Asteroid Impact Risks ‘Underappreciated’; Fascinating Video Shows Impact If an Asteroid Hit Planet Earth

Posted by on April 23, 2014 in Earth & Space, Sci-Tech with 0 Comments

BBC | 23rd April 2014

A visualisation showing where sizeable asteroids have hit the Earth in recent years has been released by the B612 Foundation.

The US-based group, which includes a number of former Nasa astronauts, campaigns on the issue of space protection.

It hopes the visualisation will press home the idea that impacts are more common than we think.

The presentation leans on data collected by the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO).

The CTBTO operates a network of sensors that listens out for clandestine atom bomb detonations.

Between 2000 and 2013, this infrasound system catalogued 26 major explosions on Earth.

None were caused by A-bombs; they were all the result of asteroid strikes.

They ranged in energy from one to 600 kilotons. By way of comparison, the bomb that destroyed the Japanese city of Hiroshima was a 15-kiloton device.

Fortunately, most of these space rocks disintegrated high up in the atmosphere and caused few problems on the ground.

A few, people will have heard about, such as the 20m-wide object that ripped across the sky above the Russian city of Chelyabinsk last year.

But many will have gone unseen because they occurred far out over the oceans.

And just one of the 26 events was detected in advance, and then by only a matter of hours.

Meteor over Chelyabinsk, 15 Feb
The Chelyabinsk impactor was small compared with some asteroids known to have struck the Earth

The advocacy group uses the frequency and size range of the impacts to say something about the probability of larger strikes in the future.

Because although Chelyabinsk was a terrifying experience for those caught up in it, the event itself was quite small compared with some of the incomers recorded through Earth history.

The foundation says the CTBTO data would suggest that Earth is hit by a multi-megaton asteroid – large enough to destroy a major city if it occurred over such an area – about every 100 years.

Remembering the Tunguska event of 1908 – it was fortunate that that object, thought to be about 45m wide, struck a very remote part of the globe.

“This is a bit like earthquakes,” explains Ed Lu, former shuttle astronaut and CEO of the B612 Foundation.

“In the cities that have a major danger – Tokyo, Los Angeles, San Francisco – they know the odds of big earthquakes by observing how many small earthquakes there are. Because there's a known distribution of earthquakes, meaning that earthquakes come in all sizes, small to large – if I can measure the small ones, I know how many big ones they're going to be. And you can do this with asteroids.

“These asteroid impacts in the last decade have been ones that we haven't had much data on until recently, and they tell us that in fact asteroid impacts are more common than we thought,” he told BBC News.

B612 is pushing its Sentinel telescope concept as a way to better quantify and mitigate the risks.

Projected to be ready for launch in 2018 and costing some $250m, the venture is being funded privately through donation.

The observatory would be sited in a Venus-like orbit, looking out towards Earth.

This would help pick up those inner-Solar-System rocks that go unseen by current telescopes at Earth because they are hidden in the glare of the Sun.

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