Messenger

New Horizons is not the only active mission at APL (The Applied Physics Lab of Johns Hopkins University). The Messenger Mission to Mercury is on track to fly by the planet on Jan 14th, and will photograph its surface for the first time since March 1975. Even better, since the original Mariner mission only caught one side of Mercury in its cameras, this will be the first time the “dark” side will be seen up close.

I put dark in scare quotes, because Mercury does indeed rotate on its axis three times each time it orbits the Sun twice (it’s in resonance, but not tidally locked). It’s orbit takes about 88 days, and it rotates to the sub-solar point on its axis in about 59 days, so it has no true dark side. But because of the charateristics of the Mariner 10 mission profile, it only “saw” one side of the planet.

Messenger is not near the start of its science mission. Ultimately, in 2011, it will settle into an orbit but not before it flies by Mercury twice more. Then it settles down into it’s final orbit to start the real science. The spacecraft has already flown by the Earth and Venus (twice) all to shed velocity so that Messenger can get slow enough to be captured by the planet.

Unless you want to carry along tons of fuel to use for braking, it’s the only way to do it.

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