UMILIATED LAST year when two missions worth $ 500 million came to grief on arriving at Mars, US space scientists are keeping alive the tantalising possibility of a manned mission to the Red Planet within 20 years.

Last month, NASA outlined plans for alanding by roving robots in January 2004.

Now its planners have made it clear that they will keep going to Earth's smaller colder, dustier neighbour every 26 months until 2010, despite last year's loss of an orbiter and a landing vehicle within a three-month period.

They intend to follow up the 2004 robot landing by launching a scientific observer orbiter in 2005 with instruments so powerful they will be able to make images of rocks the size of footballs. And in 2007 NASA could send the first of a series of "scout" missions, possibly equipped with robot baloons or even a low-flying robot aircraft to skim over the Martian landscape, for close observation over a much larger range than any tracked vehicle or robot rover could manage.

It will also try to put down a "smart" landing craft smart enough to avoid the dangerous rocks and ravines that menace a descending vehicle - fitted with a scientific laboratory. In 2009, the Americans could team up with the Italians to drop yet another orbiter into the Martian skies, this time with ground-penetrating radar to "feel" or water under the surface.

Scout missions will seek water, life forms for man to follow

he US has signed a declaration of intent with France to cooperate on a new generation of tiny landers which could "sniff" for traces of the chemistry generated only by living things, and has revealed that talks have begun with the Italians to put a communication satellite around Mars, to handle the huge traffic in data.

And, as interest in Mars grows, there could be a "biopsy" mission: in 2011 at the earliest, NASA said, a mission could land on mars, scoop up samples of rock and soil, and return to Earth.

Mars is an earthlike planet, with a thin carbon-dioxide atmosphere and hostile temperatures. The more scientists learn about other planets, the better they understand the dynamics of their own. Mars is the only rocky planet available for study. Venus is impossibly hot and masked by clouds of acid vapour.

Mars is too cold, and its atmospheric pressure too low, for liquid water to exist. Bhut a study of its landscape shows that it was once washed by seas and lakes and scoured by rivers, so it must have once held a thicker atmosphere; and been warmer.

In theory it could have had a population of creatures. Earlier this year photographs showed remarkable evidence of apparently fresh drainage patterns, as it something had burst from the soil and flowed into a deep gully. This raised the tantalising idea that if liquid water could exist under the surface, so might life.

"We are going to dig deep into the details of Mars' mineralogy, geology and climate history in a way we've never been able to do before," said Ed Weiler, one of NASA's science chiefs. "We also plan to "follow the water" so that in the not-to-distant future we may finally know the answers to the most far-reaching questions about the Red Planet we humans have asked over the generations; Did life ever arise there, and does life exist there now?"

Mars is a long and dangerous trip. Only when it and Earth are at the right places in their respective orbits are missions affordable - every 26months. Then a journey can be completed in as few as seven months. So planning has to begin early and timetables are light.

Tim Radford in London
The Hindustan Times, New Delhi
October 30, 2000