After over six years and five billion miles, The MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) probe has finally entered orbit around our solar system's innermost planet. Today, NASA has released MESSENGER's first ten images, including this one, which in case you can't tell, is in full color.
The reason that MESSENGER took so long to get to Mercury is that it's all downhill from here. If the probe had gone from Earth to Mercury in a more direct route, it would have picked up so much speed as it dropped into the sun's gravity well that there's no way it could have entered into orbit around the planet. So really, MESSENGER has spent the last six years looking for ways to slow itself down, which involved swinging around Earth, Venus, and even Mercury itself a couple times each along the way to slow down using a bunch of reverse gravity assists.
The other problem with Mercury is that it's uncomfortably close to the sun, which makes it more than a little toasty, especially when MESSENGER is sandwiched between the hot surface of the planet on one side and the even hotter sun on the other. The probe is equipped with a ceramic umbrella on one side to provide shade, and uses solar panels speckled with mirrors to keep them from overheating. It's also in a highly elliptical orbit around Mercury, which gives it a chance to periodically cool off.
Now that MESSENGER has finally made it to Mercury, it's going to start sending back pictures of the 55% of the planet that we've never seen before, and peeking into craters around the polar regions of Mercury where we've gotten hints that there might be ice. Check out the gallery for MESSENGER's first batch of Mercury pics, complete with detailed captions from NASA.