Earth is going back to Mercury.
BepiColombo, a joint mission of the European and Japanese space agencies, set off from a launchpad in French Guiana aboard an Ariane 5 rocket on a humid and mostly clear Friday night. Should the spacecraft travel as planned in the hours and days to come, it will set off on a course that makes it only the third spacecraft to visit the solar system’s innermost planet.
The mission actually contains two spacecraft that will share a ride to Mercury, but then separate to different orbits to make different observations. It will be a long wait for the main phase of the mission — the spacecraft do not begin to orbit Mercury, the solar system’s innermost and smallest planet, until December 2025.
Why does it take seven years to get to Mercury?
It is easy to get to Mercury quickly. The hard part is stopping.
Flying toward the sun is like running down a steep hill. Near the bottom of the hill, it is hard to slow down, which is essentially what BepiColombo needs to do before it can swing into orbit around Mercury, instead of just whizzing by.
The first spacecraft to go to Mercury, NASA’s Mariner 10 in 1974, made the trip in less than five months. But that was only a short flyby, passing within 450 miles of the surface. It made two additional flybys but never entered orbit.
A rocket engine could act as a brake, but that would require far more fuel than BepiColombo would be able to carry.
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SOURCE: New York Times, Kenneth Chang