In July, the Outer Solar System Origins Survey (OSSOS) team announced the discovery of new dwarf planet orbiting the Kuiper Belt. The new object is roughly 450 miles in size and has one of the largest orbits for a dwarf planet. It was discovered using Canada France Hawaii Telescope and given the name 2015 RR245 by the International Astronomical Union’s Minor Planet Center.
“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, a postdoctoral fellow with the Survey.
Dr JJ Kavelaars, another member of the OSSOS team, 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.
The team became even more excited when they realized that the object’s orbit takes it more than 120 times further from the Sun than Earth. The size of RR245 is not yet exactly known, as its surface properties need further measurement.
“It’s either small and shiny, or large and dull,” said Bannister.
The vast majority of the dwarf planets like RR245 were destroyed or thrown from the solar system in the chaos that ensued as the giant planets moved out to their present positions: RR245 is one of the few dwarf planets that has survived to the present day, along with Pluto and Eris — the largest known dwarf planets. RR245 now circles the Sun among the remnant population of tens of thousands of much smaller trans-Neptunian worlds, most of which orbit’s is unseen.
Worlds that journey far from the Sun have exotic geology with landscapes made of many different frozen materials, as the recent flyby of Pluto by the New Horizons spacecraft showed.
After hundreds of years further than 12 billion km (80 astronomical units, AU) from the Sun, RR245 is travelling towards its closest approach at 5 billion km (34 AU), which it will reach around 2096. RR245 has been on its highly elliptical orbit for at least the last 100 million years.
As RR245 has only been observed for one of the 700 years it takes to orbit the Sun, where it came from and how its orbit will slowly evolve in the far future is still unknown; its precise orbit will be refined over the coming years, after which RR245 will be given a name. As discoverers, the OSSOS team can submit their preferred name for RR245 to the International Astronomical Union for consideration.
After the OSSOS team’s initial announcement of the discovery of RR245, the Pan-STARRS1 survey on Haleakala released data related to the position of RR245. The data yielded an additional six data points for the object. With the new data, the OSSOS team calculated a more precise orbit for RR245, discovering it lies in a unique 9:2 resonance with Neptune centered at a semi-major axis near 82 AU. For reference, Pluto’s semimajor axis is 39.5 AU and Eris’ is ~67 AU. In layman’s terms, for every nine orbits that Neptune makes, RR245 makes two. RR245 is the first object discovered in a 9:2 resonance with Neptune.
RR245 is the largest discovery and the only dwarf planet found by OSSOS, which has discovered more than 500 new trans-Neptunian objects. OSSOS is only possible due to the exceptional observing capabilities of the Canada-France-Hawaii Telescope. CFHT is located at one of the best optical observing locations on Earth, is equipped with an enormous wide-field imager and can quickly adapt its observing each night to new discoveries we make.
”This facility is truly world leading,” said Brett Gladman, the OSSOS team leader.