The Likelihood of Comets Hitting Earth Is Higher Than We Thought

Tuesday, 29 December 2015 - 2:55PM
Astrophysics
Science News
Tuesday, 29 December 2015 - 2:55PM
The Likelihood of Comets Hitting Earth Is Higher Than We Thought
An asteroid armageddon has seemed more and more far-fetched in recent years, but is it more likely than we thought? According to a team of astronomers published in Astronomy and Geophysics, scientists have vastly underestimated the likelihood of huge objects smashing into Earth with potentially catastrophic consequences.

Most studies of potential asteroid collisions focus on near-Earth objects, mostly in the asteroid belt between Jupiter and Mars. But according to the researchers, the recent discovery of giant comets called centaurs calls for a reassessment of the risk of a comet collision.

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"In the last three decades, we have invested a lot of effort in tracking and analyzing the risk of a collision between the Earth and an asteroid," said co-author Bill Napier of the University of Buckingham. "Our work suggests we need to look beyond our immediate neighborhood too, and look out beyond the orbit of Jupiter to find centaurs. If we are right, then these distant comets could be a serious hazard, and it's time to understand them better."
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Centaurs are huge balls of ice and dust that are 50-100 kilometers wide, and can usually be found far beyond Neptune. They have erratic elliptical orbits, which means there's a chance that they could cross paths with the gravitational field of Neptune, Saturn, Uranus, or Jupiter, which have a tendency to hurl comets towards Earth approximately once every 40,000-100,000 years. If one of these centaurs came towards Earth, it would disintegrate as it got closer to the Sun, causing a huge comet trail that would guarantee debris hitting Earth.
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"The disintegration of such giant comets would produce intermittent but prolonged periods of bombardment lasting up to 100,000 years," the research team wrote.
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As a result, "assessment of the extraterrestrial impact risk based solely on near-Earth asteroid counts, underestimates its nature and magnitude," they argue.

The team claims that no particular risk is "known to be imminent," but concedes that cometary behavior is largely unpredictable. And if this rather alarming scenario came to pass, it could have a huge impact on life on Earth, possibly even imitating a nuclear winter.

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"A centaur arrival carries the risk of injecting, into the atmosphere... a mass of dust and smoke comparable to that assumed in nuclear winter studies," wrote the researchers. "Thus, in terms of magnitude, its ranking among natural existential risks appears to be high."
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