Pluto and its Moon Charon

In our own solar system, Pluto and its moon Charon (grey) have already become tidally locked to one another ― just as Earth and the Moon would someday sync up if given enough time. Scientists think that Charon’s large size and mass may be keeping Pluto’s smaller moons (shown here in blue, yellow, red and green) from also syncing up. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute.