Scientists have discovered an object likely to be the solar system’s second most distant dwarf planet, first found in 2014 by a research team using the Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile.
Designated as 2014 UZ224 and informally nicknamed DeeDee for “Distant Dwarf,” the object is estimated to be 395 miles (635 km) wide and massive enough to have attained hydrostatic equilibrium, meaning it is squeezed into a round or nearly round shape by its own gravity.
Being rounded by its gravity qualifies 2014 UZ224 for designation as a dwarf planet.
Using the Blanco telescope data, the researchers determined it has a very elliptical orbit and takes more than 1,100 Earth years to circle the Sun.
That orbit takes it as close to the Sun as 38 AU (astronomical units, with one AU equal to 93 million miles or 150 million km, or the average Earth-Sun distance) and as far away as 180 AU.
Its current position is at about 92 AU.
Eris, the solar system’s most distant dwarf planet, has an elliptical orbit that takes it from 37.9 AU at perihelion to 98 AU at aphelion and is currently located about 96.5 AU from the Sun. Its orbital period is 560 years.
In contrast to both 2014 UZ224 and Eris, Pluto has an orbit that takes it from 29 to 49 AU.
Because the discovery team could not determine 2014 UZ224’s size from optical observations alone, they used the Atacama Large Millimeter/submillimeter Array (ALMA) system of radio telescopes in Chile to study the object.
The heat signature of distant objects is directly proportional to their size. An object like 2014 UZ224 could be large and dark or small and bright.
“We calculated that this object would be incredibly cold, only about 30 degrees Kelvin, just a little above absolute zero,” said University of Michigan astronomer David Gerdes, who led the study.
ALMA’s measurements of its brightness in millimeter-wavelength light revealed it to be a dark object that reflects just 13 percent of incoming sunlight.
By incorporating both the Blanco and ALMA observations, the researchers found 2014 UZ224 to have a diameter of approximately 395 miles (635 km), meaning it is larger than Saturn’s moon Enceladus, which is about 313 miles (504 km) wide, and two-thirds the size of Ceres, which is 590 miles (950 km) wide.
A paper detailing the study has been published in Astrophysical Journal Letters.