A dwarf planet 700 kilometres in diameter has been discovered tumbling through space on a vast orbit that takes it between 12 billion kilometres and five billion kilometres from the sun.
The body has been designated 2015 RR245 and joins other known “dwarf planets” Pluto, Ceres, Haumea, Makemake and Eris. But there are hundreds more far out beyond Neptune in the Kuiper Belt that lies beyond Pluto on the edge of the solar system.
Most of them were ejected from the solar system as the giant planets moved into their current positions.
“The icy worlds beyond Neptune trace how the giant planets formed and then moved out from the sun,” said Michele Bannister of the University of Victoria in British Columbia in a note announcing the discovery.
The tiny bodies mainly made up of rock and ice let us piece together the history of our solar system, Bannister says.
“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.”
RR245 was found using the Canada-France-Hawaii Telescope on Maunakea, Hawaii, as part of the Outer Solar System Origins Survey (OSSOS).
It was first spotted by National Research Council of Canada’s JJ Kavelaars in February this year in OSSOS images from September 2015.
“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,” Bannister said.
So far astronomers know little about the body or its surface properties, although last year’s flyby of Pluto by the New Horizons spacecraft, and the wealth of data that has followed, shows that these bodies can be more exotic than previously thought.
RR245 takes 700 Earth years to orbit the sun on its vast elliptical path. It will reach its closest approach at 5 billion kilometres in around 2096.
OSSOS has discovered more than 500 trans-Neptunian objects, but this is the biggest body and only dwarf planet.
Bill Condie is a science journalist based in Adelaide, Australia.
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