Ice on Mars

jock & LongT

"the liquid phase has a much smaller range than on earth. Consequently when ice on Mars is exposed to its atmosphere, it very quickly "sublimates" and goes rapidly through the liquid stage directly to a gas"

"The much lower pressure on Mars is below the triple points of both, so both sublimate."

So why do they think Mars had oceans? If what you both say is true would it not be impossible to have oceans of liquid water?

Just to make sure we're on the same page...

When ice sublimates, it goes directly to gas. It doesn't melt first, then go to gas. That would be evaporation.

==NASA states it is water ice==

However, their final judgment waits for the ovens to cook the stuff.

Quietman

I don't know much about the ocean hypothesis on Mars or who takes it seriously, but I think the idea is that it would have had a denser atmosphere, and therefore more pressure. Lose the atmosphere, lose the oceans.

I'm also not sure what the current pressure is relative to the triple point of water. I was just assuming based on what Ned reported.

what about dust falling and re-covering the "ice", from looking at the before and after on jpl's site that seems like a possibility to me as well to explain the disappearance. Exciting as it may be that it is ice, it seems a little premature for him to be making that announcement

Quietman; I'm not an authority by any stretch, but it's possible that Mars never has had any oceans. It's also possible that long ago, Mar's environment was different and could have had more of an atmosphere, but I think that because of it's smaller size, it's gravitational pull never did support much of an atmosphere that would allow a liquid water phase, so I think it unlikely. I think what is interesting now is that since it looks like water vapor and ice are there, where did the oxygen come from to make H2O? Also, there is apparently is some electrical atmospheric activity because I believe you also need that to bond hydrogen and oxygen.

Haven't we known for decades that water ice existed at the poles? I have been reading this for years. Orbiters can read the signature from space so not sure why anyone is acting surprised.

If Mars had all these oceans, where did all that water come from, and, if there was all this water, where are the clouds? Even over our poles, there are clouds.

Now, if we're talkin' carbon dioxide, where's all the vegetation???

If Mars had oceans, it had it long ago when it was young. Mars (and Earth) long ago had a lot more radioactive elements in their crust (i.e., as uranium decays, it releases heat). So a long time ago the interior was warmer and there were a lot more active volcanoes on the surface. Volcanoes release a lot of gas including water and carbon dioxide. So just on that basis, there was more gas in the atmosphere.

The problem with Mars is that it's smaller. So the planet both cooled quicker (less mass to hold heat + less radioactive elements = less volcanoes) AND its gravity is less than Earth. While Earth hangs onto its gas easily, Mars lost most of it to space and doesn't produce much either. We actually have support of this from Martian meteorites.

I really enjoy science and tech news stories, its a good relief from the same old political stories. I would really like ABC news to do more on this Mars rover and other stories like it.

I have to wonder about all the fuss about "water courses" on Mars. Could it possibly be that those supposed water flows can really be the result of volcanic activity, i.e., lava flows? I'm only asking, folks, not suggesting.

Mars DOES have thin whispy clouds. The Rovers have taken pictures of them. The "water courses" have been determined to be simple dry-dirt landslides.

==If Mars had oceans, it had it long ago when it was young.==

On Earth, all the water that ever was, is and every will be is here. That water has gone nowhere, only changed states. This is a rule of the universe.

If Mars had oceans, that water is still there. But where did it go, if it ever had any? It ought still be there, and such a hugh amount ought to be forming way more clouds from even ice crystals.

Now, there IS an atmosphere on Mars. Thin, maybe, but an atmosphere. It's enough to require a heat shield on an entry vehicle arriving from Earth, or someplace else. It's enough to be able to use a parachute; that's not possible in a very thin atmosphere.

A thin atmosphere's molecules are far apart. Such an atmopshere can hold a lotta water, IF there is a lotta water.

Here, in the Phoenix area, when it's hot, the molecules are very far apart, and, when moisture comes in from the Gulf of California in July through August, if it does in sufficient amounts, and that rising, hot air cools, the molecules get closer and they squeeze out the water, and that's what you see as huge, high, towering, cumulonimbuses, or is it "nimbi." But the atmosphere deoesn't make that water visible until it cools.

If Mars had oceans -- a lotta water -- it ought to be there in some form, and it must be getting into the atmosphere. Even though it's cool there, the molecules can't get close together enough to squeeze out that water. However, the atmosphere must be humid, in that case, and that can be measured, though not visible cuz it hasn't been squeezed out.

However, again, somewhere on that planet, it must be so cold that the molecules ARE closer together, and, if there's a lotta water there, they will squeeze out the water into visibility. But no. That's not happening on Mars. The only explanation is that the water isn't there.

If the water is there in ice form, and the atmosphere is thin, that frozen water is eager to get into the atmosphere [sublimation, not evaporation], and that ice should disappear very quickly. It doesn't. And, if it is getting into the atmosphere, there should be a lotta clouds. But, again, no.

BTW, there is enough of an atmosphere that it moves and makes significant dunes, significant erosions and significant other marks on the landscape.

Mr. Incredible -

I applaud your interest in working these things out, but some of your basic assumptions are misleading you:

1. Planets are not closed systems. Water vapor (or any other gas) can escape the atmosphere entirely and be lost to the system. This is what would have happened if atmospheric pressure was lost from an earlier period with oceans. At lower pressures, the water can simply boil off into space.

2. A thin atmosphere does not "leave room" for other molecules. A thin atmosphere means that gasses are not being held by the planet well, and this applies to ALL gasses more or less equally. In fact, the atmosphere on Mars holds about all the water vapor it can, which is why thin clouds often form around mountains.

3. Cold air tends to denser than warm air, because the molecules are less active. It is the kinetic energy (speed) of the molecules that determines the "temperature" more than does the density. It does not follow that dense air is always cold or thinner air is always warm.

==Cold air tends to denser than warm air, because the molecules are less active.==

It's not cuz they are not as active, rather that they are closer together.

The only reason you see moisture is that the air has cooled to a point where the moisture in the air has been squeezed out by the air molecules that are getting closer together. Cool air cannot hold as much water as warm air.

That's why condensation trails behind jets. The engines heat the air that has moisture in it [no visible moisture], and, as it cools behind the engine, the moisture becomes visible cuz the molecules in the cooler air are closer together than in the warmer air, and the same amount of moisture in the warmer air that is not visible, is visible in the cooler air.

Mr. Incredible - Condensation has nothing to do with water molecules being "squeezed out." The behavior of water vapor does not depend on the presence of other gasses in air. Condensation would occur at the dew point even if the only gas present is water vapor. It is dependent only on the kinetic energy of the molecules. There can be more water vapor in warmer air simply because the water molecules have more energy to evaporate.

jock
That makes sense. In winter the air is always drier than summer. At the lab in NJ it ran from 60% and up in summer but 40% and down in winter. But what effect is there from lower atmospheric pressure on Mars? Would it not be more like constant winter at Martian temps?

==Condensation has nothing to do with water molecules being "squeezed out."==

Actually, it does.

When the air is thin, as when it's hot, and there is water in the air, it is not visible.

In the southwest desert, it becomes visible when the hot air, mixed with invisible water, rises and cools. The faster it rises, the more threatening the cloud that forms.

== The behavior of water vapor does not depend on the presence of other gasses in air.==

It depends on how much water is in the air, the temperature of the air and how fast it rises into cooler air.

==Condensation would occur at the dew point even if the only gas present is water vapor.==

Not true of condensation. The water doesn't become visible until the air is cooled enough to squeeze it out. THAT's the dewpoint.

==It is dependent only on the kinetic energy of the molecules.==

No, it depends on the density of the air molecules.

==There can be more water vapor in warmer air simply because the water molecules have more energy to evaporate.==

Not true.

The water stays in the air, invisible, until the air is cooled, squeezing out thde water into the visible. Virga is an example where, in the cooler regions, the water is squeezed out of the air, falls, then, in the lower regions where the air can hold the water, goes back, or evaporates, into the air before it has a chance to hit the ground.