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.
However there has long been a quest for "smoking gun" evidence for liquid water currently on the planet.
If the planet does harbor liquid water today, it would have to be deep below the surface, perhaps peeking out in a few special places, but not likely to be seen by Curiosity, Squyres said.
Just last month, scientists announced they had found a planet very likely to have liquid oceans (and thus the potential for life) 22 light years from the Earth.
WSJ: The Weekend Interview with Michio Kaku: Captain Michio and the World of Tomorrow
In addition to containing the vast majority of the liquid freshwater on the surface of our planet, humans use lakes for more purposes than any other type of water system.
They said water seemed to have flowed down two gullies in the past few years, even though liquid water cannot remain long on the planet's frigid, nearly airless surface because it would rapidly freeze or evaporate.
The habitable zone is the region of a planetary system which is neither too hot nor too cold - such that water on the surface of a planet will neither evaporate nor freeze, but instead can stay liquid.
BBC: NEWS | Science/Nature | Earth-like planets may be common
Liquid water is not something scientists expect to be apparent on Mars because the planet is so cold and dry, Squyres said.
Satellites at Mars have long captured images of channels on the planet's surface that were cut by some kind of flow, assumed to be liquid water.
The finding upends previous studies, which had estimated that the Red Planet's internal water stores were scanty at best something of a surprise, given that liquid water apparently flowed on the Martian surface long ago.
MSN: Scientists say parts of Mars interior are as wet as Earth's
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