Mercury’s dark surface may be due to cometary dust

Los Angeles Times : Mercury and the Moon are often compared because they are about the same size and both lack atmospheres. But Mercury is covered in dark material that makes it only one-third as reflective as the Moon. Most airless planetary bodies as dark as Mercury have a high iron content, but Messenger measured the planet’s surface as being just 2% iron. Now, Megan Bruck Syal of Lawrence Livermore National Laboratory and her colleagues believe they’ve found the explanation. They realized that the planet’s dark appearance could be caused by the presence of carbon-rich cometary dust, and their calculations of potential dust impacts revealed that the dust would stay on Mercury’s surface. They also determined that, because the concentration of cometary dust in the solar system is much greater closer to the Sun, Mercury gets hit by 50 times as much dust as the Moon, which explains why Mercury is so much darker. Finally, they found that firing cometary dust-like material at material similar to that found on Mercury’s surface did produce a dark layer on the surface material.