The largest object to be discovered in the Solar System since Pluto was found in 1930 was spotted by a sky survey on Tuesday.
News of the hulking object leaked out on Thursday before the researchers at Caltech could pin down the giant’s size and orbit.
Tentatively called 2004 DW, the object lies beyond Neptune in the mysterious Kuiper Belt. This shadowy belt is a collection of primordial icy bodies which circle our Sun and are thought to be the remnants of planetary formation.
Only Pluto and its moon Charon are clearly brighter than 2004 DW, but both have icy surfaces that reflect roughly half the incident sunlight.
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Typical large Kuiper Belt objects reflect only about nine percent of incident light, says Chad Trujillo of the Gemini Observatory, who works on the Caltech survey. Using that number, he estimates 2004 DW is 1650 kilometres in diameter – second only to Pluto at 2320 kilometres.
Brightness and distance
Several hundred Kuiper Belt objects larger than 100 kilometres have been spotted since David Jewitt of the University of Hawaii discovered the first in 1992, and Jewitt believes at least 70,000 exist which are larger than 100 kilometres. Larger objects are more rare, but their distribution may illuminate their origins, and their brightness will make them easier to study than smaller ones.
Jewitt calls the new discovery “a very nice object.”
The largest previously known Kuiper Belt object – christened Quaoar – was discovered by Tujillo, Mike Brown of Caltech and David Rabinowitz of Yale in 2002. At 1250 kilometres Quaoar is only slightly smaller than the 1270-kilometre Charon.
Their measurements indicate Quaoar reflects nine percent of incident light. The group planned to study 2004 DW in detail before announcing their discovery, as they had with Quaoar, but their observation was posted by mistake on the website of the Minor Planet Center at the Harvard-Smithsonian Center for Astrophysics. Two other groups saw their report and confirmed the finding on Wednesday.
With only two days of observations, most details remain uncertain. The new object “is likely to be significantly larger than Quaoar judging on its brightness and distance, but until we can specifically measure its size, we cannot say for sure,” Trujillo told New Scientist.
The new discovery “tells us that there’s lots more work to be done on the Kuiper Belt, because we remain only dimly aware of even some of the largest bodies there,” says Jewitt.
