NASA just announced that they're joining in on an international mission to send a robotic space probe to Mercury, which will only be the third spacecraft that humans have ever sent to the innermost planet of our solar system.

BepiColombo, as this spacecraft is named, is the first mission that Europe has ever sent to Mercury, and it follows up on two NASA missions — Mariner 10 that swung by in 1974 and 1975, returning our first close-up images of the planet, and then MESSENGER, which launched in 2004 and just completed an extended mission around the planet in March of this year. While in orbit, MESSENGER completed a full survey of the planet's surface, examining the composition of the planet's crust, the structure of its interior and its magnetic field, and even investigating bright radar patches at its poles (which turned out to be water ice, possibly with something else very interesting!)

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The BepiColombo mission is set to launch in 2015, but it won't be arriving at its destination until 2022. That seems like a long time, considering that it only took New Horizons roughly a year to pass by Jupiter on its way out to Pluto, and even comparing Mercury's farthest distance away from Earth and Jupiter's closest distance to Earth, Jupiter is still around three times further away. However, the trick with getting to Mercury is that you can't just fly straight there and expect to be able to put on the brakes and zip around the planet.

Think of those big funnel-things that you roll change into, where they spiral around and around and then drop into the middle. If you've ever visited the Ontario Science Centre, they have something similar, but it's a gravity well simulator that uses metal balls instead of coins. That funnel is a fairly good model of what our inner solar system would look like, if you could see the curvature of spacetime due to the Sun's gravity. The Sun would be at the middle of the funnel, and Mercury is fairly close to the centre, but it's orbiting around just fast enough that it's able to keep a fairly stable orbit.

Launching a satellite in order to get it into orbit around Mercury is like rolling a penny around the funnel. You have to set it up so that it goes around and around at a really slow pace, taking its time to gradually work its way towards the centre, otherwise it'll just get caught up by the Sun's gravity and get sucked in. MESSENGER went around the Sun nearly 16 times before it arrived at Mercury at the right speed and trajectory to get into orbit.

BepiColombo will likely take a similar route.

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This new mission would build on current findings, to tell us even more about what the planet is made of, and examine Mercury's strange magnetic field closer. All of this will add to our knowledge of not only Mercury in particular, but also how rocky planets form in solar systems.

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