Tomorrow sees the third and final flyby of Mercury by the Messenger (MErcury Surface, Space Environment, GEochemistry and Ranging) spacecraft. Rather than using fuel intensive burns to get to the closest planet to the Sun, Messenger has been using the gravitational attraction of Mercury to bring it closer and closer, much as Jupiter captured the comet Shoemaker Levy 9 in a decaying orbit before it slammed into the giant planet. Messenger won’t be doing that – the next time it approaches Mercury in 2011, it will simply enter orbit and begin further science operations.
The previous two visits by the probe have allowed us to study parts of the planet that have never been mapped (the only planet in the solar system with holes remaining to be filled) as well as providing higher resolution pictures of areas that had been mapped. This visit will be no exception, but the primary science focus will be building on observations made during the last visit. This revealed a dynamic transient atmosphere created by the solar wind blasting material off from the surface.