Asteroid 1998 SH2 Confirmed as Dark Comet After 0.02-AU Flyby Exposed Orbital Shift
Updated
Updated · ScienceAlert · Jul 26
Asteroid 1998 SH2 Confirmed as Dark Comet After 0.02-AU Flyby Exposed Orbital Shift
3 articles · Updated · ScienceAlert · Jul 26
Summary
Astronomers confirmed 1998 SH2 is a dark comet after its 2025 pass just 3 million kilometers from Earth revealed it was off its predicted path.
Optical observations from ATLAS, CFHT and ESO then detected a faint coma and weak tail, while simulations pointed to subsurface ice sublimation driving the non-gravitational acceleration.
The study says 1998 SH2 is the first object whose cometary activity was predicted from orbital perturbations and later verified with targeted observations.
At about 380 meters wide, 1998 SH2 has zero current impact odds, but the finding matters for planetary defense because comet-like outgassing can complicate orbit forecasts.
Researchers say more mislabeled near-Earth asteroids may actually be dark comets, a possibility that could reshape impact-risk tracking and theories about water delivery to early Earth.
Could other near-Earth “asteroids” actually be dark comets, quietly drifting off predicted paths because of buried ice?
Why did 1998 SH2 evade expectations for years, and how might weak outgassing change future planetary defense calculations?
The Hidden Menace of Dark Comets: Lessons from P/1998 SH2 and the Urgent Need for Next-Generation Planetary Defense
Overview
In August 2025, astronomers were surprised when asteroid 1998 SH2 went missing during a close Earth flyby, only to be found days later far from its predicted path. Careful analysis revealed the object was being pushed off course by invisible cometary outgassing, not just gravity. Powerful telescopes soon confirmed a faint tail and coma, leading to its reclassification as comet P/1998 SH2. This discovery highlights how dark comets—icy bodies that look like asteroids—can silently drift from their predicted orbits, complicating planetary defense. New infrared missions like NASA’s NEO Surveyor will help detect and track these hidden threats more accurately.