The 1998 KY26 asteroid appears to be accelerating and cannot be fully explained by gravitational pull. A new study indicates that one potential explanation that it is a dark comet ejecting gases from its sub-surface ice is less likely. Hayabusa2, which returned a sample capsule containing material from asteroid Ryugu to the Australian outback on December 6, 2020, is now heading towards 1998 KY26. Once it arrives in 2031, scientists will get a close look.The asteroid is about 36 feet (11 meters) wide, taking about 5.35 minutes to complete one rotation.A small, mysterious objectKY26 was found to be about one third smaller than previously thought, and is spinning much faster than previously thought in a 2025 study. It is only about twice the width of Hayabusa2’s solar panels and is therefore more mysterious.Observations have revealed a non-gravitational component to its acceleration, including a component perpendicular to its orbital plane. Due to this, it cannot be fully explained by gravity. Scientists have looked for other potential reasoning.One potential cause could be the Yarkovsky effect. Objects absorb solar radiation and release it as heat. This provides a small force that can affect an objects orbit over time. However, previous research has found that the acceleration observed is higher than expected from the effect. Scientists looked into whether it could be a dark comet. These objects can resemble normal asteroids, however they may contain ice beneath their surface. As the ice heats up it turns to gas and can provide a small thrust, altering its trajectory.Temperatures are too highA study by Korbin Hansen and Masatoshi Hirabayashi from the Georgia Institute of Technology looked at how much ice KY26 could be holding onto to continue emitting gases. They used current observations to calculate temperatures throughout the asteroid.They found that the object is likely to be too hot to hold onto sub-surface ice. Even the coolest regions of the asteroid have an orbit-averaged temperature of at least 212 K (−78.7°F). However, water ice would need to remain at temperatures below approximately 145 K (−198.7°F) to be stable over geological timescales.They state that any ice underneath the surface would lose water too quickly to provide the necessary emission of gases to explain the acceleration. Therefore, the researchers consider the dark-comet explanation less likely because the asteroid is unlikely to retain enough subsurface water ice to sustain the required outgassing. It is possible that the object has lost most of its water. The study does not fully explain what is causing the changes in the object’s movements. It could also be caused by the pressure from solar radiation and the heat emitted from the object itself. More observations will be needed to determine what forces are affecting it. Hayabusa2 is due to visit in 2031 which should provide scientists with a closer look at the object’s make-up and behavior. However, until then it remains a small and mysterious object. The visit could help confirm some of the explanations.