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NASA Says Mars Rocks Formed in a Salty Sea
NASA has made another announcement, live on NASA TV, regarding the discoveries of the Spirit and Opportunity rovers. They believe that the rocks examined by Opportunity were actually formed in water; that those rocks were actually sediments laid down in a shallow salty sea. They've already had outside scientists examine their data and those scientists concur with the conclusions. NASA has a story with explanations and some photos.
Acidophiles.
There is no environment on Earth too extreme for life, as long as there is liquid water.
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No, salt accumulates in the oceans from the erosion of surface soils and rocks, as the minerals wash into larger bodies of water. This may mean that Mars once had rain.
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It (probably) got there in the first place during Mars' formation, and perhaps later due to cometary bombardment.
As to why it was lost, crudely put: evaporation into outer space.
Molecules of volatile gasses, including water vapor, that waft into a planet's upper atmosphere occasionally reach escape velocity and are lost.
Why some gasses and not others? There are a bunch of factors at work:
Heavier gasses -- CO2, for example -- require more energy to get up to escape velocity. They statistically hang around longer.
Larger planets have higher escape velocities.
Planets farther from the Sun recieve less insolation, so there's less of a chance that a molecule will get kicked up to escape velocity.
Except they missed the 2/29 deadline.
No shrimp for you!
A print publication has what, a two-three month (minimum) leadtime?
Yow. Usually much longer than that - only the absolutely highest profile papers (like Nobel prize material) get into press that quickly. This might, of course, but they don't have any competition so they can take their time getting the details and analysis exactly right.
Anyway, science by press release usually isn't a good idea, but I'd make some exception for NASA. Even if they get this wrong, the mission has still been a spectacular success, and if they're right, more people will notice now than six months from now when it appears in Science or Nature.
During the news conference the possibility was raised that this water was under a protective layer of ice. So this could have happened without a thick and warm atmopshere.
The huge volcanos make it pretty clear Mars was once geologically active, I think.
The loss of oceans on mars has nothing to do with a loss in mass.
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The magnetic field Mars current has is not capable of protecting it's atmosphere by deflecting solar wind (the solar wind has been eating away at the Martian atmosphere for some time now; I'm not sure if scientists believe mars ever had a magnetic field capable of doing do, but as it's core has cooled off/solidified the magnetic field on the planet today is what it will always have).
As Mars's atmosphere is stripped away/blown into space, the atmospheric pressure drops. At a certain point, the pressure drops to a point where water cannot exist in liquid form and evaporates -- creating more atmosphere, which then gets stripped away by the solar wind
The cycle continues until all surface water has evaporated or frozen.
Striations can be laid down by wind-blown dust, or by ashfalls from volcanos, to name just two mechanisms tha tdotn require wqter at all. Adn we know that there were volcanoes. If there was an atmosphere at some point, there would have been wind-blown dust. Even in the "wet" category, layers can be created by streams or freshwater lakes. So the 'wet salty' part is also not at all implied by the observation of striated rock alone.
1. What evidence supports or rules out the presence of liquids other than H2O on the surface of Mars, at one time, in large quantities?
No evidence supports any such thing. Nothing rules it out, however, see answer to question #2.
2. How much, if any, of the present evidence could be explained by flows of liquid CO2, nitrogen, methane, ammonia, or some other liquid?
None. The chloride and bromide salts found are soluble in water, not any of those other liquids. By definition, chemical compunds classified as salts require the presence of water.
3. Which evidence, if any, points most strongly to the presence of large amounts of H2O as the liquid in question?
The presence of chloride and bromide salt deposits. They can't be formed any other way, but by precipitation from solution in water. The presence of hematite by itself is less conclusive than that, but in the presence of the salts, it adds to the certainty that water was present.
I know there are currently thought to be large, polar caps of solid H2O, but how much of the current evidence precludes the existence of large seas of some other liquid in the distant geological past?
The salt evidence excludes the other liquids.
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Short answer, temperature. It's way, way, way too warm for any liquid like N2 or methane or ammonia to form as a liquid. And it's always been too warm. So the probability that the rock formations occured from any of those liquids is precisely zero.
Secondly, H2O2 is highly unstable, it quickly decomposes into plain-old H2O and O2 in sunlight and/or temperatures above freezing. Both conditions exist and have existed on Mars for billions of years so there is zero probability that H2O2 had anything to do with it.
2. How much, if any, of the present evidence could be explained by flows of liquid CO2, nitrogen, methane, ammonia, or some other liquid?
Zero evidences for all of those substances. Again, its far, far, far too warm. First, carbon dioxide does not exist in liquid form at atmospheric pressure at any temperature. It requires a temperature of 20 degress Celsius and a pressure of 30 atmospheres to form. Mars has never had such conditions so there is again, zero chance liquid CO2 had anything to do with Mars' sedimentary rocks.
The other compounds on your list require extremely cold temperatures to form into liquids. Far, far colder than it EVER gets on Mars for most of them. It also requires a much higher atmospheric pressure than Mars had for most it's existence. Finally, there isn't sufficient quantities of some of these compounds to form rivers, lakes or oceans, nor is there any evidence of that there ever was enough.
Here's the list of temperatures:
- Nitrogen == -196 degrees Celsius @ 1 atmosphere of pressure
- Methane == -162 degrees Celsius @ 1 atmosphere of pressure
- Ammonia == -33 degrees Celsius @ 1 atmosphere of pressure
You answered your own question, the Martian polars caps consist almost entirely of ice. Enough ice that if they were melted they could form seas covering the entire surface of Mars 15 meters deep.It gets cold enough on Mars for this, but there is very, very little amounts of it.
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