Potentially Hazardous Asteroid Turns Out To Be A Gravity-Defying Pile Of Space Rubble
According to NASA, near-Earth Asteroid 1950 DA currently has one of the highest chances of colliding with Earth of any known near-Earth object. Current estimates place the odds of the 1.3km wide asteroid colliding with Earth at roughly 1 in 4000 when it makes its closest pass in the year 2880, so it's something of a relief that a team from The University of Tennessee at Knoxville, has made a significant discovery that could help future generations repel the threat.
In a new research paper, the team outlines how their observations of asteroid 1950 DA have led to the first ever detection of van der Waals force on an asteroid. Unlike many objects in our solar system, this potentially hazardous asteroid is actually a massive pile of rubble that is being held together by a gravitational force so small it could be generated by something as insignificant as a penny.
Asteroids made up of rubble piles are not uncommon in our solar system, but when the team discovered that 1950 DA was actually almost 50% space and 50% porous rubble, they noticed something that had never been seen before. Normally, such rubble piles are held together by a spinning motion that is just the right speed to generate enough gravity to hold everything together. If the rubble is spinning too slow, there isn't enough gravity to keep a large amount of rubble together; a rotation that is too quick would see the pieces of rubble thrown out of their mini orbit. But 1950 DA defies these laws. When observing the asteroid, the researchers discovered that it was rotating so fast that it was producing negative gravity, which means that if you tried to land on it you would be thrown off of it by the force being generated by the rotation.
So how was all of this rubble sticking together? Ben Rozitis, a postdoctoral research on the Knoxville team explains...
"We found that 1950 DA is rotating faster than the breakup limit for its density," said Rozitis. "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."
These interparticle cohesive forces are known as van der Waals forces, and up until this latest research, they had never been observed in an asteroid before. This discovery will have a profound effect on the efforts currently being aimed at developing techniques that could one day repel an asteroid should it be confirmed as having a collision course with Earth. Understanding the physical forces that exist within an asteroid is essential should future generations ever need to use projectiles to knock it off its potentially devastating path, a concept which is adorably explained in this discussion between Neil deGrasse Tyson and a 9 year old boy.
Rozitis puts it slightly more concisely..
"The best way to mitigate an impacting asteroid is to nudge it slightly several years before impact so that it changes course," Rozitis said. "This can be done by hitting the asteroid with a fast and heavy spacecraft. However, by hitting a fast rotating asteroid held together by cohesive forces, you risk breaking it up into several smaller, hazardous asteroids. Therefore, with such an asteroid, you want to avoid interacting with it directly to prevent it breaking up. An alternative is to use a 'gravity tractor,' or a heavy spacecraft placed near the asteroid, which uses the force of gravity to pull the asteroid off course."