Artist concept of Messenger in Orbit
Artist concept of Messenger in Orbit

The U.S. space probe Messenger has become the first spacecraft to enter orbit around Mercury, beginning a year-long observation of the solar system?s inner-most planet.   Astronomers with the U.S. space agency NASA hope the orbiting probe increases their knowledge of the fiery planet as well as the rest of the solar system.  

settled into near polar orbit around Mercury around 1254 UTC after firing its main thruster engine for 15 minutes to slow the spacecraft down and place it in the proper position for its planetary rendezvous.

There were no images of the historic event, just anxious scientists closely monitoring the space probe?s progress through data relayed back to Earth by way of NASA?s Deep Space Network of radio antennas trained on Messenger.

Ed Weiler, NASA?s associate administrator for the science mission directorate, confirmed the mission?s success and the relief of mission managers at the Johns Hopkins Applied Physics Lab in Maryland.

"The mood is fantastic," he said. "We know the engines burned, they started to burn, they burned on time and they stopped.  The Doppler shifts were correct.  And all indications are we are in orbit."

now becomes the first spacecraft to orbit Mercury.  The last close-up data of the fiery planet was collected by NASA?s Mariner 10 in a fly-by mission in the mid-1970s.

Messenger?s nearly eight-billion kilometer journey to Mercury began six-and-a-half years ago.  It included inner space fly-bys of Earth, Venus and Mercury itself for gravitational assists and dry-runs on the orbital insertion.

At the lowest point of Messenger?s elliptical orbit, the spacecraft will fly within 200 kilometers of the planet?s surface.

And at its closest point, Messenger will travel a mere 46 million kilometers away from the Sun.  

Built to withstand the blistering heat, the spacecraft is carrying seven scientific instruments that  principal mission investigator Sean Solomon hopes will answer some intriguing questions not only about Mercury, but about the solar system?s other planets.

For example, Solomon says scientists want to know why Mercury, which is as small as the moon, is twice as dense as Earth.

"This planet obeys the same laws and formed at the same time by the same processes as Earth and Mars and Venus.  It came out very different.  And so the challenge to the planetary science community is to come up with a general theory about planets formed and how planets work that can not only explain Earth, but can explain Mercury," he said.

Solomon says Messenger will begin returning images of Mercury in early April. Messenger?s orbital mission is scheduled to last one year.