Ice deposits at least six feet thick can be found in some small craters on the moon, researchers reported 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 programme to return astronauts to the moon by 2020 after a review found the $108 billion programme was underfunded and already off-track to meet most of its goals.

Mr 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 Monday, Paul Spudis of the Lunar and Planetary Institute in Houston and colleagues analysed 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 polarisation ratio to show either the surface there is unusually rough, or there are between six and 10 feet of ice there.

The second study showed that two-metre wide gully on Mars had become nearly 400 feet longer over two years.