WASHINGTON Ice deposits at least 6 feet (2 metres) thick can be found in some small craters on the moon, researchers reported on Monday in one of two studies showing more evidence of water on the moon and Mars.
The second study suggested that ice has recently melted and re-frozen on Mars, widening some of the characteristic gullies on its surface.
The two studies add to the political and scientific debate about how best to explore our solar system and the universe -- with missions that include human crews, or experiments using robots and remote surveys.
The administration of President Barack Obama last month said it would cancel the Constellation program to return astronauts to the moon by 2020 after a review found the $108 billion program was underfunded and already off-track to meet most of its goals.
Obama's plan is to contract with private companies to do some of the work needed to investigate Mars, as well as asteroids, using robots, remote sensors and perhaps some astronauts.
In one of the two studies released on Monday, Paul Spudis of the Lunar and Planetary Institute in Houston and colleagues analyzed measurements from India's Chandrayaan spacecraft to find evidence of thick ice deposits in some permanently shaded craters on the moon.
"As the moon has been bombarded with water-bearing objects such as comets and meteorites and implanted with solar wind hydrogen over geological time, some of this material must have made its way into these cold, dark areas," they wrote in Geophysical Research Letters.
They measure something called circular polarization ratio to show either the surface there is unusually rough, or there are between 6 and 10 feet (2 and 3 metres) of ice there.
The second study showed that 6-foot (2-metre) wide gully on Mars had become nearly 400 feet (120 metres) longer over two years.
Dennis Reiss of the Institute for Planetology at Westfalische Wilhelms-Universitat in Munster, Germany, and colleagues said the best explanation is the melting of small amounts of water ice.
Photographs show dark patches in the gully, as well as some smaller, new channels, they reported in the same journal. It may get warm enough at the surface to melt water on Mars, they added.
In September, several teams reported clear evidence of water, likely frozen, on the desert surfaces of both the moon and Mars and researchers have also seen it snow on Mars.
(Reporting by Maggie Fox; editing by Mohammad Zargham)