How many dwarf planets are there in our solar system? The recent discovery of 2017 OF201 makes the tally anywhere between five and 18, plus hundreds of potentially undiscovered ones, depending on ...

In 2006, the International Astronomical Union (IAU) famously demoted Pluto to a dwarf planet. Things have been a bit of a mess since then — so is it time to redefine the planet?

Like planets, dwarf planets are spherical, but unlike planets, they share their orbits around the sun with other similar-sized bodies. Dawn, which launched in 2007, is in its final and lowest ...