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Heads Up! Thirteen Years Of Asteroid Impacts On Earth

The views expressed are those of the author and are not necessarily those of Scientific American.


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(NASA/JPL-Caltech)

Since the Chelyabinsk event in early 2013, when a brilliant meteor fireball streaked across Russian skies and exploded with the energy of thirty Hiroshima bombs, humans have paid slightly more attention to the potential danger of asteroids than before. A combination of media attention and the viral spread of eyewitness videos and photos perhaps did more for the cause of Earth asteroid protection than anything else in recent history.

Later analyses that included data from a global infrasound network, designed to help monitor nuclear test-ban treaty rules on bomb detonation, have indicated that the last few decades may in fact represent a slight uptick in asteroid impacts on the Earth. The cause? The probable disruption a million years ago of parts of a mile-and-a-half sized body known as 1999 NC43.

Now the B612 Foundation – an organization devoted to the monitoring and mitigation of harmful asteroid impacts on Earth – has assembled a great visual of the last 13 years of asteroid hits with kiloton or greater explosive energy. Picked up by the infrasound network, the majority of these 26 events were ‘airbursts’, and most took place over the oceans or relatively remote areas. You can watch the animation below.

Its a sobering reminder of our rather precarious situation in a dynamic and still evolving planetary system, where even our homeworld has, in some sense, not finished assembling itself from the fossil remains of our proto-stellar nebula.

Towards the end of this video is a hint of the B612 Foundation’s privately funded ‘Sentinel’ space mission – an infrared telescope that would scour local space for objects as small as about 30 meters across, and spot 90% of objects larger than 140 meters. These are ‘near-Earth objects’ or NEOs (objects whose orbits carry them between approximately 1.3 and 0.98 astronomical units from the Sun), the asteroids whose paths have the potential to intersect the Earth’s.

Although there’s been a lot of talk over the years about spotting and deflecting Earth-hazardous asteroids, there’s yet to be a real breakthrough moment. B612′s Sentinel mission would be a terrific step to take. Right now the best data we have on NEOs is only for the big guys. It’s estimated that we’ve spotted about 93% of the NEOs larger than 1 kilometer across. Sounds good, right? The problem is that this still leaves an estimated 70 or so unseen, lumbering, kilometer-sized mountains that could pose an enormous threat to our civilization. And that’s the big, relatively easy to spot stuff. Push into the regime of bodies that are hundreds to tens of meters across and there must be tens of thousands of NEOs that we simply haven’t spotted yet.

The Chelyabinsk meteor was no more than about 20 meters across, yet it exploded with over 400 kilotons of energy. Fortunately this was at seventy-six thousand feet above ground level, mitigating the effect. Still, over a thousand people in a modestly populated region were injured.

And the sobering fact is that it is only a matter of time before something far worse happens.

Caleb A. Scharf About the Author: Caleb Scharf is the director of Columbia University's multidisciplinary Astrobiology Center. He has worked in the fields of observational cosmology, X-ray astronomy, and more recently exoplanetary science. His latest book is 'Gravity's Engines: How Bubble-Blowing Black Holes Rule Galaxies, Stars, and Life in the Cosmos', and he is working on 'The Copernicus Complex' (both from Scientific American / Farrar, Straus and Giroux.) Follow on Twitter @caleb_scharf.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. tuned 10:40 am 04/23/2014

    Overdue actually.
    That’ll change their pollution lovin’ feng shui.

    Link to this
  2. 2. TommyTheBrit 6:37 pm 04/23/2014

    I enjoyed studying impact hazards as part of my undergraduate degree; the main issue was that the US cut funding in the late 1990s to two vital programs that were focused on detecting and tracking asteroids that were in an Earth-crossing orbit: PACS and PCAS.

    There is no government strategy, like in Deep Impact or Armageddon, to deal with the threat of an extinction level event.. and often we learn about these asteroids after the impact has happened or once the rock has missed us by a hair.

    Read more: http://tommygilchrist.wordpress.com/2014/04/23/appreciating-asteroid-risks/

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  3. 3. JSBrooks 8:22 pm 04/23/2014

    I have been waiting more than 30 years since I did post graduate research in astronomy at the University of Arizona, for the astronomy community to get a clue, that asteroid and comet impacts are real and possibly the source of all of the major geological and biological epochs. So, now NASA finally has a new mission statement, detect and deflect earth threatening asteroids. It is about time.

    Link to this
  4. 4. Dr. Strangelove 4:15 am 04/25/2014

    Caleb

    The 70 unseen NEOs are in the asteroid belt. NASA has not searched the Kuiper belt which has over 100,000 objects and the Oort cloud which has over one trillion objects. Earth gets hit by giant meteors (5 km diameter) every 10 million years. The last big impact was 35 million years ago. We are overdue to be hit again.

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  5. 5. readsmore 2:26 am 05/30/2014

    asteroids certainly can be a real threat to the planet as we can see by the craters they leave behind on earth an the moon..awhile back have found melted rock in petosky michigan that could only have melted from entering through the earths atmosphere..so was checking online for more evidence and read that scientists are looking for impact crater in the upper us and canada. but as i was looking at a satalite image of michigan and the great lakes. specifically lake michigan and lake huron it appears to me that when the two lakes and michigan were under the glacier that an asteroid impact blew the two lakes out not glacier melt.. aaaaand then melt from lake superior filled lake michigan and huron…but of coarse its only theory…look at satalite image and see what you think…..

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