Mars never had a dense atmosphere?

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Ann
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Mars never had a dense atmosphere?

Post by Ann » Wed Apr 16, 2014 5:34 am

Ancient Mars May Never Have Had Enough Atmosphere For Liquid Water

The Martian atmosphere may never have been thick enough to keep water liquid for extended periods, according to a new study by Dr Edwin Kite of Princeton University and colleagues.

They studied impact craters in river deposits near Gale Crater on Mars which date back 3.6 billion years.

Some of these craters were made by very small meteorites surviving the fall through the Martian atmosphere and landing on the ground. A thicker atmosphere would have destroyed them before they landed.
The researchers compared the sizes of the craters to simulations say the atmospheric pressure of Mars 3.6 billion years ago would have been much greater than it is today.

However, that pressure is less than required to warm the surface above freezing.

Instead, short-lived surface warming by volcanic eruptions, asteroid impacts or orbital changes of the planet may have temporarily allowed liquid water on the martian surface.
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MargaritaMc
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Re: Mars never had a dense atmosphere?

Post by MargaritaMc » Wed Apr 16, 2014 1:11 pm

Here is an article in Nature:

http://www.nature.com/news/ancient-mars ... S-20140415

The full, subscription only, paper is
Low palaeopressure of the martian atmosphere estimated from the size distribution of ancient craters
Edwin S. Kite, Jean-Pierre Williams, Antoine Lucas & Oded Aharonson
http://www.nature.com/ngeo/journal/vaop ... o2137.html

I really admire the elegance of the thinking behind the study, using the size of craters  to indicate palaeo atmospheric pressures. This is from the abstract:
"The decay of the martian atmosphere—which is dominated by carbon dioxide—is a component of the long-term environmental change on Mars from a climate that once allowed rivers to flow, to the cold and dry conditions of today. The minimum size of craters serves as a proxy for palaeopressure of planetary atmospheres, because thinner atmospheres permit smaller objects to reach the surface at high velocities and form craters. The Aeolis Dorsa region near Gale crater on Mars contains a high density of preserved ancient craters interbedded with river deposits and thus can provide constraints on atmospheric density at the time of fluvial activity. "
I've found this September 2013 arXiv paper entitled Paleopressure of Mars' atmosphere from small ancient craters by the same four authors here http://arxiv.org/abs/1304.4043

The beginning of the arXiv paper abstract reads:
"Decay of the CO2-dominated atmosphere is an important component of long-term environmental change on Mars, but direct constraints on paleoatmospheric pressure P are few. Of particular interest is the climate that allowed rivers to flow early in Mars history, which was affected by P via direct and indirect greenhouse effects. The size of craters embedded within ancient layered sediments is a proxy for P: the smaller the minimum-sized craters that form, the thinner the past atmosphere. Here we use high-resolution orthophotos and Digital Terrain Models (DTMs) to identify ancient craters among the river deposits of Aeolis close to Gale crater, and compare their sizes to models of atmospheric filtering of impactors by thicker atmospheres. " 
So it sounds like the same research as is now published in Nature. 

I'm studying water on Mars currently in the Science of the Solar System course at Coursera, so this finding is getting lots of discussion there!

Margarita
"In those rare moments of total quiet with a dark sky, I again feel the awe that struck me as a child. The feeling is utterly overwhelming as my mind races out across the stars. I feel peaceful and serene."
— Dr Debra M. Elmegreen, Fellow of the AAAS

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