

There was some Earth-based spectroscopy in the 1950s that suggested the polar caps were water ice, but I'm not sure how definitive those were.

Water vapor was identified in 1963:

Spinrad H, Münch G, Kaplan LD. 1963. Letter to the Editor: the Detection of Water Vapor on Mars. Astrophysical Journal 137: 1319


Water ice in clouds in 1973:

Curran RJ, Conrath BJ, Hanel RA, Kunde VG, Pearl JC. 1973. Mars: Mariner 9 Spectroscopic Evidence for H<SUB>2</SUB>O Ice Clouds. Science 182: 381-3

[JRehling]

On a meta-level, I recall that Earth-based spectroscopy of the planets has a long history that began with inappropriately low standards of calibration, so water vapor may have been "detected" in the atmosphere of Mars a long time before it was actually detected. It may be hard to know now which early efforts actually observed water vapor in Earth's atmosphere and simply attributed it to Mars. But certainly the time came when these studies were done right.

[mcaplinger]

...I recall that Earth-based spectroscopy of the planets has a long history that began with inappropriately low standards of calibration...

Hence my caveat about Earth-based detection upthread. I didn't do any research on Mike Wolff's citation of Spinrad 1963 to form an opinion about whether it was certainly right or just happened to match reality. I'm fairly sure there was no credible result to 1950 or so; see http://en.wikipedia.org/wiki/History_of_Mars_observation for an incomplete survey of this.

[mwolff]

On a meta-level, I recall that Earth-based spectroscopy of the planets has a long history that began with inappropriately low standards of calibration, so water vapor may have been "detected" in the atmosphere of Mars a long time before it was actually detected. It may be hard to know now which early efforts actually observed water vapor in Earth's atmosphere and simply attributed it to Mars. But certainly the time came when these studies were done right.

This seems to be a somewhat disparaging comment, but it is sufficiently vague (with respect to antecedents ) as to be more puzzling than anything else. To be clear on the two citations that I made, but perhaps less brief:

The Spinrad et al. (1963) paper detects 11 weak water vapor that are detectable from ground-based measurements because of the Doppler shift of Mars at that time (and the use of very high resolution spectroscopy). Using the line equivalent widths and some guesses for the curve of grown, the arrive at an abundance of 5-10 pr-microns. This article is freely available:

http://articles.adsabs.harvard.edu/full/1963ApJ...137.1319S

This article is brief to say the least. Apparently, there was great interest in getting their publication out as quickly as possible. For more discussion of the history of water detections on Mars, one can find some useful discussion in

Kaplan LD, Münch G, Spinrad H. 1964. An Analysis of the Spectrum of Mars. Astrophysical Journal 139: 1

which is also available freely:

http://articles.adsabs.harvard.edu/full/1964ApJ...139....1K

The authors include a reasonable history of previous efforts to detect water vapor on Mars and as well as surface pressure (CO2 lines) and surface water ice.

The water ice detection of Curran et al. is also spectroscopic. You may have to apply Occam's Razor to this one...the signature is quite consistent with water ice (and is cited in the Mars literature as the first detection), but it is a single line (12 micron). You can see both the 12 and 45 micron features in Thermal Emission Spectrometer data, though instrumental issues and surface emission uncertainties have made this latter a bit problematic for facile use.

[ElkGroveDan]

ADMIN HAT ON

Let's be clear here everyone before this topic strays. It's not a discussion or debate about which evidence you may feel is or is not conclusive proof of water on mars at the time it was acquired. It was a request for a list of "evidence." Let's try and focus this on specific announcements and studies that point to water on Mars -- someone somewhere with some level of credibility pointed to data and articulated a case for water based on that data. And for Pete's sake we don't need to get into the semantics of what is meant by "water."

It's a really good question and I think all of us would be fascinated by that "list" and how it has evolved over the years.

[mcaplinger]

Umm. If we're going to get historical, let us certainly not forget the directly-observed-and-mapped-by-famous-astronomers canals of Mars...

http://en.wikipedia.org/wiki/Water_on_Mars is a reasonable, if incomplete, survey of that. Frankly I hadn't bothered to mention pre-1950 "evidence" because it's now well-known to be spurious. As an example of wishful thinking in science, though, it's certainly useful.

[JRehling]

Speaking just to the spectroscopic detection of H2O (or any other vapor/gas) in planets' atmospheres, there was a sequence of increasing sophistication. The most naive approach was to look at the body's spectrum and assume that any observed substance was present at the body. The next most sophisticated approach was to look at two bodies and presume that any substance seen on body A but not on body B must be present on body A but not on body B. By the 1960s, a much savvier test was used: To count as evidence only those spectral lines which show the correct Doppler shift given the motion of the body.

I wasn't seeking to disparage any particular result, simply to state that it's not a given that past claims that may happen to have been correct may not have been the result of a properly convincing study. Whether this was first done right in 1867, 1913, or 1963, I don't know. It's easier to look at old spectroscopic studies that claimed incorrect things and know that they were wrong, and as of the 1960s, incorrect beliefs regarding Venus still found validation in spectroscopic studies.

EDIT: The 1963 citation did use the Doppler shift as verification, which seems like exactly the right thing to do. I note that in the same time frame, the same researcher, Spinrad, used spectroscopic observations of Venus to conclude that CO2 was a minority component of Venus's atmosphere, behind N2. Which is to say that at least to some extent, the researchers of the time, that one in particular, were overestimating the informativeness of the techniques and instruments of their time.

[belleraphon1]

There was a conference earlier this month at UCLA on Mars Habitability: link below

http://planets.ucla.edu/meetings/mars-habi...y-2013/program/

Day One sessions include fascinating presentations on the possibility of transient liquid water near the surface today. Alfred McEwen gives a 30 min update on Mars RSL (Recurring Slope Lineae). They are now identifying sites at Vallis Marineris that track the sun. Also updates on Phoenix results are presented. Chemistry of perchlorates…. There are video and pdfs for most of the talks.

Two examples:
Behavior of Briny water at the Phoenix Landing site
https://connect.arc.nasa.gov/p4cbkn97lbv/?l...p;pbMode=normal

Recurring Slope Lineae (RSL): Flow of Briny Water on Present day Mars
https://connect.arc.nasa.gov/p27eg800f7b/?l...p;pbMode=normal

Craig

[marsbug]

Pardon the thread necromancy, but this seems like the best place to mention this paper from the university of Michegan. They demonstrate, using an environment chamber, a plausible mechanism whereby Martian ice could melt to form droplets of liquid water, under present day conditions.

For those without access, here's the press release.

My main criticism is that the salts used here only occur as a few percent by weight in any Martian soils we have examined. Nothing rules out higher concentrations, but fairly finely distributed grains of such salts would make Mars very mildly damp, not wet!

[serpens]

Not even mildly damp. With 1 to 2% of perchlorate found in the regolith by Phoenix this experiment where perchlorate salt is layered over ice hardly represents a simulation. Forgive my cynicism but the analogy would be using a high pressure fire hose to simulate a light drizzle to prove that spray jackets are ineffective. The TECP effectively confirmed that no brine was present in the regolith.

[marsbug]

There's certainly nothing to forgive, I think your skepticism is entirely warranted! But, if we look past the iffy connection to the phoenix mission and its 'blobs', I think this is a meaningful piece of experiment - even if the interpretation isn't all it might be: Such salts as are found on Mars can interact with near surface ice to produce liquid, even under current atmospheric conditions. If soils with much higher concentrations of such salts are ever found, or existed in the past, then such brine-y dampness might have played a role in the history of some areas. And ruling out the idea of deliquesence leading to the formation of surface liquid, even in highly salty soils, is a useful result to.

[TheAnt]

Studies done at Niels Bohr institute in Copenhagen have found that Mars has belts of glaciers consisting of frozen water.

[marsbug]

This makes me wonder: If ice, at a lattitude and altitude that put temperature and pressure in the 'liquid water range', were exposed ona sunwards facing slope today (by landslide, impact, man digging with shovel, whatever) how much hydration would the immediate surroundings actually get? Because, as I understand it, even when Martian conditions are at their most water-favourable only small amounts would form, and only briefly.

I could believe however that a liquid water pocket(s) might form beneath the translucent surface of said exposed ice, and find its way surfacewards - but it still seems as though the surroundings wouldn't get very 'wet'. I do recall experiments with pure ice under martian conditions being done, but cannot find them Of course 'chemically enhanced' (antifreeze of some kind laden) water would be more stable....

[TheAnt]

On Earth you will often find water under a glacier, on Mars the temperature is lower so it might only happen under special conditions, and if the glacier is on top of an area with a lot of salts such brine is then potentially possible.
Since Mars is thought to be in a current ice age, this report also adds a piece to the puzzle on where the 'missing' water ended up.
Some images from orbit have shown what might be comparatively recent water flows, with only few or nearly no craters. So I found this interesting since these glaciers might be part of the hydrological cycle when the climate switch to a more benign state.

[serpens]

A glacier is by definition dynamic. So are they claiming that the ice is still moving under regolith or are they identifying relict, now static deposits? The presence of huge mid to high latitude ice deposits was confirmed by Odyssey and much evidence of glaciation has been revealed over the years. If they have identified active glaciation under the insulating cover (movement of existing deposits under gravity but without any replenishment) then this is indeed a stunning discovery. Otherwise it is just a variation on a theme.

[Fran Ontanaya]

"Transient liquid water and water activity at Gale crater on Mars"

http://www.nature.com/ngeo/journal/vaop/nc...l/ngeo2412.html

[katodomo]

EGU 2015 Press Conference 5: "Water Signatures on the Martian Surface"

Basically three different teams presenting findings on various particular surface forms shaped by water they're searching for.

[TheAnt]

If they have identified active glaciation under the insulating cover (movement of existing deposits under gravity but without any replenishment) then this is indeed a stunning discovery. Otherwise it is just a variation on a theme.

You are right, and from the press release I was not able to determine if it was to be read as if they had found actual changes, though we now do have image resolution that would make it potentially possible to detect such movements.
So I did not make any speculation but only listed the press release at first, but in the follow up post after marsbug I did mention the possibility of water under such glaciers since - at least on Earth - water lessen the friction in the underlying rocks, sand and gravel so that the glacier can move.
Glaciers on Earth often ends with a flow of water, but I do not expect any such to reach the surface of Mars now these are buried. Perhaps it would be possible to detect an elevated level of humidity of water vapour to show that there's some water beneath.
-Anyhow it seem that the paper is written by a post-doc, so it might indeed be a "variation of a theme", where she's testing the water in the scientific publication world for the first time. =)

[katodomo]

Glaciers on Earth often ends with a flow of water, but I do not expect that on Mars now these are buried.

I haven't really read that much more than the abstract, but this paper on interaction between buried glaciers, permafrost ground and intrasedimental ice (on Earth) might be helpful.

[scalbers]

Will Monday's announcement be about further water evidence?

http://www.jpl.nasa.gov/news/news.php?feature=4720

[dolphin]

Rumor suggests a discovery of flowing water. I would think that the low air pressure would cause water to just boil off.

Will Monday's announcement be about further water evidence?

http://www.jpl.nasa.gov/news/news.php?feature=4720

[nprev]

If that has any validity it would probably be a reference to the slope streaks; not flowing open water, and very transient (whatever they actually turn out to be.).

However, as you said, it's just a rumor. Could be a few other things instead. We'll know on Monday.

[dolphin]

If that has any validity it would probably be a reference to the slope streaks; not flowing open water, and very transient (whatever they actually turn out to be.).

However, as you said, it's just a rumor. Could be a few other things instead. We'll know on Monday.

I suppose if its briny water, you could see flows that are, as you say, transient. We'll find out soon enough.

[drz1111]

Just like the Atacama. Cool that it happens at that T+P.

[dudley]

Clear evidence of liquid water on Mars' surface has just been announced by NASA. It's believed that the water contains salts which lower its freeezing point, allowing it to remain liquid. Whether or not such brines could allow life to flourish is apparently a point of scientific contention. Link, below, to NASA release:
nasa confirms evidence that liquid water flows on today's mars

[scalbers]

The lowered melting point in the presence of perchlorates reminds me of the possible water drops seen from Phoenix.

[JRehling]

Some rather acrobatic surface missions that we might want to pursue now are:

1) A lander/etc that could sit at the base (top?) of a promising slope and try to observe one of these events when it occurs.
2) A lander/rover/etc that could visit the surface precisely where one of these events had recently occurred.
2.1) A sample return of the above.

These are all rather challenging goals, but the interest will certainly be high.

[Gsnorgathon]

A loooong time ago I saw an item somewhere on the JPL site about a "mountaineer" mission. Basically two rovers, one of which would sit at the top of a slope and belay the other while it descended. I'd guess the proposal was first made in response to Mars Global Surveyor's initial reports of gullies.

[dudley]

There seems to be a good deal of concern that visiting sites with flowing water could contaminate them with organisms brought from Earth. Most Mars probes are apparently not fully sterilized. A 'clean' mission to an area with seasonally flowing water would be worth considering, of course.

[marsophile]

In this morning's press conference on Recurrent Slope Lineae (RSL), they mentioned there are some candidate RSLs on Mount Sharp. In answer to a question, it was said that even though contact work might be precluded due to Planetary Protection considerations, it could be useful to observe the process from a distance on the ground.

{EDIT] Sorry, I meant to post this in the main section, not the route section. Moderator: could you please transfer it?

MOD- Done!

[ElkGroveDan]

Ojha first noticed these puzzling features as a University of Arizona undergraduate student in 2010, using images from the MRO's High Resolution Imaging Science Experiment (HiRISE). HiRISE observations now have documented RSL at dozens of sites on Mars. The new study pairs HiRISE observations with mineral mapping by MRO’s Compact Reconnaissance Imaging Spectrometer for Mars (CRISM).

What is puzzling is that there is not even the slightest nod to MGS which identified these kinds of features a decade earlier. (admittedly I've only read the copy that has been released on this and didn't listen in to nay banter during the press conference.)

[Steve G]

Will someone please correct me if I am wrong. Either I am psychic or they've already shown pictures of these water trails a long time ago. When I saw this on the news I was scratching my head, thinking, this is old news.

[elakdawalla]

MGS found slope streaks; recurring slope lineae aren't the same thing, they occur at a much smaller scale. People are pretty confident that slope streaks arise from an entirely dry process.

[stevesliva]

A loooong time ago I saw an item somewhere on the JPL site about a "mountaineer" mission. Basically two rovers, one of which would sit at the top of a slope and belay the other while it descended. I'd guess the proposal was first made in response to Mars Global Surveyor's initial reports of gullies.

There was a proposal to belay into the Valles Marineris to examine the strata. I think the geological interest shifted elsewhere.

[gpurcell]

Seems to me a reasonably priced approach could be a stationary mission on a flat area below one of these sites. Have a fixed super wide angle camera and the biggest telephoto lens possible on a fast rotation mount. Have the onboard computer continually monitor the fixed camera and slew the telephoto lens to any location that shows signs of movement. Also have some really precise environmental sensors to see what is correlated with the discharges.

[atomoid]

I was also confused about the RSL vs 'slope streaks' (vs gullies for that matter) and it seems the slope streaks are the big dust avalanches, more info is in this space.com article.

The small RSL is postulated to be brine flowing just under the surface, actually 'wetting' the top layer of soil. I'm not sure how they rule out the possibility that RSL are also avalanches of a sort that are merely exposing the darker salty subsoil underneath a dusty top layer, as can be inferred from how perchlorates are suspected to be formed (Science Times article Arizona Dave shared in this post)

[dolphin]

Am I missing something? Why would briny perchlorate heavy "liquid water" be seen as remotely habitable for life or even resource mining? As to the latter, we know there is water ice trapped in the caps.

Also, this discovery has been known/suspected for 2 years now:

http://www.extremetech.com/extreme/172937-...-contaminate-it

[brellis]

One of the blurbs alluded to the possibility of an airborne source/process. The vineyards of Lanzarote (Canary Islands) are collections of pits that trap condensation from passing clouds and funnel it down to the vines at the bottoms. Could a similar process of condensation be in play here with prevailing winds?

[JRehling]

My sense is:

The subsurface ice layer (as seen under the Phoenix lander) has a ragged boundary where it ends around 40° North/South. Where it abuts steep slopes (often craters), it verges into soil that undergoes significant seasonal heating/cooling cycles. Where it does not do that, it remains at fairly constant temperatures year-round. When local conditions achieve maximum heating and cross a threshold that has not been reached before (either slightly warmer than previous summers), a bit of the edge melts and runs downslope. This partially exhausts the local supply of ice ("local" may mean meters, or even centimeters), so that the same precise spot may not undergo this activity again for a very, very long time, if ever.

If this is an accurate model of the phenomenon, then exploring it will be hard because:

1) It will be easy to list candidate locations to watch but very hard to list candidates that will actually have flows in any given year.
2) Once a location shows the phenomenon while we are watching, that may make the location very unlikely to exhibit the phenomenon again anytime soon.

By rough analogy, imagine trying to send a lander to Earth and place it where a tornado will later happen. The odds are very slim. (In fact, even with people on the ground, few successes of this kind have been achieved.)

We would have better luck if we tried to observe a place where it happened and then explore it relatively soon thereafter.

[serpens]

I have to admit to being a touch underwhelmed by this announcement.

[pac56]

I think the news is they did spectral analysis of it.
Edit: see Emily's blog http://www.planetary.org/blogs/emily-lakda...nouncement.html

[marsbug]

I'd point towards Emily's blog as well. WRT supporting life, I doubt the RSL hang about for long enough. For my two penny worth the significance of this is more as a proof of principle: We now know that the perchlorate salts on Mars can and do produce liquid water, which has been long suggested before but not shown to be actually happening. Finding evidence that it is happening boosts the chances of larger amounts of water being present in the relatively near subsurface.

As for habitability of the water... on Earth, if there's water there's microbial life (almost) without exception, even if the water is acidic or alkaline enough to be deadly to people. If there is any life on Mars I'd expect it to have adapted to use any resource, especially one as precious and scarce there as liquid water, just as it would on Earth.

[dvandorn]

It seems to me that the confirmation of liquid water mostly impacts landing site selection for future missions, in that the planetary protection protocols specifically prohibit any landings near liquid water with any lander at a sterilization level less stringent than that defined for the Viking landers (i.e., less than 30 spores per vehicle). Otherwise very attractive sites may end up on the verboten list if there are close-by RSL's.

Any idea if this might affect the landing site selection for the 2020 rover? Especially considering the fact that the 2020 rover will be caching samples for potential return -- if you land near RSL's, you have to postulate not only sterilizing the rover to the Viking standards, but also whatever follow-on vehicle collects the samples and returns them to Martian orbit...

-the other Doug

[surbiton]

It seems to me that the confirmation of liquid water mostly impacts landing site selection for future missions, in that the planetary protection protocols specifically prohibit any landings near liquid water with any lander at a sterilization level less stringent than that defined for the Viking landers (i.e., less than 30 spores per vehicle). Otherwise very attractive sites may end up on the verboten list if there are close-by RSL's.

Any idea if this might affect the landing site selection for the 2020 rover? Especially considering the fact that the 2020 rover will be caching samples for potential return -- if you land near RSL's, you have to postulate not only sterilizing the rover to the Viking standards, but also whatever follow-on vehicle collects the samples and returns them to Martian orbit...

-the other Doug

If we are so scared of contaminating Mars, why do we send anything there ?

If we really want to keep all the planets pristine, then we should leave them alone.

In fact, we should be more careful that we accidentally do not bring any "new" microbes back to earth !

[JRehling]

Any idea if this might affect the landing site selection for the 2020 rover?

I would suspect not. The two kinds of environments seem probably distinct, although I recall Spirit finding that "magic carpet" surface and wonder if it was actually on top of some briny liquid or slush.

The elephant in the room is that there are two distinct exploration pathways – Past Water vs. Current Water – and surface missions typical of ones we've seen that pursue one pathway aren't pursuing the other, so there needs to be some strategy. If only one of these pathways existed, we'd be pursuing it. Given that two pathways exist, do we "finish" one before starting the other, interleave them with separate mission architectures, or find a way to combine them?

One possibility for combining them would be to have a single craft for Mars-orbit-to-Earth sample return, and have sample returns from both kinds of environment travel from Mars surface up to that return craft. With craft weighing many tens of kg and samples weighing and 10 g, that would provide a lot of savings if we acknowledge that both kinds of sample return are desirable. Further savings would be achieved in sharing clean ground facilities on Earth for examining samples.

[marsophile]

http://www.hou.usra.edu/meetings/lpsc2015/pdf/2327.pdf

Figure 1 in the above LPSC abstract shows some candidate RSLs in Gale Crater. These were mentioned during the press conference in conjunction with the possibility of a visit by Curiosity. During the question period one of the reporters raised the issue of planetary protection. The reply suggested that they could be observed from a distance at times different from the fixed MRO flyover time, which would be useful. The panelists also suggested that Mars 2020 could have a role and it was stated that the budget included some money for sterilization.

The PC recording can be seen here:

http://www.ustream.tv/recorded/74355422

It is worth listening to the Q&A on the topic of planetary protection.

[Explorer1]

The fact that these features are spread out over so many different regions of Mars separated by thousands of km seems to imply that its false positives that would be the main concern for a future mission, not somehow contaminating the entire planet with one mission. Though like others have said, since their occurrence is almost by definition on steep slopes that can't be easily reached in any case, it's likely to remain an academic question for a good while yet....

[JRehling]

I think there are lots of ways to study/sample these areas if we want to. Of course, there are engineering challenges and a chance of failure, but it's not impossible.

A stationary lander could be paired with an aerobot with cameras on the lander and the aerobot helping the aerobot land precisely on an RSL, sample the soil there and bring it to the lander for analysis or even sample return. That would completely neutralize problems related to the steepness of the slope.

[serpens]

JRehling's post #47 proposing the water source makes good sense. In the main the popular press has reported the finding as salt water flowing on the surface of Mars giving the impression of a bubbling stream. The reality is that the RSL where hydrated perchlorates were identified are a flow in the geological sense of a land slip with ephemeral brine as the fluidizing agent.

[Explorer1]

'Fluidizing agent found on Mars' doesn't have quite the same ring to it in the headlines though....

[serpens]

This makes for rather interesting reading.

http://www.nature.com/articles/srep25106

Accumulating evidence of ocean and lakes, groundwater, streams and deltas, river valley networks seemingly traceable to precipitation, It is beginning to become clear that early Mars had an interesting hydrological cycle.

[marsbug]

The question marks around the RSL's are growing again: http://www.jpl.nasa.gov/news/news.php?release=2016-215

[serpens]

Well Spirit at Tyrone demonstrated that a thin layer of regolith can provide for a relative humidity gradient protecting hydrated salts. If the regolith is breached then the atmosphere acts as a desiccant. This could explain the appearance and then disappearance of limited amounts of hydrated salts in RSL and would not contradict this latest measurement. Or is could be something else. I suspect it will be a long time before there is consensus on RSL.

[Julius]

A study published discussing inverted river channels in Arabia terra as a sign of a warm and wet climate on early Mars talks about ancient river channels flowing from topographic highs to lower regions from south to the lower northern regions. My question is where would meridiani planum fit along this topographic gradient? The rocks stu died by opportunity rover were mainly sulphate rocks suggestive of acidic water alteration . The inverted channels discussed seem to originate on early mars where water would be expected to form different rock types from those observed by opportunity! Maybe I am getting the ages wrong. Correct me if I am wrong.

[serpens]

The linked Planetary Society blog article provides an interesting read on the faint young sun paradox with respect to long lived surface water on early Mars and puts to bed some of the hypothetical explanations. However the article did miss the hypothesis that the solar system transiting through interstellar dust clouds could have the effect of significantly increasing the sun's output through the capture of molecular hydrogen. That hypothesis has always made a lot of sense to me.

http://www.planetary.org/blogs/guest-blogs...le-paradox.html

[HSchirmer]

The linked Planetary Society blog article provides an interesting read on the faint young sun paradox with respect to long lived surface water on early Mars and puts to bed some of the hypothetical explanations. However the article did miss the hypothesis that the solar system transiting through interstellar dust clouds could have the effect of significantly increasing the sun's output through the capture of molecular hydrogen. That hypothesis has always made a lot of sense to me.

http://www.planetary.org/blogs/guest-blogs...le-paradox.html

I saw two recent papers/references that seem relevant, or at least interesting.

FIRST, was a paper on the 11/22 year solar cycle and Jupiter (yes, related to the barycenter theory) which looked at
the 11.07 year cycle of solar atmospheric tides that results from Venus-Earth-Jupiter orbital resonances.

Solar Physics - May 2019, 294:60 | A Model of a Tidally Synchronized Solar Dynamo
https://link.springer.com/article/10.1007/s11207-019-1447-1

So, let's consider that Theory #1 the "solar cycle / planetary barycenter theory" might be correct
well,
let's consider that Theory #2 "Nice-Model" might be correct as well.

In that case, the early Sun had 4 gas giants between ~5 AU and ~17 AU.
Resonances would have driven massive solar dynamo effects.

Basically, if you have 4 gas giants on circular orbits within ~17 AU, you have tides stirring the Sun and stoking the fire.

SECOND is a combination of idea, the mention of lunar GRAIL data that the lunar surface is roughly 15% void space for the first few kilometers, and a review that the breccia and impact melt under Gale crater could be 17 km deep (for comparision, the Marianas Trench on earth is ~11 km deep) with an initial void space of 3,600 cubic kilometers.
This suggests that there is plenty of "space" for liquid water to exist in the Martian subsurface.
That implies that the real trick about water on the surface of Mars is keeping it from draining back down into the regolith.

Perhaps we only see Martian rivers when they run across compacted sediments or permafrost, otherwise, the water quickly soaks into the sand and gravel.

Flip the thinking to view rivers on the surface of Mars more like the meltwater channels on the top of a glacier, as soon as they encounter a lens of clean sand or a crack, they are gone.

https://phys.org/news/2018-01-glacial-mouli...ered-rapid.html

[marsbug]

I don't know if this has been mentioned before, but the story is on several news outlets, so it seems appropriate to post the original paper here: Crocus melting on Mars:
https://iopscience.iop.org/article/10.3847/1538-4357/ab612f

[serpens]

Here is the complete abstract from the LPSC 2020 Marsbug.

https://www.hou.usra.edu/meetings/lpsc2020/pdf/1792.pdf

I believe the last sentence in the abstract is germane. There simply isn't sufficient precipitable water vapor in the atmospheric column to create meaningful brine.

[HSchirmer]

I don't know if this has been mentioned before, but the story is on several news outlets, so it seems appropriate to post the original paper here: Crocus melting on Mars:
https://iopscience.iop.org/article/10.3847/1538-4357/ab612f

I also thought this was quite interesting- but for a slightly different reason-

If a boulder can generate the necessary shadows from positive curved geometry,
wouldn't the negative geometry of a crater have a similar effect?

Also, a crater would seem to have an advantage of access to absorbed/adsorbed subsurface moisture.

[atomoid]

You're right we don't hear much on this anymore. I recall that being part of initial speculation when the first gullies were discovered by MGS some 20 years ago. i got a sense that the cold-trap model didnt hold up but nevertheless i still like to armchair-speculate such processes may remain relevant at certain points in Mars' climate intervals to accelerate erosion in applicable places and contribute to such formations.

[marsbug]

Just generally, from my physics background, layman's understanding of Martian weather and geology, and following forums and threads like this one, it has always seemed like there's no insurmountable barrier to small amount of transient liquid water forming on present day Mars, when the right conditions come together. But really solid evidence of it seems to be elusive, so perhaps, like me, people are waiting for something really direct and unarguable.

[Marz]

I'm sharing this LPSC abstract because it is quite interesting: a site that contains deltas, lake sediments, and a possible extinct underwater geyser basin

"A POSSIBLE SUBAQUEOUS HYDROTHERMAL SYSTEM IN MELAS CHASMA, MARS"
https://www.hou.usra.edu/meetings/lpsc2021/pdf/2432.pdf

[marsbug]

My apologies for the thread necromancy, but it seems that this paper and any debate on it fits exactly:

Modern water at low latitudes on Mars: Potential evidence from dune surfaces

https://www.science.org/doi/10.1126/sciadv.add8868

[HSchirmer]

My apologies for the thread necromancy, but it seems that this paper and any debate on it fits exactly:

Modern water at low latitudes on Mars: Potential evidence from dune surfaces

https://www.science.org/doi/10.1126/sciadv.add8868

Interesting summary
Snows or frosts possible as recently as 1.4 million years ago to 440,000 years ago.

Abstract
Landforms on the Martian surface are critical to understanding the nature of surface processes in the recent past. However, modern hydroclimatic conditions on Mars remain enigmatic, as explanations for the formation of observed landforms are ambiguous. We report crusts, cracks, aggregates, and bright polygonal ridges on the surfaces of hydrated salt-rich dunes of southern Utopia Planitia (~25°N) from in situ exploration by the Zhurong rover. These surface features were inferred to form after 1.4 to 0.4 million years ago. Wind and CO2 frost processes can be ruled out as potential mechanisms. Instead, involvement of saline water from thawed frost/snow is the most likely cause. This discovery sheds light on more humid conditions of the modern Martian climate and provides critical clues to future exploration missions searching for signs of extant life, particularly at low latitudes with comparatively warmer, more amenable surface temperatures.

[serpens]

This is in accord with modeled changes in the obliquity of Mars as below, resulting in cyclical sublimation and deposition of the ice caps. At higher obliquities the poles receive greater insolation and the CO2/water vapor content of the atmosphere increases. The increased greenhouse effect would cause a degree of warming with higher pressure and humidity resulting in deposition of water ice in the cooler, lower latitudes. I assume the 1.4 to 0.4 million year timescale for the features imaged by Zhurong is based on the last modeled obliquity sequence which indicates 7 or 8 cycles.

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[titanicrivers]

Not sure if this is the best topic for this post or if other members have posted this elsewhere already. Anyway, I noticed a SETI Institute Press Release of a presentation at the 54th LPSC concerning the identification of a newly discovered giant volcano on Mars located just south of the planet’s equator, in Eastern Noctis Labyrinthus and west of Valles Marineris. https://www.seti.org/press-release/giant-vo...discovered-mars. The authors’ abstract is here https://www.hou.usra.edu/meetings/lpsc2024/pdf/2745.pdf. I believe this is the same group that presented an abstract at the 53rd LPSC concerning a ‘relict glacier’ in this region. https://www.seti.org/press-release/remains-...t-low-latitudes