Mars today has a brutal environment — frigid, arid and, because of its very thin atmosphere, constantly bombarded by lethal radiation. But it was worse 600,000 years ago, according to new research that suggests the planet had a far dustier, stormier atmosphere.
“It was an unpleasant place to hang out,” said lead researcher Roger Phillips of the Southwest Research Institute in Boulder, Colo.
The evidence comes from the discovery of a huge underground reservoir of dry ice, or frozen carbon dioxide, at its south pole — much more than scientists realized. They suspect some of that store of carbon dioxide was once in Mars’ atmosphere, making it denser.
In the recent geologic past, when Mars’ axis tilted, sunlight reached the southern polar cap, melting some of the frozen carbon dioxide. This release would have made the atmosphere thicker and caused more dust to loft into the air, creating severe storms. Other times, carbon dioxide cycled back into the ground as part of a seasonal cycle.
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