The outskirts of the Solar System are a lot more crowded than we think. Beyond the orbit of Neptune, astronomers expect that there is a huge amount of small bodies and possibly even a giant planet, with astronomers keen to learn what these distant worlds are like.

2014 UZ₂₂₄, also known as DeeDee, is one of these worlds, so scientists employed the Atacama Large Millimeter/submillimeter Array (ALMA) to get a detailed analysis of this world. It has a diameter of 635 kilometers (395 miles), which is about 67 percent of the diameter of Ceres – the dwarf planet in the Asteroid Belt.

At that size, DeeDee is likely to be spherical, which is a requirement if this object hopes to get a “dwarf planet” status in the future. The analysis is reported in Astrophysical Journal Letters.

^{ALMA image of 2014 UZ224, nicknamed DeeDee. ALMA/ESO/NAOJ/NRAO}

"Far beyond Pluto is a region surprisingly rich with planetary bodies. Some are quite small, but others have sizes to rival Pluto and could possibly be much larger," lead author David Gerdes, from the University of Michigan, said in a statement. "Because these objects are so distant and dim, it's incredibly difficult to even detect them, let alone study them in any detail. ALMA, however, has unique capabilities that enabled us to learn exciting details about these distant worlds."

The discovery was announced in the fall of 2016, after two years of follow-up observations to confirm its existence. It’s the second furthest known object in the Solar System, after dwarf planet Eris. It’s currently located 92 times further from the Sun than the Earth. It takes DeeDee more than 1,100 years to complete an orbit.

Astronomers had to use ALMA because the object is very cold (about 30 Kelvins above absolute zero) and the observatory can pick up the microwave emissions from such a chilled world. It’s also a dirty world, as it reflects about 13 percent of the tiny sunlight it receives – more or less like the dry dirt of a baseball pitch.

DeeDee is a leftover fragment from the beginning of the Solar System, and anything that we can learn could open a window onto the beginning of our planet. And DeeDee is likely just one of many.

"There are still new worlds to discover in our cosmic backyard," concludes Gerdes. "The Solar System is a rich and complicated place."

^{Distance of DeeDee compared to other objects in our Solar System. Alexandra Angelich/NRAO/AUI/NSF}