Nicknamed ‘Farfarout’ and officially designated 2018 AG37, the newly-confirmed planetoid has a very elongated orbit that takes it out to 175 AU (astronomical units) at its most distant, and inside the orbit of Neptune, to around 27 AU, when it is close to the Sun. Its average distance from the Sun is 132 AU; for comparison, Pluto is only 39 AU from the Sun. 2018 AG37 will be given an official name — like Sedna and other similar objects — after its orbit is better determined over the next few years.
2018 AG37 was first detected in 2018 by astronomers using the Subaru 8-m telescope located atop Maunakea in Hawai’i.
The planetoid’s journey around the Sun takes about 1,000 years, crossing the orbit of Neptune every time.
This means it has likely experienced strong gravitational interactions with Neptune over the age of the Solar System, and is the reason why it has such a large and elongated orbit.
“A single orbit of Farfarout around the Sun takes a millennium,” said Dr. David Tholen, an astronomer in the Institute for Astronomy at the University of Hawai’i.
“Because of this long orbital, it moves very slowly across the sky, requiring several years of observations to precisely determine its trajectory.”
2018 AG37 is very faint, and based on its brightness and distance from the Sun, Dr. Tholen and colleagues estimate its diameter to be about 400 km (250 miles), putting it on the low end of being a dwarf planet, assuming it is an ice rich object.
“The discovery of Farfarout shows our increasing ability to map the outer Solar System and observe farther and farther towards the fringes of our Solar System,” said Dr. Scott S. Sheppard, an astronomer at the Carnegie Institution for Science.
“Only with the advancements in the last few years of large digital cameras on very large telescopes has it been possible to efficiently discover very distant objects like Farfarout.”
“Even though some of these distant objects are quite large, being dwarf planet in size, they are very faint because of their extreme distances from the Sun.”
“Farfarout is just the tip of the iceberg of solar system objects in the very distant Solar System.”
Because Neptune strongly interacts with 2018 AG37, the planetoid’s orbit and movement cannot be used to determine if there is another unknown massive planet in the very distant Solar System, since these interactions dominate 2018 AG37’s orbital dynamics.
“Farfarout’s orbital dynamics can help us understand how Neptune formed and evolved, as Farfarout was likely thrown into the outer solar system by getting too close to Neptune in the distant past,” said Dr. Chad Trujillo, an astronomer in the Department of Astronomy and Planetary Science at Northern Arizona University.
“Farfarout will likely strongly interact with Neptune again since their orbits continue to intersect.”
The new observations of 2018 AG37 are reported in the Minor Planet Electronic Circular.
S.S. Sheppard et al. 2021. 2018 AG37. MPEC 2021-C187