Astronomers have confirmed the most distant object ever observed in our Solar System. Measuring roughly 400 kilometers across, it likely takes over 800 years to orbit the Sun.
In February 2019, a team led by Scott Sheppard of the Carnegie Institution for Science announced the detection of an object at approximately 132 astronomical units (AU) from the Sun—where 1 AU equals the Earth-Sun distance of about 150 million km. If verified, it would be the farthest Solar System body on record.
Confirmation has arrived. Initially dubbed "FarFarOut," it now bears the provisional designation 2018 AG37, awaiting official naming by the International Astronomical Union. New observations reveal it's about 400 kilometers in diameter.
Currently at 101 AU from the Sun—101 times the Earth-Sun distance—it's closer than first estimated but still the farthest known Solar System object. For context, Pluto averages 39 AU.
Its highly elliptical orbit carries it as far as 175 AU from the Sun and as close as 27 AU, dipping inside Neptune's path. "FarFarOut was likely scattered outward by a close encounter with Neptune long ago," notes Chad Trujillo of Northern Arizona University. "It will likely interact with Neptune again, as their orbits intersect."
Details remain elusive: observed just nine times over two years, it's faint and slow-moving. Is it a massive, irregular Kuiper Belt object or a potential dwarf planet? Its orbital period is estimated at under 800 years, but precision requires years of tracking.
"FarFarOut takes its time circling the Sun," says David Tholen of the University of Hawaiʻi at Mānoa. "Its slow sky motion demands multi-year observations for an accurate orbit."
Sheppard, Tholen, and Trujillo collaborate on outer Solar System research, hunting for the hypothetical "Planet Nine." They've also discovered 12 new Jupiter moons and 20 around Saturn.
