Every asteroid known to have a distinct “neck,” the narrow waist that forms where two smaller bodies have come to rest against each other, has had exactly two lobes. Itokawa has two. Kleopatra, the dog-bone-shaped metal asteroid with its own pair of moons, has two. So does the nucleus of comet 67P/Churyumov-Gerasimenko. It is a pattern solid enough that planetary scientists built their formation models around it: two fragments, one contact point, one shape.
New images of asteroid (44) Nysa, a 75-kilometre body in the main asteroid belt, break that pattern. An international team led by Kate Minker of Lowell Observatory has resolved a second waist alongside the first, dividing Nysa into three connected lobes, joined by narrow “colli,” the term researchers use for these connecting necks. In their paper, posted to the preprint server arXiv in late July and titled “Unmasking (44) Nysa: Evidence for a Trilobate Structure,” the team describes what they believe is the first confirmed three-lobed asteroid ever imaged.
How the images were taken
The observations were not made by a spacecraft. They came from two ground-based instruments built specifically to push past what a telescope on Earth’s surface is normally capable of resolving: SHARK-VIS, mounted on the Large Binocular Telescope in Arizona, and SPHERE/ZIMPOL, on the European Southern Observatory’s Very Large Telescope in Chile. Both use adaptive optics to correct for the blurring effect of the atmosphere in real time, essentially unwinding the twinkle that makes stars shimmer to the naked eye.
Minker and her collaborators, drawing on observing runs from mid-February and late March this year, describe the results as “the closest competition to spacecraft-quality imaging ever achieved from the ground.” That is a meaningful claim on its own. Most of what is known about asteroid shapes in this kind of detail has come from missions that flew past or orbited their targets directly, such as NASA’s Lucy or the Japanese Hayabusa2, a point the University of Arizona’s writeup of the finding makes explicitly. Getting comparable resolution from telescopes on Earth, aimed at a body more than 200 million kilometres away, is the harder feat, and the one that makes an unusual finding like this easier to trust.
What the images actually show
Nysa’s surface, in the new data, is marked by two prominent valleys that wrap most of the way around its circumference, effectively cutting the asteroid into three connected sections. Beyond the shape itself, the team also identified something else nobody had catalogued around Nysa before: a small moon, provisionally designated S/2026 (44) 1, roughly a kilometre across, orbiting at a distance of at least 170 kilometres from the primary body.
None of this was expected. Nysa has been studied since its discovery in 1857 and is one of the brighter, more reflective bodies in the main belt, but nothing in its earlier light-curve data (the pattern of brightening and dimming as it rotates) hinted at three lobes rather than two, or at a satellite orbiting it. The moon and the trilobate structure both emerged only once the imaging resolution improved enough to separate features that had previously blurred together into a single elongated blob.
Whole, or built from pieces
The open question, and the one the paper is careful not to resolve, is how Nysa came to look like this. Minker’s team lays out two competing explanations. The first is that Nysa is a contact trinary, formed when fragments from an earlier collision re-accumulated at low relative speeds, possibly before Nysa reached its current place in the belt, rather than through one violent event. The second is that Nysa is what remains of a larger parent body that suffered a glancing, high-speed “hit-and-run” collision, one that reshaped it into its current three-part form without fully breaking it apart.
The paper does not adjudicate between these two scenarios, and on the evidence available, it probably cannot. Both processes have been proposed before for two-lobed contact binaries; distinguishing between them typically requires more than shape alone; it requires data on internal density and composition that ground-based imaging cannot provide. Whether Nysa was born this way or assembled from three separate collisions is, at this point, an open question the available data cannot settle.
A well-known object, mostly unread
Part of what makes this finding land is that Nysa is not an obscure object. It is one of the largest and most reflective bodies in the main belt, bright enough that amateur observers with modest equipment can pick it out during favourable oppositions, and it has been tracked since the mid-nineteenth century. Its size and brightness made it a natural early target once ground-based imaging improved enough to attempt this kind of shape reconstruction, but that same long observation history is also what makes the finding notable: a body this well catalogued still had two features, a hidden second neck and an orbiting moon, that nobody had confirmed until this year.
Earlier surveys were working at the limit of what their instruments could distinguish. Light-curve data can reveal that an asteroid is elongated or irregular, but it cannot easily separate an object with one neck from one with two unless the geometry of the observation happens to catch both waists edge-on at once. Nysa’s case suggests that gap between “irregular shape” and “precise shape” may be wider, for some bodies, than the field had assumed.
Why a third lobe matters
The reason a single unusual asteroid draws attention beyond its own case is that formation models for small bodies in the solar system have largely been built and tested on the two-lobed pattern. Every confirmed contact binary until now has fit that template, which made it a reasonable working assumption that whatever process builds these bodies naturally produces two-part shapes and stops there. A body with three connected lobes does not necessarily overturn that assumption, but it does mean the model needs to accommodate at least one exception, and researchers will now be looking more closely at other apparently two-lobed asteroids to see whether any of them have a second, more subtle neck that has simply gone unresolved until better instruments came along.
Nysa’s own history, at 169 years of observation, is a reminder of how much detail depends on the sharpness of the instrument doing the looking. It took resolution rivalling a spacecraft flyby, achieved from two telescopes on two continents, to reveal a shape that had been sitting in plain sight the entire time.