Asteroid Nysa’s rare three-lobed structure challenges formation models
Named for the mythical valley where the god Dionysus was raised in secret by nymphs, the asteroid 44 Nysa inhabits the asteroid belt between Mars and Jupiter. Through observations by the Hubble Space ...
Named for the mythical valley where the god Dionysus was raised in secret by nymphs, the asteroid 44 Nysa inhabits the asteroid belt between Mars and Jupiter. Through observations by the Hubble Space Telescope, astronomers have determined it to be the largest and brightest known member of a rare category of asteroids called "E-types," made of unusually bright, enstatite-rich material similar to some rare meteorites found on Earth. Separately, models built from how its brightness flickers as it spins hinted it might have an elongated, lopsided shape, often seen in large asteroid pairs.
In a new article posted to the arXiv preprint server, a team led by Kate Minker of Lowell Observatory has made some of the clearest observations of 44 Nysa to date, revealing a three-lobed structure even stranger than astronomers anticipated.
Fresh observations
Minker's team made its observations using the SHARK-VIS instrument on the Large Binocular Telescope in Arizona and SPHERE/ZIMPOL on the Very Large Telescope in Chile. Both instruments use adaptive optics, which cancels out the blurring caused by Earth's atmosphere. This allowed the team to capture the sharpest visible-light images of Nysa ever taken—sharp enough to make out individual features on its surface.
Where previous models had predicted that Nysa has a simple, elongated shape, these new observations showed distinct valleys carving the asteroid into separate sections, along with other unusual markings. In the leftover data after processing the images, the researchers also spotted a faint, small companion object orbiting Nysa.
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2026-03-21 SHARK-VIS observations of Nysa, color scale shows relative brightness and is tuned to enhance the visibility of shadows, indicative of surface indentations or valleys in the sky-East (upper panel) and -West (lower panel) facing geometries. Credit: arXiv (2026). DOI: 10.48550/arxiv.2607.25786 -
Residuals of R-band images of the Nysa system on 2026-02-15 after processing with the blind deconvolution method. The position of the satellite is marked with a pink arrow. Credit: arXiv (2026). DOI: 10.48550/arxiv.2607.25786
A subtle companion
Based on this evidence, the researchers concluded that Nysa is a binary system: a small moon circling a much stranger central body. This central body appears to have three lobes, making it the first object of its kind ever identified in the asteroid belt.
For Minker's team, this could have two possible explanations: Either Nysa is a "contact trinary," where three separate rocks are orbiting so closely together that they touch, or it is a single, solid object with an extraordinarily irregular shape, unlike anything astronomers have documented before.
The team's intriguing findings could now inspire a rethink of how asteroids form. If Nysa is really a contact trinary, it would suggest that multi-body coalescences may be more common and more stable than astronomers had expected. If it is instead just a single body, it would suggest that asteroids can hold together in far stranger configurations than current formation models assume. By probing these possibilities in more detail, Minker's team ultimately hopes that astronomers could gain deeper insights into the building blocks of our solar system.
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Publication details
Kate Minker et al, Unmasking (44) Nysa: Evidence for a trilobate structure, arXiv (2026). DOI: 10.48550/arxiv.2607.25786
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