Page last updated at 13:35 GMT, Wednesday, 8 October 2008 14:35 UK

Messenger extends Mercury vista

By Jonathan Amos
Science reporter, BBC News

Mercury (NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)
An extensive pattern of rays is visible on this new image

The Mercury Messenger probe has returned another batch of stunning pictures of the innermost world.

The Nasa spacecraft swept over the surface of the planet on Tuesday, passing just 200km above the rocky terrain at closest approach.

Some 1,200 images were obtained - many of regions never before been seen up close by a probe.

The flyby also gave Messenger the gravity tug it needed to get on to the right path to go into orbit in 2011.

"The Messenger team is extremely pleased by the superb performance of the spacecraft and the payload," said chief scientist Sean Solomon of the Carnegie Institution of Washington.

Mercury (NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)
Closest planet to the Sun; smallest in Solar System
Visited by Mariner 10 in 1970s; by Messenger currently
Diameter: 4,880km, about one-third the size of Earth
Second densest planet in Solar System; 5.3x that of water
Caloris basin is largest known feature (1,300km in diameter)
Possibility of water-ice in permanently shadowed craters
Huge iron core takes up more than 60% of the planet's mass
Surface temperatures swing between 425C and -180C
Has an extremely thin atmosphere (exosphere)
Only inner planet besides Earth with global magnetic field

"We are now on the correct trajectory for eventual insertion into orbit around Mercury, and all of our instruments returned data as planned from the side of the planet opposite to the one we viewed during our first flyby.

"When these data have been digested and compared, we will have a global perspective of Mercury for the first time."

The first planet from the Sun has not been the target of spacecraft mission since Mariner 10 made three flyby in the 1970s. But the probe managed to map less than half of the planet's surface.

On Messenger's first flyby in January, its cameras returned pictures of about 20% of the surface area missed by Mariner 10.

On Tuesday's pass, Messenger captured another 1,200 high-resolution and colour images, revealing a further 30% of Mercury's surface that had never before been seen by spacecraft before.

The pictures show the expected mix of craters, ridges and scarps. The previously unseen regions also reveal an extensive pattern of rays - what look almost like stripes - that run from north to south.

The Messenger team will study the data in detail to try to gain new insights into this remarkable world.

Mercury (NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)
A portion of Mercury's surface imaged by the spacecraft for the first time

So long neglected, Mercury is once again the subject of great interest.

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

It will be launched in 2013. 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 2019 after a six-year, seven-billion-km flight towards the inner Solar System.

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