NASA spacecraft approaches Mercury

NASA's MESSENGER spacecraft has finished it 12,000 mile-per-hour flyby of Mercury, losing some data to a communications glitch, but successfully setting its course for a 2011 final rendezvous with the planet. Never seen before, a volcanic pit, a double crater and smooth plains revealed themselves on the spacecraft's 142-mile high passage over Mercury on Monday.

“This third and final flyby was MESSENGER’s last opportunity to use the gravity of Mercury to meet the demands of the cruise trajectory without using the probe’s limited supply of on-board propellant,” says the MESSENGER team's Eric Finnegan of the Johns Hopkins University Applied Physics Laboratory (APL) in Laurel, Md. On its present orbit, MESSENGER will be gravitationally captured by Mercury in March of 2011.

The flyby completed the mapping of most of Mercury from space started in two earlier MESSENGER flybys. After a "carrier" signal was dropped by the spacecraft during the flyby, it went into "safe" mode, halting some of its observations, but keeping intact already-recorded data.

Even with any missing observations, "we are on course to Mercury orbit insertion less than 18 months from now, so we know that we will be returning to Mercury and will be able to observe the innermost planet in exquisite detail," said mission principal investigator Sean Solomon of the Carnegie Institution of Washington.