Scientists think there was probably water on the planet long ago.

科学家们认为很久以前在那个行星上可能有水存在。

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However, if the planet is in a good position, astronomers look for three key things: water, air and rock.

然而如果这颗行星处于很好的位置，天文学家会寻找三样关键的东西：水、空气和岩石。

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To be able to support life, the new planet would need not only to have water, but it would also need to be solid.

为了能够维持生命，这个新的星球不仅要有液态水，而且它的土表还必须是固态的，就像地球这样。

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His theory was that Martians were trying to bring water to the warm areas near the equator of the planet.

VOA: special.2010.07.11

Water exists on Earth and the planet Mars.

VOA: special.2009.09.30

And the world's insatiable appetite is depleting the planet's fisheries and using up land and fresh water at an alarming rate.

VOA: standard.2010.06.04

"The results suggest that water was incorporated during the formation of Mars and that the planet was able to store water in its interior during the planet's differentiation, " Hauri said.

MSN: Scientists say parts of Mars interior are as wet as Earth's

Lucas' clones are created by strange-looking aliens on a fantastic, stormy water planet.

FORBES: Scientists Fret Over 'Clones'

The reason why that's exciting, is one of the properties we'd like to have on a habitable planet is liquid water on the surface.

BBC: Tiniest extrasolar planet found