Did you know that Mars has gas? NASA has been monitoring Mars' atmosphere with spectrometers at their Infrared Telescope Facility in Hawaii. A few years ago, they detected plumes of methane in the Martian northern hemisphere, mainly during the warmer seasons. One of those plumes contained about 19,000 metric tons.
Methane is the simplest hydrocarbon, a carbon atom with four hydrogens attached. Here on Earth, organisms release methane when they digest nutrients. This means that there maybe microscopic Martian life on Mars.
Mars is a really cold place to live, but it's possible that life may be growing below the permafrost line where water would be liquid. Here on earth there are bacteria surviving on radioactive energy, hydrogen, and sulfur that live almost two miles underground. Scientists aren't sure whether or not the methane is coming from living organisms. Methane can be produced by geological events, too.
When iron oxide or rust is converted to other minerals it creates methane. Volcanoes also release methane. Even though Mars isn't volcanically active anymore, the methane from ancient eruptions might be trapped in ice and just be escaping to the surface when the ice thaws. So we don't know if Mars has life or not, but we do know that it has methane gas. That's just the way science works. One discovery at a time.