The closest planet to the sun will be getting a long-awaited close-up next Monday when Mercury gets its first visit from a space probe in 33 years.
NASA's Messenger probe will fly by the tiny planet on Monday as part of a complicated flight pattern that will see two more flybys before it finally enters orbit in 2011.
The scientists who've studied the planet hope Messenger can help provide details of a planet astronomers know very little about.
"Mercury is a real oddball," said Sean Solomon of the Carnegie Institution of Washington and Messenger's principal investigator during a NASA teleconference on Thursday.
Among the unique features of Mercury is its density and the presence of a magnetosphere, features that lead scientists to believe the planet is made up mostly of iron metals and may have a molten core.
The small planet's close proximity to the sun, slow rotation and thin atmosphere create a huge difference in surface temperatures between the side facing the sun and the dark side, with temperatures getting as hot as 467 C and as cold as –170 C.
The Messenger team hopes the mission, which NASA said cost $446 million US, can shed light on planetary and solar system formation and better their understanding of how magnetic fields and planetary cores work.
Solomon said the mission, first conceived in 1996, was a long time coming because advances were needed to create materials for the probe capable of withstanding radiation from the sun. Mercury orbits the sun at an average distance of about 58 million kilometres. Earth, by comparison, is on average about 150 million km from the sun.
On Monday morning Messenger will begin collecting data from Mercury, taking more than 1,300 pictures in 55 hours, said Eric Finnegan, a mission systems engineer from Johns Hopkins University.
The data collected, when presented on Jan. 30, will represent a treasure trove of information for astronomers, said Solomon.
It's the first time a spacecraft has travelled past the planet since Mariner 10 mapped less than half the planet's surface during visits that began in March 1974. The other 55 per cent of the planet's surface has never been seen, he said.
Astronomers have also avoided pointing orbital telescopes in Mercury's direction because they did not want the bright light from the sun to "fry" a telescope's sensitive instruments, said Solomon.
Getting to Mercury has also proved a challenge, said Solomon.
Launched Aug. 3, 2004, Messenger is just over halfway through its winding, 7.9-billion km journey. It has flown past Earth once and Venus twice, and will use the pull of Mercury's gravity during this month's pass and others in October 2008 and September 2009 to bring it closer to the planet's orbit.
It is expected to reach orbit in 2011 and is scheduled to continue in that position for at least a year.