Near-Earth Object 1998 SH 2 Shows Cometary Activity After 27 Years of Astrometry
Updated
Updated · Nature.com · Jul 10
Near-Earth Object 1998 SH 2 Shows Cometary Activity After 27 Years of Astrometry
2 articles · Updated · Nature.com · Jul 10
Summary
Astronomers confirmed that near-Earth object (875163) 1998 SH 2 is active, detecting a faint coma and a tail more than 20 arcseconds long and giving it the comet designation P/1998 SH 2.
A 1998-2025 orbital record showed a non-gravitational acceleration of about −1.4 × 10^-11 m/s^2—10 times too large for the Yarkovsky effect—after the object missed a predicted 2025 radar pointing by 153 arcseconds.
Large telescopes found activity that ATLAS survey images had missed: CFHT saw a weak tail on Sept. 17, VLT confirmed a longer narrow tail on Sept. 30, and reprocessed Danish Telescope images showed it was already present by Sept. 13.
Dust modeling indicates grains were released continuously from roughly Aug. 29 to Sept. 7, 2025, favoring sublimation-driven outgassing over an impact or rotational shedding.
The finding suggests more near-Earth objects now labeled asteroids—especially 285 potentially hazardous bodies in Jupiter-family-like orbits—could be weak comets, complicating impact-risk forecasts and deflection planning.
An asteroid just became a comet. How many more unpredictable 'dark comets' are hiding near Earth?
Does this 'stealth comet' finally solve the enduring mystery of interstellar visitor ‘Oumuamua’s strange journey?
1998 SH2 Reclassified: The Discovery of a "Dark Comet" and Its Impact on NEO Risk and Cosmic Origins
Overview
For 27 years, 1998 SH2 was thought to be a typical asteroid, but in August 2025, astronomers detected a significant orbital anomaly that hinted at non-gravitational forces at work. This discovery prompted detailed investigations using advanced deep imaging techniques. Researchers then visually confirmed a faint coma and subtle tail, revealing that 1998 SH2 is actually an active comet. This reclassification challenges our understanding of near-Earth objects and highlights how careful observation and new technology can uncover hidden activity in objects once considered ordinary.