Why Binary Asteroids might Pose a Greater Threat to Earth than Single ones

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Recent re-evaluations of craters on the Earth's surface have led some scientists to the conclusion that a binary asteroid wiped out the dinosaurs. A binary asteroid is either an asteroid with a satellite orbiting it or two asteroids orbiting one another, rotating around a single center of gravity. This news about the infamous dinosaur-extinction asteroid as well as other information uncovered by the research strongly indicates that binary asteroids may be a greater threat to Earth than single asteroids. 

The dinosaur-killing asteroid was originally thought to be one large one with a diameter between 7 and 10 kilometers, but now it appears that it was actually likely to have been two more widely spaced out asteroids with a combined diameter of that distance. The two asteroids were probably about 80 kilometers apart. For years now scientists have puzzled over the discrepancy between binary near-Earth asteroids and the amount of binary craters on Earth. Around 15 percent of near-Earth asteroids are, in fact, binary, but binary craters are rare. The Clearwater Lakes of Canada were the result of such an asteroid, but other examples are hard to find. Approximately 1 out of 50 craters is a pair, like those of the Clearwater Lakes, which is roughly 2 percent of craters. That is quite a discrepancy.

Katarina Miljkovi and her colleagues at the Institute of Earth Physics in Paris have run numerous simulations and surprisingly concluded that binary asteroids typically collide with the Earth in such a way that they only form a single crater. It has been long known that craters are often up to 10 times the diameter of the asteroid. Only when the binary pairs are extremely far apart, which is uncommon, do they form two distinct craters. Otherwise, they instead form a single large, somewhat asymmetrical crater. The Chicxulub crater - thought to be the result of the asteroid that killed the dinosaurs - is asymmetrical. 

Impacts from binary asteroids are far more likely than once believed. Binary asteroids would also be more difficult to deflect. Current asteroid deflection theories and techniques have only accounted for a single asteroid. Different methods would be required to remove both asteroids accurately from their course, but then there is the problem of detecting binary asteroids in time to deploy the appropriate defense. 

In 2019, the Asteroid Impact and Deflection Assessment (AIDA) is set to launch two spacecraft toward the Didymos asteroid. Didymos is actually a binary system consisting of the large main asteroid, which is 800 meters across, and a smaller asteroid of about 150 meters. The smaller asteroid orbits the larger one every 12 hours. This will give scientists their first up-close look at a binary asteroid and also shed light on how to deflect them. One of the spacecraft, the Double Asteroid Redirection Test (DART), will intentionally crash into the smaller asteroid while the other craft, the Asteroid Impact Monitor (AIM), collects data. AIDA also hopes to determine what the asteroid is made of, because that will also affect how people interact with any approaching the planet.   

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