Today's big science news is the Messenger flyby of Mercury. The Messenger spacecraft is scheduled to do a flyby of the planet about four hours from now, en route to it's final destination - Mercury - which it will reach in 2011, after completing additional flybys of the planet Mercury in October, and the planet Mercury in 2009. (Apparently, the orbital dynamics of getting a spacecraft into orbit around a relatively small planet that's relatively close to a star are a bit complex.)
The main part of the scientific mission might not start for another few years, but there are still going to be a lot of firsts that are coming out of today's flight past the planet. Even though Mercury is closer to Earth than Mars is, we know much less about it. We can look at Mars without having to look almost directly into the sun at the same time, and we can put a probe into orbit around Mars without having to deal with as much of a fight with the Sun's gravity. This means that although we've now mapped all of Mars and have really good photographs of most of the surface of the planet, we haven't done either for Mercury. The last time that a mission passed close to Mercury was the Mariner 10 mission in 1974, and that one mapped and photographed less than half of Mercury's surface.
Today's flyby won't map the entire surface, of course, but if all goes well it will produce new information about Mercury. Today's flyby will make a closer approach to the planet's surface than Mariner achieved, and will take photographs of portions of the planet that we haven't seen yet. A laser altimeter will produce high resolution measurements of some of the surface topography, while other instruments measure the magnetic field, the space around the planet, and the elemental composition of some of the surface.
Data from the pass won't be available today. According to the mission website, the spacecraft won't transmit information back to Earth until after the measurements are complete. Hopefully, though, we'll be able to look at at some pictures of a part of our solar system that we've never seen before by tomorrow.
Always nice to hear we are spending more time with our solar system neighbors! If this keeps up we may end up having a Nanny cam satellite over Mars that people can watch their kids on, while on the way to Jupiter! LOL!
Dave Briggs :~)