Astronomers have found an icy world that ranges far beyond the orbit of Neptune and may well rank as a dwarf planet alongside Pluto.
The newly detected object, designated 2015 RR245, is thought to be less than a third the width of Pluto (435 miles vs. 1,474 miles), but its orbit is more eccentric. Its distance from the sun ranges from about 34 to more than 120 astronomical units, where each AU equals the distance between Earth and the sun. In comparison, Pluto’s orbit has a range of 30 to 50 AU.
“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,” Michele Bannister, an astronomer at the University of Victoria in British Columbia, said in a statement.
Astronomers don’t yet know the dimensions of 2015 RR245 precisely. The diameter estimate of 435 miles is based on the brightness of the object. “It’s either small and shiny, or large and dull,” Bannister said. She told GeekWire that observations made during a future stellar occultation could tell the tale.
2015 RR245 is passing through the Kuiper Belt, a band of icy objects that lie beyond Neptune at a distance of 30 to 50 AU from the sun. The researchers say it could qualify as a dwarf planet – that is, an object massive enough to crush itself into a round shape through self-gravity.
The International Astronomical Union has recognized five dwarf planets so far: Eris, Pluto, Makemake, Haumea and Ceres. Astronomers assume there are more dwarfs out there, potentially including recently discovered icy worlds such as Sedna, Quaoar, 2012 VP113 (also known as Planet Biden) and 2007 OR10 (which made a splash in May).
Bannister stirred up some buzz in March when she presented data about a different object in the far reaches of the solar system, known as uo3L91. At the time, Caltech astronomer Mike Brown – who was part of a team that discovered Eris back in 2005 – said the object’s far-flung orbit could serve as evidence for the existence of a super-distant super-Earth he dubbed “Planet Nine.” However, Bannister said 2015 RR245 has no connection to the case of uo3L91 or the search for Planet Nine.