Near-Earth Object 1998 SH2 (875163), initially classified as an asteroid, has uncovered a surprising truth: it may actually be a comet. Recent research published in Nature Astronomy sheds light on its enigmatic identity.
This artist’s concept depicts a near-Earth asteroid with an elongated orbit. Such objects can experience significant perturbations around the Sun, potentially becoming comets with faint tails and comas like SH2 in 1998. Image credit: NASA/JPL-Caltech.
The intrigue began on August 28, 2025, when 1998 SH2 safely passed Earth at a distance of 3 million kilometers (approximately 1.86 million miles) during its four-and-a-half-year solar journey.
Dr. Davide Farnocchia and his team at NASA’s Jet Propulsion Laboratory aimed to track it using the Deep Space Network’s planetary radar and its known orbit for precise predictions.
However, the object didn’t appear as expected, raising suspicions of anomalous forces influencing its path.
This “something” was identified as gas emissions, a hallmark of cometary activity linked to comet tails.
“Upon measuring the non-gravitational forces affecting 1998 SH2’s motion, we concluded it was more compatible with an active comet rather than an asteroid,” stated Dr. Farnocchia.
Median stack of exposures of 1998 SH2 taken by the ATLAS Chile telescope on September 3 and 4, 2025. No coma or tail is evident. Image credit: ATLAS/Farnocchia et al., doi: 10.1038/s41550-026-02913-7.
Delving into observations from its 1998 discovery, researchers hypothesized that sunlight warms the icy material within, transforming it into gas and generating weak jet-like thrust.
Unlike typical comets with prominent tails, this activity was subtle enough to evade most telescopes.
The August 2025 flyby provided an invaluable chance to test their theory, utilizing equipment from the Canada-France-Hawaii Telescopes, ESO’s Denmark Telescope, and the Very Large Telescope.
The images captured showcased a faint yet undeniable tail, confirming that 1998 SH2 is indeed a comet.
Subsequently, it was reclassified as P/1998 SH2 to reflect its new status.
“Observations from these telescopes revealed a weak but clear tail, confirming that 1998 SH2 is a comet,” remarked Dr. Olivier Hainaut from ESO.
“This exemplifies the scientific process: forming a hypothesis and then rigorously testing it.”
“The data we obtained were crucial in substantiating our hypothesis that 1998 SH2 is a comet.”
Dr. Farnocchia emphasized the significance of consistently monitoring near-Earth objects. “Due to gas emissions, the motion of comets is more disturbed compared to asteroids.”
“Detecting these disturbances can serve as an essential diagnostic tool for planetary defense, helping us differentiate between comets and asteroids, track their orbit evolution, and assess the potential risks they pose to Earth.”
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D. Farnocchia et al. Non-gravitational acceleration indicating the cometary activity of near-Earth objects. Nat Astron published online on July 10, 2026. doi: 10.1038/s41550-026-02913-7
Source: www.sci.news
