Past readings of methane detected in the Martian atmosphere by telescopes on Earth have now been corroborated by ESA's Mars Express orbital craft.
This find is significant for two reasons:
1 - It can only have come from active volcanoes, or life. Since volcanoes are easier to detect by many orders of magnitude, and we have found no active ones in decades of observations, it seems unlikely that they explain the gas.
Active volcanoes being identified as the source would not preclude the possibility of life, since volcanic activity infers heat, which could provide both the melt-water and mineral deposits required to sustain possible Martian anaerobic bacteria.
2 - Methane breaks down rapidly in the Martian atmosphere. This means that the detected volumes were recently produced (within about 100 years), and probably being replenished constantly.
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