A near-Earth object previously categorized as an asteroid, 1998 SH2, has been reclassified as a comet following a study led by NASA’s Jet Propulsion Laboratory. The discovery originated when the object failed to appear at its predicted location during a close approach to Earth on August 28, 2025. Researchers noted that the object’s trajectory deviated from expectations, suggesting that non-gravitational forces were influencing its path.

By analyzing orbital data dating back to 1998, scientists hypothesized that the object was venting gas as solar heat turned its internal ice into vapor. This process, which typically creates a visible tail and coma, was initially too faint to be detected. To verify this, the team utilized high-powered observatories, including the Canada-France-Hawaii Telescope and the European Southern Observatory’s Very Large Telescope. These observations successfully captured a faint tail, confirming the object's cometary nature.

"The images we collected from these observatories showed a weak but clear tail, thus confirming that 1998 SH2 is, in fact, a comet," said Olivier Hainaut, an astronomer with the European Southern Observatory and coauthor of the study. As a result of these findings, the object has been given the additional designation P/1998 SH2.

The study also highlights the existence of "dark comets," which exhibit similar orbital irregularities but lack visible signs of activity. Researchers believe that many objects currently classified as asteroids may actually be comets that require more sensitive equipment to identify. Understanding these perturbations is considered a vital component of planetary defense, as it helps scientists better predict the movement and potential impact risks of near-Earth objects. NASA plans to further this research with the upcoming Near-Earth Object (NEO) Surveyor mission.

Source: NASA