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Messenger probe enters Mercury orbit
"Everybody was whooping and hollering; we are elated. There's a lot of work left to be done, but we are there."
- chief engineer, Eric Finnegan
Nasa's Messenger spacecraft has successfully entered into orbit around the planet Mercury - the first probe to do so.
Mercury is often dismissed as a boring, featureless world that offers little to excite those who observe it, but planetary scientists who know it well beg to differ. It is a place of extraordinary extremes.
Mercury's proximity to the Sun means exposed equator surfaces can reach more than 600C; and yet there may be water-ice at the poles in craters that are in permanent shadow.
It is so dense for its size that more than two-thirds of the body has to be made of an iron-metal composition.
Mercury also retains a magnetic field, something which is absent on Venus and Mars.
In addition, the planet is deeply scarred, not just by impact craters and volcanic activity but through shrinkage; the whole body has reduced in size through Solar System history.
And Mercury fascinates because it may be our best guide to what some of the new planets might be like that are now being discovered around distant suns.
Many of these worlds also orbit very close in to their host stars.