New Dwarf Planet Discovered in Outer Solar System

Astronomers have spotted another dwarf planet, 435 miles in diameter, beyond the orbit of Neptune.

Artist rendering of the orbit of newly found RR245 (orange line). Objects as bright or brighter than RR245 are labeled. The Minor Planet Center describes the object as the 18th largest in the Kuiper Belt. Credit: Alex Parker/OSSOS Astronomers have found another Pluto-like dwarf planet located about 20 times farther away from the sun than Neptune.

The small planet, designated 2015 RR245, is estimated to be about 435 miles in diameter and flying in an elliptical, 700-year orbit around the sun.

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At closest approach, RR245 will be about 3.1 billion miles from the sun, a milestone it is expected to next reach in 2096.

At its most distant point, the icy world is located about 7.5 billion miles away.

It was found by a joint team of astronomers using the Canada-France-Hawaii Telescope (CFHT) on Maunakea, Hawaii, in images taken in September 2015 and analyzed in February. The discovery was announced on Monday in the Minor Planet Electronic Circular.

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"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," Michele Bannister, a postdoctoral fellow with the University of Victoria in British Columbia, said in a press release.

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The Minor Planet Center describes RR245 as the 18th largest object in the Kuiper Belt.

"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," the CFHT said. "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."

Observations of RR245 will continue. Once its precise orbit is known the dwarf planet will get an official name. As discoverers, the Outer Solar System Origins Survey team has naming rights.

GALLERY: Explore the Dwarf Planets' Moons

Haumea's moons Namaka and Hi'iaka

Haumea's moons were discovered in 2005 and make it part of a very exclusive group: of the five known dwarf planets in our solar system, only two of them (Haumea and Pluto) have more than one moon attached to the system. What's more, the moons of Haumea don't appear to match the moons of Pluto.

New observations of Haumea (led by Yale University's Luke Burkhart) suggest that it doesn't have tiny moons like Pluto does. The researchers scoured the system using the Hubble Space Telescope and came up empty.

It's possible that the systems of Pluto and Haumea formed very differently, but researchers emphasized that more observations of Haumea will be needed to learn more.

Image credit: NASA

Makemake's moon S/2015 (nickname: "MK")

Orbiting far away from its parent dwarf planet, Makemake, is a tiny moon that was just announced in April, 2016. The moon is only about 100 miles across and is approximately 13,000 miles away from Makemake, which is 870 miles in diameter.

The moon (called S/2015 and nicknamed "MK") was discovered using the Hubble Space Telescope. The Southwest Research Institute's Alex Parker led the image analysis for the observations. The discovery opens up exciting new possibilities to learn more about Makemake, NASA said in a press release. This includes measuring the system's mass, and figuring out how it involved (whether the moon was captured or not).

The observations also may resolve a long-standing mystery about Makemake, where some parts of the surface appeared to be warmer than others. Now astronomers believe the "warmer" parts were actually MK 2 passing in front of Makemake.

Image credit: NASA, ESA, and A. Parker (Southwest Research Institute)

Eris and its moon Dysmonia

Eris is famous in the planetary science community because after it was found in 2005 by a team led by the California Institute of Technology's Mike Brown, the discovery prompted a debate about what constitutes a planet. This led to the International Astronomical Union (IAU) forming a new category of planets called "dwarf planets" and reassigning Pluto (then called a planet) to that category.

Once a moon, Dysmonia, was discovered, Brown returned to observing the system to see if his team could figure out the mass. They found that, by observing the moon's orbits, Eris has a mass of 2.3 grams per cubic centimeter, which shows that the body must be a mix of ice and rock (similar to Pluto, or Neptune's moon Triton).

Image credit: R. Hurt, IPAC

Pluto and its moons Charon, Nix, Hydra, Kerberos and Styx

Luckily for planetary scientists, the New Horizons spacecraft flew by Pluto, Charon and the dwarf planet's myriad moons in July 2015. Data is still flowing in from the encounter, providing scientists reams of information about the moons that they are working to understand.

A recent release from SETI (the Search for Extraterrestrial Intelligence) summarizes some of the latest findings on Charon: it has red northern plains due to the molecule tholin, and some spots with ammonia ice. It doesn't appear to be as geologically active as Pluto, either, which surprised scientists by showing off mountains shortly after the encounter.

Scientists are also working to understand the origins of other moons discovered around Pluto. Charon was found in 1978, but its smaller moons Nix, Hydra, Kerberos and Styx were all discovered between 2005 and 2012.

Image credit: NASA-JHUAPL-SWRI