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Messenger at Mercury

March 15, 2011

The little planet Mercury is putting in its best evening sky-appearance for the year this month. It's in the west at sunset, and looks like a fairly bright star. And today, it's close to the right of Jupiter, which outshines all the other stars and planets in the sky at that hour.

Mercury is the closest planet to the Sun, so the angle between the two as seen from Earth is never very large. That makes Mercury a difficult world to study.

Optical telescopes have little luck making out features on its surface, and couldn't even tell us how fast Mercury turns on its axis. Radio telescopes aren't blinded by the sunlight, so they can see more detail. They revealed that Mercury turns on its axis every 59 days, and they found evidence of ice at Mercury's poles.

The best view comes from spacecraft. Two craft have each flown past Mercury three times. They've mapped most of the planet's surface, and provided important details on its composition and structure. And one of those craft, Messenger, is scheduled to enter orbit around Mercury this week.

Over the next year, it'll map the planet's entire surface. It'll also measure Mercury's contours and the composition of its surface, and study its magnetic field and its interaction with the Sun. Eventually, it'll peek into craters at the poles to confirm that they contain frozen water -- giving us by far the clearest look at this elusive little planet.

More about Messenger tomorrow.

Script by Damond Benningfield, Copyright 2011


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