A an asteroid the size of the Empire State Building has little chance of hitting Earth. However, don’t worry. The asteroid collision will not happen anytime soon. At least it’s still a few centuries away.
At a press conference Wednesday (11/8), NASA scientists said there was a 1 in 1,750 chance that an asteroid named Bennu, which is slightly wider than the Empire State Building’s height, could collide with Earth between now and 2300.
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The latest statement was actually slightly higher than the previous estimate of 1 in 2,700 over the shorter period, between now and 2200.
“This is not a significant change,” said Davide Farnocchia, a scientist at NASA’s Jet Propulsion Laboratory in California and lead author of the paper published in the journal Icarus.
“I am no more worried about Bennu than before. The probability of the impact remains very small,” he said as reported by Antara Nytimes.com (12/8).
After all, Bennu’s trajectory is known precisely enough that the chance of a collision is exactly zero for the next century. However, the ‘crystal ball’ becomes more blurred in 2135. In that year, Bennu will still be approaching Earth and will come quite close, to be about 125,000 miles or so or about half the distance from Earth to the moon.
The exact distance is crucial, because Earth’s gravity will pull Bennu as he passes. If the asteroid passed a certain distance at a certain time, what planetary scientists call a ‘gravity keyhole’, it would be sent on a trajectory that could indeed intersect with Earth about half a century later.
Scientists say the most worrying day is September 24, 2182. However, there is only a 0.037 percent chance of it being a bad day.
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Bennu is about 500 meters wide. It was barely large enough to cause the extinction of the entire planet. Even so, it can still cause a sizeable swath of destruction.
“Usually you can, by a rule of thumb, say the size of the crater will be 10 to 20 times the size of the object,” said Lindley Johnson, planetary defense officer at NASA.
“So, an object measuring half a kilometer will create a crater that is at least five kilometers in diameter, and the diameter can reach 10 kilometers. But the area of destruction would be much, much wider than that. As much as 100 times the size of the crater. So a Bennu-sized object impacting an East Coast state would destroy a lot of things above and below the coast,” Johnson explained.
Estimates from Spaceship
The increased probability comes from NASA’s OSIRIS-REX spacecraft, which spent two years studying Bennu up close. The spacecraft left Bennu three months ago and is now heading back to Earth to unload samples of rock and debris collected from the asteroid for detailed laboratory studies by scientists.
When the spacecraft was in orbit around Bennu, Dr Farnocchia and his colleagues were able to precisely pinpoint the asteroid’s orbit. This allowed them to increase their estimate of Bennu’s position in 2135 by a factor of 20.
The OSIRIS-REX observations also allow the calculation of the small forces exerted on Bennu caused by heating and cooling of the surface.
The mission manager chose Bennu in part because it appears to be loaded with the kind of carbon molecule that may have provided the building blocks of life on Earth. But they also chose it in part because Bennu is what is known as a near-Earth asteroid. Its orbit crosses Earth, and as soon as it was discovered in 1999, planetary scientists were able to see that it poses a potential danger to our planet.
If an asteroid looks like it’s about to collide with Earth, humanity could try to deflect it into an orbit away from the planet. NASA will experiment using this technique with an asteroid called Didymos in 2022 by sending the Double Asteroid Redirect Test (DART) spacecraft to propel it out of orbit. The spacecraft is slated for launch later this year.
Johnson said that if there had been warning decades in advance, such a deflection would have worked for an asteroid the size of Bennu, although it would have required multiple impactors.(aru)
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