Overview
- A failed radar detection during the object's close pass in August 2025 prompted observers to search for 1998 SH2 after it appeared far from its predicted position.
- Careful astrometry across the 1998–2025 data arc detected a small nongravitational transverse acceleration of about 1.4×10⁻¹⁰ m/s² that is roughly ten times larger than the Yarkovsky effect can explain for an object of this size.
- Targeted stacked imaging with the Canada‑France‑Hawaii Telescope, ESO’s Danish Telescope and the Very Large Telescope revealed a faint tail and weak coma, and the Minor Planet Center assigned the comet designation P/1998 SH2 after the team published results in Nature Astronomy.
- The paper estimates a roughly 380‑meter nucleus with very low reflectivity (~6%) and reports no current Earth impact risk for P/1998 SH2 based on available orbital forecasts.
- The case validates using precise orbital residuals to flag subtle cometary activity, highlights a population of 'dark comets' that can hide in asteroid catalogs, and strengthens calls for continuous astrometric tracking and next‑generation surveys to reduce orbit uncertainty for planetary defense.