/ Science / Scientists discover some asteroids defy gravity, are mostly empty space

Scientists discover some asteroids defy gravity, are mostly empty space

Andrea on August 17, 2014 - 9:36 am in Science
asteroids
You probably imagine asteroids as huge monolithic chunks of rock, like mountains floating through space. While that’s probably what many of them are, researchers from the University of Tennessee have identified a class of asteroids that seem to defy gravity. The only way these objects could match up with the observations is if they weren’t a single rock, but a collection of smaller ones held together in space.

The team came to this conclusion (as reported in the journal Nature) by studying the near-Earth asteroid 1950 DA. This asteroid is potentially dangerous to the planet and has been given a 1-in-4000 chance of hitting us in 2880. 1950 DA is about 1.1km across (0.68 miles), but it rotates completely around once every 2.1 hours. It simply shouldn’t have enough gravity to hold itself together at that speed. The team took careful readings of this object to figure out what was going on.

The reflective surface of 1950 DA indicated it was largely composed of metal, but density readings pointed to a much lower number than would make sense. The team hypothesizes that 1950 DA and similar objects are groups of small rocks clumped together–they’re mostly empty space. So how do they stay stuck together when spinning so quickly? The researchers say the most likely candidate is the van der Waals force, which we usually see on a much smaller scale.

asteroid-1950da

The van der Waals force is simply the sum of attractive forces between molecules with a dipole (distributions of positive and negative charges). It’s like a very weak magnet, but if you spread that attractive force over a lot of molecules, it can have a real world effect. The van der Waals forces allow geckos to walk on walls and cause flour to clump together. Now we know it might also do the same for space rocks.

Knowing that some asteroids are actually collections of smaller rocks could affect the way we defend Earth from a future impact. Any attempt to directly influence such an object (like attaching rockets or shooting it with something big) would just cause it to break up. You definitely don’t want that. You’d just turn one object into a cosmic shotgun blast capable of even more destruction. Coaxing the asteroid into a different orbit by placing something massive nearby could be quite effective, though. We’ll need to get a closer look at one of these objects to know for sure, though. Well, not too close.

Source: Science – Geek.com

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