NASA probe makes Mercury flyby

A space probe soared within 200 kilometres of the surface of Mercury Monday afternoon, providing NASA with its first look at the planet in more than 30 years.

The NASA probe reached the 200 kilometre mark just after 2 p.m. ET, although it took about 10 minutes for flight controllers in Maryland to confirm the position.

The Messenger spacecraft flew 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.

On Sunday, the probe began taking three colour images every 20 minutes of the side of the planet opposite from Earth, which has never been viewed by a spacecraft. That rate is expected to rise as it gets closer to the planet; the probe should take more than 1,300 pictures in a 55-hour span, said Eric Finnegan, a mission systems engineer from Johns Hopkins University.

The data collected, which is expected to start arriving on Earth on Tuesday, will be presented on Jan. 30.

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.

Since that time, priorities have changed, said Canadian Space Agency astronomer Victoria Hipkin, with later voyages to Mars and the outer planets drawing attention away from Mercury.

"There have been other places to visit, and more excitement to be found in places like Mars," Hipkin said. "When we went to look at Mercury, we found that it was a rocky, moon-like planet unsuitable for life."

Hipkin is interested in the Messenger results, however, mainly because 55 per cent of the planet's surface has never been seen.

Sean Solomon of the Carnegie Institution of Washington and Messenger's principal investigator said during a NASA teleconference on Thursday he hopes Messenger can help fill in details of a planet astronomers know very little about.

Mercury may be iron metals around molten core

"Mercury is a real oddball," he said. 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 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 kilometres from the sun.

Astronomers have 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, Solomon said.

Getting to Mercury has also proved a challenge, he said.

Launched Aug. 3, 2004, Messenger is just over halfway through its winding, 7.9-billion kilometre 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.