- The latest data returned from Europe's Mars Express orbiter
confirms there are substantial quantities of water-ice held at the Red
Planet's south pole.
- Scientists say the spacecraft has seen the water-ice
in three distinct zones: mixed with carbon dioxide, all on its own and
in vast tracts mixed with dust.
- The data was collected during the local summer when the
southern cap was small.
- Jean-Pierre Bibring and colleagues tell the journal Nature
that the probe will map the water-ice changes over time.
- The data was collected by a French-led instrument called
Omega. This visible and infrared spectrometer is able to identify chemical
elements thanks to the way sunlight is reflected off the planet's surface.
- The Omega researchers believe the most interesting find
is the mix of water-ice and dust which is present "along vast zones
expanding down slope in stratified terrains, tens of kilometres wide, and
tens of kilometres away" from the bright polar cap.
- The darkness of the ice-dust mix explains why these reserves
have not been observed before, the team says.
- The ratio of dust to frozen water varies and there appears
to be no correlation with local topography. It is thought the dust is included
with the ice when the water precipitates out of the atmosphere.
- Going underground
- Although a range of studies have now established the
southern cap contains huge quantities of water-ice, the question has remained
about the extent to which this is mixed with frozen carbon dioxide.
- "We know now that carbon dioxide's only a very thin
veneer of ice over a much larger body of water," Professor Bibring,
from the Institute of Space Astrophysics, Orsay, told BBC News Online.
- He said there appeared to be much more water in the southern
polar ice cap than anywhere observed so far on Mars - but this did not
mean it was necessarily the prime water reservoir on Mars.
- A better idea of how much water-ice is retained on the
planet will be gained when Mars Express deploys the Marsis (Mars Advance
Radar for Subsurface and Ionospheric Sounding) instrument from May.
- It should enable a volume to be determined for the surface
water-ice seen by Omega at the south pole and compare this with the volume
of water thought to lurk below the Martian surface.
- It is this subterranean permafrost that has been considered
up until now as the major Mars water reservoir.
- Omega is now looking at Mars' northern polar region.
Its cap has long been thought to be composed mainly of water-ice.
- © BBC MMIV