The Kuiper Belt, the vast asteroid belt of ice and rock that lies beyond Neptune, is home to three objects big enough to be considered dwarf planets: Haumea, Makemake, and our old friend Pluto. And now, we might have found three more.
Astronomers used the Warsaw Telescope at Chile's Las Campanas Observatory to sweep the southern skies for any undiscovered large objects in the Kuiper Belt. They found fourteen such objects among the colossal conglomeration of debris. While eleven of these were simply oversized chunks, three of them appear to be big enough to meet the definition of a dwarf planet.
According to the International Astronomical Union, there are two criteria that a body must meet in order to be considered a dwarf planet. First, it must be massive enough that its gravity forces it into a spherical shape, and second, it must orbit the Sun, eliminating a number of moons that would otherwise deserve to be dwarf planets and, indeed, are actually larger than the official dwarf planets.
Currently, there are just five bodies recognized as dwarf planets: Ceres in the asteroid belt, the three in the Kuiper Belt, and Eris, the largest dwarf planet and the only one that lies beyond the Kuiper Belt. There are as many as forty additional objects in the far reaches of the solar system that might well classify for dwarf planet status, but we simply don't have the observations yet to make an official classification.
These three latest discoveries would be found right at the lower limit of what a dwarf planet could be. They are likely only about 250 miles wide - far less than Pluto and Eris, which are both about 1,450 miles wide. If these three new objects were composed of anything other than ice, they'd likely be too small to round themselves into a spherical shape. But, as icy bodies, they likely squeak by as dwarf planet candidates.
This survey pretty much completes the search for big objects in the Kuiper Belt — now the question will simply be figuring out just what each of the discovered objects are. As for further discoveries, astronomers now turn their attention to the even more distant regions of the solar system, a search that begins with the dwarf planet candidate Sedna. This particular object has one of the most extreme elliptical orbits in the solar system, traveling between 75 and 960 times the distance between Earth and the Sun in its 10,000 year orbit.
Project scientist Scott Sheppard explains:
"Sedna is basically the frontier right now in the solar system. We've found one object, and it's likely there's a bunch more out there. But the technology right now is just barely at the ability for us to efficiently detect these things. There could still be Mars- or even Earth-size objects way out there, at hundreds of AU, that would be too faint for us to detect. It's pretty amazing when you think about it. It's unlikely, but it's possible."
Via Space.com. Artist's conception of Makemake by IAU.