An asteroid that inexplicably grew a comet-like tail is actually disintegrating slowly in a process seen only once before, a team of Hawaii scientists and collaborators announced Thursday.

The plight of asteroid 6478 Gault is chronicled in a study involving some 18 scientists who deployed a handful of telescopes in Hawaii, the Canary Islands and India, as well as NASA’s Hubble Space Telescope.

The unusual behavior was first spotted in early January by an astronomer in Northern Ireland who was looking at survey data collected from the ATLAS telescopes on Mauna Loa and Haleakala.

Ken Smith thought he was looking at a newly discovered comet with a tail. It turns out it was a known asteroid, discovered in the main asteroid belt in 1988, that had developed a tail of dust grains ejected from the object’s crumbling surface.

Astronomers believe the phenomenon is caused by the long-term subtle effect of sunlight that acts to slowly spin an object until it begins to shed material.

“You never get to see this process come into play and throwing this material off,” said researcher Jan Kleyna of the University of Hawaii’s Institute for Astronomy.

While asteroids have a reputation for being static space rocks that orbit the sun endlessly without much fuss, this finding adds evidence to an assertion that the objects can be more dynamic than many believe.

Still, astronomers estimate this type of event is rare, occurring roughly once a year among the 800,000 known asteroids found between Mars and Jupiter.

After Gault’s tail was discovered, UH colleagues Larry Denneau and Robert Weryk went to work, checking archival data from ATLAS (Asteroid Terrestrial-impact Last Alert System) and UH’s Pan-STARRS (Panoramic Survey Telescope and Rapid Response System) telescopes. The tail, they found, was also seen as far back as December 2018.

In mid-January, a second shorter tail was spotted by Kleyna using the Canada France Hawaii Telescope on Mauna Kea, as well as by other observers. An analysis of both tails suggests the two dust releases occurred from the 2.3 mile-diameter asteroid around Oct. 28 and Dec. 30 .

The discovery prompted scientists from around the world to point their telescopes at the asteroid, and they even scored prized observation time on NASA’s Hubble Space Telescope, whose images revealed two narrow, comet-like tails of debris — evidence that Gault is beginning to come apart.

Scientists said analyzing an asteroid’s debris in these tails offers another clue into the formation of planets in the early solar system.

Followup observations with telescopes in the Canary Islands and India measured a two-hour rotation period for the object, which is close to the top speed at which a loose “rubble-pile” asteroid like Gault begins to break up.

The researchers said this destructive process, known as YORP (Yarkovsky-O’Keefe-Radzievskii- Paddack) torque, likely began hundreds of millions years ago, and Gault could have been on the brink of instability for millions of years.

“Gault looks like the best smoking-gun example of YORP disruption we’ve ever seen,” Kleyna said.

The study, accepted to appear in the science journal Astrophysical Journal Letters, suggests that as the asteroid increased its rotation and reached a critical point, landslides sent debris floating off into space at a few miles per hour — or the speed of a strolling human. Gault’s weak surface gravity was incapable of holding the dust grains any longer.

While some have speculated that a collision or impact was responsible for the tail, an analysis of the asteroid’s immediate surroundings in images taken by Hubble revealed no signs of excess dust, ruling out that possibility, the study said.

According to the research, dust was released in short bursts, lasting anywhere from a few hours to a few days and creating a tail that stretches over a half million miles and roughly 3,000 miles wide. The shorter tail is about a quarter as long.

But the slender tails will begin to fade in a few months as the dust disperses, the study said.

The researchers said they hope to monitor Gault for more dust events.

Said Kleyna, “We will be watching the object closely.”