The European Space Agency's Mars Express has returned compelling evidence that the red planet once hosted an enormous ocean in its northern plains. The probe's radar detected sediments reminiscent of an ocean floor, within areas that have been suspected to be shorelines.
Jérémie Mouginot from the Institut de Planétologie et d'Astrophysique de Grenoble (IPAG), the University of California in Irvine, and colleagues analysed more than two years of data from Mars Express' Marsis (Mars Advanced Radar for Subsurface and Ionosphere Sounding) radar.
The radar can penetrate deep into the planet's ground, and reveal the first 60 to 80 metres of the planet's subsurface. At these depths, the team found that the northern plains are covered in low-density material.
"We interpret these as sedimentary deposits, maybe ice-rich," says Mouginot. "It is a strong new indication that there was once an ocean here."
The notion of water on Mars and big ideas of oceans in the planet's ancient history are nothing new. But this research provides some of the best evidence yet that there were once large bodies of liquid water on Mars, and it is further proof that water played a role in martian geological history.
"Previous Mars Express results about water on Mars came from the study of images and mineralogical data, as well as atmospheric measurements," said Olivier Witasse, a Mars Express project scientist at the European Space Agency.
This data supports a proposed theory where Mars has had two oceans in its lifetime. One four billion years ago when warmer conditions prevailed, and another three billion years go when subsurface ice melted following a large impact.
This later ocean would have been very temporary. It would only have lasted about a million years or less, Mouginot estimates, and then the water would have either frozen back in place or turned into vapour and lifted gradually into the planet's weak atmosphere.
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"I don't think it could have stayed as an ocean long enough for life to form," Mouginot says.
A recent study from Imperial College London doesn't offer much good news for martian life-hunters, either. Soil analysis at the site of Nasa's Phoenix mission suggest that surface of Mars has dry as a bone for hundreds of millions of years, making it too hostile for any life to survive on the planet's surface
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