This is MESSENGER's very first photo from Mercury orbit, a wide-angle view that reaches right to Mercury's south pole, exposing a very tiny sliver of territory not previously seen by spacecraft. It was taken at 09:20 UTC today, March 29, 2011, the first in a set of 363 that formed MESSENGER's first downlink of orbital images, the first downlink of very many. This particular image is not necessarily any more important than any other image; its importance lies in the fact that it was taken and downlinked right on schedule, indicating the spacecraft is performing exactly as planned. There'll be a press briefing tomorrow with more images released, which I'll be listening in on.
NASA / JHUAPL / CIW
MESSENGER's first image from Mercury orbit
MESSENGER captured its first image of Mercury from orbit, a wide-angle shot of the southern hemisphere, on March 29, 2011.
To get an idea of what this photo covers, and where the previously unseen territory lies, you can compare it to this wide-angle view of Mercury from the second flyby. The upper part of the new image covers the bottom part of this global view. The big bright-rayed crater Debussy is prominent in both images.
NASA / JHUAPL / CIW / color mosaic by Jason Perry
Mercury in color from MESSENGER
As it departed from its second flyby of Mercury, MESSENGER snapped a color mosaic of the planet using its wide-angle camera; this version is a four-frame (2x2) mosaic of images captured through the red, green, and blue filters. Mercury's color variations are very subtle. This view consisted almost entirely of territory not previously seen from a spacecraft and included a spectacular set of rays radial to a small impact crater located near Mercury's north pole that was later named Hokusai.
Here's another useful map for comparison, showing which areas have and have not been seen by spacecraft.
NASA / JHUAPL / CIW
Map of Mercury after MESSENGER’s third flyby
Following MESSENGER's final Mercury flyby before entering orbit, the map coverage of Mercury is nearly complete. Mariner 10 mapped about 45% of the planet (green outline). MESSENGER covered another 20% on its first flyby (blue outline). The second flyby nailed 25% more (red outline). The most recent flyby filled in another 5%, including the last missing piece of the equator and mid-latitudes. Now only 5% of the planet remains unmapped, most of it poleward of 60° north and south latitude.
In fact, the released image should contain the area of the never-before-seen south pole, a place scientists are really interested in because there may be cold traps holding water in its permanently shadowed deep crater floors. I've compared the released image to the team's map of where the image was supposed to lie on a Mercury globe, and I thinkI've got the "X" just about where the south pole is. Guess what -- it's dark! With basically zero axial tilt, the Sun is always at the horizon at the poles -- Mercury's poles are in perpetual twilight. It's going to take a lot of images over the course of a long, long Mercury day (two Mercury years or half an Earth year), plus a lot of image processing and patience, to compose an image map of that south polar territory.
NASA / JHUAPL / CIW / Estimate at location of X by Emily Lakdawalla (YMMV)