Asteroid (44) Nysa reveals a three-lobed shape and has a mini moon
An international team of astronomers has uncovered striking new evidence that asteroid (44) Nysa, one of the brightest and largest asteroids with an enstatite-like (E-type) surface composition in the main belt, possesses an extraordinary three-lobed structure and is accompanied by a small moon. The discovery, based on high-resolution adaptive optics imaging and high precision photometry from some of the world’s most advanced telescopes, provides a rare glimpse into the complex history of one of the solar system’s most enigmatic asteroids.
The findings, presented in the study “Unmasking (44) Nysa: Evidence for a Trilobate Structure,” reveal that Nysa is unlike any asteroids previously observed. For more than a century, astronomers have studied Nysa, whose unusual brightness and composition made it a compelling target for investigation. Earlier observations hinted at an elongated or potentially bilobate shape, but the asteroid’s true form remained elusive.
Using the Italian SHARK-VIS instrument on the Large Binocular Telescope in Arizona and the SPHERE/ZIMPOL instrument on the European Southern Observatory’s Very Large Telescope in Chile, researchers obtained the highest-resolution images ever acquired of Nysa. These unique datasets revealed multiple large surface features, including two prominent valleys that appear to wrap around the asteroid’s circumference. The team interprets these features as “colli” or neck-like connections between separate lobes.
“The images reveal a remarkably unusual object,” said lead author Kate Minker of Lowell Observatory. “The most likely explanation is that Nysa is either a contact trinary, consisting of three connected components, or an extremely irregular coherent body unlike anything we’ve previously observed.”
“We used the ULiège TRAPPIST telescopes to monitor the asteroids during several nights with high precision photometry to build dense light curves in order to determine the asteroids rotation period and help constrain its shape model”, explains Emmanuel Jehin, FNRS Research Director and head of the COMETA group at the STAR Institute of the University of Liège. The TRAPPIST telescopes are used almost every night to observe asteroids and comets of the solar system.
Minker adds, “These observations likely represent the closest competition to spacecraft-quality imaging ever achieved from the ground, made possible by an exceptional combination of advanced instrumentation and sophisticated data-reduction techniques.”
The study also reports the detection of a previously unknown moon, temporarily designated S/2026 (44) 1. The satellite was independently identified in observations obtained during two separate observing campaigns. Researchers estimate the moon measures roughly one kilometer in diameter and orbits at least 170 kilometers from the 75-kilometer-diameter primary asteroid.
“We borrowed a specialized technique from another field of astronomy, known as ‘high-contrast imaging’, to detect the small moon whose faint light was overwhelmed by the intense brightness of the primary asteroid” says Gianluca Li Causi of the SHARK-VIS team at the Italian National Institute for Astrophysics (INAF).
Future observations of the newly discovered satellite will allow researchers to determine Nysa’s mass and density more precisely, helping to distinguish between competing theories for the asteroid’s remarkable structure.
The discovery provides an important clue to Nysa’s formation and evolution. Scientists suggest the unusual structure may have formed through low-velocity reaccumulation of fragments from an ancient collision, possibly before Nysa reached its current location in the asteroid belt. Another possibility is that Nysa represents the remnants of a dramatic hit-and-run collision involving a larger parent body.
If confirmed, Nysa would join a growing class of solar system objects whose distinctive shapes preserve evidence of ancient collisions and mergers dating back billions of years, offering scientists a unique window into the early history of the solar system.
© Kate Minker
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© Kate Minker
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© Kate Minker
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© Kate Minker
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Asteroid (44) Nysa image with the SHARK-VIS instrument of the Large Binocular Telescope. Left column shows observations from 15 February 2026 UTC, the right column shows observations from 21 March 2026 UTC. Upper row is optimized to display shadows on the asteroid’s surface, the lower row is optimized for the visibility of Nysa’s tiny moon, S/2026 (44) 1.
Scientific reference
Kate Minker, Anthony Berdeu, Gianluca Li Causi, Josef Hanuš, Michaël Marsset, Al Conrad, Fernando Pedichini, Simone Antoniucci, Piero Vaccari, Nick Moskovitz, Benoit Carry, Tom Polakis, Marin Ferrais, Emmanuël Jehin, Roberto Bonamico, Rhiannon Hicks, Daejhanae Smith, M. Amine Miftah, Ester Marini
"Unmasking (44) Nysa: Evidence for a trilobate structure"
