Wet Mars? Not Recently

Speaking of Mars, there’s been some fascinating developments over the red planet. Looks like a mineralogical report release last week lays out the Martian geological history, and it is a dry and dusty story.

The Mars Express orbiter arrived in orbit around the red planet in late 2003, and mapped the planet’s surface in excruciating detail. The OMEGA instrument created mineral maps that suggest three distinct eras on Mars; an initial warm and wet period, a fiery volcanic interlude, and the long deep freeze that continues today.

The OMEGA team, led by Jean-Pierre Bibring of the Institut d’Astrophysique Spatiale in France, found about two dozen sites rich in clay minerals, which form in water and in conditions of low acidity. These sites are scattered around the planet in ancient craters and where an overlying layer of volcanic cover or wind-blown sand and dust has been removed.

That suggests the clays formed early in the planet’s history, says Bibring: “The clays may have been formed on a large scale but we only see them where they have been exposed by erosion, outflows, or impacts.”

The spectrometer also found sulphate minerals, such as gypsum and grey haematite, concentrated in a few places. These locations include Valles Marineris – the Red Planet’s “Grand Canyon” – and Meridiani, where NASA’s Opportunity rover landed and also found sulphate-rich rocks. Sulphates require water to form, but some detected by OMEGA must also have been created in acidic conditions.

Finally, OMEGA found minerals rich in ferric oxides that had not been altered by water. These minerals are found over most of the planet and are thought to be caused by the slow weathering of rocks through chemical interactions with the atmosphere.

This mineral evidence ties in with current thinking about the planet’s history. For the first 600 million years, Mars had a warm and wet atmosphere and large bodies of surface water, conditions ripe for the development of life.

Then the eon of supervolcanos began. Massive Olympus Mons and the Tharsis Bulge speak to the size and power of this volcanic era. The volcanism release huge amounts of sulphur into the atmosphere, creating sulphuric acid and covering the surface of Mars in sulphates that require acidic water to form. This lasted for approximately 500 million years.

Finally, the failing heat of the planet’s core shut down the volcanism and the internal dynamo that generated Mars’ magnetic field collapsed. The atmosphere, exposed to the solar wind, bled away into outer space like fog dissipating on a sunny morning. The loss of atmospheric pressure put Mars into a deep freeze, desiccating the planet’s surface for 3.5 billion years.

Scientists are most interested in those early clay layers which formed during the wet and warm period. The Mars Reconnaissance Orbiter will probably focus its big cameras on those regions, looking for evidence of the planet’s brief springtime and the possibility of life.

If liquid water still exists, it lies beneath the ice just like those lakes in Antarctica. The surface of Mars is an inhospitable, dry frozen wasteland, bathed in solar radiation.