The quest to discover life on Mars has concentrated on seeking liquid water. However, all life on Earth needs other nutrients as well, many of which are likely to be universally required. Despite Matt Damon's fictional success in growing potatoes in Martian soil, Mars is very low on certain nutrients. However, a new theory proposes these are being supplemented by material from space.
The Earth has exceptionally diverse geology, thanks to a combination of plate tectonics and the widespread presence of water and oxygen. Mars, on the other hand, is mostly made of weathered basalt, leaving it deficient in the basic chemicals life may need to feed itself. The nutrients required in most abundance, carbon and biologically available nitrogen, are known to exist there, but others may be equally essential.
Iron is abundant on Mars, but it has oxidized into the red sand that gives the planet its distinctive color. The reduced iron early Earth life-forms are thought to have needed is harder to find, as is reduced phosphorus, sulfur, or nickel.
All of this raises the question, if life ever did appear on Mars, and managed to access water, would it have enough nutrients to grow?
Dr Andrew Tomkins of Monash University doesn't have an opinion on whether Mars has life, but he thinks if it exists these nutrients may not be too much of an obstacle. Shortages of what Tomkins calls “home-grown nutrients” are assuaged by micrometeorites, also known as cosmic dust, he argues in The Journal of Geophysical Research.
Earth experiences a steady rain of micrometeorites containing a rich variety of elements. However, Tomkins told IFLScience these burn up in the atmosphere, converting the iron and phosphorus in particular to oxidized forms, likely to be less useful to life.
Mars, of course, has a much thinner atmosphere than Earth, with even less oxygen, and Tomkins calculates much of the material from space would make it to the Martian surface in a form useful to life.
“The surface of Mars is very old,” Tomkins said in a statement. “Some areas are millions of years old, and the infalling cosmic dust builds up over time.” To try to understand how this would work, Tomkins went to the most Mars-like place on Earth he could find, Australia’s Nullarbor desert. He studied the way grains of different size move around. By comparing this with the results from Martian rovers, Tomkins concluded the nutrients are likely to become concentrated in cracks in rocks, saying: “Some places on Mars may be a smorgasbord for Martian bugs.” These could be the best places for future exploration on Mars.