Astronomers Spot Rare Disintegrating Asteroid
Asteroids don’t usually put on a light show, but astronomers from Queen’s University Belfast have spotted one doing just that. The 2.5-mile (4-kilometer) object known as (6478) Gault is spinning so fast that it’s tearing itself to pieces. The result is a comet-like tail, which attracted the attention of researchers on the lookout for supernovae.
Gault completes one rotation every two hours, and that’s generally considered the limit for asteroids. Any faster than that, and they can’t hold themselves together indefinitely. The light from these rare spinning asteroids used to go unnoticed, but now telescopes are scanning a broad swath of the sky in search of astronomical phenomena.
In January of this year, Ken Smith of the Astrophysics Research Centre at Queen’s University Belfast was using the Asteroid-Terrestrial Impact Last Alert System (ATLAS) in Hawaii when he saw something in the asteroid belt between Mars and Jupiter that looked like a comet. Upon further inspection, he realized it was (6478) Gault. Followup observations were conducted using the Hubble telescope. That isn’t the first case of comet-asteroid confusion. It took scientists a few tries to correctly identify the interstellar visitor ‘Oumuamua as a very old comet.
Gault is a relatively loose collection of rocky material known as a rubble pile. The longer of the two tails is about 500,000 miles (800,000 kilometers) long, and the brighter one is 125,000 miles (200,000 kilometers) in length. Analysis of (6478) Gault with Hubble suggests most of the dust making up that tail flew off the surface in two events near the end of last year. High rotation makes rubble piles highly unstable — a tiny pebble impact could have triggered the recent burst of dust from the surface.
How did it get spinning so fast, though? Scientists point to a process called the Yarkovsky–O’Keefe–Radzievskii–Paddack effect (YORP effect). Asteroids reflect solar radiation as heat, but some of them do so asymmetrically. This causes a tiny rotational force that can build up over millions of years. So, (6478) Gault has been spinning faster and faster for eons and has only recently started coming apart.
Scientists will continue observing (6478) Gault as it spins. It will be interesting to see if the particle releases continue or if it holds together for a bit longer.
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