The Moon is, well, the Moon. It is the closest object to us in space and the only stellar object humans have traveled to and returned from that is not Earth. Despite this though, we are still learning about it.
For a while researchers have seen evidence that the Moon is shrinking in features called lobate scarps. These features can be found across its surface and suggest the Moon contracted by as much as 300 feet in the (geologically) recent past. What no researcher expected though was to find long valleys called graben, which are the result of the Moon’s surface stretching. The graben form when the crust is pulled apart and surface material falls into the trough.
Exactly what is causing stretch marks, researchers do not yet know, but NASA's Lunar Reconnaissance Orbiter will be looking for it. With only half the Moon’s surface imaged in high resolution though, there could be many more surprises to come.