Astronomers confirm orbit of most distant object ever observed in our solar system

A team of astronomers, including Associate Professor Chad Trujillo of the Department of Astronomy and Planetary Science at Northern Arizona University, has confirmed a planetoid that is almost four times farther from the Sun than Pluto, making it the subject the most distant ever observed in our solar system. The planetoid, nicknamed “Farfarout”, was first detected in 2018, and the team has now gathered enough sightings to locate its orbit. The Minor Planet Center has now given it the official designation of 2018 AG37.

Farfarout’s nickname set him apart from the previous record holder “Farout”, found by the same team of astronomers in 2018. Besides Trujillo, the discovery team includes Scott S. Sheppard of the Carnegie Institution for Science and David Tholen of the ‘University of Hawaii. Institute for Astronomy, which is conducting an ongoing investigation to map the outer solar system beyond Pluto.

Farfarout will receive an official name (like Sedna and other similar objects) once its orbit is better determined over the next few years. It was discovered at the 8-meter Subaru telescope atop Maunakea in Hawaii, and recovered using the Gemini North and Magellan telescopes in recent years to determine its orbit based on its idle in the sky.

The average distance from Farfarout to the Sun is 132 astronomical units (au); 1 au is the distance between the Earth and the Sun. For comparison, Pluto is only 39 AU from the Sun. The newly discovered object has a very elongated orbit which brings it to 175 AU at its furthest point, and within Neptune’s orbit, at about 27 AU, when it is near the sun.

Farfarout’s journey around the Sun takes about a thousand years, each time crossing the orbit of the enormous planet Neptune. This means that Farfarout likely experienced strong gravitational interactions with Neptune during the Solar System Age, and this is the reason why it has such a large and elongated orbit.

“A single orbit of Farfarout around the Sun takes a millennium,” Tholen said. “Because of this long orbital, it moves very slowly across the sky, requiring several years of observations to precisely determine its trajectory.”

Farfarout is very faint, and based on its brightness and distance from the Sun, the team estimates its size to be around 400 km in diameter, which puts it in the lower part of a dwarf planet, assuming that ‘it is an object rich in ice.

“The Farfarout discovery shows our increasing ability to map the outer solar system and to observe further and further to the fringes of our solar system,” Sheppard said. “It is only with the progress made in recent years in large digital cameras on very large telescopes that it has been possible to effectively discover very distant objects like Farfarout. Even though some of these distant objects are quite large, being dwarf planets, they are very small due to their extreme distances from the Sun. Farfarout is just the tip of the iceberg of solar system objects in the far distant solar system. “

Because Neptune strongly interacts with Farfarout, Farfarout’s orbit and motion cannot be used to determine if there is another massive unknown planet in the far distant solar system, since these interactions dominate the orbital dynamics of Farfarout. Only objects whose orbits remain in the far distant solar system, well beyond the gravitational influence of Neptune, can be used to probe for signs of a massive unknown planet. These include Sedna and 2012 VP113, which, although they are currently closer to the Sun than Farfarout (at around 80 AU), never approach Neptune and would therefore be strongly influenced by the eventual planet X in place.

“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,” Trujillo said. “Farfarout is likely to interact strongly with Neptune again as their orbits continue to intersect.”