|Spirit Rover, courtesy JPL|
--recently, NASA has come upon one heck of a realization thanks to the data which Spirit sent Earthward: Mars had an oxygen-rich atmosphere way before we did — at least 1.5 billion years, if their data is correct.Chronology notwithstanding, is this really a shocking discovery? Mars is the "Red Planet," after all. It gets that rusty color from iron oxide—as in oxygen. They just realized that now?
How does iron oxide form? The most common way is exposure to liquid water. That implies that the majority of Mars' surface was exposed to liquid water in the past. Now that's curious. Mars doesn't have the gravity to hold a dense enough atmosphere for very long, and that means water wouldn't remain liquid for very long. It's almost as if a whole bunch of water slammed into Mars all at once and then evaporated away to leave the planet rusty red. Beyond Earth explores some major clues pointing to such a scenario. See my previous post about this, "Mars like Earth in the Past?"