A University of Hawaii research team has confirmed that Farfarout is officially the most distant object in our solar system.
Scientists first discovered the planetoid, nicknamed “Farfarout,” in 2018. They found it at an estimated distance of 140 astronomical units (AU) from the sun. 1 AU is the distance between the Earth and Sun. For comparison, Pluto is only 34 au from the Sun. That means Farfarout is almost four times farther from the Sun than Pluto. This makes it the most distant object ever observed in our solar system.
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However, the team has now collected enough observations to pin down its orbit. The Minor Planet Center has now given it the official designation of 2018 AG37.
“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 Scott S. Sheppard, of 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.”
Farfarout’s current distance from the Sun is 132 astronomical units. The object has a very elongated orbit. It takes it out to 175 AU at its most distant and to around 27 AU — inside Neptune’s orbit — when it’s closest to the sun. That elliptical orbit is thanks to gravitational sculpting by Neptune.
A single orbit of Farfarout around the Sun takes a millennium. And because it moves very slowly across the sky, the object requires years of observations to precisely determine its trajectory.
By looking at its brightness, scientists found Farfarout is about 250 miles (400 kilometers) wide. That’s barely enough to qualify for dwarf planet status. But the size estimate assumes the world is largely made of ice, and that assumption could change with more observations.
Scientists will give Farfarout an official name after they better determine its orbit over the next few years.
The team of astronomers discovered the object using the Subaru 8-meter telescope located atop Maunakea in Hawaii. They also used the Gemini North and Magellan telescopes in the past few years to determine its orbit.
Neptune plays such a large role in Farfarout’s life. Thus, scientists cannot use Farfarout’s orbit and movement to determine if there is a Planet Nine out there. Planet Nine is the big hypothetical world that some scientists think lies unseen in the far outer solar system. The scientists who predicted the planet’s existence did so based on the strange highly elliptical orbits of around thirty so-called trans-Neptunian objects.
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 this unknown massive 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 thus would be strongly influenced by the possible Planet Nine 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 Chad Trujillo, an exoplanet astronomer at Northern Arizona University. “Farfarout will likely strongly interact with Neptune again since their orbits continue to intersect.”
However, Farfarout’s distance record refers to its current location. There are several other objects, such as the dwarf planet Sedna, whose orbits take them much farther away from the sun at points than Farfarout will ever get. And scientists think there are trillions of comets in our solar system’s Oort Cloud, which begins about 5,000 AU from the sun.