Three Dwarf-Planet Candidates Found at Solar System’s Edge

A new survey of the Kuiper belt — the distant area of the solar system beyond the orbit of Neptune — has turned up three new icy worlds that may be dwarf planets like Pluto.

The frosty Kuiper belt lies roughly 30 to 55 astronomical units (AU) from the Sun. In comparison, the Earth orbits at just 1 AU. Like a frozen asteroid belt, it’s littered with chunks of ice and frozen methane and ammonia.
Scott Sheppard, of the Carnegie Institution of Washington, and a team of astronomers used the 1.3-meter Warsaw Telescope at Las Campanas Observatory in Chile to hunt for objects in previously overlooked areas of the belt, including the southern skies and the galactic plane.
His team sniffed out 14 curious objects. 11 of them are far too small to be considered planetlike, and were probably just regular chunks of ice and rock.
But three of the objects seem to be more than 250 miles wide, which is potentially big enough to be molded into a sphere by their own gravity, and likely qualify them for that oh so prestigious dwarf planetstatus.
The category “dwarf planet” came around in 2006. Astronomers had found at least three new objects that were as big as Pluto (Quaoar, Sedna and Eris), and the International Astronomical Union needed to find a new way to classify exactly what makes a planet a planet.
To be a planet, a celestial body must be “in orbit around the Sun, [have] sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and, [have] cleared the neighborhood around its orbit.”
Those new rules cast Pluto out, and put it in a new, and very exclusive, club of just five confirmed dwarfs in the solar system: Pluto, Ceres, Haumea, Makemake and Eris.
NASA is very interested in studying these dwarf planets more closely, and two spacecraft have the dinky worlds on their agendas. NASA’s New Horizons spacecraft is currently en-route to the Pluto system, and in July 2015 it will fly by and study the dwarf planet and its moons.
Another probe, Dawn, is currently at Vesta (a protoplanet), but will move onto Ceres after a year of study.
Image: Dan Durda/SwRI/NASA

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