Asteroid Nysa's rare three-lobed structure challenges formation models

Named after the mythical valley where Dionysus was raised in secret, asteroid 44 Nysa resides in the asteroid belt between Mars and Jupiter. Recent Hubble Space Telescope observations classified it as the largest and brightest known E-type asteroid, composed of unusually bright, enstatite-rich material akin to some rare Earth meteorites.

Models of its brightness variations suggested a lopsided, elongated shape. However, Kate Minker's team at Lowell Observatory captured the most detailed observations of 44 Nysa yet, revealing a striking three-lobed structure. Utilizing the SHARK-VIS instrument on the Large Binocular Telescope in Arizona and the SPHERE/ZIMPOL on the Very Large Telescope in Chile, both employing adaptive optics to counteract atmospheric distortion, the team obtained the sharpest visible-light images ever taken of Nysa.

Previous models had predicted a simple elongated shape, but these new observations exposed distinct valleys, carving the asteroid into separate sections and other unusual markings. Additionally, the researchers detected a faint, accompanying object orbiting Nysa, indicating a binary system: a small moon circling a peculiar central body.

This central body's unique three-lobed form could either signify a contact trinary, where three rocks orbit so close they touch, or represent a single asteroid with an unprecedented irregular shape. The team's findings challenge current asteroid formation and structural stability models, potentially inspiring a reevaluation of how asteroids evolve.

If Nysa is indeed a contact trinary, it suggests that multi-body coalescences may be more frequent and stable than previously thought. Conversely, if it is a single object, it implies that asteroids can maintain stability in far more unusual configurations than current models assume. The researchers aim to further investigate these possibilities to gain deeper insights into the building blocks of our solar system.