Messenger Settles into Orbit Around Mercury

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A well-traveled NASA probe made history March 17, becoming the first spacecraft ever to enter into orbit around Mercury.

NASA’s Messenger spacecraft fired its main thruster in a 15-minute orbital insertion burn to slow down by about 3,000 kilometers per hour, enough to enter Mercury’s gravitational influence and settle into orbit around the planet.

About an hour after the 8:54 p.m. EDT engine burn it was official: Messenger was in a looping, 12-hour orbit around the solar system’s innermost planet.

“This is when the real mission begins,” said Sean Solomon, Messenger’s principal investigator at the Carnegie Institution of Washington, after the probe arrived at Mercury. “It’s just all coming together and we are really ready to learn about one of Earth’s nearest neighbors for the first time.”

The spacecraft, built by the Johns Hopkins Applied Physics Laboratory (APL) in Laurel, Md., soon will begin mapping Mercury and studying the planet’s composition, geology and tenuous atmosphere from its orbital perch.

“The spacecraft is ready, and the team is ready,” Messenger mission operations manager Andy Calloway of APL told reporters before the insertion burn. “On April 4, we’ll begin prime science.”

Messenger launched in August 2004 from Cape Canaveral, Fla., aboard a Delta 2 rocket. Over the past 6.5 years, Messenger has completed 15 orbits of the sun and traveled about 7.9 billion kilometers. During that time, it made one flyby of Earth, two flybys of Venus, and three of Mercury, primarily to slow the probe down in preparation for tonight’s orbital insertion maneuver.

Messenger also took pictures during these close encounters. Its Mercury observations were the first spacecraft data returned from the planet since NASA’s Mariner 10 probe made three flybys in the mid-1970s.

Over the next 12 months, Messenger will map Mercury’s surface in unprecedented detail and investigate the planet’s composition, magnetic field, geologic history and thin, tenuous atmosphere, among other features. Scientists hope the probe helps them better understand what makes the tiny planet tick.

“Mercury is a planet where there’s many things going on,” Solomon said. “What we’ve learned from the flybys is that all of these things are connected.”

Over the next few weeks, the mission team will turn on and check out Messenger’s suite of seven science instruments, making sure everything is working properly.

Messenger’s first pictures of Mercury from orbit should start trickling out in about two weeks, Solomon said, but the real data flood will come with the official start of the probe’s science operations on April 4.

From that point on, Messenger will be beaming home the equivalent of two flybys’ worth of information every day, Calloway said.