for National Geographic News
Since NASA's twin robot geologists Opportunity and Spirit landed on Mars in January 2004, a steady trickle of scientific analysis has confirmed that water once soaked the red planet, raising the possibility of life there.
Now, scientists may know where to look for life first.
Images recently taken by the European Space Agency's Mars Express spacecraft, which is orbiting Mars, show a frozen body of water, about the size of Earth's North Sea, beneath the surface of Mars (see enlarged image).
"I believe this makes the possibility of the discovery of life on Mars much closer than was previously thought," said John Murray, a research scientist at the Open University in Milton Keynes in England. Murray led the research group that made the discovery of the frozen sea.
Scientists now say that Mars has been shaped by flowing water, lava, and ice in the recent geological age. The sea formed within the last few million years, as volcanic eruptions or tectonic activity caused the area to flood.
A separate study shows that explosive eruptions about 350 million years ago created depressions on the flank of the Martian volcano Hecates Tholus. Glacial deposits formed inside those depressions as recently as five million years ago.
"It indicates that Mars is still a geologically active planet, and geological activity is generally agreed to be important to the development and continuance of life, which requires such a source of energy," Murray said.
The discoveries are reported this week in the science journal Nature.
The first camera images taken of Mars and atmospheric data collected from the red planet in the 1960s led scientists to believe that Mars had been continuously cold and dry.
This view changed in the 1970s, when pictures taken from the Mariner 9 and Viking orbiters revealed river valley networks and huge channels carved by cataclysmic floods.
However, scientists long believed that hydrological events were limited to the time of Mars's formation, between 3.8 and 3.5 billion years ago.
SOURCES AND RELATED WEB SITES