A small asteroid has been caught in the process of spinning so fast it's throwing off material, according to to new data from NASA's Hubble Space Telescope and other observatories.
Images from Hubble show two narrow, comet-like tails of dusty debris streaming from the asteroid (6478) Gault.
Discovered in 1988, the 2.5-mile wide (4-kilometer-wide) asteroid has been observed repeatedly, but the debris tails are the first evidence of disintegration. Gault is located 214 million miles (344 million kilometers) from the Sun. Of the roughly 800,000 known asteroids between Mars and Jupiter, astronomers estimate that this type of event in the asteroid belt is rare, occurring roughly once a year.
Watching an asteroid become unglued gives astronomers the opportunity to study the makeup of these spaces "We did not have to go to Gault," explained Olivier Hainaut of the European Southern Observatory in Germany, 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 the sand particles) are close to the object, and the smallest grains are the farthest away, because they are pushed fastest by the sunlight pressure. "
Gault is The only second asteroid whose disintegration has been strongly linked to a process known as the YORP effect. (YORP stands for "Yarkovsky-O'Keefe-Radzievsky-Paddack," the names of the four scientists who contributed to the concept.) When the sunlight heats an asteroid, infrared radiation escaping from its heated surface carries off the angular momentum as well as heat. This process creates a tiny torque that can cause the asteroid to continually spin faster. When the resulting centrifugal force starts to overcome gravity, the asteroid's surface becomes unstable, and landslides can send dust and rubble into the space at a few miles per hour or the speed of a strolling human. The researchers estimate that Gault could have been slowly spinning over for over 100 million years.
Piecing together Gault's recent activity is a astronomical forensic investigation involving telescopes and astronomers around the world. All-sky surveys, ground-based telescopes, and space-based facilities like the Hubble Space Telescope are part of their efforts to make this discovery possible.
The initial clue was the fortuitous detection of the first debris tail, observed on Jan. 5, 2019, by the NASA-funded Asteroid Terrestrial Impact Last Alert System (ATLAS) telescope in Hawaii. The tail also turned up in archival data from December 2018 from ATLAS and the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) telescopes in Hawaii. In mid-January, a second shorter tail was hit by the Canada-France-Hawaii Telescope in Hawaii and the Isaac Newton Telescope in Spain, as well as by other observers. An analysis of both tails suggests the two dust events occurred around Oct. 28 and Dec. 30, 2018.
Follow-up observations with William Herschel Telescope and ESA (European Space Agency) Optical Ground Station in La Palma and Tenerife, Spain, and the Himalayan Chandra Telescope in India measured a two-hour rotation period for the The object is close to the critical speed at which a loose rubble-pile asteroid begins to break.
"Gault is the best" smoke gun as an example of a fast rotator right at the two-hour limit, "said team member of Jan Kleyna of the University of Hawaii in Honolulu
An analysis of the asteroid's environment by Hubble reveals no signs of more widely distributed debris, which excludes the possibility of a collision with another asteroid causing outbreaks.
The asteroid's narrow streers suggest that the dust was released in short bursts, lasting from anywhere from a few hours to a few days. These sudden events puffed away enough debris to make a "dirt ball" about 500 feet (150 meters) across if compacted together. The tails will begin to fading away in a few months as the dust disperses into interplanetary space.
Based on observations by the Canada-France-Hawaii Telescope, the astronomers estimate that the longer tail stretches over half a million miles (800,000 kilometers) and is roughly 3,000 miles (4,800 kilometers) wide. The shorter tail is about a quarter as long.
Only a couple of dozen active asteroids have been found so far. Astronomers may now have the ability to detect many more of them because of the enhanced observation capabilities of observatories such as Pan-STARRS and ATLAS, which scan the entire sky. "Asteroids such as Gault can not escape detection anymore," Hainaut said. "That means that all these asteroids that start misbehaving get caught."
The researchers hope to monitor Gault for more dust events.
The team's results have been accepted for publication by The Astrophysical Journal Letters.
The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated by NASA by the Association of Universities for Research in Astronomy in Washington, DC
Paper: The Sporadic Activity of (6478) Gault: A YORP-Driven Event?