Astronomers Reveal 80-Km Asteroid Nysa Has 3 Lobes, Defying Known Bilobed Shapes

Q: What secret does Nysa's newly discovered tiny moon hold about the true internal structure of this bizarre asteroid?

Nysa’s tiny newly detected moon could reveal whether the asteroid is really a loosely bound “contact trinary” — three merged pieces — or instead a single, more coherent rock that was severely deformed by impacts. The key is the moon’s orbit. If astronomers confirm the satellite and measure its period and speed around Nysa, they can calculate Nysa’s mass. Combined with the asteroid’s newly modeled size and volume, that gives its bulk density. Density is the best clue to internal structure: a low density would point to a porous rubble-pile body made of reaccumulated fragments, while a higher density would suggest a stronger, more intact interior. That matters because the new images show a bizarre three-lobed shape with two narrow necks, something not previously seen so clearly in a main-belt asteroid. Surface images alone cannot tell whether those lobes are separate pieces gently stuck together or one battered body that only looks that way. The moon can provide the missing test. Researchers say this is why the satellite, provisionally named S/2026 (44) 1, is so important. At only about 1 kilometer wide and orbiting roughly 170 to 180 kilometers from Nysa, it acts like a natural probe of the asteroid’s gravity. In effect, the moon may expose Nysa’s hidden interior — and settle the debate over how this unusual asteroid formed.

3 articles · Updated · Futura · Aug 10

New high-resolution observations show (44) Nysa—an asteroid in the main belt between Mars and Jupiter—has three distinct lobes linked by two narrow necks, a structure astronomers say has not been seen before.
Images from ESO’s Very Large Telescope and the Large Binocular Telescope, aided by adaptive optics, finally resolved Nysa’s shape after more than 160 years of uncertainty; the asteroid is about 80 kilometers wide.
Researchers propose two explanations: Nysa was heavily deformed from a single body by collisions, or three smaller objects merged and left necks where their surfaces met.
The finding challenges the usual interpretation of necked asteroids as two-lobed objects and could refine models of asteroid collisions, family formation and the early building blocks of planets.