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Discoveries in the Kuiper Belt: The 148780 Altjira System
The challenge of understanding the motion of three gravitationally interacting bodies in space has intrigued mathematicians for ages. This complex phenomenon has gained mainstream attention through the novel and television series “3 Body Problem.” However, researchers have recently identified what they believe to be a stable trio of icy objects in the Kuiper Belt, with findings supported by data from both NASA’s Hubble Space Telescope and the W. M. Keck Observatory in Hawaii.
If confirmed, the 148780 Altjira system would mark the second three-body system identified in this region. The discovery could imply that there are additional similar configurations that could enhance our understanding of the solar system’s evolution and the formation of Kuiper Belt objects (KBOs).
Lead author Maia Nelsen, a graduate in physics and astronomy from Brigham Young University, emphasized the significance of this finding: “The universe hosts a variety of three-body systems, including our nearest star system, Alpha Centauri. The Kuiper Belt seems to conform to this trend.”
KBOs, which have been recognized since 1992, consist of primitive icy remnants from the solar system’s formative years, located beyond Neptune’s orbit. As of now, over 3,000 such objects have been recorded, with estimates suggesting hundreds of thousands more remain to be discovered, particularly those exceeding 10 miles in diameter. Pluto stands out as the largest of these KBOs.
The identification of Altjira bolsters a theory regarding KBO formation. This hypothesis posits that three small rocky bodies could not have originated from collisions within the crowded Kuiper Belt. Instead, it suggests they formed as a trio from the gravitational collapse of material in the disk surrounding the early Sun, approximately 4.5 billion years ago. While the gravitational collapse of gas has long been understood as a process that forms stars in pairs or triples, the idea that similar processes could shape objects like those in the Kuiper Belt remains a subject of ongoing study.
The Altjira system resides in the solar system’s farthest reaches, approximately 3.7 billion miles away, which is 44 times greater than the distance from Earth to the Sun. Hubble’s imaging revealed two KBOs separated by about 4,700 miles (7,600 kilometers). However, researchers suspect that one of these bodies may actually consist of two closely bound objects that cannot be differentiated at this vast distance.
Nelsen noted the challenges posed by such distant small objects, explaining, “The proximity of the inner members of the system is so minimal that they only appear as a fraction of a pixel in Hubble’s camera. Non-imaging techniques are necessary to identify its triple nature.”
To reach these conclusions, scientists have meticulously compiled a 17-year observational dataset from both Hubble and the Keck Observatory, tracking the outer object’s orbital dynamics.
Darin Ragozzine, a co-author from Brigham Young University, described their findings: “We observed changes in the outer object’s orbit orientation over time, which indicated that the inner object could be either very elongated or possibly two distinct entities.” Nelsen added, “Our modeling efforts best fit a triple system scenario. There are other explanations, such as the inner object being a contact binary—where two bodies are sufficiently close to touch—or even an unusually flat configuration.”
Currently, around 40 binary objects have been documented in the Kuiper Belt. The identification of two potential triples suggests that rather than being an anomaly, the research team could be uncovering a population of three-body systems formed under similar conditions. However, establishing a more comprehensive understanding will require additional time and repeated observations.
Pluto and the smaller celestial body Arrokoth, which was visited by NASA’s New Horizons mission in 2015 and 2019 respectively, are the only KBOs that have been thoroughly analyzed to date. The New Horizons mission confirmed Arrokoth to be a contact binary, representing two objects that have drawn closer together over time to the point of contact or merging, often resulting in a peanut-like shape. Ragozzine referred to Altjira as a “cousin” of Arrokoth, suggesting that while Altjira is substantially larger—estimated at 124 miles (200 kilometers) wide—it belongs to the same general category of KBOs.
Although there are no immediate plans for a mission aimed specifically at Altjira for detailed analysis similar to Arrokoth, Nelsen highlighted an exciting upcoming opportunity for the study of this intriguing system. “Altjira has entered a phase where the outer body will pass in front of the central body over the next decade, providing a unique chance for further investigation,” said Nelsen. Additionally, NASA’s James Webb Space Telescope will contribute to the inquiry by examining whether the system’s components exhibit uniform characteristics during its forthcoming Cycle 3 observations.
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