|Still my favourite Mars picture. Cape St Vincent, one of the cliffs of Victoria crater. Credit: Nasa/Reuters|
I recommend an article by Ian Sample, the Guardian’s science correspondent, for more about snow on Mars and other amazing data being sent back by NASA’s rovers there.
|Rock formations on Mars|
That's over then. The image on the right, says NASA, indicates a once habitable environment, not too acidic or alkaline, with chemical gradients that would have created energy for microbes, and a distinctly low salinity, which would have helped metabolism if micro-organisms had ever been present. Data from several instruments on the Curiosity rover all support this interpretation. What we see in the image are very fine-grained sediments.
Too extreme for life
The rock on the left on the other hand is evidence of an environment that is thought not to have been habitable. NASA reaches this conclusion due to various factors. One is the extreme acidity of the water, another is extreme salinity which would have impeded metabolism. Moreover, if any micro-organisms had ever been present, too little energy would have been available, due to very limited chemical gradients. This rock, scientists think, was formed from sulphate-rich sandstone, and the particles were in part formed and cemented in the presence of water; and the bumps on the rock face were formed in the presence of water.
As a footnote, we should recall that the Antarctic Lake Vida tells us to be cautious before saying “life couldn’t survive here”. In November microbes were found thriving in conditions of extreme salinity and cold.
The two rock images have been adjusted to look as they would if they were on Earth. The one on the right puts me in mind of a seaside rock pool but sadly that’s an illusion, there's no water there now.
See NASA Jet Propulsion Laboratory for more particulars of these two images and how NASA scientists interpret them.
Finally, in all the excitement we mustn’t forget that habitability is not the same thing as life. Here's a link to a discussion of Is there life on Mars?, and why after years of discovery the question still eludes us.