Martian glaciers: did they originate from the atmosphere? (Forwarded)

ESA News
http://www.esa.int

20 January 2006

Martian glaciers: did they originate from the atmosphere?

The spectacular features visible today on the surface of the Red Planet indicate the past existence of Martian glaciers, but where did the ice come from?

An international team of scientists have produced sophisticated climate simulations suggesting that geologically recent glaciers at low latitudes (that is near the present-day equator) may have formed through atmospheric precipitation of water-ice particles.

Moreover, the results of the simulations show for the first time that the predicted locations for these glaciers match extensively with many of the glacier remnants observed today at these latitudes on Mars.

For several years, the presence, age and shape of these glacier remnants have raised numerous questions in the scientific community about their formation, and about the conditions on the planet when this happened.

To start narrowing down the rising number of hypotheses, a team led by Francois Forget, University of Paris 6 (France) and interdisciplinary scientist for ESA's Mars Express mission, decided to 'turn back the clock' in their Martian global climate computer model, a tool usually applied to simulate the detail of present-day Mars meteorology.

As a starting point, Forget and colleagues had to make some assumptions -- that the north polar cap was still the ice reservoir of the planet, and that the rotation axis was tilted by 45 deg with respect to the planet's orbital plane.

"This makes the axis much more oblique than it is today (about 25 deg), but such an obliquity has probably been very common throughout Mars's history. Actually, it last occurred only five and a half million years ago," says Forget.

As expected with such a tilt, the greater solar illumination in the north polar summer increased the sublimation of the polar ice and led to a water cycle much more intense than today.

The simulations showed water ice being accumulated at a rate of 30 to 70 millimetres per year in a few localised areas on the flanks of the Elysium Mons, Olympus Mons and the three Tharsis Montes volcanoes.

After a few thousand years, the accumulated ice would form glaciers up to several hundreds of metres thick.

When the team compared the location and shape of the 'simulated' glaciers with the actual glacier-related deposits of Tharsis -- one of the three main regions on the planet where signs of glaciers are seen -- they found an excellent agreement.

In particular, the maximum deposition is predicted on the western flanks of the Arsia and Pavonis Montes of the Tharsis region, where the largest deposits in this area are actually observed.

In their simulations, the team could even 'read' why and how ice was accumulated on the flanks of these mountains in the Tharsis region millions of years ago.

Back then, constant year-long winds similar to monsoons on Earth would favour the upslope movement of water-rich air around Arsia and Pavonis Montes.

While being cooled down by tens of degrees, water would condense and form ice particles (larger than those we observe today in the Tharsis region's clouds) that settled on the surface.

Other mountains like Olympus Mons show smaller-scale deposits because, according to the simulations, they were exposed to the monsoon-type strong winds and water-rich air only during the northern summer.

"The north polar cap may not have always been the only source of water during the planet's high obliquity periods," adds Forget.

"So we ran simulations assuming that ice was available in the south polar cap. We could still see ice accumulation in the Tharsis region, but this time also on the east of the Hellas Basin, a six-kilometre deep crater."

This would explain the origins of another major area where ice-related landforms are observed today, the eastern Hellas Basin. indeed.

"The Hellas basin is in fact so deep as to induce the generation of a northward wind flow on its eastern side that would carry most of the water vapour sublimating from the south polar cap during summer. When the water-rich air meet colder air mass over eastern Hellas, water condense, precipitate, and form glaciers," said Forget.

However, the team could not predict ice deposition in the Deuterolinus-Protonilus Mensae region, where glaciers could have been formed by other mechanisms. The scientists are considering several other hypotheses on the formation of recent glaciers.

For instance, observations of Olympus Mons by the High Resolution Stereo Camera on board Mars Express suggest that movement of water from the subsurface to the surface due to hydrothermal activity may have led to the development of glaciers on the cold surface.

The results appear in 20 January issue of the scientific journal Science, in an article titled 'Formation of glaciers on Mars by atmospheric precipitation at high obliquity', by F. Forget (Laboratoire de Météorologie Dynamique, Institut Pierre Simon Laplace (IPSL), France), R.M. Haberle (NASA Ames Research Center, USA), F. Montmessin (Service d'Aéronomie, IPSL, France), B. Levrard (Inst. de Mecanique Celeste, Paris, France), J.W. Head (Brown Univ., Rhode Island, USA).

The Martian global climate computer model is a tool designed by the Laboratoire de Météorologie Dynamique, France, with the support of CNRS, ESA and CNES. It is used to simulate the present-day climate on Mars and so support the analysis of many of the current observations at Mars, including those of ESA's Mars Express.

The version used here provides the distribution of atmospheric vapour and clouds; it describes the exchange between surface ice and atmospheric water, transport and turbulent mixing of water in the atmosphere, and the microphysics of cloud formation.

For further information, please contact:

Francois Forget, Mars Express Interdisciplinary Scientist
Laboratoire de Météorologie Dynamique, IPSL, Université Paris 6, France
E-mail: Francois.Forget @ lmd.jussieu.fr

Agustin Chicarro, ESA Mars Express Project Scientist
E-mail: agustin.chicarro @ esa.int

Recent images

* Mars Express image browser
  http://www.esa.int/SPECIALS/Mars_Express/SEMVZF77ESD_0.html
* Sulphate deposits in Juventae Chasma
  http://www.esa.int/SPECIALS/Mars_Express/SEMMLKMZCIE_0.html
* 'Butterfly' impact crater in Hesperia Planum
  http://www.esa.int/SPECIALS/Mars_Express/SEMZLM8A9HE_0.html
* Fly over the Chasma Boreale at Martian north pole
  http://www.esa.int/SPECIALS/Mars_Express/SEM8T86Y3EE_0.html
* The Biblis Patera volcano
  http://www.esa.int/esaSC/SEMKW9A5QCE_index_0.html
* Water ice in crater at Martian north pole
  http://www.esa.int/SPECIALS/Mars_Express/SEMGKA808BE_0.html
* Nicholson Crater on Mars
  http://www.esa.int/SPECIALS/Mars_Express/SEMLWL6DIAE_0.html
* Coprates Chasma and Coprates Catena
  http://www.esa.int/SPECIALS/Mars_Express/SEMIRE1DU8E_0.html
* Ancient floods on Mars: Iani Chaos and Ares Vallis
  http://www.esa.int/SPECIALS/Mars_Express/SEMIKO0DU8E_0.html
* Crater Holden and Uzboi Vallis
  http://www.esa.int/SPECIALS/Mars_Express/SEM9YX2IU7E_0.html
* Tithonium Chasma up close
  http://www.esa.int/SPECIALS/Mars_Express/SEMMFP2IU7E_0.html
* The mesas of Aureum Chaos
  http://www.esa.int/SPECIALS/Mars_Express/SEMF19NQS7E_0.html
* The Medusa Fossae formation on Mars
  http://www.esa.int/SPECIALS/Mars_Express/SEMSSZRMD6E_0.html
* 'Hourglass' shaped craters filled with traces of glacier
  http://www.esa.int/SPECIALS/Mars_Express/SEMN3IRMD6E_0.html

More information

* High Resolution Stereo Camera
  http://berlinadmin.dlr.de/Missions/express/indexeng.shtml
* Behind the lens ...
  http://www.esa.int/SPECIALS/Mars_Express/SEMSXE1PGQD_0.html

IMAGE CAPTIONS:

[Image 1:
http://www.esa.int/esaSC/SEMS3PMZCIE_index_1.html]
A perspective view obtained by the HRSC on board ESA's Mars Express, showing an unusual 'rock glacier' in the eastern Hellas region. Ice-rich material seems to have flowed from a small, 9 km wide crater into a larger 16 km wide crater below. The ice may have precipitated from the atmosphere a few millions years ago.

This unusual structure with traces of a glacier is located in Promethei Terra at the eastern rim of the Hellas Basin, at about latitude 38 deg South and longitude 104 deg East. This view is looking south-east.

Credits: ESA/DLR/FU Berlin (G. Neukum)

[Image 2:
http://www.esa.int/esaSC/SEMS3PMZCIE_index_1.html#subhead1]
This map shows an excellent match between the geological structure of the Tharsis region on present-day Mars (left), where glaciers remnants are indicated in yellow, and a simulation of glacier formation by atmospheric precipitation in the same region a few millions year ago (right).

In the simulation, performed by a Martian climate computer modelling tool, it is assumed that the rotation axis of the planet was tilted by 45 deg with respect to the planet’s orbital plane, about 20 deg more than today. Here, the results of the simulation are superimposed on a topographical map of the Tharsis area made by NASA's Mars Global Surveyor MOLA altimeter.

Credits: A: courtesy D.H. Scott, K.L. Tanaka, USGS. B: Lab. de Meteorologie Dynamic, IPSL (Paris, France)/MGS MOLA

[Image 3:
http://www.esa.int/esaSC/SEMS3PMZCIE_index_1.html#subhead2]
This is a simulation of water-ice accumulation (millimetres per Martian year) from the atmosphere, as predicted to have taken place in the Eastern Hellas basin a few million years ago by the Martian climate computer model. Such ice accumulation is in agreement with the glacier-like landforms observed today in this region.

Credits: Lab. de Meteorologie Dynamic, IPSL (Paris, France)/MGS MOLA
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