On December 12, 2024, astronomers announced the discovery of seven new rocky bodies exhibiting comet-like behavior, termed 'dark comets.' This finding suggests that these objects, which resemble asteroids, could constitute up to 60% of near-Earth objects previously classified as standard asteroids.
Dark comets were first suspected in 2016 and confirmed in 2023. They differ from traditional comets, which are primarily icy and produce a coma as they approach the Sun. Unlike asteroids, which are rocky and lack ice, dark comets appear to have subsurface ice that causes them to move in ways that defy gravitational influence.
A study published in the Proceedings of the National Academy of Sciences details the identification of these seven new dark comets, increasing the total known to 14. Researchers categorize them into 'outer' and 'inner' dark comets based on size and orbital characteristics. Outer dark comets are larger, with eccentric orbits, while inner dark comets are smaller and follow nearly circular paths.
The implications of dark comets extend to understanding the origins of water on Earth. Aster Taylor, lead author of the study, noted that while it remains uncertain whether these bodies delivered water to our planet, they represent a potential pathway for ice from elsewhere in the solar system to reach Earth.
Estimates suggest that between 0.5% and 60% of near-Earth objects could be dark comets, indicating a need for further research to refine this range. The team highlights that near-Earth objects do not remain in their orbits for long, suggesting a continuous influx from a larger source in the solar system.