What shape is an asteroid? For (44) Nysa, the honest answer until now has been that nobody knew. It is one of the brightest and largest E-type asteroids in the main belt, a class with a surface rich in enstatite, and its ...
An international team led by Kate Minker at Lowell Observatory has now brought two of the world's heaviest instruments to bear on it: SHARK-VIS on the Large Binocular Telescope in Arizona, and SPHERE/ZIMPOL on the Very Large Telescope in Chile. With adaptive optics correcting for the churn of our atmosphere and purpose-built processing to sharpen what came back, they have produced the finest images of Nysa ever obtained. Minker describes them as close to spacecraft-quality, achieved without ever leaving the ground.
What those images show is two prominent valleys wrapping around the asteroid's circumference. The team read them as necks, the pinched joints where separate bodies have come to rest against one another: Three lobes, gently welded into one.
We have seen this before, but never in triplicate. Comet 67P looks like a rubber duck, and the Kuiper Belt object Arrokoth resembles a flattened snowman. Both are contact binaries, two pieces that drifted together slowly enough to stick rather than shatter. Nysa would be the first contact trinary on the books. The findings are published on the arXiv preprint server.
The team is careful to leave the door open on the formation theory. The alternative reading is that Nysa is simply a single body so deeply battered and indented that it merely resembles three, which would itself be a first—nothing else known looks like that either. Either way, it's peculiar.
Asteroid (44) Nysa imaged with the SHARK-VIS instrument on the Large Binocular Telescope. The tiny moon S/2026 (44) 1, arrowed, was pulled from the asteroid's glare using techniques borrowed from exoplanet hunting. Credit : SHARK-VIS/LBT Observatory
Arrokoth, photographed by New Horizons in 2019 - two bodies that drifted together gently enough to stick rather than shatter. Nysa may be the same trick performed with three. This is a red-blue anaglyph image, view it with 3D glasses and the two lobes separate into real depth. Credit : NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute/National Optical Astronomy Observatory
Asteroid Dinkinesh with its satellite Selam, seen by NASA's Lucy spacecraft in 2023. Small asteroids with moons have turned out to be common and each moon helps us to understand the properties of its parent body. Credit : NASA/Goddard/SwRI/Johns Hopkins APL/NOIRLab