Spaceflight Now: Breaking News

Rocks may hold key to water search on other planets
BY JEFF FOUST
SPACEFLIGHT NOW

Posted: January 25, 2001

  Gully on Mars
A gully on the south-facing wall of an impact crater in the southern hemisphere of Mars. Photo: NASA/JPL/Malin Space Science Systems
 
Scientists seeking to understand how much water might have once existed on Mars and Venus may find answers locked up in the rocks on those planets, according to research published this week.

In an article published in Thursday's issue of the journal Nature, a team of scientists from MIT and the University of Tennessee reported that Martian volcanic rocks once contained relatively large amounts of water: enough, perhaps, to be a source for the liquid water that once was thought to exist on the planet's surface.

That conclusion was based on the study of Shergotty, a Martian meteorite found in India in 1865. Shergotty is a young meteorite, geologically speaking -- about 175 million years old -- and is thought to come from the volcanic Tharsis region of the planet.

The meteorite itself is quite dry, containing no more than 350 parts per million of water. However, the MIT and Tennessee team examined the minerals contained within the meteorite and found some that, on the basis of experiments conducted on 'synthetic' Mars rocks, could only form in the presence of water. Those minerals led them to conclude that the water concentration in Shergotty was once as high as 2 percent.

"What my experiment can do is estimate how much water was involved in the process that led to the formation of Mars meteorites," said Tim Grove of MIT. "The only way you can reproduce the unique chemical composition of these minerals is to have water present."

Grove and colleagues believe that the water formed as hot magma rose in the interior of the planet and came into contact with hydrogen-bearing minerals in the surrounding rock. The hydrogen combined with oxygen to form water, which was released as vapor when the magma reached the planet's surface.

Such a process might explain how the water formed on the Martian surface earlier in its history, when the planet was warmer and more geologically active. How large of a role volcanic activity played versus other sources, such as impacting comets, remains to be determined.

While work continues to understand water on the Red Planet, another team of scientists believes that another mineral, also formed in the presence of water, could be the key to understanding how much water might have existed on the planet Venus.

  Venus
A global view of the surface of Venus from the Magellan spacecraft's synthetic aperture radar. Photo: NASA/JPL
 
In a paper published in January's issue of the planetary science journal Icarus, researchers at Washington University in St. Louis identified one type of mineral linked to the presence of water that could survive the harsh conditions found on Venus today.

Scientists found that tremolite, a mineral on Earth associated with some types of limestone, could survive the high temperatures of the surface of Venus for up to four billion years without decomposing. If found on the planet, tremolite could be the definitive proof that the planet once had liquid water.

"We have shown that tremolite can withstand extreme temperatures and remain intact for billions of years," said Natasha Johnson of Washington University. "If we can go to Venus and find tremolite, or some other hydrous mineral, then we would have proof that Venus had water in its past."

To date tremolite has not been found on Venus; the planet's mineralogy is poorly known as a thick shield of clouds cloaks the surface. Scientists suspect that Venus once had water: the planet's atmosphere has a high ratio of deuterium (a heavy isotope of hydrogen) to ordinary hydrogen. Since the lighter hydrogen is more easily lost to space than deuterium, a high "D/H" ratio suggests Venus once had a considerable amount of hydrogen, likely in the form of water. However, that evidence is not considered sufficient enough to prove the planet once had water.

Such minerals could be detected by infrared spectrometers, particularly those that could be deployed under the planet's cloud deck by balloons or other devices. However, there are no plans by NASA or other space agencies to mount missions of any kind to Venus in the foreseeable future, meaning that the mystery of the planetıs water may remain unsolved for years to come.