Self-destructing asteroid is spinning itself to death
NASA has released images from the Hubble Space Telescope showing an asteroid that is tearing itself apart. Located 214 million mi (344 million km) from the Sun, the 2.5-mile-wide (4-km) asteroid (6478) Gault is spinning so fast that it is self-destructing and throwing off debris tails half a million miles (800,000 km) long.
Sometimes it seems like the world is falling apart, but for Gault, this is literally the case. First discovered in 1988, it sits in the asteroid belt between Mars and Jupiter, and might have just been catalogued as another unexceptional rock, except that observations from the Hubble telescope, the Canada–France–Hawaii Telescope, the Asteroid Terrestrial-Impact Last Alert System (ATLAS) and the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) telescopes in Hawaii, the William Herschel Telescope in La Palma, ESA's (European Space Agency) Optical Ground Station in Tenerife, and the Himalayan Chandra Telescope in India have shown that Gault is anything but unexceptional.
For one thing, there are two huge tails spreading out behind Gault. One is over 500,000 mi (800,000 km) long and 3,000 mi (4,800 km) wide, while the other is a quarter as long. These comet-like tails are being pushed out by the solar winds, but unlike comet tails, which are made of gas and ice crystals, these are made of dust and rubble being flung off by the asteroid at about a walking pace.
This flinging is occurring because Gault is spinning at a rate of about once every two hours, which is fast enough to cause landslides and hurl the debris away at escape velocity. Equally important, there's nothing in the neighborhood of Gault that indicates it could have been impacted by another object, so whatever is spinning the asteroid and tearing it apart is something much more subtle.
Gault is disintegrating because of what is called the Yarkovsky–O'Keefe–Radzievskii–Paddack (YORP) effect. According to NASA, when sunlight shines on an asteroid, it heats up and then re-radiates that heat as infrared radiation. As it does so, it also carries away a tiny bit of angular momentum as well. This puts torque on the asteroid, making it spin faster. If this effect is asymmetrical, it becomes cumulative over millions of years and the asteroid spins faster and faster until the centrifugal force becomes too much for the asteroid's structure and debris is shed in a series of landslides.
From the observations made of Gault, astronomers have deduced that debris in the two tails appeared on about October 27 and December 30, 2018. These tails were the result of two bursts of debris that could have made a ball 500 ft (150 m) in diameter and will fade away over the next few months, but it's hoped that more such events will be seen on Gault.
The space agency says that such self-destructing asteroids are rare, occurring about once a year. So far, only a couple of dozen have been seen, but more may be found now that whole-sky scans by Pan-STARRS and ATLAS are on line. And aside from the drama of such a break up, such asteroids allow scientist to learn more about them without having to visit them.
"We didn't have to go to Gault," says Olivier Hainaut of the European Southern Observatory in Germany and a member of the Gault observing team. "We just had to look at the image of the streamers, and we can see all of 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."
The results of the research will be published in Astrophysical Journal Letters.