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