Mars Atmosphere Once Held Enough Moisture for Dew or Drizzle
Written by Nancy Atkinson
Data from Mars orbiters and landers have suggested that any past water on the Red Planet’s surface probably came from subsurface moisture bubbling up from underground. But a new study of Martian soil data implies that Mars’ atmosphere was once thick enough to hold moisture and that dew or even drizzle hit the ground. Geoscientists at the University of California Berkeley combined data from the Viking 1 and 2 landers, the Pathfinder rover, and the current rovers Spirit and Opportunity. The scientists say tell-tale signs of this type of moisture are evident on the planet's surface.
"By analyzing the chemistry of the planet's soil, we can derive important information about Mars' climate history," said Ronald Amundson, UC Berkeley professor of ecosystem sciences and the study's lead author. "The dominant view, put forward by many now working on the Mars missions, is that the chemistry of Mars soils is a mix of dust and rock that has accumulated over the eons, combined with impacts of upwelling groundwater, which is almost the exact opposite of any common process that forms soil on Earth. In this paper, we try to steer the discussion back by re-evaluating the Mars data using geological and hydrological principles that exist on Earth."
The team says soil at the various spacecraft landing sites have lost significant fractions of the elements that make up the rock fragments from which the soil was formed. This is a sign, they say, that water once moved downward through the dirt, carrying the elements with it. Amundson also pointed out that the soil also shows evidence of a long period of drying, as evidenced by surface patterns of the now sulfate-rich land. The distinctive accumulations of sulfate deposits are characteristic of soil in northern Chile's Atacama Desert, where rainfall averages approximately 1 millimeter per year, making it the driest region on Earth.
Researchers compared images such as this image of the Atacama Desert with the above image taken by the Opportunity rover on Mars, which show similar surface patterns.
"The Atacama Desert and the dry valleys of Antarctica are where Earth meets Mars," said Amundson. "I would argue that Mars has more in common geochemically with these climate extremes on Earth than these sites have in common with the rest of our planet."
Amundson noted that sulfate is prevalent in Earth's oceans and atmosphere, and is incorporated in rainwater. However, it's so soluble that it typically washes away from the surface of the ground when it rains. The key for the distinctive accumulation in soil to appear is for there to be enough moisture to move it downward, but not so much that it is washed away entirely.
The researchers also noted that the distribution of the chemical elements in Martian soil, where sulfates accumulate on the surface with layers of chloride salt underneath, suggest atmospheric moisture.
"Sulfates tend to be less soluble in water than chlorides, so if water is moving up through evaporation, we would expect to find chlorides at the surface and sulfates below that," said Amundson. "But when water is moving downward, there's a complete reversal of that where the chlorides move downward and sulfates stay closer to the surface. There have been weak but long-term atmospheric cycles that not only add dust and salt but periodic liquid water to the soil surface that move the salts downward."
Amundson pointed out that there is still debate among scientists about the degree to which atmospheric and geological conditions on Earth can be used as analogs for the environment on Mars. He said the new study suggests that Martian soil may be a "museum" that records chemical information about the history of water on the planet, and that our own planet holds the key to interpreting the record.
"It seems very logical that a dry, arid planet like Mars with the same bedrock geology as many places on Earth would have some of the same hydrological and geological processes operating that occur in our deserts here on Earth," said Amundson. "Our study suggests that Mars isn't a planet where things have behaved radically different from Earth, and that we should look to regions like the Atacama Desert for further insight into Martian climate history."
Original News Source: EurekAlert
Filed under: Book Reviews, Mars
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June 26th, 2008 at 12:31 pm
Hmmm . . . where do you suppose the water on Mars, if it ever existed, disapeared to? Was it evaporation? With Mars gravity at about .38% that of earth, it doesn't seem likely it escaped to space or did it? Or did it soak into porus soil? Probably not! Was the planet warmer in early life where water was in a liquid state? But how can that be with surface temparature not friendly to liquid water? More questions than answers!
June 26th, 2008 at 5:19 pm
Where did all the water go? Some of it, as we now know, is frozen under the soil in the polar regions. But a lot is probably gone forever.
UV light can slowly split water into hydrogen and oxygen ions. Since these are charged particles the charged solar wind can pick them up and carry them away because Mars has no magnetic field to protect it from the solar wind. The same this is known to be happening on Venus; it's gradually losing what's left of its water. Earth is OK because we are shielded by our strong magnetic field- the hydrogen and oxygen stay in our atmosphere and presumably turn back into water.
June 28th, 2008 at 5:21 am
is it coincidence that we have a magnetic field and a large moon? Is it the moon perturbing the interior of the earth which keeps the core molten and with it the magnetic field ? If mercury was venus's moon, would it be a very different place than it is now???
June 28th, 2008 at 3:09 pm
According to current theories, Earth's magnetic field is generated by the movement of molten iron inside its core. It's all very complicated and I barely understand it, but to create a magnetic field you need three things:
*A conducting liquid. Molten iron is perfect for this.
*Convection. You hot liquid to be able to go up, and cold liquid down.
*Rotation. The planet needs to be spinning.
Venus as far as we know has a molten iron core, but its day is 243 earth days long which is only enough to generate a weak magnetic field. Also, it has virtually no convection in its core. This is because there is no temperature gradient in its core. On Earth, plate tectonics allow some of the heat to escape so that parts of the core are always cooling and there's a temperature gradient. Venus has no plate tectonics. Slow rotation and no convection = bugger all magnetic field.
Mars has a day short enough to power a dynamo, but it also has no plate tectonics, and its core is more solid than Earth's or Venus'.
June 28th, 2008 at 6:41 pm
Now to finish my lengthy ramble…
What would happen if we magically grabbed Mercury and put it into orbit around Venus? Would it help?
Well, the gravitational effect of Mercury would gradually change Venus's rotational period. This has already happened in the Pluto/Charon system, so that the two always keep the same face to each other, and the same thing is happening with the Earth and the moon. But would Venus speed up or slow down. It would only slow down if Mercury's orbit took longer than Venus's day (243 earth days). That's too far out for Venus to hold on to Mercury against the Sun's gravity. I did some quick calculations and I think the biggest stable orbit would be about 50 days long. So Mercury would slowly speed up Venus's rotation, which helps. (On the other hand, Earth's day is shorter than the Moon's orbit. So our day is getting longer and our own dynamo should be very slowly weakening.)
If Mercury's orbit was eccentric (and it would be, because the Sun would be constantly causing little disturbances) you'd also get tidal forces within Venus. The core would be stretched and pulled, generating heat. The same thing is happening in the large satellites of Jupiter- particularly Io where tidal heating creates tremendous heat that powers its volcanoes. More heat means the core will be more molten, and stay molten for longer. That also helps.
The big sticking point is convection. You still need a temperature gradient in the core and, as far as we know, tectonics is the thing to do it by releasing heat through cracks in the crust. I don't see how the presence of a moon can start plate activity on a planet that doesn't have any. I don't know if tidal forces alone can set up convection currents in a planet's core, but it seems doubtful.
I suppose, after all that, a moon might help a little bit if you want a magnetic field but not very much.