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Earth is likely safe for now from asteroids -- probably

GRAND FORKS -- Good news, everyone! The sky isn't falling--for now. NASA scientist Joseph Nuth noted recently at the annual meeting of the American Geophysical Union that Earth could now be "due" for an extinction-level asteroid or comet strike. ...

Mike Gaffey, a UND Chester Fritz Distinguished Professor of space studies, last week shows off a meteorite he keeps in his office in Grand Forks. Gaffey, an asteroid expert, said asteroid tracking programs predict Earth is safe from collisions until 2060, the last year we're currently able to forecast. (Joshua Komer / Grand Forks Herald)
Mike Gaffey, professor of Space Studies shows a meteor that he keeps in his office in Grand Forks, ND on Wednesday, December 21, 2016. (Joshua Komer / Grand Forks Herald)

GRAND FORKS - Good news, everyone! The sky isn't falling-for now.

NASA scientist Joseph Nuth noted recently at the annual meeting of the American Geophysical Union that Earth could now be "due" for an extinction-level asteroid or comet strike. Such major impacts tend to occur about 50 million to 60 million years apart, Nuth said, so the fact that the last catastrophic knock to our planet occurred 65 million years ago-and killed off the dinosaurs-could be grounds to expect another.

Nuth did emphasize such events occur at random intervals and can't be predicted with past incidents alone. Still, as Earthlings have no real defense against giant space hail, Nuth advocated for the construction of an interceptor rocket to be kept at the ready for fending off any space invader that wanders too close.

Mike Gaffey, asteroid expert and Chester Fritz Distinguished Professor of space studies at the University of North Dakota, compared impacts by space rocks to "winning the lottery," but with a potentially apocalyptic jackpot.

Gaffey said asteroid search programs conducted by NASA and other spacefaring organizations have been busy cataloging the near-Earth bodies that whiz through our planet's personal space. Along with an approximation on size, such programs also chart the speed and trajectories of their subjects to determine how close they might pass by us as they meander along wide orbits throughout our solar system.

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"At this point, we don't know of anything on the collision course of the Earth for 60 years," Gaffey said. "We don't know beyond that, but there's been a few close calls, like in 1999 and 2002." Asteroids have passed near Earth in more recent years, too. A meteor did more than just get close in 2013 when it exploded at an altitude of about 14 miles above the Russian city of Chelyabinsk. The explosion of the 20-meter-wide rock produced a blast with the kinetic energy equivalent of about 500 kilotons of TNT and shattered windows within a 30-mile radius. The airburst caused injuries in more than 1,200 people, most of whom were hurt by broken glass and other building debris.

Gaffey said our planet is due for at least one close fly-by expected for April 2029. The extraterrestrial visitor, a roughly 300-meter-wide space rock named 99942 Apophis, made an earlier pass in 2006 and originally was believed to be a possible collider for 2036.

At this point, astronomers believe Apophis will miss us in 2029 by about 30,000 kilometers. For the sake of comparison, the moon hangs out at an average distance of 384,4000 kilometers from Earth.

Gaffey said Apophis isn't very big, as far as large asteroids and energy contents go.

"It'd only be about-and I use 'only' advisably here-650 megatons of energy released by an impact," he said. "Which you can compare to the largest hydrogen bomb ever exploded, the Tsar Bomba the Russians exploded, which was about 50 megatons."

The atomic blast at Hiroshima measured about 15 kilotons, Gaffey added, or 0.015 megatons.

The full roster of logged doom-bringers has ballooned over the past 20 years of sky-scouring. Gaffey said NASA started out with a list of about 300 planet-crossing asteroids when it began its near-Earth object search program in late 1995. As of October, researchers have cataloged more than 15,000 asteroids.

Simply knowing if and when we're about to get pelted doesn't mean we're safe from falling rock though, and asteroids can still catch observers unaware, especially if they approach from the obscuring direction of the sun. If an asteroid were on a collision course with Earth today, it's not entirely clear what we could do to stop it.

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Gaffey said the main idea right now would be to either slow it down or speed it up to the point of throwing it off sync with our own movement through space.

"It's like cars at an intersection; they won't collide unless they're at the same place at the same time," he said. "If you could slow it down by even a small amount a year in advance, you could change its arrival time to avoid contact."

There are a number of different proposals in the works exploring ways to do just that, but Gaffey said there's no existing hardware that could get the job done. The purpose of asteroid tracking programs is to give some forewarning-and hopefully some motivation-to the powers of Earth to get something together in time to avoid utter destruction. Last January, NASA established the Planetary Defense Coordination Office to tie together the tracking of near-Earth asteroids with the coordination of an actual plan to mitigate any threat from above.

As to our planet being due for a major impact, Gaffey said the randomness of the universe makes any individual space event near-impossible to predict outright.

"If I play poker that way, I lose money," he said. "The last big impact was about 65 million years ago. The next one could be in 100 million years, it could be tomorrow or it could be 200 million years from now. The programs are intended to let us know with enough time to do something about it."

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Mike Gaffey, professor of Space Studies poses for a portrait in his office in Grand Forks, ND on Wednesday, December 21, 2016. (Joshua Komer / Grand Forks Herald)

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