Revisiting a forgotten planet

Engineers are readying a NASA spacecraft for a May 11 launch to one of the least-explored planets in the solar system. If all goes according to plan, the craft will begin orbiting Mercury, the sun’s closest planet, in 2009 and take the first close-up images of the pockmarked body since 1975.

MISSION TO MERCURY. Artist’s impression of the MESSENGER spacecraft at Mercury. NASA, JHU APL, CIW

The craft, known as MESSENGER (for Mercury Surface, Space Environment, Geochemistry, and Ranging), will be the first to image the entire planet, a place of extremes (SN: 7/8/00, p. 24: Available to subscribers at Forgotten Planet). At any given moment, one side of Mercury is hot enough to melt zinc while the other is cold enough to freeze methane—a temperature range of 600°C.

During its mission, MESSENGER will search for signs of ice in permanently shaded craters and attempt to determine, by closely examining the orb’s rotation, whether Mercury has a liquid core. To protect itself from the planet’s intense heat, MESSENGER has a ceramic-fabric sunshade and will pass only briefly over hot spots on the surface.

To reach its final destination, MESSENGER must get several gravitational boosts. They’ll come from its three scheduled fly-bys of Venus, this November and in 2005 and 2006, and two of Mercury, in 2007 and 2008, before settling into its specific, year-long orbit around Mercury.

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