Plate Nº 61 · recorded November 11, 2026
Space & AstronomyReported finding
Simulations weaken the dark-comet case for asteroid 1998 KY26
Across 13 simulations, near-Earth asteroid 1998 KY26 stayed too warm to preserve ice, weakening the idea that escaping water drives its odd acceleration.
By Elena Vasquez3 min read698 words
In brief
- Across 13 simulation runs, no modeled part of 1998 KY26 could preserve ice over the long term.
- Ice would need temperatures below about –128°C (–198°F); the coldest modeled regions averaged –47°C (–53°F) or warmer.
- Even a 1% water inventory would be exhausted in roughly 2,000 years under the model.
- The asteroid measures 11 m (36 ft) and completes a rotation in just under 5.5 minutes.
- Hayabusa2 is due to arrive at 1998 KY26 in 2031.
By Elena Vasquez
Across all 13 simulation runs, even the coldest parts of near-Earth asteroid 1998 KY26 averaged about –47°C (–53°F) or warmer, far too warm to preserve ice for long periods.
A report dated Nov. 10, 2026, presents findings by Korbin Hansen and Masatoshi Hirabayashi of the Georgia Institute of Technology. Their 3D thermal model makes the 11-meter body an unlikely “dark comet” and strengthens the case for sunlight pressure and heat radiation as the cause of its odd acceleration.
What makes 1998 KY26 so unusual?
At just 11 m (36 ft) across, 1998 KY26 ranks among the fastest-spinning asteroids ever found. It completes one rotation in just under five and a half minutes. While orbiting the Sun, it also receives a small but unexpected push out of its orbital plane, the flat path it follows around the Sun.
That motion has prompted a still-theoretical “dark comet” hypothesis. In this proposed model, escaping water gas supplies thrust without producing the glowing cloud and tail of an ordinary comet. The question has been whether the asteroid's interior can stay cold enough to hold ice while that gas escapes.
Other studies have proposed sunlight pressure, combined with heat radiating away from the surface, as an explanation that needs no escaping gas. Reflected-light measurements support that alternative: they suggest 1998 KY26 is a bright, rocky asteroid of a type thought to contain very little water.
In short, the unusual motion is clear, but a gas-driven explanation now looks weak.
How did researchers test the gas-driven idea?
Hansen and Hirabayashi built a 3D computer model to calculate how solar heat moves through 1998 KY26's surface and deep interior. They compared modeled temperatures throughout the asteroid's orbit, then used those temperatures to estimate how quickly buried ice could turn directly into vapor and escape.
Because several physical properties remain uncertain, the researchers varied the asteroid's size, reflectivity, or how much sunlight its surface returns; thermal conductivity, or how easily heat passes through it; and the direction of its spin axis. They ran 13 versions of the model. The key point was not one idealized asteroid, but whether any plausible set of conditions could keep the interior cold.
In short, the model found no plausible set of conditions that could sustain a long-term store of ice.
Was 1998 KY26 cold enough to keep ice?
For ice to survive inside the asteroid over long periods, temperatures would need to stay below about –128°C (–198°F). Even the coldest modeled regions averaged around –47°C (–53°F) or warmer. No point on the surface or in the interior stayed cold enough to preserve ice for the long term.
The researchers also estimated how much water could remain. Even if water accounted for a generous 1% of the asteroid's mass, it would all be lost in roughly 2,000 years under the model's conditions. That result points to an asteroid strongly depleted in ice, rather than one capable of sustaining comet-like gas production.
In short, the heat would destroy even a modest reservoir of ice.
What does this mean for the asteroid's acceleration?
The findings make 1998 KY26 a highly unlikely dark comet. They strengthen the case that radiation pressure from sunlight, plus heat radiating away from the surface, drives its unusual acceleration. In plain terms, sunlight pushes on the asteroid, and the heat it radiates into space can also affect its motion.
The conclusion is strong but not final. Researchers do not know how long 1998 KY26 has occupied its current orbit, and the authors say only Hayabusa2's arrival in 2031 can confirm the asteroid's true nature.
Until then, the study gives astronomers their clearest expectation: a warm, ice-depleted body, with light and heat explaining the acceleration better than sustained gas venting.
The paper, titled Thermally unfavorable conditions of volatile existence in near-Earth asteroid 1998 KY26, the Hayabusa extended mission's target, is listed in Icarus for 2027, with DOI 10.1016/j.icarus.2026.117361.
The 2031 visit remains the decisive check on a model that already points away from ice.
via phys.org/rss-feed/ (Source)
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Correspondent covering money, funding and market shifts around general science news at SciBeat.
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