The smallest planet in the Solar System is getting smaller.
Measurements have shown that Mercury has shrunk as much as 8.6 miles in diameter - over 4 billion years, that is.
From USA Today:
The planet diminished as it cooled over the years, a realization scientists made in the mid-1970s based on photographs taken by the Mariner 10 probe.
But recent images from NASA's Messenger satellite have allowed scientists to more precisely map how much the planet's surface has changed as the single rocky plate in its surface contracts.