London, Nov 9 : Scientists have indicated that the next time man sets foot on a planetary body, it would most probably be on Phobos and Deimos, the two moons of Mars. This trip might be possible within the next 10 years.

Though the Earth's Moon is only a short three-day spaceflight, scientists would prefer sending astronauts to the two moons of Mars.

A primary reason for this is that the Moon's gravity is one-sixth of Earth's. It's strong enough that a landing craft has to fire retrorockets to slow its descent to the surface, and again to leave. This wastes tonnes of heavy, expensive fuel and adds millions of dollars to the cost of a mission.

On the other hand, the two moons of Mars are relatively smaller. Phobos is the size of Manhattan and Deimos is about a third as large, just 6.3 kilometres wide. So their gravitational pull is only one-thousandth that of Earth, making landing on them more like docking with another spaceship.

This might also mean big savings for a crewed mission to the moons compared with even one to the Martian surface.

"Putting a person on Mars could cost $200 billion to $300 billion dollars, including the cost of decades of research," said S Fred Singer of the Science and Environmental Policy Project. "The bill for a run to Deimos could be as low as $30 billion," he adds.

"Phobos and Deimos are the most accessible planetary bodies in our solar system," said Pascal Lee of the Mars Institute in California.

For now, the only planned missions to the moons are robotic. Russia is gearing up to launch the Phobos-Grunt mission in 2009 that will attempt to land a craft on Phobos, collect the first samples from the moon's surface and return them to Earth. The project could help determine if there is any hydrogen or water present, which astronauts on a later crewed mission could use.

According to scientists, a crewed mission should first go to Phobos as it is bigger than Deimos and closer to Mars as well.

Because of its proximity, Phobos is more likely to harbour ancient meteorites blasted up from Mars's surface. The rocks could stretch deep into the planet's past, and would be better preserved in Phobos's near-vacuum than the harsh oxidising conditions found on Mars.

But the manned mission to the moons would not be without its hare of perils.

"For one thing, dust could be a huge problem in Phobos's weak gravity field," said Michael West of the Australian National University in Canberra. "There could be a layer of dust four or five metres thick that would be easily mobilised," he adds. Also, the slightest disturbance could raise a massive dust cloud on Phobos. Even exposure to radiation would present a hazard.

Scientists have theorised that the moons may be asteroids captured by Mars's gravity, or that they may be remnants of a single moon that was blasted apart by a massive impact. "We know almost nothing about these moons, other than their density, size and their colour, which is black as asphalt," said Lee. (ANI)