The 1000-Year Orbit of “Farfarout” –Most Distant Known Object in Our Solar System


Farfarout Planetoid


The discovery in 2018 of the most distant known object at the very edge our solar system, a planetoid aptly named “Farfarout,” shows our increasing ability to map the outer fringes of our solar system in the last few years with the advent of large digital cameras on very large telescopes, said astronomer Scott Shepard of the Carnegie Institution for Science. Shepard’s comment unwittingly fulfills Edwin Hubble’s observation in 1936 that “with increasing distance, our knowledge fades, and fades rapidly. Eventually, we reach the dim boundary—the utmost limits of our telescopes. There, we measure shadows, and we search among ghostly errors of measurement for landmarks that are scarcely more substantial.”

“Even though some of these distant objects are quite large, being dwarf planet in size,” says Shepard, 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.”

Beyond the fringe of our solar system lies Interstellar space and a giant, thick-walled bubble known as the Oort Cloud made of billions, or even trillions, of icy space debris the sizes of mountains and sometimes larger. Astronomers, reports NASA,  suspect that the Oort Cloud could extend as far as three light-years from our solar system, or more than halfway to the nearest stars, the Centauri triple star system, which is slightly more than four light-years from Earth.

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Four Times Farther from the Sun than Pluto

A team of astronomers, including Chad Trujillo of Northern Arizona University, have confirmed the planetoid – giving it the official designation of 2018 AG37 by the Minor Planet Center. It is almost four times farther from the Sun than Pluto, making it the most distant object ever observed in our solar system. The team has now collected enough observations to pin down its orbit.

Farfarout’s nickname distinguished it from the previous record holder “Farout,” found by the same team of astronomers in 2018. In addition to Trujillo, the discovery team includes Sheppard and David Tholen from the University of Hawaii’s Institute for Astronomy, who have an ongoing survey to map the outer solar system beyond Pluto.

Large and Elongated Orbit

Farfarout was discovered at the Subaru 8-meter telescope located atop Maunakea and recovered using the Gemini North and Magellan telescopes in the past few years to determine its orbit based on its slow motion across the sky. Farfarout’s orbit around the Sun takes a millenium, about a thousand years, crossing the massive planet Neptune’s orbit every time. This means Farfarout 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. “Because of this long orbital, it moves very slowly across the sky, requiring several years of observations to precisely determine its trajectory,” says Tholen

The faint icy object, and based on its brightness and distance from the Sun, is estimated to be about 400 kilometers across, putting it on the low end of being a dwarf planet. It’s average distance from the Sun is 132 astronomical units (au); 1 au is the distance between the Earth and Sun. For comparison, Pluto is only 39 au from the Sun. The newly discovered object has a very elongated orbit that takes it out to 175 au at its most distant, and inside the orbit of Neptune, to around 27 au, when it is close to the Sun.

Undetermined –Unknown Massive Planet in the Distant Solar System

Because Neptune strongly interacts with Farfarout, Farfarout’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 Farfarout’s orbital dynamics. Only those objects whose orbits stay in the very distant solar system, well beyond Neptune’s gravitational influence, can be used to probe for signs of an unknown massive planet. These include Sedna and 2012 VP113, which, although they are currently closer to the Sun than Farfarout (at around 80 AU), they never approach Neptune and thus would be strongly influenced by the possible Planet X instead.

“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 Trujillo. “Farfarout will likely strongly interact with Neptune again since their orbits continue to intersect.”

Maxwell Moe, NASA Einstein Fellow, University of Arizona, via Northern Arizona University  and University of Hawaii 

Image credit top of page: Roberto Molar Candanosa, Scott S. Sheppard from Carnegie Institution for Science, and Brooks Bays from University of Hawaiʻi.); edit body image credit: Wikipedia21. The Daily Galaxy. All rights reserved.



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