New dwarf planet discovered in Kuiper Belt

A dwarf planet has been discovered in the ring of icy worlds beyond Neptune, on a 700-year orbit.

Illustration showing the orbit of RR245 as an orange line.
Credit: Alex Parker OSSOS team

A new dwarf planet has been discovered beyond Neptune in an area at the edge of the Solar System full of other small, icy bodies known as the Kuiper Belt.

2015 RR245 is about 700km wide, making it big enough to study in detail. Its massive, highly elliptical orbit takes the dwarf planet 120 times farther from the Sun than Earth is, and it takes 700 years to complete one orbit.

The dwarf planet was spotted in February 2016 in images captured by the Canada-France-Hawaii Telescope as part of the Outer Solar Systems Origins Survey.

"There it was on the screen - this dot of light moving so slowly that it had to be at least twice as far as Neptune from the Sun,” says Dr Michele Bannister of the University of Victoria in British Columbia.

Most dwarf planets were thrown from the early Solar System by the destructive forces of the giant planets moving far from the Sun to their current positions. Just beyond Neptune, there lies a population of tens of thousands of small, icy worlds known as the Kuiper Belt, which survived the process. This ring of bodies contains dwarf planets like Pluto, Ceres and now RR245. In fact, the International Astronomical Union’s Minor Planet Center has named it the 18 largest in the Kuiper Belt.

"The icy worlds beyond Neptune trace how the giant planets formed and then moved out from the Sun,” says Dr Bannister. “They let us piece together the history of our Solar System. But almost all of these icy worlds are painfully small and faint: it's really exciting to find one that's large and bright enough that we can study it in detail."

Due to RR245’s elliptical orbit, it has been travelling farther than 12 billion km from the Sun for hundreds of years, but is now making its return journey and will reach its closest approach of 5 billion km from the Sun about 2096.

Astronomers will continue to monitor the dwarf planet’s orbit over the coming years, and the team behind the discovery will be allowed to name it.

"OSSOS was designed to map the orbital structure of the outer Solar System to decipher its history," says Prof. Brett Gladman of the University of British Columbia in Vancouver. "While not designed to efficiently detect dwarf planets, we're delighted to have found one on such an interesting orbit".

Carousel image: Artist’s illustration of a Kuiper Belt object on the edge of the Solar System.
Credit: NASA, ESA, and G. Bacon (STScI)


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