What's inside Mars? From orbit, the Mars Global Surveyor (MGS) spacecraft has recorded detailed images of the red planet since July 1997. Still, its cameras can not look beneath the surface. But minute...

Launched in the summer of 1977, NASA's Voyager 1 and 2 spacecraft are now over 4.5 billion miles from the Sun. Still operational, the Voyagers are being tracked and commanded through the Deep Space Network.