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The Engineer

The Life and Times of Donald F. Simmons

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Messenger flies past Mercury

The Messenger probe is making a close fly-by of Mercury today, the first of three that will ultimately manoeuvre the spacecraft into orbit in 2011.

Mercury has been visited by a grand total of one space probe to date, a consequence of the fact that the planet orbits the Sun more than twice as fast as the Earth does, so it's really expensive in energy terms to rendezvous with it. Mariner 10 made three fly-bys in 1974 and 75 but only managed to obtain close up images of one side of the planet. Today's fly-by will get us our first good images of the other side.

There's a lot of mystery about Mercury and how it formed. It's the only other rocky planet besides Earth with an appreciable magnetic field, and it's very dense for its size. Data from Messenger may ultimately help clear up questions on how the Solar System formed.