Tracked by NASA since 1998, missing asteroid reappears as mysterious dark comet

An asteroid discovered in 1998 failed to show up decades later where it should have been, which led to a whole new revelation. Astronomers now say it isn't an asteroid at all, but a dark comet, a class of space objects that are still a mystery to humans. The space rock was missing when scientists were observing it last year. According to their calculations, it should have been in that particular region in space. They were stumped to see that it had missed its date with them.

After a year of analysis, a team of researchers has stated that this mysterious object is not an asteroid, and showed activity consistent with another cosmic object. The study, published in the journal Nature Astronomy, states that 1998 SH2 is not a common space rock. Astronomers have observed it for nearly three decades, during which time they have calculated its orbit and noted other things about it. Turns out, they had it all wrong. And they only found this out while waiting for it in August 2025.

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Asteroid 1998 SH2 was due to return at this time, and so the astronomers were ready with their telescopes. But it did not show up on its orbital path. Later, Brazil’s Southern Observatory for Near Earth Asteroids Research caught it, but it had moved beyond its expected position and path. This was unusual for a near-Earth asteroid, and experts went back to the drawing board to understand what they had missed.

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Jet Propulsion Lab and Caltech researcher Davide Farnocchia and his team now have the answer. They noted in the study that the object displayed weak cometary outgassing, where jets of gas were escaping from beneath its surface. This is something that happens with comets. However, it had none of the other characteristics of a comet, which presented another mystery. There was neither a glowing tail, nor a coma. This is why initially astronomers didn't suspect that it could be a comet.

Layered composite imagery in follow-up analysis revealed faint traces of these features. This led them to conclude that 1998 SH2 was a type of dark comet, a space rock that is not commonly seen in the universe.

‘Oumuamua, the most famous dark comet

The finding has presented a new challenge for planetary defense. There is a high chance that many more asteroids could be comets. These objects can change orbits and acceleration, complicating tracking efforts. Notably, the first interstellar object ‘Oumuamua, was also classified as a dark comet.