Artist’s impression, not an encounter photograph. ESO/M. Kornmesser. Asteroid: T. Santana-Ros et al. Hayabusa2 model: SuperTKG (CC-BY-SA). Unchanged artwork; ESO reuse terms.
A rock barely eleven metres wide is waiting for a spacecraft to visit. It spins once every 5.35 minutes, and its motion has raised a deceptively simple question: what’s giving it an extra push?
The asteroid is 1998 KY26, Japan’s Hayabusa2 spacecraft’s planned destination in 2031. A new thermal study posted on November 6 challenges the idea that buried ice can keep supplying gas that nudges it along.
The ice theory runs into a heat problem
Korbin Hansen and Masatoshi Hirabayashi tested thirteen sets of thermal assumptions. Their models put temperatures throughout the asteroid above the level at which exposed ice can remain stable in a vacuum. They conclude that water would escape too quickly for buried ice to last under its present conditions.
That’s an argument against calling this particular object a “dark comet”: a body whose movement suggests comet-like activity without a visible cloud of material. It isn’t a photograph of the interior, and the study doesn’t turn the asteroid into an artificial object.
There are other ordinary mechanisms to investigate. The paper notes earlier work suggesting that sunlight pressure and the uneven release of absorbed heat could account for the measured acceleration. A push beyond gravity isn’t automatically a push beyond physics.
A destination that shrank
KY26 had already complicated the mission plans. Observations announced by the European Southern Observatory in September 2025 revised its estimated width from roughly thirty metres to eleven, while cutting its rotation period approximately in half.
ESO’s researchers used large ground-based telescopes and earlier radar measurements to work out the revised dimensions. The surface appears bright, and the object may be a solid piece of rock, although a loosely assembled structure wasn’t completely excluded.
That leaves a spacecraft trying to approach a destination not dramatically larger than itself. The illustration makes the contrast with its previous target, the roughly 900-metre asteroid Ryugu, especially clear. These are model-based illustrations, not close-up photographs of KY26.
The spacecraft is already on its second assignment
JAXA’s mission record supplies the longer story. Hayabusa2 reached Ryugu in 2018, collected material during two touchdowns in 2019 and delivered its sample capsule to Earth in December 2020. The spacecraft itself kept going.
Its extended journey includes the Torifune flyby completed in 2026 and Earth swing-bys planned for 2027 and 2028, before the KY26 rendezvous. JAXA wants to learn how to operate around an exceptionally small, fast-spinning body, not just collect another distant point of light.
The new thermal calculations narrow one explanation before that visit. Getting close could reveal what the tiny target actually looks like and how it behaves. For now, the interesting mystery is specific: how this little rock responds to sunlight, heat and space, with a spacecraft on the way to take a much better look.
Read next
The asteroid behind Arecibo’s ‘cosmic disc’ story
Another asteroid story where the measurement matters: why 2003 UX34’s radar shapes were misread. A different object and question, not an explanation of KY26.
Leave a Reply