Despite their proximity to the sun, portions of the surface of Mercury appear to be covered in ice, scientists said Thursday after analyzing about 20,000 new images of the solar system’s smallest planet.
The pictures beamed to Earth by the Messenger spacecraft strongly suggest that frozen water -- and perhaps other frozen substances -- coat portions of impact craters near the planet’s north and south poles. Permanently enshrouded in shadow, these surfaces are typically 300 degrees below zero Fahrenheit.
“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 at a news conference in Washington.
The pictures taken by Messenger reveal that the planet closest to the sun -- once considered “the burnt-out cinder of the solar system,” as Green put it -- is a world unlike any other.
Messenger, 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 U.S.
Scientists can see, in great detail, faults formed when pieces of Mercury’s crust were pushed together, as well as numerous impact craters that have been covered over by lava flows. They are also getting a close-up look at the dark area around the central peak of the Degas crater in the planet’s northern hemisphere and the scar-like remnants of pyroclastic flows, once fast-moving, boiling rivers of gas and rock.
The pictures were taken with Messenger’s Mercury Dual Imaging System, which has narrow- and wide-angle cameras that use 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 smallest and one of the densest of the solar system’s eight planets. It has the oldest surface and most extreme daily surface 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, while larger planets such as Mars do not?
Data collected so far show that Mercury’s magnetic field is not simply a miniature version of the one on Earth, as scientists had thought.
Instead of having a magnetic field equator that is the same as its geographical equator, as Earth does, the one on Mercury is shifted toward its north pole.
A closer look at Mercury’s surface also suggests that the building blocks that formed the planet were different than those that gave rise to Earth.
For instance, Mercury has 10 times as much sulfur as is found in the crust of the Earth or the moon -- a byproduct, perhaps, of volcanic gases and a potential clue to the history of volcanism on Mercury.
Messenger orbits Mercury twice in one Earth day and has completed about a quarter of its mission. It will run out of fuel in about nine months and will eventually crash into the planet.