Originally posted by the Voice of America. Voice of America content is produced by the Voice of America, a United States federal government-sponsored entity, and is in the public domain. US Space Probe Enters Mercury Orbit Jessica Berman | Washington March 18, 2011 Artist concept of Messenger in Orbit Photo: NASA Artist concept of Messenger in Orbit The U.S. space probe [1]Messenger has become the first spacecraft to enter orbit around Mercury, beginning a year-long observation of the solar systemâs 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.  Messenger 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 probeâs progress through data relayed back to Earth by way of NASAâs Deep Space Network of radio antennas trained on Messenger. Ed Weiler, NASAâs associate administrator for the science mission directorate, confirmed the missionâs 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." Messenger now becomes the first spacecraft to orbit Mercury. The last close-up data of the fiery planet was collected by NASAâs Mariner 10 in a fly-by mission in the mid-1970s. Messengerâs 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 Messengerâs elliptical orbit, the spacecraft will fly within 200 kilometers of the planetâs 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 systemâs 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. Messengerâs orbital mission is scheduled to last one year. References 1. http://www.nasa.gov/mission_pages/messenger/main/ .