Origin Of Perennial Water-ice At South Pole Of Mars

Combined with models of the Martian climate, scientists can now suggest how the orbit of Mars around the Sun affects the deposition of water ice at the Martian South Pole.

The OMEGA instrument on board ESA's Mars Express has characterised the types of ice deposits present in the South polar cap of Mars as the arrows, superimposed on an image taken by the HRSC instrument, indicate. (Credit: ESA - DLR - FU Berlin (G. Neukum)) Early during the mission, the OMEGA instrument (Visible and Infrared Mineralogical Mapping Spectrometer) on board Mars Express had already found previously undetected perennial deposits of water-ice.

They are sitting on top of million-year old layered terrains and provide strong evidence for a recent glacial activity. However, only now a realistic explanation for the age of the deposits and the mechanism of their formation could finally be suggested. This was achieved thanks to the OMEGA mapping and characterisation of these ice deposits, combined with the computer-generated Martian Global Climate Models (GCMs).

The mapping and spectral analysis by OMEGA has shown that the perennial deposits on the Martian South Pole are of essentially three types: water-ice mixed with carbon dioxide (CO2) ice, tens-of-kilometres-wide patches of water-ice, and deposits covered by a thin layer of CO2 ice.

The discovery of the ice deposits of the first type confirms the long-standing hypothesis that CO2 acts as a cold-trap for water-ice. But how were the other two types of deposits, not ‘trapped’ by CO2, accumulated and preserved over time? Franck Montmessin, from the Service d'Aéronomie du CNRS/IPSL (France) and lead author of the findings, explains how the deposits of water ice at the Martian's poles 'behave'. "We believe that the deposits of water-ice are juggled between Mars’ North and South Poles over a cycle that spans 51,000 years, corresponding to the time span in which the planet's precession is inverted."

Precession is the phenomenon by which the rotation axis of a planet wobbles. Montmessin and colleagues came to the conclusion by turning back time in their Mars climate computer model. This was done by changing the precession together with other orbital information. The scientists set the clock 21,000 years back, when the closest vicinity of the planet to the Sun corresponded to the northern summer – a situation opposite to that of today. The model has shown that water at the North Pole was in an unstable condition and was easily transported to the South Pole in the form of water vapour, to then re-condense and freeze on the surface.

Up to 1 millimetre of water ice was deposited at the South Pole every year. After Mars has spent more than 10,000 years in that climatic configuration, this accumulation led to a layer up to 6-metre thick. About 10,000 years ago the precession cycle was inverted, and started to return to its current configuration. Water-ice at the South Pole became unstable, and was forced to progressively return back to the North.

About 1000 years ago, by a not-yet-well explained trigger mechanism, the erosion of the water-ice deposits at the South pole was blocked as soon as layers of CO2 ice were deposited on the water-ice and trapped it, as OMEGA has observed them. Mars is currently experiencing 'Southern summer' – that is, water ice is more likely to accumulate at the North Pole.

The findings appear in the paper 'On the origin of perennial water ice at the South Pole of Mars: a precession-controlled mechanism?', by F. Montmessin, R. M. Haberle, F. Forget, Y. Langevin, R. T. Clancy and J.-P. Bibring, accepted for publication in the JGR Planets journal, and presented at the 7th International Conference on Mars, Pasadena, California (9-13 July 2007).

Note: This story has been adapted from a news release issued by European Space Agency.

Volunteers sought for Mars test

The Aurora programme envisages Europeans on Mars

The European Space Agency (Esa) is seeking volunteers for a simulated human trip to Mars, in which six crew spend 17 months in an isolation tank.

They will live and work in a series of interlocked modules at a research institute in Moscow. Once the hatches are closed, the crew's only contact with the outside world is a radio link to "Earth" with a realistic delay of many minutes.

It sounds like Big Brother, but there are no plans to televise the test.

The modular "spacecraft" measures some 550 cubic metres (19,250 cubic feet), the equivalent of nine truck containers. It is based at the Russian Institute for Biomedical Problems in the Russian capital. The goal is to gain insight into human behaviour and group dynamics under the kinds of conditions astronauts would experience on a journey to Mars.

Big commitment

With the exception of weightlessness and radiation, the crew will experience most other aspects of long-haul space travel, such as cramped conditions, a high workload, lack of privacy, and limited supplies.

The volunteers will be put through a number of scenarios, such as a simulated launch, outward journey of up to 250 days, an excursion on the Martian surface, followed by the return home. The 500-day duration is close to the minimum estimated timescale needed for a human trip to the Red Planet. The Earthbound astronauts will have to deal with simulated emergencies and perhaps even real ones.

But, while Esa says it will do nothing that puts the lives of the simulation crew at unnecessary risk, officials running the experiment have made it clear they would need a convincing reason to let someone out of the modules once the experiment had begun.

"The idea behind this experiment is simply to put six people in a very close environment and see how they behave," Bruno Gardini, project manager for Esa's Aurora space exploration programme, told BBC News.

Team ethic

In all, 12 European volunteers will be needed. They must be aged 25-50, be in good health, have "high motivation" and stand up to 185cm tall. Smokers, or those with other addictions, to alcohol or illicit drugs, for example, will be rejected. Esa is also looking for a working knowledge of both English and Russian.

"We will do pre-selection, medical tests, psychological tests, etc. But at the end, you really have to see how they react in as close to a real situation as possible on Earth," explained Mr Gardini.

He added that the results would help define the selection criteria for a future Mars mission.

"This is the beginning; it will be a long time before we go to Mars," the Esa official said.

"But this is a field which is difficult to quantify. It's human behaviour, so there's no method. The Russians have done lots of study in the past and we will be sharing some data.

"We have to look at the mix of people; at the end of the day, we want a team."

Robots first

Marc Heppener, of Esa's Science and Application Division, said the crewmembers would get paid 120 euros (158 dollars) a day. Viktor Baranov, of Russia's Institute of Biomedical Problems, said his organisation had received about 150 applications, only 19 of which had come from women. A precursor 105-day study is scheduled to start by mid-2008, possibly followed by another 105-day study, before the full 520-day project begins in late 2008 or early 2009. European scientists have been asked to submit proposals for experiments in the areas of psychology, medicine, physiology and mission operations.

Mounting a mission to Mars would face many other hurdles, not least of which would be shielding the crew against the potentially deadly dose of radiation they would receive on the journey. Esa's Aurora programme has already begun preparations to land a rover - called ExoMars - on the Red Planet. It has the stated aim, however, of trying to get European astronauts to Mars at some time in the future.

By Paul Rincon Science reporter, BBC News, Paris Air Show