What I Learned Today

Many of us have a mental image of Mercury that’s black-and-white, like 1950’s TV. We liken it to the Moon: a pale, devastated landscape pock-marked with staccato craters and blanketed with the finest grey dust imaginable. But this view, it turns out, is somewhat mistaken–probably influenced by the classic view at right, captured by Mariner 10 in 1975. Mariner 10 did take some color images as well, but they are lower resolution, and only about half of the planet was imaged in color, so they get less press.

Enter MESSENGER, the NASA mission that just executed its second close flyby of Mercury, on its way to a 2011 orbital insertion. With its more capable imaging system, MESSENGER has captured close approximations of “true color” for Mercury, although as always this isn’t as simple as snapping a photograph (CCDs just don’t respond to color the way the human eye does!).

Further, false color is often more scientifically useful than the our mineralogically impoverished RGB views. MESSENGER recently released a color movie that pans across the surface of the planet in fascinating detail. Color differences here yield clues to compositional differences. Note also that you can see a definite change in resolution; later in the movie, the crater edges are less crisp and somewhat fuzzy. I assume that this is because it was imaged during a flyby, not in regular orbit; the spacecraft was only 200 km from the surface at closest approach, but then would have been moving rapidly away. The movie has been adjusted to correct for the geometric distortion, but the reduced resolution remains. Check it out!