Giant dust cloud cooks red planet

On June 26, 2001, the Hubble Space Telescope spotted a dust storm brewing in Hellas Basin on Mars. A day later the storm "exploded" and became a global event

By Richard Stenger
CNN

(CNN) -- A colossal dust storm engulfed much of Mars and superheated its atmosphere this week, as a NASA probe passed the halfway mark on its 200-day journey to the red planet.

The amazing cloud, one of the largest seen in 25 years, has raised the temperature of the cold martian atmosphere by a stunning 30 degrees Celsius, Mars scientists said. It has become so big that amateur astronomers can observe it with ordinary telescopes.

The storm began as a small dust cloud inside the Hellas Basin, a deep impact crater in the southern hemisphere, said Phil Christensen of Arizona State University.

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Then about three weeks ago, "the storm exploded. It crossed some critical threshold and really began to grow," Christensen said. By early July, the cloud had erupted from the basin and spread over the entire planet.

Scientists remain unsure how modest storms proliferate into planetary monsters. Some theorize that airborne dust absorbs sunlight and warms air in the vicinity, which rush toward colder air pockets, generating strong winds.

The winds push more dust off the surface, further heating the atmosphere, fueling a positive feedback loop that transforms small dust clouds into storms of epic proportions.

Such storms can last for weeks and months. While unpredictable in their duration, they tend to happen after the planet, which has an elliptical orbit, swings nearest the sun. During this revolution, Mars made its closest approach on June 13.

"The biggest dust storms don't usually begin until one or two months after perihelion," Christensen said. "This one coming so early in the season makes me think Mars is heading for a spell of big dust storms."

Such howlers do not besiege our planet thanks to the abundance of water, whether in the oceans or the air, which prevents airborne dust from cooking the atmosphere.

Probe halfway to stormy planet

Fortunately, the Mars 2001 Odyssey will not have to endure the choking dust when it reaches the red planet in October.

The $300 million spacecraft will remain in orbit above the winds and storms, where it will measure radiation levels and scan the surface for mineralogical signs of water.

Launched in April, the NASA probe will be the first to visit Mars since two NASA spacecraft disappeared as they approached the surface in 1999.

"Odyssey is now closer to Mars than Earth. The spacecraft is healthy and all systems are looking good," said David Spencer, the mission manager at NASA's Jet Propulsion Laboratory. "Planning for Mars approach and orbit insertion is our primary focus right now."

Mission flight controllers are making preparations to slow the spacecraft in the upper martian atmosphere before the craft settles into orbit.

Currently, Odyssey is more than 28.5 million miles (45.8 million kilometers) from Earth and about 19 million miles (30 million kilometers) from Mars, traveling at a speed of 58,000 mph (93,000 km/h) relative to the sun.