Astronomers Discover Rare Three-Lobed Structure on Asteroid (44) Nysa

Unprecedented Trilobate Structure Discovered on Asteroid (44) Nysa

The observations were captured using the SPHERE instrument on the European Southern Observatory’s (ESO) Very Large Telescope in Chile and the SHARK-VIS instrument on the Arizona (LBT). Both facilities utilized advanced adaptive optics systems to correct atmospheric blur. The LBT achieves high-resolution imaging using a primary mirror spanning 27 feet—three times the diameter of the Hubble Space Telescope—paired with an array of 672 ultra-fast, computer-controlled actuators that deform the secondary mirror to counteract atmospheric turbulence. Continuous observations on February 15 provided detailed data on the system, which was also imaged in March.

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The images reveal a remarkably unusual object, said Dr. Kate Minker, an astronomer at Lowell Observatory and lead author of the study. 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.

Asteroid (44) Nysa Revealed to Have Rare Three-Headed Structure

Al Conrad, associate staff scientist at the Large Binocular Telescope Observatory and a co-author on the paper, noted that the new images align with earlier clues regarding the body. For the first time, we can directly investigate whether those clues point to a deeply indented body or to a true multi-lobed structure, Conrad said.

Composition and the Search for Origins

Nysa is one of the brightest and largest asteroids located in the main belt between Mars and Jupiter, a target of scientific study for more than a century. E-type asteroids like Nysa feature an enstatite-like surface composition rich in enstatite, a magnesium-rich silicate mineral associated with meteorites such as aubrites and enstatite chondrites. Because these chemical traits suggest they formed close to the Sun, E-type asteroids are thought to originate from the same feedstocks as terrestrial planets and may preserve a record of the inner Solar System’s earliest phases.

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Furthermore, Nysa is exceptionally dense at more than 5 grams per cubic centimeter, indicating a composition of mixed rock and metal. Researchers point out that both strong materials and strong minerals would be necessary to support such an unusual shape against self-gravity, whereas weaker rubble-pile asteroids typically pull themselves into more spherical forms over time.

If all of Nysa’s mass were compressed into a sphere, it would measure 75 kilometers across, placing it among the larger bodies evaluated in asteroid studies—surpassed in that group only by Lutetia, Vesta, and Ceres. Despite its strength, explaining how the asteroid acquired its distinct arch shape remains a challenge for researchers.

Formation Hypotheses and Companion Moon

The research team has proposed two primary formation mechanisms for Nysa’s odd morphology, though neither is considered entirely satisfactory:

• Impact Deformation: Nysa may be the solid remnant of a single parent body heavily deformed through repeated collisions with smaller objects, though it remains difficult to explain how two narrow necks could be carved via impact whittling.
• Contact Trinary: The asteroid may be a composite of three separate objects whose orbits decayed until they touched, forming necks at the points of contact. However, maintaining the stability of an arch shape against self-gravity without the lobes closing the hollow space remains problematic.

To account for these structural challenges, researchers suggest the asteroid may have experienced multiple disruptions, such as an impactor knocking loose one or more lobes that subsequently reconnected while the shape continued to evolve.

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In addition to resolving Nysa’s shape, the observations uncovered a previously unknown, kilometer-sized companion moon orbiting at a distance of about 180 kilometers from Nysa’s center of mass. The moon has been temporarily designated as S/2026 (44) 1. Astronomers note that further research is required to clarify the true history and evolutionary path of this unusual system.