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List of evidence for water on Mars
pumpkinpie
post Feb 5 2013, 04:59 PM
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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.
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elakdawalla
post Feb 5 2013, 05:09 PM
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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.


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pumpkinpie
post Feb 5 2013, 06:10 PM
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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. laugh.gif

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." smile.gif
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elakdawalla
post Feb 5 2013, 06:36 PM
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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.


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JRehling
post Feb 6 2013, 06:15 PM
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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.
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pumpkinpie
post Feb 6 2013, 07:57 PM
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Simple, but very helpful! Thanks!
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mcaplinger
post Feb 6 2013, 08:01 PM
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QUOTE (JRehling @ Feb 6 2013, 11:15 AM) *
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.


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nprev
post Feb 6 2013, 10:58 PM
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IIRC, they did the same around the same time for the clouds.


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mwolff
post Feb 8 2013, 03:36 PM
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QUOTE (mcaplinger @ Feb 6 2013, 02:01 PM) *
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


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JRehling
post Feb 8 2013, 07:56 PM
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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.
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mcaplinger
post Feb 8 2013, 08:35 PM
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QUOTE (JRehling @ Feb 8 2013, 12:56 PM) *
...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.


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mwolff
post Feb 10 2013, 03:28 PM
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QUOTE (JRehling @ Feb 8 2013, 01:56 PM) *
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.
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ElkGroveDan
post Feb 10 2013, 05:01 PM
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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.


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mcaplinger
post Feb 10 2013, 10:11 PM
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QUOTE (dburt @ Feb 10 2013, 11:44 AM) *
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.


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JRehling
post Feb 12 2013, 12:17 AM
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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.
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