If an asteroid disintegrates in space and nobody is around to hear it, does it make a sound? No, because there’s no air, silly. But it does make for a stunning photo.
Two narrow, comet-like tails of debris streaming from an asteroid known as 6478 Gault were captured from ground-based telescopes, all-sky surveys, and space-based facilities including the Hubble Space Telescope. The tails indicate material from the object is being released into space, telling astronomers that the asteroid is slowly undergoing self-destruction.
“Gault is a very ordinary and boring asteroid, which means it’s most likely just a very loosely held pile of dust and rubble of various sizes – everything from boulders to dust all mashed together,” lead author Jan Kleyna told IFLScience in an interview, adding that it’s the circumstances surrounding the space object that make it of particular interest to sky watchers.
Measuring around 4 kilometers (2.5 miles) in size, Gault was first discovered in 1988 but only recently became one of just a few asteroids ever observed undergoing YORP torque, a process where sunlight warms the surface of an asteroid and releases infrared radiation. Heat and momentum that are then released cause a small force that spins the asteroid faster and faster. If the centrifugal force overcomes gravity, then the asteroid becomes unstable, and landslides on the space-drifting object can release rubble into space like the tails seen on Gault.
The “rare” event was first picked up by an early alert system in Hawaii that is designed to provide some degree of warning for potential Earth impactors. After analyzing archival data, the team found that the asteroid’s larger tail had first been documented in December 2018 by various telescopes around the world. Follow-up observations made by various ground-based telescopes and dust modeling, which scientists used to deduce that the asteroid is rotating at two-hour intervals.
“The interesting thing at a two-hour rotation is that is the speed at which centrifugal force beings to balance out gravity,” explained Kleyna. “Our hypothesis is that this thing spun up until its gravity is weakened by the centrifugal force, at which point the object experiences these landslides that throw dust into space.”
Researchers aren’t sure what triggered the outburst, but believe it could have been something as tiny as a pebble given the fact that the asteroid increases in speed “really, really slowly” – hovering on the brink of instability for the last 10 million years. What they do know is that observations like Gault help to shed light on the importance of space science.
“This really shows the value of all-sky surveys in that they find things that can then be followed up with conventional facilities. All those facilities were incredibly valuable, but it took the ATLAS survey to find this thing in a very brief window because the dust will probably be gone in a few months. If ATLAS surveyed once a year instead of once every couple of days then we would have missed it."
The observations have been accepted for publication in the Astrophysical Journal Letters.