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The Sciences

Ice is nice, even on Mars

Bad AstronomyBy Phil PlaitJune 25, 2008 1:00 AM

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By now you've heard that Phoenix found ice on Mars. This is cool -- har har -- but we need to be careful here. Basically, Phoenix scooped up some of the Martian regolith (what most people call soil), revealing some white solid beneath. Was it salt, or ice? A picture taken a little while later showed that some of the white stuff had disappeared. Sounds like ice to me! Better yet, the temperatures on Mars at that location preclude it being dry ice (frozen carbon dioxide), meaning it must be water ice. Yay! That's what the scientists in charge of Phoenix were hoping for. But while I was at TAM a lot of folks were asking me about it, and it became clear that some of them thought that this was the first time ice had been seen on Mars. But that's not the case: we've known about the polar ice caps on Mars for centuries! The southern cap has lots of both water and CO2 as a permanent feature, while the northern cap is mostly water ice with a temporary cap of dry ice frost that appears in the winter and sublimates away in the summer. That's why Phoenix went north; we knew before the mission started that there was water ice there! Don't get me wrong; this is a tremendous development and very exciting to the mission. it just wasn't the first time we've seen water ice on Mars.

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