快猫短视频

WHILE Mars shows off its rusty face in the evening sky this
month鈥攄uring its closest approach to Earth in more than a
decade鈥攊mages captured by the Mars Orbiter Camera suggest that ground ice
was present in the Red Planet鈥檚 soil only 10 million years ago. That鈥檚 just a
moment ago in geological terms.

The pictures suggest that there were once ice deposits near Mars鈥檚 equator,
probably no more than 5 metres below the surface. 鈥淚f ground ice was present
within 5 metres of the surface only a few million years ago, it is very likely
to persist today within about the upper 10 metres,鈥� says Alfred McEwen from the
University of Arizona. Finding water is vital to any hopes of discovering
microbial life on Mars.

The orbiter returned images of tens or possibly even hundreds of conical
craters, similar in shape and size to the so-called pseudocraters found in
Iceland, which are also known as 鈥渞ootless cones鈥�. Earlier hints of conical
craters on Mars appeared to be arranged in curved lines near the equator, rather
than being dotted about.

Pseudocraters can form when magma rises through the crust and meets pockets
of volatile substances such as water or solid carbon dioxide near the surface,
instantly vaporising them. The resulting explosion creates the cone-shaped
holes. However, they can also form when a heavy weight, such as sediment,
presses down on volatile material. The scientists believe the cones were caused
by rising magma. Dave Rothery of the Open University in Milton Keynes agrees:
鈥淚n these examples, the cones do look like they are on lava flows.鈥�

Exactly where the ice might have come from is the subject of much debate.
Some say that it was left over in the crust from when the planet formed, but
others reckon it condensed out of the atmosphere or drained down from the
surface.

The team that made the observations, from the University of Arizona and the
University of Hawaii, reject the first theory because they do not believe that
ground ice could have survived near the equator for 4 billion years. They think
it鈥檚 more likely that the water condensed from the atmosphere. 鈥淗owever, because
these cones appear to be near outflow channels, we think that the water that
formed the cones is probably recharged from floods,鈥� says Peter Lanagan from the
University of Arizona.

快猫短视频s hope to learn more about the cones when the British-led lander
Beagle 2 touches down in late 2003. Its landing site has not yet been chosen and
it could be sent to explore one of the cones.

鈥淭he evidence is mounting up,鈥� says Rothery. 鈥淚t looks like we鈥檝e got
volatiles on Mars.鈥�