From Physorg.com, findings from the red planet shows that the amount of methane (CH4) in the Martian atmosphere is not caused by meteorites. So now the thinking is that it is caused by the reaction of rock with water and CO2 or it is biological.
Given the amount of CO2 in Mars’ atmosphere, I’m leaning toward the geologic origin. But one can dream of Martian Microbes.

From the Universe today, So how would a scientist know if a newly discovered planet has life? Two scientists will create an equation that will answer the question. Figuring in variables such as the presence of water, habitability, radiation, etc. the equation will determine the likelihood of life arising.