NASA鈥檚 Messenger spacecraft is set to make its third and final flyby of Mercury on Tuesday. If all goes well, the manoeuvre will use Mercury鈥檚 gravity to slow the probe down enough to go into orbit around the planet in 2011.
Until Messenger鈥檚 first flyby of Mercury last year, the only spacecraft to view the diminutive planet up close was NASA鈥檚 Mariner 10. Over the course of three flybys in 1974 and 1975, the Mariner probe collected thousands of images of some 45 per cent of the planet鈥檚 surface.
Since then, Messenger has helped fill in the rest of the map. Another 50 per cent of the planet was imaged for the first time at close range during Messenger鈥檚 first two flybys. This last flyby, which will take Messenger within 230 kilometres of the planet鈥檚 surface around 2200 GMT, is expected to photograph much of the remaining 5 per cent.
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Although Messenger will collect most of its data after it reaches orbit on 18 March 2011, the spacecraft鈥檚 flybys have produced some tantalising results.
Messenger鈥檚 first pass above Mercury鈥檚 surface on 12 January 2008 revealed more evidence that the planet harbours a molten inner core and seems to have shrunk more than expected.
The spacecraft鈥檚 second flyby nine months later uncovered a bizarre spoke-like pattern in the planet鈥檚 second-largest impact basin and revealed yet more evidence of an unidentified dark, bluish material, patches of which now seem to be spread all around the planet.
