for National Geographic News
A new look at the solar system's innermost planet is revealing bright young craters and an extensive pattern of rays, suggesting that Mercury undergoes weathering processes like those on the moon.
NASA's MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging) spacecraft turned toward Earth in the wee hours this morning and began transmitting images and data from its second planetary flyby.
A previous flyby in January was the first in a series of maneuvers designed to position MESSENGER in orbit around Mercury in 2011. That encounter imaged 20 percent of the planet's surface that had never been seen before.
The latest images represent the first spacecraft views of the northern portion of Mercury, encompassing another 30 percent of the surface missed during previous missions.
"It's been a wonderful day," said MESSENGER principal investigator Sean Solomon at the Carnegie Institution of Washington. "I'm excited that we have a nearly global perspective."
Mercury appears to harbor "extremely deformed regions" and "extraordinarily bright craters, with rays that extend halfway across the planet," Solomon added.
The craft will continue to beam data and images to Earth through Wednesday morning.
Craters and Rays
Based on studies of the lunar surface, Solomon said, the freshest craters on Mercury are probably bright because their minerals haven't yet been exposed to weathering. (Watch a crash-course video about lunar science.)
But more detailed studies are needed to fully explain the features, as Mercury and the moon have some key differences.
The biggest contrast is that iron, which is on the moon, hasn't yet been found on Mercury.
Fresh craters on the moon appear bright because material is newly exposed. But as the craters age, weathering of iron makes the lunar features look darker.
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