Rare ‘Self-Destructing’ Asteroid Is Spinning Itself Apart

As it’s wildly spinning away, the asteroid is slowly being eroded by its own rotation, shedding surface material that trails behind it in a comet-like tail of debris.

Hubble photo of self-destructing asteroid Gault, which is slowly shedding surface material into two comet-like tails of debris.
NASA, ESA, K. Meech and J. Kleyna (University of Hawaii), O. Hainaut (European Southern Observatory) (CC BY 4.0)

As it’s wildly spinning away, the asteroid is slowly being eroded by its own rotation, shedding surface material that trails behind it in a comet-like tail of debris.

Some 214 million miles from the sun, between the orbits of Mars and Jupiter, a peculiar asteroid is hurtling through space, gradually spinning itself apart. Known as 6478 Gault, this particular space rock is part of a group of rare “self-destructing” asteroids that are slowly crumbling away as a result of their own rotation, explains NASA.

Measuring just 2.5 miles across, Gault is spinning so quickly that it has begun to slowly shed surface material (rock and dust grains called regolith), leaving a long trail of dusty particle behind. The fascinating thing about this unraveling asteroid is that the dusty debris chipped off of its spinning surface is actually streaking behind it, forming two comet-like tails that give it an eerie, almost ethereal look.

These bright streaks of material have been caught on camera by the Hubble Space Telescope, which observed the asteroid in the throes of self-destruction and managed to snap a clear photo of its long, thin debris tails. The spectacular snapshot was released yesterday by NASA and is completely bewildering.

“Each tail represents an episode in which the asteroid gently shed its material — key evidence that Gault is beginning to come apart.”

Interestingly enough, the asteroids comet-like tails originated a few months apart and sport a significant difference in size. While both of them share un uncanny resemblance to the coma of a comet, the longer tail stretches more than 500,000 miles and is roughly 3,000 miles wide. Meanwhile, the shorter tail is about a quarter as long.

According to the Hubble Space Telescope website, these tails will only be visible for about a few months, ultimately dispersing into interplanetary space.

Hubble photo of self-destructing asteroid Gault, which is slowly shedding surface material into two comet-like tails of debris.
Hubble photo of self-destructing asteroid Gault, which is slowly shedding surface material into two comet-like tails of debris. NASA, ESA, K. Meech and J. Kleyna (University of Hawaii), and O. Hainaut (European Southern Observatory)

The reason for Gault’s odd self-destructive behavior – and its strange, comet-like appearance – has to do with a phenomenon dubbed the YORP effect. Short for “Yarkovsky–O’Keefe–Radzievskii–Paddack” (the names of the scientists who contributed to the concept), the YORP effect causes asteroids to continually spin faster as a result of the tiny torque produced when their surface is heated by the sun and begins to leak infrared radiation, which carries off both angular momentum and heat.

As it’s wildly spinning away, the asteroid becomes unstable and, therefore, subject to landslides, which slowly release rubble and dust into space. The material is sent drifting into the cosmos at relatively slow speeds of no more than 2 mph, or the speed of a strolling human. This allows the debris to gradually accumulate behind the asteroid, creating the fantastic comet-like tails captured in the Hubble photo.

Olivier Hainaut of the European Southern Observatory in Germany, a member of the Gault observing team, pointed out that the asteroid’s tails are neatly organized, with the dust grains “well-sorted by size.”

“All the large grains (about the size of sand particles) are close to the object and the smallest grains (about the size of flour grains) are the farthest away because they are being pushed fastest by pressure from sunlight.”

While astronomers have known about the existence of Gault for a little over three decades – the asteroid was first discovered in 1988 – it is only recently that the space rock has begun its process of self-ruin. In fact, clues about its strange behavior were only picked up earlier this year, when Gault was imaged by the ATLAS telescope in Hawaii – a NASA-funded asteroid-tracking observatory that stands for Asteroid Terrestrial-Impact Last Alert System.

Gault’s longer tail was spotted by ATLAS on January 5. The intriguing discovery prompted astronomers to take a look at archival data. To their surprise, they ended up uncovering signs of the tail in both ATLAS data and in observations made with the Pan-STARRS telescope, also in Hawaii.

The second, shorted tail was detected about two weeks later by the Canada–France–Hawaii Telescope in Hawaii and the Isaac Newton Telescope in Spain. The finding piqued astronomers’ interest to such an extent that various observatories all across the globe – as well as all-sky surveys and space telescopes – rallied behind the effort to study Gault’s unusual behavior.

After analyzing the data, researchers traced back the origin of the asteroid’s tails to two dust events that occurred last year, one around October 28 and the other around December 30.

“The asteroid’s narrow streamers suggest that the dust was released in short bursts, lasting anywhere from a few hours to a few days,” notes NASA.

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“These sudden events puffed away enough debris to make a ‘dirt ball’ approximately 500 feet across if compacted together.”

As the space agency points out, Gault is the second known asteroid in which scientists have observed the YORP effect. Researchers estimate that the phenomenon occurs roughly once a year among the 800,000 known asteroids that reside within the main asteroid belt between Mars and Jupiter.

“This self-destruction event is rare”, said Hainaut, noting that “active and unstable asteroids, such as Gault, are only now being detected by means of new survey telescopes that scan the entire sky.”

“That means that all these asteroids that start misbehaving get caught.”

The team is hoping that, by studying the material that makes up Gault’s debris tails, they will be able to get more insight into the history of planet formation in the early days of the solar system. Their conclusions and observations on the rare self-destructing asteroid are due for publication in The Astrophysical Journal Letters.