If life once flourished on Mars and some survived the changing conditions, would it be able to move around the planet, finding new locations as old ones dry up? New evidence from the Atacama Desert provides a tentative yes.
It's unlikely the best place for life on Mars today is the same as the best place a million, let alone a billion, years ago. So for microbes to have made it across the vast expanse of time between Mars' wet period and our robotic arrival, they probably needed the capacity to travel. However, it's not likely they could do this under their own steam, so something would need to have carried them, with wind the obvious candidate.
In an effort to see if this is realistic, Dr Armando Azua-Bustos of Universidad Autónoma de Chile went to arguably the most Mars-like place on Earth, the Atacama Desert, to study how microbial migrations occur. There are much colder places on Earth, but none is as dry as the central Atacama, which can also match the Mars' mix of sand, rocks, and intense ultra-violet radiation.
At six sites in the driest part of the Atacama, Azua-Bustos found 23 bacterial and eight fungal species. Moreover, some of these are particularly unlikely to be local in origin, including Oceanobacillus oncorhynchi, which as its name suggests is a marine bacterium. Other species appear to live on the plants that occupy the fog oases at the tops of hills in the desert's coastal fringe. There was surprisingly little overlap between the species found at different sites.
The microscopic life forms reached these locations by catching a ride on wind-borne dust grains. Mars' atmosphere is 100 times thinner, but we know this is still enough to whip up vast dust storms that sometimes envelope the whole planet. Moreover, Azua-Bustos demonstrates in Scientific Reports that many microbes survive the UV exposure on route.
Most of the life Azua-Bustos and co-authors found was carried by the prevailing winds from the Pacific ocean, arriving during the afternoon and dispersing through the desert the following morning. The fact that most of the movement happens in the late afternoon and night (when UV levels cease to be lethal) may play a big part in the capacity of the arriving life forms to flourish in the food dishes Azua-Bustos set out for them.
For all Mars' differences, Azua-Bustos' work suggests that if life ever evolved there, it could be transported to suitable locations. It also suggests placing Martian dust in growth media could be a great way to detect its presence. On the other hand, the paper notes the importance of sterilizing vehicles we send to Mars, lest they contaminate not just their landing site but the entire planet.