Question: Why do you think Mars would be a good 'candidate' as planet that could support life?

Sara Imari Walker answered on 20 Jun 2011:

Hi smccall. Typically when we talk about habitability (the ability of a planet or moon to support life) we are talking about supporting microbial life. Microbial life on Earth is everywhere, including the most extreme environments known to man. Microbes are found in deep, scalding hot hydrothermal vents on the ocean floor, in the frigid ice caps of the Artic, in the Atacam desert, the driest place on Earth, and even in deep mines, going 2 miles underground. These are places where no other life can live. A lot of times we have been really surprised to find microbes thriving in these environments. So then, why not Mars???

Mars is really a good candidate for a number of reasons. For one, early in its history it was a lot like Earth. It had liquid water, a nice CO2 rich atmosphere and it was warm! And, even now there is probably liquid water just under the surface. In fact, parts of Mars are much more hospitable than the environments listed above. For example, Atacama is often used as a Mars analog site. That means scientists study things there because conditions are so similar to those on Mars. Additionally, microbial life has been shown to survive journeys through space if it is embedded in a rock such as a meteorite. With large impacts, material is ejected from the surface of Mars and Earth has been ejected into space a lot, sometimes landing on the other body. Some hypothesize this interplanetary exchange means that life on Earth may have originated on Mars or vice versa.

Given all this, I don’t think there is any way we can rule out the possibility of life on Mars. We’ll just have to go there to find out!