Jul 4, 2013 9:50 AM by Stephen Bowers
A report from LiveScience.com suggests Mercury, the planet in our solar system closest to the sun, is about 4.5 billion years old. The oldest parts of the planet's surface, however, may closer to 4 billion years old.
NASA's Simone Marchi says research he has done implies the first 400-500 million years of Mercury's history may have been erased by volcanoes on the planet.
It's hard to know for sure, though, since we do not have samples of Mercury's terrain, just how hold the planet is. Scientists suspect it formed around the same time period as Earth.
NASA is studying Mercury with a probe called "Messenger," which has been orbiting Mercury since 2011.