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Developing a risk assessment for Asteroids Earth collision is not about knowing when the next big impact of an asteroid on Earth will be. As a matter of fact it is to understand, for example, if:
But let’s not get ahead of ourselves and proceed one step at a time to quantify the risks (Probability associated to different consequences scenarios) of an asteroid-earth collision.
Potential colliding objects range from very small (a few millimeters) to small objects, burning up in the atmosphere as shooting stars. At the end of the scale lie very large rocks, say 10 kilometres “diameter”, likely the size that wiped out non-avian dinosaurs some 65 million years ago.
There are agencies responsible for monitoring the asteroid hazard. Among these, for example, the European Space Agency’s Space Situational Awareness project. Monitoring, however is not perfect. Indeed, the recent Chelyabinsk impact (2013), for example, caught everyone by surprise.
The largest impacts may occur every 100 million years (10-8), so widely in the “incredible” range of probabilities from a human point of view), but their impact could mean the end of Humanity. The date is unknown, despite the efforts of scientists. They have reportedly recorded 90% of the “space-monsters” and have come to the conclusion that there is “no immediate threat”, whatever that may mean, when dealing with “incredible” phenomena.
However, there are millions of asteroids in the 15m to 140m “diameter” range. 140m is reportedly the threshold for regional damage at the scale of a country or a continent.
Reportedly a 40m object was the culprit in the largest impact in recent history. It exploded over Tunguska, Siberia, on June 30, 1908: 80 million trees were flattened over approximately 2,000km2 of a sparsely populated region. That area is the same covered by some modern mega-cities like London, Tokyo, Sao Paolo.
Experts consider the frequency of Tunguska sized events in the 1/300 (3.3*10-3) range, i.e. comparable to large Earthquakes and in the realm of credible events (like tailings dams failures). There is a significant difference however: earthquakes destroy buildings that are not built to withstand them, but there is little to do against a “nuclear blast”-like impact coming from a colliding space object.
More recently, the 2013 Chelyabinsk impact damaged thousands of building and hurt many people from flying glass.
That type of object impact may be in the 1/10 (10-1) frequency. It likely corresponds to a 20m “diameter object” exploding in the atmosphere with up to multiple Hiroshima bombs power equivalent. The consequences in 2013 were relatively benign. Approximately 5,000 buildings’ windows were blown and over 1,200 people wounded.
Europe is setting up a network of telescopes to provide us with a heads-up before a collision.
The schedule calls for completion in about two years. The network will scan systematically the sky. It will reportedly be able to detect any asteroid with potential collision trajectory. That will allow a warning time of approximately two to three weeks.
At the very least, it will enable to evacuate cities or to issue a shockwave warning.
Asteroid collision seems to be the only predictable large natural hazard that good monitoring and mathematics can predict. Tsunamis, earthquakes and volcanoes remain widely unpredictable, despite monitoring efforts.
An asteroid deflection system would reportedly require “something in the order of 300-400 million euros” (dollars)—a minuscule amount compared to the cost of disaster.
The United Nations declared June 30 International Asteroid Day. The aim was to raise public awareness about what event organizers describe as “humanity’s greatest challenge”.