New dwarf planet discovered lurking beyond Neptune

illustration of the orbit of dwarf planet 2015 RR245

The newly discovered dwarf planet 2015 RR245 travels along a 700-year-long orbit (illustrated in yellow) that takes it well beyond the Kuiper belt, the ring of icy debris past Neptune. The orbits of the eight planets are shown in blue; other large bodies in the Kuiper belt are also labeled.

Alex Parker/OSSOS

The family of known dwarf planets orbiting the sun just got a new member. The tiny world, designated 2015 RR245, lives in the Kuiper belt, the icy debris field beyond Neptune that’s home to Pluto. RR245 is currently about 9.6 billion kilometers from the sun, or roughly 64 times as far as Earth, and it loops around the sun on an elongated orbit every 700 years or so.

Astronomers first noticed RR245 in February as a drifting speck of light in images taken last September at the Canada-France-Hawaii telescope in Hawaii. The planet’s size is hard to determine without knowing how reflective its surface is; it could be large and dark or tiny and bright.  But if its surface is similar to other worlds in the Kuiper belt, then RR245 might be about 700 kilometers wide, just one-fifth the diameter of the moon. 

Christopher Crockett is an Associate News Editor. He was formerly the astronomy writer from 2014 to 2017, and he has a Ph.D. in astronomy from the University of California, Los Angeles.

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