Carnegie Science | Spring 2019 12 On December 17, 2018, the International Astronomical Union’s Minor Planet Center announced the discovery of the most distant body observed in our Solar System so far, by the dynamic trio of Sheppard, Tholen, and Trujillo. It was provisionally designated 2018 VG18. 2018 VG18 is the first known Solar System object that has been detected at a distance that is more than 100 times farther than Earth is from the Sun. Its Distance 2018 VG18, nicknamed “Farout,” is at about 120 astronomical units (1 AU is the Sun-Earth distance). The second most distant observed Solar System object is Eris, at about 96 AU. Pluto, currently at about 34 AU, makes 2018 VG18 more than three-and- a-half times more distant than that most famous dwarf planet. 2018 VG18 was also discovered as part of the team’s search for extremely distant Solar System objects. The team doesn’t know 2018 VG18’s orbit very well yet, so they don’t know if it could be shaped by Planet X. “2018 VG18 is much more distant and slower moving than other observed Solar System objects, so it will take a few years to fully determine its orbit,” said Sheppard. “But it was found in a similar location on the sky to the other like-objects, suggesting it might have the same type of orbit. The orbital similarities shown by many of these small, distant Solar System bodies was the catalyst for our original assertion that there is a distant, massive planet at several hundred AU shepherding these smaller objects.” Other Characteristics “All that we currently know about 2018 VG18 is its extreme distance from the Sun, its approximate diameter, and its color,” added Tholen. “Because 2018 VG18 is so distant, it orbits very slowly, likely taking more than 1,000 years to take one trip around the Sun.” The discovery images of 2018 VG18 were taken at the Japanese Subaru 8-meter telescope on November 10, 2018. Once 2018 VG18 was found, it needed to be re-observed to confirm its distance. 2018 VG18 was seen for the second time in early December at the Magellan telescope in Chile. These observations included the addition of graduate student Will Oldroyd of Northern Arizona University. Over the next week, they monitored 2018 VG18 with the Magellan telescope to secure its path and obtain physical properties such as brightness and color. The Magellan observations confirmed that 2018 VG18 is around 120 AU, making it the first Solar System object observed beyond 100 AU. Its brightness suggests that it is about 500 kilometers (310 miles) in diameter, likely making it spherical and a dwarf planet. It is pinkish, a color associated with ice-rich objects. An International Achievement “This discovery is truly an international achievement in research using telescopes located in Hawaii and Chile, operated by Japan, and a consortium of research institutions and universities in the United States,” concluded Trujillo. “With new wide-field digital cameras on some of the world’s largest telescopes, we are finally exploring our Solar System’s fringes, far beyond Pluto.” More far, far out objects will continue to be in the researchers’ sights.  Finding “Farout” Solar System distances are shown to scale with the newly discovered 2018 VG18, compared to other known Solar System objects. Illustration by Roberto Molar Candanosa and Scott Sheppard, Carnegie Institution for Science This artist’s concept shows 2018 VG18, nicknamed “Farout.” Illustration by Roberto Molar Candanosa, Carnegie Institution for Science SUPPORT: The Subaru telescope is owned and operated by Japan. The valuable telescope access that the team obtained was thanks to a combination of time allocated to the University of Hawaii and the U.S. National Science Foundation (NSF) through telescope time exchanges between the U.S. National Optical Astronomy Observatory (NOAO) and National Astronomical Observatory of Japan (NAOJ). M e r u r y E a r t h P l u t o N e p t u n e U r a n u s S a t u r n J u p i t e r M a r s V e n u s 34 AU E r i s 80 AU 96 AU 120 AU S e d n a “ T h e G o b l i n ” 2 0 1 5 T G 3 8 7 “ B i d e n ” 2 0 1 5 V P 1 1 3 “ F a r o u t ” 2 0 1 8 V G 1 9 Scale: 1AU