Astronomers Identify 'Dark Comet' After Unexpected Orbital Shift

• Astronomers have identified a "dark comet" by observing unexpected orbital deviations in an object previously classified as an asteroid.
• The object 1998 SH2 (now also designated P/1998 SH2) was found to be deviating from its calculated path by 190 km, a discrepancy too large to be explained by gravity or the Yarkovsky effect.
• Researchers confirmed the object is outgassing, creating a faint cometary tail and coma that were previously invisible.

Discovery and Analysis

• 1998 SH2, a 380-meter rock, was targeted for radar observation in August 2025 at a distance of 0.02 AU but was missing from its predicted position.
• The Southern Observatory for Near Earth Asteroids Research later located it 153 arcseconds (190 km) away from the calculated path.
• Investigations using the Canada-France-Hawai’i Telescope and the Very Large Telescope revealed a tail of dust grains approximately 400 micrometers in size.
• Outgassing activity peaked weeks after the object’s perihelion, suggesting ice reserves located deep beneath the surface.

Implications for Planetary Defense

• This discovery marks the first time an object's cometary nature was predicted via orbital dynamics and later confirmed through imaging.
• Approximately 285 near-Earth objects classified as "potentially hazardous" share these comet-like orbits.
• Because outgassing is a chaotic, non-gravitational process, it renders standard orbital simulations unreliable for predicting the trajectories of such objects.
• Experts urge continued monitoring of these bodies to refine trajectory data and better assess potential impact risks.