17-03-11 Messenger probe set to orbit Mercury

NASA Messenger spacecraft is primed and ready to enter into orbit around Mercury - the first probe to do so.The US space agency has uploaded commands to the robotic explorer that should initiate a 14-minute burn on its main thruster on Friday (GMT).This is expected to slow the spacecraft sufficiently so it can be captured by the planet's gravity.Being so close to the Sun,Mercury is a hostile place to do science.Surface temperatures would melt lead.In this blistering environment,the probe has to carry a shield to protect it from the full glare of our star.And even its instruments looking down at the planet have to be guarded against the intense heat coming back up off the surface.But principal investigator Sean Solomon,of the Carnegie Institution of Washington,is hoping for some remarkable discoveries in coming months."We started the Messenger mission as a proposal to Nasa 15 years ago," he told BBC News.

"We have been building for the orbit insertion and the observations that will follow for a decade and a half."To say that the science team is excited about what is to come is a huge understatement.We are really pumped."Just getting to Mercury has proved a challenge.Messenger has had to use six planetary flybys - one of Earth,two of Venus and three of Mercury itself - to manage its speed as it ran in closer to the Sun and its deep gravity well.The orbit insertion burn by probes 600-Newton engine should finally park it into a 12-hour,highly elliptical orbit about the planet.The strategy devised by scientists and engineers is to have Messenger gather data with its seven instruments during the close approaches (some 200km from the surface) and then return that information to Earth when the probe is cooling off at maximum separation from the planet (up to 15,000km from the surface)