A Mysterious Asteroid Is Accelerating in Space, And We're Running Out of Explanations
Simulations indicate the near-Earth asteroid 1998 KY26 is too warm to retain water ice, undermining the leading "dark comet" hypothesis that sublimating gas propels its unexplained acceleration. Japan's Hayabusa2 spacecraft is en route for a 2031 rendezvous to directly study the 30-meter object. With the ice mechanism now unlikely, astronomers lack a confirmed explanation for the non-gravitational forces altering its orbit.
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- ✓ Asteroid 1998 KY26 exhibits non-gravitational acceleration that astronomers have struggled to explain.
- ✓ Japan's Hayabusa2 spacecraft is scheduled to arrive at 1998 KY26 in 2031 for a close-up investigation.
- ✓ A new heat model finds 1998 KY26 is too warm to preserve water ice, casting doubt on the dark-comet hypothesis.
What changed
A new thermal model published in November 2026 shows 1998 KY26's surface temperature prevents ice preservation, challenging the primary explanation for its anomalous acceleration.
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New Heat Model Rules Out Ice-Driven Acceleration for Asteroid 1998 KY26
Simulations indicate the near-Earth asteroid 1998 KY26 is too warm to retain water ice, undermining the leading "dark comet" hypothesis that sublimating gas propels its unexplained acceleration. Japan's Hayabusa2 spacecraft is en route for a 2031 rendezvous to directly study the 30-meter object. With the ice mechanism now unlikely, astronomers lack a confirmed explanation for the non-gravitational forces altering its orbit.
Why it matters
Discovered in 1998, KY26 is a fast-spinning, tiny asteroid whose trajectory cannot be explained by gravity alone. The dark-comet theory proposed that hidden ice venting gas provided thrust, similar to a comet but without a visible tail. Hayabusa2, after returning samples from Ryugu, was retargeted to KY26 specifically to test this idea. The new thermal model forces a re-evaluation before the spacecraft arrives.
What is confirmed
- Asteroid 1998 KY26 exhibits non-gravitational acceleration that astronomers have struggled to explain.
- Japan's Hayabusa2 spacecraft is scheduled to arrive at 1998 KY26 in 2031 for a close-up investigation.
- A new heat model finds 1998 KY26 is too warm to preserve water ice, casting doubt on the dark-comet hypothesis.
Still unconfirmed
- The acceleration may be caused by the Yarkovsky effect or other thermal recoil forces rather than outgassing.
What to watch next
- Publication of the peer-reviewed thermal modeling study detailing temperature constraints.
- Analysis of alternative acceleration mechanisms such as the Yarkovsky effect or solar radiation pressure.
- Hayabusa2 trajectory corrections and observation plans ahead of the 2031 encounter.
confidence 88%Sources used for this update (6)
- ScienceAlert — A Mysterious Asteroid Is Accelerating in Space, And We're Running Out of Explanations
- ua.news — Modeling showed that 1998 KY26 is too warm to preserve ice — ScienceAlert
- Around Prague — Asteroid 1998 KY26 Too Warm to Be a Dark Comet, New Heat Model Finds
- JournalArta — 1998 KY26: Scientists Question Dark-Comet Explanation for Acceleration
- Phys.org — Simulations cast doubt on unusual asteroid's 'dark comet' status
- gizmodo.com — A Japanese Spacecraft Is Chasing a Space Rock That Defies Gravity. The Best Explanation Just Took a Hit
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