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Friday, November 30, 2012 - Page updated at 10:00 p.m.

NASA finds lots of ice — on planet closest to the sun

By KENNETH CHANG
The New York Times

Mercury is as cold as ice.

Indeed, Mercury, the planet closest to the sun, possesses a lot of ice — 100 billion to 1 trillion tons — scientists working with NASA's Messenger spacecraft reported Thursday.

Sean Solomon, principal investigator for Messenger, said there was enough ice there to encase Washington, D.C., in a frozen block 2-½ miles deep.

That is a counterintuitive discovery for a place that also ranks among the hottest in the solar system. At noon at the equator on Mercury, the temperature can hit 800 degrees Fahrenheit. But near Mercury's poles, deep within craters where the sun never shines, temperatures dip to as cold as minus 370.

"In these planetary bodies, there are hidden places, as it were, that can have interesting things going on," said David Lawrence, a senior scientist at the Johns Hopkins University Applied Physics Laboratory working on the Messenger mission.

The findings appear in a set of three papers published Thursday on the website of the journal Science. The ice could be a target for a robotic lander or a resource for astronauts in the far future.

Planetary scientists had strong hints of the ice a couple of decades ago when telescopes bounced radio waves off Mercury and the reflections were surprisingly bright. But some researchers suggested the craters could be lined with silicate compounds or sulfur, which might also be highly reflective. A closer look from the Messenger, which swung into orbit around Mercury in March 2011, found the linings were ice.

Between the equator and the poles, temperatures on Mercury can be temperate, especially a few feet below the surface, an ideal spot to build a colony, scientists said.

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