Adaptive-optics observations obtained with the Large Binocular Telescope's SHARK-VIS instrument reveal the unusual shape of asteroid (44) Nysa. The asteroid appears highly concave and may consist of three connected lobes, making it a potential contact-binary object. Continuous observations on Feb. 15 provided the most detailed view of Nysa to date. The asteroid's tiny moon, S/2026 (44) 1 is marked with a pink arrow.
Image Credit: Kate Minker et al.
Scientific Frontline: Extended "At a Glance" Summary: Asteroid (44) Nysa
The Core Concept: Asteroid (44) Nysa is a massive, extraordinarily bright E-type asteroid located in the main belt between Mars and Jupiter that possesses a rare three-lobed structure and is accompanied by a newly discovered small moon.
Key Distinction/Mechanism: Unlike conventional, roughly spherical or simply elongated asteroids, high-resolution imaging reveals that Nysa is either a contact trinary—consisting of three connected components—or an extremely irregular coherent body. It features two prominent valleys that function as "colli," or neck-like connections, between its distinct lobes.
Origin/History: Although first discovered and named in 1857, Nysa's true shape remained an elusive mystery for over a century. In 2026, astronomers finally resolved its trilobate structure using the Large Binocular Telescope's SHARK-VIS instrument and the European Southern Observatory's SPHERE/ZIMPOL instrument.
Major Frameworks/Components:
- E-type (Enstatite-like) Composition: The asteroid's bright surface matches the light-reflecting signature of enstatite, an iron-free mineral, suggesting it originally formed close to the sun.
- Trilobate Structure: Nysa consists of three distinct lobes, which scientists hypothesize formed through the low-velocity re-accumulation of fragments following an ancient, dramatic collision.
- Adaptive Optics: Advanced technologies like the SHARK-VIS instrument capture "fast imaging" footage that freezes optical distortions caused by atmospheric turbulence, producing unprecedented image sharpness.
- Satellite S/2026 (44) 1: A newly detected moon measuring roughly 0.6 miles (one kilometer) in diameter, orbiting at least 100 miles (170 kilometers) from the 46-mile-wide (75-kilometer) primary asteroid.
Branch of Science: Astronomy, Planetary Science, and Astrophysics.
Future Application: By tracking the orbital velocity and periodicity of Nysa's satellite, astronomers will be able to precisely calculate the primary asteroid's mass and density, which will help validate competing theories regarding the structural evolution of complex planetary bodies.
Why It Matters: Because Nysa's enstatite-rich composition shares chemical traits with the building blocks of Earth, understanding its unique structure and collision history provides a vital window into the formative processes and dynamic environments of the early inner solar system.
An international team of astronomers has uncovered striking new evidence that (44) Nysa, one of the brightest and largest known asteroids populating the main belt between Mars and Jupiter, possesses an extraordinary three-lobed structure and is accompanied by a small moon.
The discovery provides a rare glimpse into the complex history of one of the solar system's most enigmatic asteroids. The findings are based on high-resolution adaptive optics imaging from some of the world's most advanced telescopes, including the Large Binocular Telescope on Mount Graham in southeastern Arizona, which is managed by the University of Arizona. The LBT observations were made possible by a high-contrast optical imaging instrument, dubbed SHARK-VIS, and a new adaptive optics system, which compensates for the blurring induced by atmospheric turbulence.
Nysa belongs to a population of asteroids known as enstatite-like, or E-type, asteroids, referring to their surface composition, which makes them appear bright and matches the light-reflecting signature of the iron-free mineral enstatite. Because their composition suggests they formed close to the sun and share chemical traits with the building blocks of Earth, E-type asteroids may preserve a record of the enstatite-rich inner solar system. Therefore, understanding Nysa's origin may shed light on processes that operated during the earliest phases of solar system formation.
The findings, presented in the study "Unmasking (44) Nysa: Evidence for a Trilobate Structure," reveal that Nysa is unlike any asteroid 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 LBT with SHARK-VIS 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 observations, combined with specially developed image processing techniques, 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 in Flagstaff, Arizona. "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."
SHARK-VIS allows the LBT to fully take advantage of the telescope's outstanding adaptive optics system. The instrument houses a fast, ultralow-noise camera that allows it to observe the sky in "fast imaging" mode, capturing slow-motion footage that freezes the optical distortions caused by atmospheric turbulence, and to post-process data to an unprecedented sharpness.
To better understand the asteroid's shape, scientists combined the adaptive optics images with extensive photometric observations from observatories around the world. They generated a detailed three-dimensional model of Nysa. The reconstructed shape strongly supports the presence of three distinct lobes connected by narrow neck regions.
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.
"These new images appear consistent with several earlier clues that Nysa is not a conventional asteroid," said Al Conrad, associate staff scientist at the Large Binocular Telescope Observatory and a coauthor of the paper. "For the first time, we can directly investigate whether those clues point to a deeply indented body or to a true multilobed structure."
The images obtained with LBT and SHARK-VIS are sharper than those of the Hubble Space Telescope, thanks to LBT's primary mirror spanning 27 feet—three times the diameter of Hubble—and its adaptive optics system, which uses an array of 672 ultrafast, computer-controlled actuators that subtly deform the secondary mirror to compensate for blurring by atmospheric turbulence.
The study also reports the detection of a previously unknown moon, temporarily designated S/2026 (44) 1. Researchers estimate the moon measures just over 0.5 miles (1 km) in diameter and orbits at least 100 miles (170 km) from the primary asteroid, whose diameter spans about 46 miles (75 km).
The team hopes that future observations of the newly discovered satellite—such as the velocity and periodicity of its orbit—will make it possible to determine Nysa's mass and density more precisely, helping to distinguish between competing theories for the asteroid's remarkable structure.
"Our technique is a bit like figuring out Christmas presents while they're wrapped," Conrad said. "You may be wondering whether the box you're eyeing contains a clock radio or a bag of socks, so to get a clue of which it is, you pick it up and get a feel for the weight. In a way, you intuitively are measuring density to find out the composition."
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.
When asteroid (44) Nysa was discovered and named in 1857, nobody knew it would puzzle astronomers for almost two centuries. Still, Conrad pointed out, the name is a fitting reference to Nysa, the land where, according to Greek mythology, nymphs raised Dionysus, a god associated with masks and theater.
"In this paper, we're finally unmasking the asteroid's true nature, long after it was discovered," he said.
Published in journal: arXiv
Title: Unmasking (44) Nysa: Evidence for a trilobate structure
Authors: 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, and Ester Marini
Source/Credit: University of Arizona | Lowell Observatory and Daniel Stolte
Edited by: Scientific Frontline
Reference Number: astr073026_01
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