Mission to Mercury: Nasa's Messenger probe set to begin orbiting the Swift Planet

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• Vessel begins its year-long mission today, orbiting once every 12 hours

More than six years after it was launched from Earth, Nasa's Messenger spacecraft fired its main engine for 15 minutes to ease it into orbit around Mercury.
'The Messenger spacecraft went into orbit around Mercury tonight; we canconfirm that through the Doppler signals we've seen,' said systems engineer Eric Finnegan.The close encounter with the nearest planet to our Sun is an engineering and scientific milestone and marks the first local rendezvous with the rocky little planet since 1975.

Astronomers are interested in Mercury, the closest planet to the sun, because it is a terrestrial likeEarth, not gassy like Jupiter.Itis also an extremely difficult place for scientists to explore due to the planet's surface temperature, which would melt lead.There are many such rocky orbs around stars outside our solar system, which means Mercury could offer clues to other worlds as well, Nasa said.

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'Now that so many new planets are being discovered around stars in other solar systems, we need to know the effects of space weathering on rocky surfaces so we can accurately interpret telescopic and other remote sensing data we obtain from other rocky or dusty worlds,' said Ann Sprague of the University of Arizona's Lunar and Planetary Laboratory, one of the scientists working on the project.

Flyby: On October 6, 2008, the Messenger probe successfully completed its second flyby of Mercury, sending reams of data back to Earth. Messen! ger - an acronym for Mercury Surface, Space Environment, Gwochemistry and Ranging - has been journeying toward the planet since August 3, 2004, 'dancing' around Earth, the moon and Mercury itself, mostly to keep it from being drawn in by the sun's gravitational pull.The spacecraft will orbit about once every 12 hours and fill in the visual gaps left by it's two earlier flybys and the images snapped by Mariner 10 between 1974 and 1975.

The spacecraft, with two solar panelsfor power and a sunshade to keep it cool enough to operate, will study the geologic history, magnetic field, surface composition and other mysteries of this largely unexplored planet. Once the mission ends, the craft will drop to the surface of the planet.
Witha diametre just slightly larger than the moon's - about 3,000miles - Mercury should have solidified to its core. But the presence of a magnetic field suggests it is partly molten inside.

An artist's impression of Messenger orbiting Mercury. Astronomers are interested in Mercury, the closest planet to the sun, because it is a terrestrial like Earth, not gassy like JupiterFordecades, scientists who wanted to study Mercury used images made by Mariner 10, which only showed one side of the planet, along with ground-based observations and data obtained from Mars and meteorites.Onthe way to Mercury, Messenger managed to make pictures of much of what Mariner 10 missed, leaving only about 5 per cent of the planet unseen.Those areas are largely at the poles, and Messenger will attempt to make images of them during its orbital mission.