Not so fast. Not sure how I missed this last week, but scientists have discovered large quantities of methane in Mars' atmosphere, and indication that the planet is active "geologically or biologically".
The origin of methane could either be geologic where water reacts with hot rock and produces methane gas which escapes through pores in the planet's surface in a process called serpentinization. Or it could be evidence of biology under the surface, where the methane generated by microbes could accumulate and then escape through the rocks.
