Asteroid 1998 KY26 Too Warm to Be a Dark Comet, New Heat Model Finds

A small, fast-spinning asteroid called 1998 KY26 is speeding up in a way that gravity and sunlight alone were not expected to explain. A new study suggests one popular theory for the oddity, that it is a disguised "dark comet" pushed along by escaping gas, is unlikely to be right, according to ScienceAlert.

Two aerospace engineers at the Georgia Institute of Technology, Korbin Hansen and Masatoshi Hirabayashi, calculated that the rock is too warm to keep the buried ice such a push would require. Their work is a computer model, not a direct measurement, and it was published in the journal Icarus.

What is odd about 1998 KY26?

ScienceAlert reports that the asteroid is about 11 meters (36 feet) across and rotates once every 5.35 minutes. Its path shows an unusual acceleration perpendicular to the plane of its orbit. Most asteroids are nudged mainly by gravity and by radiation pressure from the Sun, so this extra motion stands out.

What is a dark comet, and why was it suggested?

Asteroids are mostly rock. Comets contain ice that turns to gas and escapes, which can give them a small extra push. Dark comets are thought to release gas too, but so faintly that they show no visible tail and look like ordinary asteroids. Because that hidden outgassing could explain extra acceleration, scientists considered whether KY26 might be one.

How did the researchers test the idea?

They combined what is known about the object: its size, orbit, reflectivity and likely composition. From those, they modeled temperatures on its surface and deep inside.

According to the report, buried water ice needs to stay below about 145 Kelvin (-128 degrees Celsius) to survive for long periods. The researchers found that even the coldest regions of KY26 average at least 212 Kelvin (-61 degrees Celsius) over an orbit around the Sun.

At those temperatures, they calculated that water ice making up 1 percent of the asteroid's mass would vanish in just over 2,000 years. If that ice were driving the unusual acceleration, it would be gone in 62 years.

Does this rule out ice completely?

Not entirely. ScienceAlert notes an important caveat: it is unclear how long KY26 has been in its current orbit, so it could still hold some ice. The report adds that an earlier paper traced the asteroid to a possible origin in the asteroid belt, and that, together with the new result, makes the ice scenario less likely.

What could be causing the acceleration instead?

The report points to sunlight. Radiation pressure from the Sun is a small force, but ScienceAlert says it could be strong enough to account for the asteroid's behavior. The new study does not prove this. It mainly weakens the dark-comet explanation.

Why it matters, and what happens next

The result narrows the list of explanations for how a tiny rock can move in unexpected ways, and it helps clarify what KY26 is made of. It is a finding about one small object and rests on modeling, so it is not the final word.

A direct look may be coming. ScienceAlert reports that the Japanese space agency's Hayabusa2 spacecraft is traveling toward KY26, with a rendezvous planned for July 2031. Up-close observations could show whether sunlight, ice or something else is behind the acceleration.

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Around Prague, based on reporting by ScienceAlert