Mission To Orbit Long-Neglected Planet

When was the last time you thought about Mercury? No, not the Ford. No, not the boat engine. Mercury -- the planet.

It's been 29 years since man has sent a spacecraft to the solar system's inner-most planet. In light of the Mars missions and the remarkable images beamed back from Saturn by the Cassini vehicle, you might well imagine that Mercury is suffering from exporation envy.

The Messenger spacecraft should change all that. Set to launch next Monday, the probe will take its time getting to mercury. But by 2011, if all goes according to plan, Messenger should orbit Mercury in hopes of delving into some of the planet's peculiarities.

For instance, Mercury is mostly metal. While much of the planet is seared by the sun, other parts are suspended in a deep freeze. Because of its bizarre orbit, the sun appears to rise, then backtrack and even stand still before eventually setting -- 176 days (Earth days, that is) later.

"We think Mercury has a lot to tell us about how the Earth was formed, how the inner planets were formed, and how they all turned out so differently," said scientist Sean Solomon, principal investigator for the mission, in an interview with the Dallas Morning News.

Messenger will examine the incredible magnetic field that surrounds the tiny planet, as well as the gases that comprise its thin atmosphere. And by the way, is that ice at Mercury's south pole?

In fact, it's pretty difficult to tell. Because Mercury is so obviously close to the sun, it's hard to capture images of the surface. Messenger will carry several cameras to photograph the surface -- meteor craters in particular. It will lso carry a magnometer to measure variations in the planet's magnetic field. Other instruments will detect and quantify the gases in the atmosphere.

Since Messenger will operate so close to the sun, it will be protected by a big ceramic shade, capable of bleeding away the intense heat very quickly. Mission scientists say the shade should keep Messenger's insrumentation at close to room temperature.

If all goes the way it's supposed to, Messenger wil spend a year orbiting the small planet before it nosedives in.

Messenger will be the first probe to visit Mercury since 1975, but it probably won't be the last. The ESA, together with Japan, is working on a probe called BepiColombo, tentatively scheduled to launch as early as 2012.

FMI: http://messenger.jhuapl.edu/index.html