Flung into the outer solar system by Neptune's gravity
At the outermost edge of our solar system, a small icy world called Farfarout has been confirmed as the most distant object humanity has ever detected in orbit around the Sun — sitting 132 astronomical units away, nearly four times beyond Pluto. Discovered in 2018 by astronomers at the University of Hawaii and patiently tracked across years of slow celestial motion, this 400-kilometer dwarf planet carries within its strange, elongated path the memory of an ancient gravitational encounter with Neptune. Its existence reminds us that the solar system is far larger and more storied than our maps have yet captured, and that the boundary between the known and the unknown continues to recede.
- Farfarout orbits so far from the Sun that a single journey around it takes roughly a thousand years, swinging between 27 and 175 AU in a wildly elliptical arc.
- Its extreme remoteness meant the object moved so imperceptibly across the sky that years of observation were required just to confirm what it was and where it was going.
- The leading explanation for its bizarre orbit points to a violent gravitational slingshot by Neptune billions of years ago, during the chaotic formation of the early solar system.
- Because Farfarout's path still crosses Neptune's, the two bodies continue to interact — giving scientists a rare, living record of how the giant planet migrated and evolved.
- The confirmation marks a milestone in a deliberate Hawaiian-led effort to chart the outer solar system, a region that remains one of the last great frontiers of planetary science.
In 2018, astronomers at the University of Hawaii's Institute for Astronomy detected something faint and slow-moving at the very edge of the solar system. Years of careful observation have since confirmed it as the most distant object ever found in orbit around the Sun. They have named it Farfarout — a playful tribute to its predecessor in the record books, a similarly remote Hawaiian discovery called Farout.
The scale of its remoteness is difficult to absorb. Farfarout currently sits 132 astronomical units from the Sun — nearly four times farther than Pluto. Its orbit is sharply elliptical, ranging from 27 AU at its closest to 175 AU at its most distant, completing a single revolution in roughly a thousand years. Based on its brightness, astronomers estimate it spans about 400 kilometers, large enough to qualify as a dwarf planet if, as expected, it is composed primarily of ice.
The Subaru Telescope on Maunakea was the primary instrument used to track the object's glacially slow movement across the sky. Astronomer Chad Trujillo of the University of Arizona explains that Farfarout was almost certainly hurled into its extreme orbit by a close gravitational encounter with Neptune during the solar system's turbulent early history. Crucially, its orbital path still intersects with Neptune's, meaning the two bodies continue to interact — and studying that relationship may illuminate how Neptune itself migrated and settled into its current position.
Farfarout is ultimately a point of light on a distant screen, but one that extends our picture of the solar system and hints at how much still waits to be found in the dark beyond Pluto.
In 2018, astronomers at the University of Hawaii's Institute for Astronomy spotted something extraordinary at the edge of the known solar system. They called it 2018 AG37 at first, a provisional designation for an object so distant it barely registered in our understanding of where the solar system ends. Years of careful observation have now confirmed what they suspected: this is the most remote body we have ever detected orbiting the sun. The team has given it a proper name—Farfarout—a playful nod to its predecessor in the record books, another Hawaiian discovery from the same year called Farout.
The numbers alone convey the strangeness of this place. Farfarout orbits at a current distance of 132 astronomical units from the sun. One AU is the distance from Earth to the sun, roughly 150 million kilometers. To put this in perspective, Pluto, once the solar system's most famous outcast, sits at only 34 AU. Farfarout is nearly four times farther away. But its orbit is wildly elliptical. At its closest approach, it swings in to 27 AU, still well beyond Neptune. At its farthest, it stretches out to 175 AU, a journey that takes roughly a thousand years to complete.
The Subaru Telescope, an eight-meter instrument perched on Maunakea in Hawaii, has been the primary tool for tracking this distant wanderer. Based on its brightness and distance, astronomers estimate Farfarout measures about 400 kilometers across—large enough to qualify as a dwarf planet, assuming it is composed primarily of ice, as the evidence suggests. The object moves so slowly across the sky that years of observations were necessary just to map its trajectory with enough precision to confirm its identity and orbital characteristics.
The real intrigue lies in how Farfarout got there. Chad Trujillo, one of the astronomers from the University of Arizona involved in the discovery, explains that the planetoid was almost certainly flung into the outer solar system by a close encounter with Neptune billions of years ago, during the chaotic early period when the solar system was still taking shape. Neptune's gravity acted like a cosmic slingshot, hurling Farfarout into this extreme, elongated orbit. What makes this discovery particularly valuable is that Farfarout's orbital path still intersects with Neptune's. The two bodies continue to interact gravitationally, and studying how they move relative to each other offers a window into Neptune's own formation and evolution—how it migrated through the young solar system and settled into its current position.
The confirmation of Farfarout represents the culmination of a deliberate effort by Hawaiian astronomers to map the outer solar system beyond Pluto, a region that remains largely mysterious. Each new discovery in this distant realm adds another piece to the puzzle of how our planetary neighborhood came to be. For now, Farfarout remains a point of light on a distant screen, a reminder that the solar system extends far beyond what most of us imagine, and that there are still discoveries waiting in the dark.
Citações Notáveis
Farfarout's orbital dynamics may help us understand how Neptune formed and evolved, since the planetoid was likely ejected into the outer solar system after passing too close to Neptune in the past— Chad Trujillo, University of Arizona
A Conversa do Hearth Outra perspectiva sobre a história
Why does it matter that we found this one object so far away? Isn't the solar system already mapped?
The solar system's outer edges are still largely unknown. Finding Farfarout tells us the solar system is bigger and stranger than we thought, and objects this distant hold clues about how planets formed and moved around in the early solar system.
You mentioned Neptune threw it out there. How do we know that actually happened?
We don't know it with certainty, but the orbital dynamics tell the story. Farfarout's path is so extreme—swinging from 27 to 175 AU—that it's nearly impossible to explain without a gravitational encounter with a massive body like Neptune early on.
And it takes a thousand years to orbit the sun once?
Yes. That's what makes it so difficult to study. You need years of observations just to see it move enough to calculate where it's going. It's patient work.
So what happens next? Do we send a probe?
Not anytime soon. Farfarout is too far and too slow-moving for current technology. But by watching how it moves relative to Neptune, we can learn about Neptune's own history—where it came from, how it migrated. That's the real prize.