Asteroid 1998 KY26 is just 11 metres across, completes one rotation every 5 minutes and 21 seconds — and is accelerating through space in a way astronomers still cannot fully explain. A new study published in the scientific journal Icarus has ruled out one of the leading explanations for this behaviour: that the object is a "dark comet" disguised as an asteroid.
A small, fast and mysterious object
Discovered on 28 May 1998 by the University of Arizona's Spacewatch project, 1998 KY26 is a near-Earth Apollo asteroid with a 1.36-year orbit around the Sun. In 2023, a study led by Darryl Seligman detected significant non-gravitational acceleration — including perpendicular to the plane of its orbit — too large to be explained by the Yarkovsky effect alone with the data available at the time. The team proposed that the object could be a "dark comet": a rocky body that releases gas invisibly, without producing the typical comet tail.
What the new study says
The new study, by aerospace engineers Korbin Hansen and Masatoshi Hirabayashi of the Georgia Institute of Technology, tested that idea with a thermal model of the object. The result was clear: even the coldest regions of the asteroid average at least 212 kelvin (-61 °C) over the course of its orbit. For buried water ice to survive for long periods, temperatures would need to stay below 145 kelvin (-128 °C). According to the calculations, if ice made up 1% of the object's mass, it would disappear in just over 2,000 years — and if it were driving the observed acceleration, it would be gone in only 62 years. The authors conclude that 1998 KY26 is a "dehydrated" asteroid that lost its water long ago.
With the dark-comet hypothesis weakened, the remaining candidates are solar radiation pressure and thermal emission — the so-called Yarkovsky effect, in which the asteroid absorbs sunlight and re-emits it as heat unevenly, receiving a small, constant push. There is an important caveat: ice may still exist on the object, since it is unclear how long it has occupied its current orbit. In addition, a 2025 reanalysis led by Davide Farnocchia concluded that the Yarkovsky effect, calculated with the asteroid's updated properties, fully explains the observed acceleration.
A far more speculative idea is also circulating: Harvard astronomer Avi Loeb has suggested that 1998 KY26 could be an abandoned Soviet spacecraft, launched almost 40 years ago. This is speculation: the Icarus study does not address the idea, and there is no evidence to support it.
The answer will come in 2031
The definitive answer may come from Hayabusa2, the Japan Aerospace Exploration Agency (JAXA) spacecraft. It collected samples from asteroid Ryugu in 2019 and delivered them to Earth in 2020; since then it has continued on an extended mission and flew by asteroid Torifune on 5 July 2026. The next step is an Earth swing-by in December 2027, before the rendezvous with 1998 KY26 in July 2031 — when it will become the smallest asteroid ever visited by a spacecraft. Before that, in 2028, the object will make another close approach to Earth and may be observed by the James Webb Space Telescope. The asteroid poses no threat to Earth: if it were on a collision course, it would most likely explode in the upper atmosphere.
Image credit: shape model of asteroid 1998 KY26, by Toni Santana-Ros et al. (2025), via Wikimedia Commons.
Sources: ScienceAlert; IFLScience; Universe Magazine; Wikipedia (1998 KY26); JAXA/ISAS — Hayabusa2; Eos.
Transparency: this article was produced with the assistance of artificial intelligence, based on cross-checking public posts and the online sources listed above. We recommend consulting the original sources to verify the information.
By Muse
