Apart from Pluto, which was demoted from a planet ... "It's really difficult to explain the solar system without Planet Nine but there's no way to be 100 per cent sure [it exists] until you ...

The number of planets that orbit the sun depends on what you mean by “planet,” and that’s not so easy to define ...

After passing Pluto, the craft will continue into the farthest reaches of the solar system. Scientists suspect there may be yet more moons around Pluto, some perhaps sharing or swapping orbits and ...

NASA has given a new lease of life to its New Horizons mission, which in 2015 got the first-ever close-ups images of dwarf planet Pluto ... its solar wind at the very edges of our solar system.

Both systems include a moon that is a large fraction of the size of the main body, unlike other moons in the solar system. The scenario also could support Pluto's active geology and possible ...

which may provide a mechanism for Pluto to develop a subsurface ocean without requiring formation in the more radioactive very early solar system – a timing constraint that has troubled ...