With the recent meteor explosion over Russia coincident with the safe-passing of asteroid 2012 DA14, and an expectant spectacular approach by comet ISON due towards the end of 2013, one could suggest that the Year of the Snake is one where we should look to the skies and consider our long term safeguard against rocks from space.
Indeed, following the near ‘double whammy’ last week, where a 15 meter meteor caught us by surprise and caused extensive damage and injury in central Russia, while the larger anticipated 50 meter asteroid swept to within just 27,000 km of Earth, media reported an immediate response from astronomers with plans to create state-of-the-art detection systems to give warning of incoming asteroids and meteoroids. Concerns can be abated.
ATLAS, the Advanced Terrestrial-Impact Last Alert System is due to begin operations in 2015, and expects to give a one-week warning for a small asteroid – called “a city killer” – and three weeks for a larger “county killer” — providing time for evacuation of risk areas.
Deep Space Industries (a US Company), which is preparing to launch a series of small spacecraft later this decade aimed at surveying nearby asteroids for mining opportunities, could also be used to monitor smaller difficult-to-detect objects that threaten to strike Earth.
However — despite ISON doom-merchants — we are already in relatively safe hands. The SENTRY MONITORING SYSTEM maintains a Sentry Risk Table of possible future Earth impact events, typically tracking objects 50 meters or larger — none of which are currently expected to hit Earth. Other sources will tell you that comet ISON is not expected to pass any closer than 0.42 AU (63,000,000 km) from Earth — though it should still provide spectacular viewing in our night skies come December 2013. A recently trending threat, 140-metre wide asteroid AG5 was given just a 1-in-625 chance of hitting Earth in February 2040, though more recent measurements have reduced this risk to almost nil. The Torino Scale is currently used to rate the risk category of asteroid and comet impacts on a scale of 0 (no hazard) to 10 (globally-impacting certain collisions). At present, almost all known asteroids and comets are categorized as level 0 on this scale (AG5 was temporarily categorized at level 1 until recent measurements, and 2007 VK184, a 130 meter asteroid due for approach circa 2048–2057 is the only currently listed one categorized at level 1 or more).
An asteroid striking land will cause a crater far larger than its size. The diameter calculated in kilometers is = (energy of impact)(1/3.4)/106.77. As such, if an asteroid the size of AG5 (140-meter wide) were to strike Earth, it would create a crater over twice the diameter of Barringer Meteor Crater in northern Arizona and affect an area far larger — or on striking water, it would create a global-reach tsunami. Fortunately, the frequency of such an object striking Earth is quite low — perhaps once every 100,000 years. It is the smaller ones, such as the one which exploded over Russia last week which are the greater concern. These occur perhaps once every 100 years and are not easily detectable by our current methods — justifying the $5m funding NASA contributed to the new ATLAS development in Hawaii.
We are a long way from deploying a response system to deflect/destroy incoming meteors, though at least with ATLAS we will be more confident of getting out of the way when the sky falls in. More information on ATLAS: http://www.fallingstar.com/index.php