Today is the ten-year anniversary of a nor'easter that went on to star in its own movie - you know it as "The Perfect Storm." Recently that nickname was used by planet-watchers at NASA to describe the biggest global dust storm seen on Mars in decades.

This dust storm has engulfed the entire Red Planet since June, and the dust has had an important effect on the temperature of the Martian atmosphere. As the Sun warms the airborne dust, the temperature of Mars' upper atmosphere has gone up by about 80^oF. This heating has actually expanded Mars' thin envelope of air, extending it outward slightly.

This tiny expansion of Mars' atmosphere is more than just an astronomical curiosity. When a spacecraft orbits a planet, the craft uses friction with the planet's atmosphere to slow down, so it's vital to know how extensive the atmosphere is. And coincidentally, the latest Mars spacecraft, NASA's Mars Odyssey, just began orbiting the Red Planet last week.