90377 Sedna is a large trans-Neptunian object. It was discovered by Mike Brown, Chad Trujillo and David Rabinowitz on November 14, 2003. Sedna is about 1250-1800 km in diameter and takes roughly 10,500 years to orbit the Sun. That's much longer than most known trans-Neptunian objects. It is one of the most distant known objects in the Sol system. Sedna's surface temperature never rises above -240°C. It's considered as a likely candidate as a dwarf planet.
The name "Sedna" originates from the Inuit goddess of the sea, who's thought to live at the bottom of the Arctic Ocean.