Van der Waals prevents asteroid spinning apart

A near-Earth asteroid rotates so quickly that it defies gravity and is held together by van der Waals cohesive forces, a phenomenon never before seen on an asteroid. Researchers from the University of Tennessee made the discovery while monitoring asteroid 1950 DA and say their work could protect the world from future collisions with asteroids. Previous research has shown asteroids are loose piles of rubble held together by friction and gravity, but researchers in the Department of Earth and Planetary Sciences wanted to find out what stops the body from breaking apart. Thermal images and orbital drift data were used to calculate thermal inertia and bulk density, the team detected the action of cohesive forces in an environment with little gravity. “We found that 1950 DA is rotating faster than the breakup limit for its density,” said Ben Rozitis, a postdoctoral researcher. “So if just gravity were holding this rubble pile together, as is generally assumed, it would fly apart. Therefore, interparticle cohesive forces must be holding it together.” The rotation is so fast at the equator that the asteroid effectively experiences negative gravity – an astronaut attempting to stand on the surface would fly off unless anchored. Although van der Waals has been predicted in small asteroids, this is the first time any evidence has been seen. This finding could provide important information to aid efforts to stop an asteroid impacting Earth. "Following the February 2013 asteroid impact in Chelyabinsk, Russia, there is renewed interest in figuring out how to deal with the potential hazard of an asteroid impact," said Rozitis. "Understanding what holds these asteroids together can inform strategies to guard against future impacts." This research has also revealed some potential techniques which could worsen the impact's effects. For example, kinetic impactor – which would deploy a massive object on a collision course with the asteroid – could destabilise the forces keeping the asteroid together, causing it to break apart into several threatening asteroids headed for Earth. "With such tenuous cohesive forces holding one of these asteroids together, a very small impulse may result in a complete disruption," said Rozitis. The work has been published in Nature. Cohesive forces prevent the rotational breakup of rubble-pile asteroid (29075) 1950 DA