A space rock that astronomers once labeled a harmless asteroid has been hiding a secret. It is actually a comet. NASA researchers announced that 2016 WJ1, a near-Earth object first spotted in 2016, has a faint tail of dust and gas. That makes it a comet, not an asteroid.
The discovery came from a team at NASA's Jet Propulsion Laboratory in California. They used data from the agency's NEOWISE infrared telescope, which scans the sky for objects that come close to Earth. The telescope picked up signs of material streaming off the rock. That material forms a comet's signature tail.
A rock that refused to fit the mold
Asteroids are mostly rocky or metallic. Comets are icy bodies that heat up and release gas and dust as they approach the sun. 2016 WJ1 orbits the sun every 3.8 years and crosses Earth's path. It is about 0.6 miles wide. For years, scientists classified it as an asteroid because it did not show obvious signs of activity. But NEOWISE caught it releasing dust in a way that only a comet can.
Why this matters for people on Earth
Local astronomers and planetary defense experts took notice. The object is classified as a potentially hazardous asteroid because of its size and orbit. But knowing it is a comet changes how scientists predict its behavior. Comets can change brightness and trajectory as they vent material. That makes tracking them more complex. For people who follow near-Earth objects, this reclassification means a known risk now comes with new unknowns.
What the telescope revealed
NEOWISE observed 2016 WJ1 multiple times between 2016 and 2020. The telescope measures infrared light, which is better at detecting heat from dust than visible light telescopes. The data showed a faint but clear trail of particles behind the object. That trail is the comet's tail. The finding was published in a NASA study that confirmed the object's true identity.
A reminder that the sky holds surprises
This is not the first time a near-Earth object has changed categories. But it shows how much scientists still do not know about the rocks and ice that share our solar system. The same telescope that found this comet has also discovered dozens of asteroids and comets. Each new finding helps refine the map of what is out there. For now, 2016 WJ1 is a comet. And it will stay on the watch list.
