Maunakea, Hawaiʻi – A team of researchers using data from W. M. Keck Observatory on Maunakea, Hawaiʻi Island and NASA’s Hubble Space Telescope have discovered what is likely a stable trio of icy space rocks in the solar system’s Kuiper Belt.
If confirmed as the second such three-body system found in the region, the 148780 Altjira system suggests there could be similar triples waiting to be discovered, which would support a particular theory of our solar system’s history and the formation of Kuiper Belt objects (KBOs).
The study, led by Brigham Young University, is published in today’s issue of the journal The Planetary Science Journal.
“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 the study’s lead author Maia Nelsen, a physics and astronomy graduate of Brigham Young University in Provo, Utah.
Known since 1992, KBOs are primitive icy remnants from the early solar system found beyond the orbit of Neptune. To date, over 3,000 KBOs have been cataloged, and scientists estimate there could be several hundred thousand more that measure over 10 miles in diameter. The largest KBO is dwarf planet Pluto.
The team used a series of Keck Observatory NIRC2 narrow-field infrared camera data between 2006 and 2020 to model Altjira in different configurations.
“This discovery is scientifically fascinating because we don’t know how to distinguish between different models of how this part of the solar system formed, and the existence of triple systems helps rule one model out,” said John O’Meara, Keck Observatory Chief Scientist and Deputy Director. “With AO, we can be as sharp an eye on the sky as a space telescope, complimenting Hubble’s strengths.”
The Hubble finding is crucial support for a KBO formation theory, in which three small rocky bodies would not be the result of collision in a busy Kuiper Belt, but instead form as a trio directly from the gravitational collapse of matter in the disk of material surrounding the newly formed Sun, around 4.5 billion years ago. It’s well known that stars form by gravitational collapse of gas, commonly as pairs or triples, but that idea that cosmic objects like those in the Kuiper Belt form 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, or 44 times the distance between Earth and the Sun. Hubble images show two KBOs located about 4,700 miles (7,600 kilometers) apart. However, researchers say that repeated observations of the objects’ unique co-orbital motion indicate the inner object is actually two bodies that are so close together they can’t be distinguished at such a great distance.
“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, so you have to use non-imaging methods to discover that it’s a triple,” said Nelsen
That is where Keck Observatory’s unique capabilities comes into play. “Keck Observatory is the one ground-based telescope that was able to do high-quality enough observations of Altjira for our study. All of our other observations were from HST, but those alone were not enough of an observational baseline for our models,” said Nelsen. “The extra points from Keck Observatory made for a better and more statistically robust result giving more credence to the strength of the hierarchical triple orientation of Altjira.
“In this case, its 10-meter mirror, coupled with its laser guide star adaptive optics system, provided small scales on the sky, which is what you need to do this type of work,” added O’Meara.
To conduct this research, scientists gathered a 17-year observational baseline of data from Keck Observatory and Hubble, watching the orbit of the Altjira system’s outer object.
“Over time, we saw the orientation of the outer object’s orbit change, indicating that the inner object was either very elongated or actually two separate objects,” said Darin Ragozzine, also of Brigham Young University, a co-author of the Altjira study.
Currently, there are about 40 identified binary objects in the Kuiper Belt. Now, with two of these systems likely triples, the researchers say it is more likely they are looking not at an oddball, but instead a population of three-body systems, formed by the same circumstances. However, building up that 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 showed that Arrokoth is a contact binary, which for KBOs means that two objects that have moved closer and closer to one another are now touching and/or have merged, often resulting in a peanut shape. Ragozzine describes Altjira as a “cousin” of Arrokoth, a member of the same group of Kuiper Belt objects. They estimate Altjira is 10 times larger than Arrokoth, however, at 124 miles (200 kilometers) wide.
While there is no mission planned to fly by Altjira to get Arrokoth-level detail, Nelsen said there is a different upcoming opportunity for further study of the intriguing system.
Altjira has entered an eclipsing season, where the outer body passes in front of the central body. This will last for the next ten years, giving scientists a great opportunity to learn more about it,” Nelsen said. NASA’s James Webb Space Telescope is also joining in on the study of Altjira as it will check if the components look the same in its upcoming Cycle 3 observations.
If confirmed as the second such three-body system found in the region, the 148780 Altjira system suggests there could be similar triples waiting to be discovered, which would support a particular theory of our solar system’s history and the formation of Kuiper Belt objects (KBOs).
The study, led by Brigham Young University, is published in today’s issue of the journal The Planetary Science Journal.
“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 the study’s lead author Maia Nelsen, a physics and astronomy graduate of Brigham Young University in Provo, Utah.
Known since 1992, KBOs are primitive icy remnants from the early solar system found beyond the orbit of Neptune. To date, over 3,000 KBOs have been cataloged, and scientists estimate there could be several hundred thousand more that measure over 10 miles in diameter. The largest KBO is dwarf planet Pluto.
The team used a series of Keck Observatory NIRC2 narrow-field infrared camera data between 2006 and 2020 to model Altjira in different configurations.
“This discovery is scientifically fascinating because we don’t know how to distinguish between different models of how this part of the solar system formed, and the existence of triple systems helps rule one model out,” said John O’Meara, Keck Observatory Chief Scientist and Deputy Director. “With AO, we can be as sharp an eye on the sky as a space telescope, complimenting Hubble’s strengths.”
The Hubble finding is crucial support for a KBO formation theory, in which three small rocky bodies would not be the result of collision in a busy Kuiper Belt, but instead form as a trio directly from the gravitational collapse of matter in the disk of material surrounding the newly formed Sun, around 4.5 billion years ago. It’s well known that stars form by gravitational collapse of gas, commonly as pairs or triples, but that idea that cosmic objects like those in the Kuiper Belt form 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, or 44 times the distance between Earth and the Sun. Hubble images show two KBOs located about 4,700 miles (7,600 kilometers) apart. However, researchers say that repeated observations of the objects’ unique co-orbital motion indicate the inner object is actually two bodies that are so close together they can’t be distinguished at such a great distance.
“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, so you have to use non-imaging methods to discover that it’s a triple,” said Nelsen
That is where Keck Observatory’s unique capabilities comes into play. “Keck Observatory is the one ground-based telescope that was able to do high-quality enough observations of Altjira for our study. All of our other observations were from HST, but those alone were not enough of an observational baseline for our models,” said Nelsen. “The extra points from Keck Observatory made for a better and more statistically robust result giving more credence to the strength of the hierarchical triple orientation of Altjira.
“In this case, its 10-meter mirror, coupled with its laser guide star adaptive optics system, provided small scales on the sky, which is what you need to do this type of work,” added O’Meara.
To conduct this research, scientists gathered a 17-year observational baseline of data from Keck Observatory and Hubble, watching the orbit of the Altjira system’s outer object.
“Over time, we saw the orientation of the outer object’s orbit change, indicating that the inner object was either very elongated or actually two separate objects,” said Darin Ragozzine, also of Brigham Young University, a co-author of the Altjira study.
Currently, there are about 40 identified binary objects in the Kuiper Belt. Now, with two of these systems likely triples, the researchers say it is more likely they are looking not at an oddball, but instead a population of three-body systems, formed by the same circumstances. However, building up that 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 showed that Arrokoth is a contact binary, which for KBOs means that two objects that have moved closer and closer to one another are now touching and/or have merged, often resulting in a peanut shape. Ragozzine describes Altjira as a “cousin” of Arrokoth, a member of the same group of Kuiper Belt objects. They estimate Altjira is 10 times larger than Arrokoth, however, at 124 miles (200 kilometers) wide.
While there is no mission planned to fly by Altjira to get Arrokoth-level detail, Nelsen said there is a different upcoming opportunity for further study of the intriguing system.
Altjira has entered an eclipsing season, where the outer body passes in front of the central body. This will last for the next ten years, giving scientists a great opportunity to learn more about it,” Nelsen said. NASA’s James Webb Space Telescope is also joining in on the study of Altjira as it will check if the components look the same in its upcoming Cycle 3 observations.
About NIRC2
The Near-Infrared Camera, second generation (NIRC2) works in combination
with the Keck II adaptive optics system to obtain very sharp images at
near-infrared wavelengths, achieving spatial resolutions comparable to
or better than those achieved by the Hubble Space Telescope at optical
wavelengths. NIRC2 is probably best known for helping to provide
definitive proof of a central massive black hole at the center of our
galaxy. Astronomers also use NIRC2 to map surface features of solar
system bodies, detect planets orbiting other stars, and study detailed
morphology of distant galaxies.
About W. M. Keck Observatory
The W. M. Keck Observatory telescopes are among the most scientifically
productive on Earth. The two 10-meter optical/infrared telescopes atop
Maunakea on the Island of Hawaii feature a suite of advanced instruments
including imagers, multi-object spectrographs, high-resolution
spectrographs, integral-field spectrometers, and world-leading laser
guide star adaptive optics systems. Some of the data presented herein
were obtained at Keck Observatory, which is a private 501(c) 3
non-profit organization operated as a scientific partnership among the
California Institute of Technology, the University of California, and
the National Aeronautics and Space Administration. The Observatory was
made possible by the generous financial support of the W. M. Keck
Foundation. The authors wish to recognize and acknowledge the very
significant cultural role and reverence that the summit of Maunakea has
always had within the Native Hawaiian community. We are most fortunate
to have the opportunity to conduct observations from this mountain. For
more information, visit: www.keckobservatory.org.
This artist’s concept depicts one of the possible scenarios for the 148780 Altjira system in the solar system’s Kuiper Belt. It is likely a hierarchical triple formation, in which two very close companions are orbited by a third member at a greater distance. NASA, ESA, Joseph Olmsted (STScI).
This artist’s concept depicts one of the possible scenarios for the 148780 Altjira system in the solar system’s Kuiper Belt. It is likely a hierarchical triple formation, in which two very close companions are orbited by a third member at a greater distance. NASA, ESA, Joseph Olmsted (STScI).
