There are many gravitationally bound three-body systems in the universe, from triple star systems to planets like Mars with two moons. Now, new research suggests that the Kuiper Belt - the distant region of icy objects in our solar system - may also harbor such systems. Scientists have discovered a second potential triplet system in the Kuiper Belt, in which an object previously thought to be a binary star may actually contain a hidden third member. This third object is so close to its companion that it can be detected only through its influence on the system's orbital motion.
The newly discovered Kuiper Belt trio may be the second of its kind, and could provide strong evidence that these distant objects were not formed by collisions but by gravitational collapse - just like stars.
If confirmed, the discovery would raise the possibility that there are more hidden triplet systems in the Kuiper Belt. This theory holds that Kuiper Belt Objects (KBOs) were not formed through collisions, but instead formed triple systems through gravitational collapse.
Predicting the motions of three gravitationally bound objects has puzzled mathematicians for centuries, and more recently, the novel and TV series The Three-Body Problem have brought the problem to the forefront. However, researchers have now discovered three seemingly stable icy space rocks in the distant Kuiper Belt of the solar system. The discovery was made using data from NASA's Hubble Space Telescope and the W.M. Keck Observatory in Hawaii.
If confirmed, the 148780 Altjira system would be only the second known three-body system in the region, suggesting that more three-body systems may exist. The discovery would support certain theories about the history of the solar system and the formation of Kuiper Belt Objects (KBOs).
"The universe is filled with three-body systems, including the Alpha Centauri system, the closest star to Earth, and what we found in the Kuiper Belt may be no exception," said Maia Nelson, lead author of the study and a graduate of Brigham Young University in Provo, Utah, who majored in physics and astronomy.
First discovered in 1992, KBO is an ancient icy remnant of the early solar system located beyond the orbit of Neptune. So far, more than 3,000 have been cataloged, but scientists estimate there could be hundreds of thousands more, each more than 10 miles across. The largest known KBO is the dwarf planet Pluto.
Hubble's discovery is important support for the KBO formation theory, in which the three small rocky objects were not the result of collisions in the busy Kuiper Belt, but were formed directly from the gravitational collapse of material in the newly formed disk of material around the sun about 4.5 billion years ago. It is known that stars form through the gravitational collapse of gas, usually in pairs or trios, but the idea that cosmic objects like those in the Kuiper Belt formed in a similar way is still under investigation.
The Altjira system is located in the outer reaches of the solar system, 3.7 billion miles away (about 44 times the distance between the Earth and the sun). Hubble images show that the two KBOs are about 4,700 miles (about 7,600 kilometers) apart. However, repeated observations of the two objects' unique co-orbital motion indicate that the inner object is actually two objects that are so close together that they are simply indistinguishable at such great distances, the researchers said.
"For such a small and distant object, the distance between the two members within the system is only a fraction of a pixel on the Hubble camera, so you have to use non-imaging methods to discover that this is a triplet," Nelson said.
This takes time and patience. Scientists collected 17 years of baseline observation data from the Hubble Observatory and the Keck Observatory to observe the orbits of objects outside the Altjira galaxy.
"We see changes in the orbital orientation of the outer objects over time, suggesting that the inner objects are either very elongated or are actually two separate objects," said Altjira study co-author Darin Ragozzine of Brigham Young University.
"When we put the Hubble data into different modeling scenarios, the triplet system was the best fit," Nelson said. "Other possibilities are that the inner object is a contact binary, where two separate objects are close together and touching each other, or is actually a weird flat object, like a pancake."
Currently, there are approximately 40 confirmed binaries in the Kuiper Belt. Now that two of these systems may be three-body systems, the researchers say it's more likely they're not seeing a single freak but a swarm of three-body systems that formed under the same circumstances. However, building evidence takes time and repeated observations.
The only Kuiper Belt objects that have been explored in detail are Pluto and the smaller object Arrokoth, which NASA's New Horizons mission visited in 2015 and 2019, respectively. New Horizons shows that Arrokoth is a contact binary, which to the KBO means the two objects are getting closer and are now touching and/or have merged, typically forming a peanut shape. Ragozzine describes Altjira as a "cousin" of Arrokoth, a Kuiper Belt object. However, they estimate that Altjira is 10 times larger than Arrokoth and 124 miles (200 kilometers) wide.
Nelson said that while there are currently no missions planned to fly over Altjira to obtain details of the Arokos class, a different opportunity is imminent to further study this fascinating system.
"Altjira has entered its eclipse season, when outer objects pass in front of the central object. This will last for ten years, giving scientists an excellent opportunity to learn about it," Nelson said. NASA's James Webb Space Telescope has also joined the study of Altjira as it will examine whether the components look the same during its upcoming Cycle 3 observations.
Hubble's research was published in the Journal of Planetary Science.
Compiled from /scitechdaily