Astronomers have discovered what they believed to be a rare stable trio of gravitationally bound Kuiper Belt objects, offering new clues to the enduring “3-body problem.”
The discovery, made using NASA’s Hubble Space Telescope and Hawaii’s Keck Observatory, revealed what astronomers identified as possible support for a controversial theory that certain Kuiper Belt objects (KBOs) could have been formed by the gravitational collapse of primordial material around the Sun. The theory contrasts with widely held ideas that most KBO formation occurs through collisions.
If verified, the intriguing system, known as 148780 Altjira, would represent only the second confirmation of a three-body system beyond Neptune and may indicate that such triple systems are more common features in the Kuiper Belt than previously believed.
The 3-Body Problem
In physics, the 3-body problem refers to the dynamics of objects (such as planets, stars, or other celestial objects) in systems where three separate bodies exist and how they exert gravitational forces against each other.
“The universe is filled with a range of three-body systems, including the closest stars to Earth, the Alpha Centauri star system, and we’re finding that the Kuiper Belt may be no exception,” said Maia Nelsen, a physics and astronomy graduate of Brigham Young University and lead author of a new study detailing the discovery.
A Growing Catalog of Kuiper Belt Objects
Considered remnants of the early solar system, more than 3,000 KBOs have been cataloged since their initial discovery in the early 1990s. Scientists estimate that hundreds of thousands more could exist, measuring greater than 10 miles in diameter.
Although once considered a planet, Pluto is now categorized as the largest known KBO. Given its size, a wealth of information has been gleaned about Pluto, unlike its smaller kindred in the Kuiper Belt, whose smaller size and extreme distance from Earth make their study far more complex.
Astronomers have only obtained close-up images of two KBOs: Pluto and Arrokoth, the latter of which scientists call a contact binary. NASA’s New Horizons mission made both observations possible.
Scientists describe Altjira as a “cousin” of Arrokoth, but it is believed to be nearly ten times larger, with a width of about 124 miles (200 kilometers).
Altjira’s Unique System, Revealed
At 3.7 billion miles from the Sun, the Altjira system has a trio of gravitationally bound objects (KBOs). Recent images obtained by the Hubble Telescope initially revealed two KBOs that were judged to be separated by nearly 4,700 miles.
However, additional analysis revealed that the innermost object was two separate bodies, so close that visually distinguishing between them was impossible.
“With objects this small and far away, the separation between the two inner members of the system is a fraction of a pixel on Hubble’s camera,” Nelsen said, “so you have to use non-imaging methods to discover that it’s a triple.”
By employing close to 17 years of observations from Hubble and the Keck Observatory, the team could track the system’s movement, analyzing the orbit of the outermost body. Their study of the object revealed peculiar shifts in motion, suggesting that it either possesses an atypical ellipsoid shape or that two objects are actually moving together.
Wow! signal
The 3-Body Problem and Altjira’s Mysteries
“A triple system was the best fit when we put the Hubble data into different modeling scenarios,” according to co-author Darin Ragozzine, also of Brigham Young University. Ragozzine and his colleagues believe there are still other possibilities, such as a binary—two objects that are touching each other—or that the suspected innermost pair is an oddly-shaped object either resembling an ellipsoid or a flattened “pancake” shape.
If confirmed, the potential discovery of another three-body system would be important since it would hint at the possibility that these KBO “triplets” aren’t as uncommon as previously believed.
Further, additional discoveries of triple systems could lend weight to the idea that KBOs may have formed as multi-body systems early on instead of remnants of impacts or mergers that occurred much later.
“Altjira has entered an eclipsing season, where the outer body passes in front of the central body,” Nelsen recently said. “This will last for the next ten years, giving scientists a great opportunity to learn more about it.”
Over the course of the next decade, the recent Hubble imagery of Altjira is expected to be complemented by further studies using NASA’s James Webb Space Telescope, which will significantly contribute during upcoming Cycle 3 observations that will help astronomers better characterize the unusual KBO system.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. He can be reached by email atmicah@thedebrief.org. Follow his work atmicahhanks.comand on X:@MicahHanks.