Astronomers have reidentified the near-Earth object 1998 SH2 as a rare dark comet after observing faint gas escaping from its surface [1, 2].
This discovery is significant because it exposes a fundamental weakness in the mathematical models used to protect Earth from potential cosmic impacts. Most planetary defense calculations rely on gravity-only orbital models, which cannot account for the unpredictable movement caused by comet outgassing.
For 27 years [2], the object was catalogued as an asteroid [2]. Because it possessed a dark surface, it did not exhibit the typical bright coma or tail associated with comets, allowing it to remain disguised as a rocky asteroid for nearly three decades.
Recent observations by NASA and international research teams revealed that gas was leaking from beneath the object's dark crust [1, 2]. This process, known as outgassing, acts like a natural thruster, subtly pushing the object and altering its trajectory over time [1, 2].
The shift in classification from asteroid to comet means that the previous tracking data for 1998 SH2 was based on an incomplete understanding of its physics [2]. While the object was tracked from Earth-based observatories, the unexpected movement caused by the gas emissions derailed the existing planetary defense math [2].
This event highlights the difficulty in identifying "dark comets"—objects that look like asteroids but behave like comets. Without the visual cue of a glowing tail, astronomers must rely on precise trajectory monitoring to detect these anomalies [1].
“The object was catalogued as an asteroid for 27 years before re-classification.”
The reclassification of 1998 SH2 demonstrates that current planetary defense strategies may be over-reliant on gravitational physics. If a significant number of near-Earth objects are actually dark comets, their trajectories could shift unpredictably due to outgassing, rendering long-term impact predictions unreliable and necessitating a shift toward more dynamic, observation-heavy tracking methods.
