Hopes that water may exist in big quantities outside the Earth are boosted by new studies published Thursday which suggest Mars has vast icy deposits lurking close to its surface, while Callisto, one of Jupiter's moons, has a deep subterranean ocean.
Geologists at Brown University, Rhode Island, believe pictures of pitted, hummocky terrain captured by NASA's Mars Global Surveyor orbiter indicate shallow reservoirs of ice just below the dusty martian surface.
The layer occurs in the planet's mid-latitudes, in bands between 30 and 60 degrees, they report in Nature, the British science weekly.
Their calculation is that the reservoir is the equivalent of a layer of water between 10 and 40 centimetres (four and 16 inches) deep covering the entire planet.
Comparing this evidence with previous models of Mars's climate, the geologists suggest the reservoir was created during the red planet's last ice age, 100,000 years ago.
Separately, a study by Javier Ruiz at Madrid's Universidad Complutense contends the cratered and pitted surface of Callisto, one of Jupiter's four big moons, may conceal a deep ocean.
His conclusion is based on a reappraisal of data from a flyby by the spacecraft Galileo, which detected a magnetic field around the moon.
Excited researchers initially believed that this field was caused by an ocean of salt water whose dynamic, fluctuating currents were conducting an electric current.
But these hopes were dashed when calculations, based on the rate at which Callisto's surface convects heat, seemed to show that any sub-surface ocean would have frozen solid long ago.
But, Ruiz says in Nature, those calculations are flawed. The chilly moon is probably coated with a hard icy shell which would prevent heat loss, and this would skew the convection arithmetic.
"The implication is that Callisto may have retained an ancient liquid ocean, now some 20 kilometers (12 miles) thick," said commentator Kristin Bennett of Los Alamos National Laboratory in New Mexico.
Two other big Jupiter moons, Europa and Ganymede, are already considered by space experts to be good potential sources of underground water.
The case for Mars has been raging for more than a year, with experts fighting over the interpretation of pictures sent back by the Mars Global Surveyor.
The next contributor should be the United States' 2001 Mars Odyssey, which is scheduled to enter orbit around the planet in late October.
AFP