"One of the great ironies is that Mercury may have more ice at its poles than even our own moon," Jim Green, director of NASA's planetary-science division, said during a news conference.
Once considered "the burnt-out cinder of the solar system," as Green put it, the pictures taken by Messenger reveal that the planet closest to the sun is a world unlike any other.
The spacecraft, which entered Mercury's orbit in March, is providing panoramic views of expansive, smooth volcanic plains that cover an area roughly half the size of the continental United States.
Scientists can see, in great detail, the faults formed when pieces of Mercury's crust were pressed together and numerous impact craters that have been covered over by lava flows and are now ghost craters.
They are also getting a close-up view of the dark area around the central peak of Degas Crater in the northern hemisphere and the scarlike remnants of the planet's pyroclastic flows, once fast-moving rivers of sizzling gas and boiling rock.
The pictures were taken with Messenger's Mercury Dual Imaging System, which has narrow- and wide-angle cameras that use a technology similar to that found in digital cameras. The craft also has instruments to collect data on the planet's chemical composition, topography, and magnetic field.
Mercury is the densest and smallest of the solar system's eight planets. It has the oldest surface and most extreme daily temperature fluctuations. Because of the intense heat associated with its proximity to the sun, Mercury is also the least explored.
The Messenger mission, conceived 40 years ago and launched in 2004, is supposed to unravel some of the central mysteries surrounding the innermost planet: How did it evolve? Why is it so dense? Why does it have a magnetic field, when larger planets such as Mars do not?
