Two NASA researchers (Carol Stoker and Larry Lemke of Ames Research Center) are claiming that there is evidence of (microbial) life on Mars. Their research, which is under peer-review for publication in journal Nature in May, suggests that small pockets of life, sustained by underground water, might be found in Martian caves. Mars has a deep network of caves/ravines, which are nearly completely isolated from sunlight and duststorms that ravage the surface. High concentrations of methane gas have recently been detected by the martian rovers, and ESA's Mars Express orbiter. Methane on earth is produced through biological processes, and it is being suggested that the martian methane might also have a similar origin.

Martian Landscape (Courtesy: NASA)Stoker, along with a joint U.S./Spanish team went to southwestern Spain in 2003 to look for subsurface life around the Rio Tinto river, where iron has dissolved in the higly acidic water, giving it a reddish tint. Since Martian soil has a lot of iron, it is reasonable to assume that any water on Mars must have a lot of iron dissolved in it, and any lifeform that lives in that water must have developed some unique strategies. By comparing the microbes near the Rio Tinto river to the chemical signatures obtained from Mars (such as methane concentration, and a mineral called jarosite), the scientists say they have a very strong case that the Martian underground has (at least) microbial form of life.
Move over Little Green Men! Here come the Littler Red Microbes :-):-).