A team of astronomers from different universities has just confirmed the discovery of a planetoid that is at least four times farther from the Sun than Pluto, which makes it the most distant object observed so far in the Solar System. Christened by scientists as ‘Farfarout’ to distinguish it from ‘Farout’, which until now held the record for the farthest object and also discovered by the same team of scientists, the planetoid, about 400 km in diameter, was detected for the first time in 2018, but only now are sufficient data available to pinpoint its orbit. The name, however, is not official and will be changed to another once its orbit is determined more accurately in a few years. The Center for Minor Planets has designated it 2018 AG37.
Farfarout is currently 132 astronomical units (AU) from the Sun. One AU is equal to 150 million km, which is the distance between the Earth and the Sun. The object is therefore 132 times further away from our star than our planet is. In comparison, it is enough to think that Pluto is ‘only’ 34 AU from the sun king. Farfarout follows a very elongated orbit, taking it as far as 175 AU at its most distant point and just 27 AU (within the orbit of Neptune), at its closest point. The object takes about a thousand years to complete each orbit, and in all of them it crosses the orbit of Neptune, so the researchers think that it is very likely that it has experienced strong gravitational interactions with the giant planet throughout its history, something that would explain the reason for its long and long orbit.
“A single Farfarout orbit around the Sun takes a millennium,” explains David Tholen of the University of Hawaii at Manoa and a co-author of the discovery. Due to this long orbital period, the object moves very slowly across the sky, requiring several years of observation to determine its path accurately.
The planetoid was discovered by the Subaru telescope, located on top of Mount Maunakea, in Hawaii, and was later followed by other telescopes (the Gemini North and the Magellan) to determine its orbit as accurately as possible. Of course, and at this enormous distance from the Sun, its brightness is very low, although it was enough for its diameter to be estimated at about 400 km, which places it just below the minimum size of dwarf planets. Hence its classification as a planetoid. The researchers believe that the object also has large amounts of ice. “Farfarout’s discovery,” says Scott S. Sheppard of the Carnegie Institution and another of the object’s discoverers, “demonstrates our growing ability to map the outer solar system and observe ever closer to its limits. Only with the advancements of recent years, with powerful digital cameras in very large telescopes, has it been possible to efficiently discover objects as distant as this one. And although some of these distant objects are quite large, almost as large as a dwarf planet, their brightness is very dim due to their extreme distances from the Sun. Farfarout is just the tip of the iceberg of distant solar system objects.
Because Neptune often interacts with Farfarout, altering its trajectory, the orbital and motion data of this object cannot be used to infer whether a very massive and hitherto unknown planet exists in the confines of the Solar System (the famous Planet 9). . In fact, to look for signs of the existence of this great and hypothetical planet, only objects whose orbits never approach Neptune’s can be used, leaving them outside its gravitational influence.
This is the case of Sedna or 2012 VP113, which despite being closer to the Sun than Farfarout (at about 80 AU) never gets close to the gas giant, so their orbits could be influenced by the possible unknown planet. Instead, as Chad Trujillo of the Department of Astronomy and Planetary Sciences at the University of Arizona and another team member explain, “Farfarout’s orbital dynamics can help us understand how Neptune itself formed and evolved. that Farfarout was likely thrown into the outer solar system by getting too close to the gas giant in the distant past. And Farfarout is likely to interact with Neptune again in the future, as their orbits continue to intersect.