The origin of perennial water-ice at the South Pole of Mars

July 13, 2007
The origin of perennial water-ice at the South Pole of Mars
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. Credits: ESA - DLR - FU Berlin (G. Neukum)

Thanks to data from ESA's Mars Express mission, 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.

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.

Source: European Space Agency

Related Stories

Recommended for you

A mission to a metal world—The Psyche mission

October 9, 2015

In their drive to set exploration goals for the future, NASA's Discovery Program put out the call for proposals for their thirteenth Discovery mission in February 2014. After reviewing the 27 initial proposals, a panel of ...

What are white holes?

October 9, 2015

Black holes are created when stars die catastrophically in a supernova. So what in the universe is a white hole?

Image: Pluto's blue sky

October 9, 2015

Pluto's haze layer shows its blue color in this picture taken by the New Horizons Ralph/Multispectral Visible Imaging Camera (MVIC). The high-altitude haze is thought to be similar in nature to that seen at Saturn's moon ...

Blue skies, frozen water detected on Pluto

October 8, 2015

Pluto has blue skies and patches of frozen water, according to the latest data out Thursday from NASA's unmanned New Horizons probe, which made a historic flyby of the dwarf planet in July.

How to prepare for Mars? NASA consults Navy sub force

October 5, 2015

As NASA contemplates a manned voyage to Mars and the effects missions deeper into space could have on astronauts, it's tapping research from another outfit with experience sending people to the deep: the U.S. Navy submarine ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.