Rocks reveals Mars' watery past

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Message Jeu 15 Fév 2007 - 22:08

Désolé en anglais.

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Exquisite colour images of the Martian surface give a tantalising glimpse into the Red Planet's watery past.

Shots of the deep valley Candor Chasma show light coloured areas of rock where water could have flowed.

These "haloes" surround fractures in the Martian bedrock which provide a promising target in the search for evidence of past life on the planet.

The images, published in Science journal, were taken by a camera aboard Nasa's Mars Reconnaissance Orbiter.

"It lends support to the idea that a substantial body of groundwater existed on Mars in the past and may still persist to the present day," said Professor Stephen Clifford of the Lunar and Planetary Institute in Houston, Texas.

"The fact that there is such persuasive evidence of joints and fractures in the crust also suggests that this groundwater had the ability to flow enormous distances."

Huge rift

The High Resolution Imaging Science Experiment (HiRise) camera started its surveys in November 2006, eight months after Mars Reconnaissance Orbiter (MRO) entered orbit around the Red Planet.

It is best known for capturing stunning images of Nasa's robot explorers Spirit and Opportunity as they surveyed the planet from the ground.

Clay-like minerals are found in the Red Planet's Mawrth Vallis region

Enlarge Image

Nasa has recently admitted that some of the detectors on the camera are starting to fail.

The newly analysed images were taken last year. They show a snapshot of conditions in Candor Chasma, an area of the great Martian rift valley Valles Marineris.

This deep gash, the length of the United States, is up to seven times deeper than the Grand Canyon in places.

The images show a hilly landscape composed of alternating bands of light and dark coloured rock, suggesting the layers were deposited by regular cycles of water, wind or volcanic activity.


Reached Mars in March 2006
Two-year primary mission
HiRise images are the clearest pictures of Mars
Two detectors on the camera have developed problems
Cutting across the striped scenery, the researchers identified a network of cracks, known as joints, surrounded by prominent haloes of bleached rock.

Writing in Science, the University of Arizona team said that similar features on Earth were "a clear indication of chemical interactions between fluids circulating within the fracture and the host rock."

Likely fluids include water, liquid carbon dioxide or a combination of the two, and may have flowed up from deep underground reservoirs.

Protected habitats

Previously, Europe's Mars Express mission had detected the signature of minerals altered by water in the Candor Chasma area.

The washed-out features, which have been "cemented" by minerals contained in the fluids, now stand proud from the valley walls.

They have been exposed by millions of years of erosion.

However, the fact that they were once underground has important implications for their ability to support life.

"The overlying areas of rock would have acted as a buffer against any harsh environmental conditions on Mars at that time," said Dr Chris Okubu of the University of Arizon and one of the authors on the paper.

"These areas would be nice protected areas for any biological processes to occur."

Erosion has uncovered rocks that were altered by the action of fluids

Enlarge Image

This is not the first time that scientists have found evidence of fluids upwelling from deep inside the Martian interior.

Last year, Nasa's Mars Global Surveyor (MGS) spacecraft spotted gullies and trenches thought to have been recently carved by outpourings of water or liquid carbon dioxide.

Other features, including dried-up lake beds, springs and river valleys, lend further weight to the theory that the planet was once awash with water and could therefore have supported life.

Nasa is examining all of these sites as possible targets for future ground based robotic missions.

However, the space agency says that if it has a chance of finding evidence of life on the planet, it must broaden its search.

"Following the water is a central aspect of exploration but the habitability issue also requires addressing the source of energy for life," said Dr David des Marais of the Nasa Ames Research Center.

Possible future targets include areas of the planet where the building blocks of life, such as carbon, can be found.

"We not only need to follow the water but we also need to follow the energy," said Professor des Marais.

The findings were presented at the American Association for the Advancement of Science (AAAS) annual meeting in San Francisco, US.

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Message Ven 16 Fév 2007 - 10:07

Sujet recurant, en francais

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De l'eau a bien coulé sur Mars !

De nouvelles images acquises par la caméra Hirise de la sonde Mars Reconnaissance Orbiter de la région martienne Candor Chasma montrent que de l'eau sous forme liquide a bel et bien existé dans le passé de la planète ! Mieux encore, elles renforcent encore plus l'hypothèse selon laquelle la vie a pu se développer sur Mars, très tôt dans son histoire. Ces écoulements ont vraisemblablement favorisé l'apparition de niches biologiques, permettant l'émergence d'une vie microbienne, soutenue par la chaleur résiduelle de la jeune planète, vestige de sa formation.

Ces images d'Hirise sont incroyablement claires … pour un œil exercé. Elles montrent des indices pour ainsi dire irréfutables que l'eau a coulé le long de fractures dans les roches stratifiées de Candor Chasma. Les parois du canyon sont composées de couches fracturées, alternativement claires et foncées. Pour les astronomes qui ont travaillé sur ces images, les éléments de couleur claire, appelés " microfissures ", recoupent les couches foncées. Ces microfissures semblent être des zones où la roche a été modifiée, soit par cimentation ou par décoloration, par l'eau coulant le long des fractures.

Site d'atterrissage

Cette découverte de dépôts stratifiés dans Candor Chasma s'ajoute à liste des terrains les plus propices à explorer pour en apprendre d'avantage sur l'histoire de l'eau sur Mars. Une liste déjà bien remplie avec d'anciens lits de rivières, les lacs et autres paléosources asséchées.

The High-Resolution Imaging Science Experiment (HiRISE)

Cette caméra de 65 kg de l'Université de l'Arizona a été construite par la firme américaine Ball Aerospace & Technologies. Il s'agit ni plus ni moins de l'instrument de ce type le plus puissant jamais envoyé autour d'une autre planète que la Terre. La capacité d'observation de cette caméra sera d'autant plus renforcée que Mars Reconnaissance Orbiter évoluera sur l'orbite la plus basse jamais décrite par une sonde autour de Mars.

Son miroir primaire mesure 50 cm de diamètre. La résolution attendue est de 25 à 32 centimètres par pixel de sorte que l'on doit voir des détails d'environ 1 mètre. La caméra sera également capable de prendre des images en stéréo.

Plus de 10.000 images en très haute définition sont attendues tout au long de la mission primaire de deux ans (2006 - 2008) de Hirise.

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Message Ven 16 Fév 2007 - 10:14

D'ailleurs le site d'HiRISE propose les photos en haute résolution, ici:

Il existe aussi un film réalisé par l'équipe en Arizona sur le sujet (573 Mo):

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