Keck Observatory helps identify possible triple system in Kuiper Belt

A team of researchers using data from W. M. Keck Observatory on Maunakea, Hawaiʻi Island, and NASA’s Hubble Space Telescope has likely discovered a stable trio of icy space rocks in the solar system’s Kuiper Belt. If confirmed, the 148780 Altjira system would be the second known three-body system in the region, suggesting similar triples may exist and supporting a theory about the solar system’s history and early formation of Kuiper Belt objects.

The study, led by Brigham Young University, was published in “The Planetary Science Journal” on Tuesday.

“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.

Kuiper Belt objects are icy remnants from the early solar system, found beyond Neptune. More than 3,000 have been cataloged since their discovery in 1992, with scientists estimating hundreds of thousands more over 10 miles in diameter.

Using Keck Observatory’s NIRC2 narrow-field infrared camera, researchers analyzed Altjira from 2006 to 2020. Their findings suggest that the system’s inner body consists of two objects too close together to be distinguished with Hubble’s imaging. This discovery supports a theory that Kuiper Belt objects formed through gravitational collapse rather than collisions.

“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.

Altjira is located 3.7 billion miles from Earth. Its outer object orbits at a distance of 4,700 miles, and changes in that orbit led researchers to conclude the inner body is two objects rather than one.

“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,” Nelsen said.

This is where the Keck Observatory played a crucial role: “Keck Observatory is the one ground-based telescope that was able to do high-quality enough observations of Altjira for our study,” Nelsen said.

Only about 40 binary systems have been identified in the Kuiper Belt. With two now appearing to be triples, researchers believe they may be seeing a broader pattern rather than isolated anomalies.

NASA’s New Horizons mission previously explored Kuiper Belt objects Pluto and Arrokoth, the latter being a contact binary. Altjira is considered a “cousin” of Arrokoth but is significantly larger, at 124 miles wide.

Future observations could provide more insight, as Altjira has entered a 10-year eclipsing season, allowing scientists to study how its objects pass in front of each other. 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.