2007-06-07 | SCIENCE
MESSENGER Probes Venus' Atmosphere

MESSENGER is on a mission to Mercury, not Venus. But the spacecraft must pass by Venus for a gravity assist en route. In passing, researchers hope to learn a few things about Earth's "evil twin," an Earth-sized world with sulfuric acid clouds, a choking carbon dioxide atmosphere, and a surface hot enough to melt lead.

"We are treating the Venus flyby as a full dress rehearsal for the first flyby of Mercury in January 2008," says Sean Solomon, the mission's principal investigator at the Carnegie Institution of Washington. "All of the spacecraft's science instruments will be turned on during the flyby."

Of particular interest is the laser experiment, which aims to measure the location of Venus' cloud decks. "It could either fizzle or be a major result," says Ralph McNutt, MESSENGER's project scientist at the Johns Hopkins University Applied Physics Lab. "We've never sent a laser to Venus before. This could give us some unique information about the planet's clouds."

The name of the laser is MLA--short for Mercury Laser Altimeter. It was designed to map the rocky topography of Mercury, but MLA turns out to have some nice properties for the study of Venus. Solomon explains: "Venus' atmosphere and clouds are nearly transparent at several infra-red wavelengths." The wavelength of the laser (1064 nm) is close to one of these spectral "windows," so it may be able to penetrate deep into the atmosphere. "It's a long shot, but we may even see returns from the surface of Venus," he speculates.

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