Researchers have discovered that a rapidly spinning asteroid is actually a pile of rubble held together by Van der Waals forces. This may change how we approach defending against asteroids in the future.
1950 DA is a near-earth asteroid, which back in 2003 was thought to pose quite a serious threat to our planet. It is expected to hit the earth in the year 2880, and a simulation showed that an impact in the Atlantic ocean would produce a tsunami 200 feet high, which would cause serious damage to Europe, Africa and the Americas.
A month ago however, astronomers discovered that 1950 DA is in fact, not as dangerous as previously thought. What was once thought to be a large rock is actually more akin to a pile of rubble. The asteroid, which is 1km in diameter, turns out to be roughly 50% empty space, and it can be shattered into fragments with even a small impact.
As if this wasn’t curious enough, here is where the story of this asteroid takes a turn for the strange: 1950 DA is spinning rapidly. It is in fact, spinning so rapidly that under normal circumstances, the gravitational field it produces would be unable to hold the rubble pile together. An astronaut landing on the rock pile would feel negative g-forces and be flung out into space if not anchored to the asteroid. As such, the asteroid must be held together in some other way.
A study by researchers at the University of Tennessee, Knoxville, have made a discovery that they believe can explain everything. They looked at thermal images and orbital drift for the asteroid and used those to find it’s bulk density and thermal inertia. They discovered that, instead of gravity, the asteroid is actually being held together by Van der Waals forces, a weak intermolecular force you might remember reading about in high school. Such forces have previously been suspected of having a role in holding asteroids together, but actual proof has never been found before.
Tsunami predictions from the asteroid, before it was known that 1950 DA was a pile of rubble.
“We found that 1950 DA is rotating faster than the breakup limit for its density,” said Ben Rozitis, a postdoctoral researcher on the team. “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 new discovery has important implications. If many other asteroids share similar compositions, it could be of great benefit for preventing future asteroid impacts. “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.”
Unfortunately, it also causes complications for the prospect of mining asteroids. Mining a loose pile of rubble may be much more difficult than landing on a big rock and drilling into it.