Page last updated at 16:42 GMT, Wednesday, 16 December 2009

Best ever atlas of 'iron planet'

By Jonathan Amos
Science correspondent, BBC News, San Francisco

About 2% of the planet's surface remains to be mapped

The most complete and most detailed atlas of Mercury has been assembled.

It is only now thanks to the Messenger spacecraft that researchers have the imagery necessary to construct a truly global map of the innermost planet.

The probe's latest pictures added to those of the earlier Mariner 10 mission give near-total coverage.

Mapping experts at the US Geological Survey have been working to piece together all of these images in their possession into a giant mosaic.

This has been displayed here at the American Geophysical Union's (AGU) Fall Meeting, the world's largest annual gathering of Earth scientists.

"Mariner 10 in the 1970s took about 40% of the images of the surface and with the flybys of Messenger, we've now got 98% of the surface; and the only parts that we don't have are at the poles - parts of the north pole and the south pole," explained Kris Becker, a cartographer and programmer at the USGS Astrogeology Research Center in Flagstaff, Arizona.

In March 2011, Messenger will go into orbit around Mercury and it will begin systematic mapping of the planet. The expectation is that the finished atlas of the "iron planet" will have a resolution of 200m per pixel.

Even so there will still be some small areas in permanently shadowed craters that will remain unseen.

Crater posterity

Many people will have used "stitch software" that comes with their digital cameras to turn holiday snaps into panoramas. The USGS is doing something similar when it joins up the Messenger and Mariner images, but the task is obviously a great deal more complex and sophisticated.

"It's a bit of a challenge," said Mr Becker.

"You've got different resolutions and different lighting conditions in there. So we have software that helps us start a control network that ties all the image common features together, and it basically creates a minimisation of the errors in among all those pictures."

A good atlas will be an important tool for mission scientists when Messenger finally settles into orbit. It will be used to target better the scientific observations made by the probe's instruments.

One critical task ahead will be naming all the features visible in the atlas. Cliffs on Mercury are named after the ships of famous explorers. The planet's craters can carry the names of long-dead artists, musicians, or authors.

The European Space Agency (Esa) has recently approved construction of a mission to the planet called BepiColombo.

It will be launched in 2014. The mission consists of two spacecraft - an orbiter for planetary investigation, led by Esa, and one for magnetospheric studies, led by the Jaxa (Japan Aerospace Exploration Agency).

The satellite duo will reach Mercury in 2020 after a six-year, seven-billion-km flight towards the inner Solar System.

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