소행성으로 인한 지구적 종말을 두려워 마십시요, 당신이 생각하는 것보다 지구는 더 안전 합니다.

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On 30 June 1908, an asteroid struck the Tunguska region of Russia, devastating a forested area the size of a large city. Next Tuesday, on theanniversary of the Tunguska blast, a group led by astrophysicist and Queen guitarist Brian May and film-maker Grigorij Richters will host Asteroid Day, a celebrity-studded event in San Francisco and London designed to raise awareness of the potentially catastrophic risk of an impact.

But should we really be concerned about apocalyptic asteroids? There is no doubt that massive space rocks have the potential to harm life on Earth – just ask the dinosaurs.

Backers of Asteroid Day – including Chris Hadfield, Brian Cox and Richard Dawkins – call for a 100-fold acceleration of efforts to detect near-Earth asteroids in the next decade and increased funding to achieve this goal.

But asteroid-trackers say existing sky surveys already keep us safe, and events like Asteroid Day risk scaring people unnecessarily.

"The asteroid impact threat is very easy to overstate and misunderstand," saysEric Christensen of the University of Arizona in Tucson. "The popular conception of asteroids is that they are menacing and going to kill us all, and it's just not true."

How do we know the risk?

Christensen heads the Catalina Sky Survey, a NASA-funded initiative tasked with identifying potentially hazardous asteroids using sensitive ground-based telescopes. In the past decade or so, Catalina, other ground-surveys, and NASA's WISE space telescope have spotted thousands of near-Earth objects(NEOs).

As you would expect, larger asteroids are easier to spot, but there are fewer of them. Surveys show that we have found nearly all of the potentially world-destroying asteroids – those larger than a kilometre – but many smaller objects remain uncatalogued.

Here's how we know: astronomers can estimate how many asteroids of a given size are out there, even if we haven't seen them all, by looking at the rate of re-detection, or how often we see the same asteroid a second time. If we consistently see the same set of kilometre-sized rocks, and no new ones, then we can be pretty sure we have found them all.

When we look at rocks below that size, the gap between the number of asteroids we've seen and the number we think are out there widens (see graph below), according to a recent paper published in the journal Icarus that lays out the known unknowns.

Gap in our knowledge

Asteroid Day supporters think those smaller rocks are worth fretting over. This gap in our knowledge puts us at risk of being blindsided by an unseen threat, they argue.

"We're talking about things that might 'only' set the world economy back by a thousand years, or might 'only' kill 100 million people, those are the kinds of things we haven't yet found," says Ed Lu, chairman of the B612 Foundationbased in Mill Valley, California. B612 – named after the asteroid in The Little Prince - is a non-profit organisation aiming to build a private asteroid-hunting space telescope.

A meteor that exploded over Chelyabinsk, Russia (pictured below), in 2013 illustrated the potential risk. Although the rock was only around 20 metres across, it was the most energetic impact recorded since Tunguska. No one died, but about 1500 people were injured as the blast blew out windows and damaged buildings.

The event was alarming, especially because no one saw it coming;: not only was it too small to detect in advance, most telescopes were aimed at a larger, unrelated object that passed Earth harmlessly later the same day. But astronomers still don't expect another any time soon. Chelyabinsk-sized rocks are expected to hit Earth every few decades, but because the vast majority of the planet is either ocean or uninhabited, the risk to humans is minimal.

What will the next rock hit?

"It's probably going to be centuries before an asteroid like that hits over a populated area," says Christensen. "If you go up to the size of a Tunguska impactor, the next one will likely hit us within a few centuries and impact over the ocean."

So if we're safe from the really big asteroids, and the smaller, more frequent ones are likely to hit without major incident, what's the problem? It all depends on how much risk you're willing to accept, and how much money you're willing to spend to mitigate it.

Martin Rees of the University of Cambridge, who has signed the Asteroid Day declaration, says it's the same as calculating an insurance premium: you multiply the risk of impact by the cost of damage. By that measure, it is worth spending a billion dollars a year on reducing asteroid risk, he says.

How much should we spend?

That's 25 times as much as what we spend now. NASA currently spends around $40 million annually on asteroid surveys and other asteroid-related activities, and has instructions from US Congress to find all space rocks above 140 metres by 2020. In a report last year, NASA's Inspector General stated that the agency is unlikely to meet that without additional funding, so NASA has asked Congress to approve a further $10 million in 2016

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Don't worry, the sky's not falling in.............

[푸른강가]

소행성보다 두려운건
요사이 인간들의 잔악함과 욕심과
양심없슴 입니다

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네...

[Jenny]

공감합니다.

[정답조아]

들리는 소행성 소식으로 보건데 이때껏은 맞는말이라봅니다만 .. 앞으로에대해선 전혀 신빙성 없다 보입니다

[레프트사이드]

소행성 신경쓸 여력이 없네요.. ㅠㅠ

후쿠사마 원전 헬게이트 열렸는데..

고리원전, 경주방폐장 지전 암반층 아래 위치.. 덜덜덜..

[moon]

그게 무슨 말씀이신지..좀 자세히 써 주세요

[레프트사이드]

후쿠시마 원전 멜트다운.. 아무도 막을 수도 멈출 수도 없지요.. 인류에게는 멜트다운을 막을 기술이 없거든요.. 지층을 뚫고 어디까지 내려갈지 알 수가 없는 상황인데다..

원전 오염폐수는 2011년 3월 이후로 끊임없이 방사능 오염 폐수가 속절없이 태평양으로 흘러들어가고 있습니다.. 하루 3000톤씩..

근데 경주방폐장 위치 선정할 때.. 원전마피아 인간쓰레기들이 국민들을 속였다는 사실 아십니까.
손석희 뉴스에도 난 건데, 이것도 한 참 된 뉴스죠.. -_-
경주 방폐장에 지금 방사능 폐기물이 잔뜩 저장되어 있는데..

그곳 본래 지진대라더군요.. 덜덜덜..

경주 사람들은 시한폭탄 끓어앉고 먹고 자고 싸고 하는 거란 말이죠..