Creating a warmer, wetter Mars

Satellite images of Mars taken since the 1970s suggest that the planet, now frigid and bone dry on its surface, was once warmer and wetter. A new study adds to the evidence that material carried to the Martian surface by volcanoes created an environment more habitable than today’s.

Roger J. Phillips of Washington University in St. Louis and his colleagues homed in on one of the most prominent features on Mars, a 10-kilometer-tall edifice known as the Tharsis rise.

Located in the planet’s western hemisphere, Tharsis covers an area of 30 million square kilometers, more than three times the area of the United States. Combining topographic data and gravity maps derived from the Mars Global Surveyor spacecraft, Phillips and his collaborators find that the creation of the Tharsis rise had a huge impact on the planet. It likely accounts for the trough that surrounds Tharsis, as well as the Arabia bulge, an elevated region residing exactly on the planet’s opposite side. The scientists report their findings in the March 16 Sciencexpress (http://www.scienceonline.org/).

According to the researchers’ calculations, the creation of the Tharsis rise required an eruption of 300 million cubic kilometers of lava, enough to create a 2-km-deep layer of molten rock atop the entire planet. The sheer weight of the Tharsis rise generated the surrounding trough and the Arabia bulge, says Phillips.

Think of Mars as a beach ball and the concentrated weight of the Tharsis rise as a fist pushing into it, suggests Phillips. “If you stick your fist into a beach ball, it will affect the entire shape of the beach ball,” he says.

The same volcanic activity that wrought the Tharsis rise would have spewed enormous amounts of carbon dioxide gas and water vapor–enough to dramatically alter the Red Planet’s environment, Phillips’ team concludes.

Indeed, the researchers found that atmospheric levels of carbon dioxide would have been high enough to create a greenhouse effect, warming the planet to a temperature at which water on the surface would remain liquid. If the water vapor carried to the surface by the buildup of Tharsis was distributed over the entire planet, it could have created a 120-meter-deep ocean. Another recent report also suggests that volcanic activity brought huge amounts of water to the Martian surface (SN: 2/24/01, p. 123).

There’s additional evidence that the development of the Tharsis rise introduced and helped maintain liquid water on the surface of Mars, Phillips and his collaborators note. A detailed examination of Martian topography suggests that the planet’s network of channels, which resemble dried-up river beds on Earth, didn’t form until after the Tharsis rise was created. That’s the best explanation for the orientation of the channels, because the birth of Tharsis could have provided both the water for the channels and the slope those channels had to follow, says Philips. The channels in both the Tharsis region and the Arabia bulge follow the highs and lows induced by the Tharsis rise rather than older contours of the planet at large.

The team estimates that the Tharsis rise came into existence toward the end of the Noachian period on Mars, some 3.5 billion years ago. It may have taken a few hundred million years for the rise to form completely. The flow of water and the temperate climate on the Red Planet may have been limited to that time span, Phillips notes.