for National Geographic News
The first-ever mineralogical map of the entire Martian surface suggests that the red planet was wet during its early years, new research says.
Martian history can be divided into three epochs, the map revealsone wet and probably relatively warm, another wet but highly acidic, and the third cold and dry.
Scientists created the new map using an instrument called OMEGA (Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité), which has been peering down on the Martian surface from the European Space Agency's Mars Express orbiter.
OMEGA is designed to look at the planet's surface in more than 350 different "colors" of light (related images: the Martian surface).
Some of these colors are visible, but most are infrared, said Jean-Pierre Bibring, lead author of a paper about the map to be published in tomorrow's edition of the journal Science.
Using both visible and infrared light makes it easier to distinguish between minerals that would look similar when viewed solely in visible light, he says.
Of particular interest are minerals indicating the effect of water on Martian rocks.
In the oldest regions of Mars the team found signs of clay minerals whose formation would have required massive amounts of water persisting for millions of years.
"In all the places where we see clays, we can say that water was present," Bibring said.
Then the planet slowly dried out until, a few hundred million years after it was formed, it underwent a radical climate shift.
Bibring thinks the cause of this shift was massive volcanism.
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