Free Astronomy Magazine May-June 2021

52 MAY-JUNE 2021 ASTRO PUBLISHING T hese discovery images of Farfarout (2018 AG 37 ) were taken with the Subaru Telescope on the nights of 15 and 16 Janu- ary 2018 Universal Time (UT). By comparing the images with each other, it is possible to see that Farfarout (marked by blue horizontal lines) moves while the background stars and galaxies do not. [S. Sheppard] Carnegie Institution for Science’s Magellan Telescopes in Chile to de- termine its orbit. They have now confirmed that Farfarout currently lies 132 astronomical units (au) from the Sun, which is 132 times farther from the Sun than Earth is. (For com- parison, Pluto is 39 au from the Sun, on average.) Farfarout is even more remote than the previous Solar System distance record-holder, which was discovered by the same team and nicknamed “Farout.” Provisionally designated 2018 VG 18 , Farout is 124 au from the Sun. However, the orbit of Farfarout is quite elongated, taking it 175 au from the Sun at its farthest point and around 27 au at its closest, which is inside the orbit of Neptune. Because its orbit crosses Nep- tune’s, Farfarout could provide insights into the history of the outer Solar System. “Farfarout was likely thrown into the outer Solar System by getting too close to Neptune in the distant past,” said Trujillo. “Farfarout will likely interact with Neptune again in the future since their orbits still in- tersect.” Farfarout is very faint. Based on its brightness and distance from the Sun, the team estimates it to be about 400 kilometers (250 miles) across, putting it at the low end of possibly being designated a dwarf planet by the International Astro- nomical Union (IAU). The IAU’s Minor Planet Center in Massachusetts announced that it has given Farfarout the provisional des- ignation 2018 AG 37 . The Solar Sys- tem’s most distant known member will receive an official name after more observations are gathered and its orbit becomes even more refined in the coming years. “Farfarout takes a millennium to go around the Sun once,” said Tholen. “Because of this, it moves very slowly across the sky, requiring sev- eral years of observations to pre- cisely determine its trajectory.” Farfarout’s discoverers are confident that even more distant objects re- main to be discovered on the out- skirts of the Solar System, and that its distance record might not stand for long. “The discovery of Farfarout shows our increasing ability to map the outer Solar System and observe far- ther and farther towards the fringes of our Solar System,” said Sheppard. “Only with the advance- ments in the last few years of large digital cameras on very large tele- scopes has it been possible to effi- ciently discover very distant objects like Farfarout. Even though some of these distant objects are quite large — the size of dwarf planets — they are very faint because of their extreme distances from the Sun. Farfarout is just the tip of the ice- berg of objects in the very distant Solar System.” !