Thermal Model Rules Out 'Dark Comet' Explanation for Asteroid 1998 KY26

Overview

• A study published Tuesday in Icarus by Korbin Hansen and Masatoshi Hirabayashi found that even the coldest regions of 1998 KY26 average about 212 K (−61 °C), well above the ≈145 K (−128 °C) needed to keep buried water ice stable.
• The authors calculated that a 1% ice reservoir would sublimate in roughly 2,000 years under those temperatures and would vanish in about 62 years if it were producing the measured thrust, making sustained outgassing an implausible source of the acceleration.
• With the outgassing (dark-comet) idea effectively ruled out, researchers now regard solar radiation pressure and the Yarkovsky thermal-recoil effect as the leading physical explanations for the non-gravitational acceleration.
• The asteroid’s tiny size (about 11 meters across) and very fast spin (5.35-minute rotation) give it a low mass-to-area ratio and uneven heating that amplify sunlight-driven forces and complicate remote measurements.
• Japan’s Hayabusa2 spacecraft is scheduled to rendezvous with 1998 KY26 in July 2031 to make in-situ measurements that should determine the asteroid’s composition and the exact cause of the anomaly, a result that will improve small-body science and orbit predictions.