Messenger at Mercury

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• 13 of 1970
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Like two people on a first date, a spacecraft and a planet are scheduled to get acquainted tomorrow -- the first of three "dates" before they settle into a longer-term relationship.

The planet is Mercury, the closest planet to the Sun. And the spacecraft is called Messenger, which will fly within a couple of hundred miles of Mercury's surface. Messenger will fly past Mercury two more times before settling into orbit around the planet in 2011.

Messenger will keep on going tomorrow because its path and speed aren't quite right for entering orbit. It would take much more fuel to achieve an orbit on this first pass, which would have made the craft too heavy.

So Messenger is following a looping path through the inner solar system. It's already flown past Earth once and Venus twice. Messenger uses each planet's gravity like a booster rocket, changing its speed and direction. After two more passes by Mercury, it'll be in just the right position to start orbiting the planet.

Despite the brevity of this encounter, Messenger will conduct some important observations. Only one other craft has visited Mercury, and it saw only one side of the planet. Messenger will fill in some of the details on the other side. It'll photograph Mercury in color, too, and measure its gravity and magnetic field, which reveal details about its interior. So learning a little about the outside and a little about the inside isn't bad for a first date.

Script by Damond Benningfield, Copyright 2007

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