Astronomers Discover Dwarf Planet 8 Billion Miles Past Pluto

Rendering of the orbit of RR245 (orange line). Objects as bright or brighter than RR245 are labeled. The blue circles show the projected orbits of the major planets. The Minor Planet Center describes the object as the 18th largest in the Kuiper Belt. Credit: Alex Parker OSSOS team.
The yellow ellipse represents the orbit of the newly-discovered dwarf planet, RR245  Objects as bright or brighter than RR245 are labeled. The blue circles show the projected orbits of the major planets. Pluto is currently 3 billion miles from the sun. The Minor Planet Center describes the object as the 18th largest object in the Kuiper Belt, a belt of icy asteroids beyond Neptune. Credit: Alex Parker, OSSOS team.

Pluto’s got company. An international team of astronomers has discovered a new dwarf planet orbiting in the Kuiper Belt of icy asteroids beyond Neptune. The new object is roughly 435 miles  (700 km) in size and has one of the largest orbits known for a dwarf planet. Called 2015 RR245, it was found using the Canada-France-Hawaii Telescope in Hawaii as part of the Outer Solar System Origins Survey (OSSOS). That makes six dwarf planets discovered to date along with Pluto, Ceres, Makemake, Haumea and Eris. All except Ceres reside in the Kuiper Belt at many times Earth’s distance from the sun. Ceres orbits within the traditional Main Belt located between Mars and Jupiter.

These discovery images of RR245 show its slow motion across the sky over three hours. Credit OSSOS team.
These discovery images of RR245 show its slow motion across the sky over three hours. Credit OSSOS team.

National Research Council of Canada’s Dr JJ Kavelaars first sighted RR245 in February 2016 in the 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.” said Bannister. After enough observations were made to determine an orbit, astronomers realized the new object takes it more than 120 times further from the sun than Earth or more than 11 billion miles (17.7 billion km) miles away. That’s so unbelievably far away that it takes 700 years to circle the sun.

So we’re clear, a dwarf planet is defined as a celestial body in orbit around the sun (not a moon around another planet) that’s massive enough for gravity to crunch it into a sphere, but doesn’t possess the gravitational might to clear its orbit of other small bodies. The team doesn’t know RR245’s precise diameter yet. If it’s a shiny, icy object it may be smaller than the estimate or larger if dark.

The sizes of the five previously known and recently discovered dwarf planets are compared to the moon. Credit: the-dialogue.com/
The sizes of the five previously known and recently discovered dwarf planets are compared to the moon. The newest, 2015 RR245, is about 150 miles smaller than Ceres. Credit: the-dialogue.com/

The vast majority of the dwarf planets like RR245 were destroyed or tossed from the solar system in the chaos that ensued as the giant planets Jupiter and Saturn migrated to their present positions long ago. RR245 is one of the few dwarf planets that has survived to the present day — along with Pluto and Eris — and now circles the Sun among tens of thousands of much smaller asteroids beyond Neptune.

“The icy worlds beyond Neptune trace how the giant planets formed and then moved out from the Sun. 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.” said Dr Michele Bannister of the University of Victoria in British Columbia, who is a postdoctoral fellow with the Survey.

Artist depiction of the distant Kuiper Belt, where a possible new planet may be hiding. Credit: NASA
Artist depiction of the distant Kuiper Belt, home to Pluto and all the known dwarf planets besides Ceres. Credit: NASA

The new dwarf planet revolves around the sun in a highly elongated orbit called an ellipse and slowly headed towards perihelion (closest point to the sun) of 3.1 billion miles (5 billion km) in 2096. Once the RR245’s orbit has been calculated with precision it will be given a formal name.

Previous surveys have mapped almost all the brighter dwarf planets, but more remain to be found. Astronomers estimate there may be up to 200 still waiting to be discovered in the Kuiper Belt. 2015 RR245 may be one of the last large ones to be found until larger telescopes come online in the mid 2020s.