NASA Mistook Near-Earth Object 1998 SH2 for Asteroid for 28 Years, It Is a Comet

28-Year-Old Mistake Corrected

For nearly three decades, NASA catalogued a near-Earth object known as 1998 SH2 as an asteroid. That classification turned out to be wrong. The space agency has now confirmed that 1998 SH2 is actually a comet.

The object was first spotted in 1998. Back then, astronomers saw a faint, rocky-looking body moving through the inner solar system. They logged it as a near-Earth asteroid. No one thought to look closer — until now.

What Changed Astronomers' Minds

New observations from NASA's NEOWISE telescope caught 1998 SH2 doing something an asteroid shouldn't. It developed a faint tail, or coma — a cloud of gas and dust that only comets produce.

Further analysis revealed a small jet of gas escaping from the object's surface. That is a classic comet behaviour. The gas jet gives the comet a tiny push, altering its orbit in ways that pure rock cannot explain.

Scientists at NASA's Jet Propulsion Laboratory re-analysed old data and new images. They concluded that 1998 SH2 had been active all along, but the activity was too weak to be seen with older instruments.

Why the Mix-Up Happened

Asteroids and comets are not always easy to tell apart. Many comets go through dormant phases. When a comet gets far from the Sun, its ice stops vaporising, and it looks exactly like a dark, rocky asteroid.

1998 SH2 was in such a dormant state when it was first discovered. It stayed quiet for years. Only when it made a close approach to the Sun did it wake up enough to show its true nature.

This case is not unique. Astronomers have found several objects that were first labelled as asteroids and later reclassified as comets. The distinction matters because comets carry volatile materials that asteroids do not.

Implications for Planetary Defence

Knowing which near-Earth objects are comets is important for planetary defence. Comets can behave unpredictably. When they heat up, they can release gas in bursts, which changes their trajectory.

An asteroid's path can be calculated years in advance with high accuracy. A comet's path is trickier. The gas jets act like tiny thrusters, pushing the comet off its predicted course.

If a comet were on a collision course with Earth, those unpredictable pushes would make deflection harder to plan. That is why NASA keeps a close watch on all near-Earth objects, not just the big ones.

1998 SH2 poses no threat to Earth. Its orbit is well understood, and it will not come dangerously close anytime soon. But the reclassification reminds scientists that the catalogue of near-Earth objects is not perfect.

What Happens Next

NASA will continue monitoring 1998 SH2 as it moves away from the Sun. Scientists expect its activity to fade again, but they will keep watching for any further surprises. The object's new status as a comet will be updated in official databases, and astronomers will re-examine other suspected asteroids for hidden tails.