A study using data from monitoring stations designed to enforce a nuclear test ban treaty shows that the Earth is enduring far more dangerous asteroid impacts than previously thought.

Between 2000 and 2013, the Earth was hit by 26 asteroids that exploded with a force of between one and 600 kilotons – an average of one every six months. Even more concerning is that in all cases the asteroids themselves weren't detected in space and only came to light when they detonated in Earth's atmosphere.

The study was carried out by the B612 Foundation, a group set up by three former astronauts who are worried about the threat of asteroids to life on Earth. The foundation's CEO (and former shuttle pilot) Dr. Ed Lu presented the report's findings at a press conference in Seattle's Museum of Flight on Tuesday.

"While most large asteroids with the potential to destroy an entire country or continent have been detected, less than 10,000 of the more than a million dangerous asteroids with the potential to destroy an entire major metropolitan area have been found by all existing space or terrestrially operated observatories," said Lu.

"Because we don't know where or when the next major impact will occur, the only thing preventing a catastrophe from a 'city-killer' sized asteroid has been blind luck," he concluded.

The study notes that four of this century's collisions have been larger than the atomic bombs that took out Hiroshima and Nagasaki. In 2013, over a thousand people were injured when an asteroid exploded over Chelyabinsk, and 20 kiloton impacts were recorded over Indonesia, the Southern Ocean, and the Mediterranean.

All of these are dwarfed by the 1908 Tunguska impact, when the earth wandered into the path of a comet or large asteroid that exploded with a force of around 10 megatons – an explosion that leveled the surrounding forests and blasted down trees for 2,150 square kilometers (830 sq miles.)

NASA's Spaceguard project, named after the fictional asteroid-watching body described by Arthur C. Clarke, has done a good job at finding larger clumps of space junk that could seriously threaten human life on Earth, but it is missing a lot of the smaller debris that could just wipe out a city or cause a tsunami.

To spot this material, the B612 Foundation wants to build and launch a privately funded orbital asteroid detector, dubbed the Sentinel Space Telescope Mission. The designs have already been completed and the team estimates it could find 200,000 smaller asteroids a year after its planned 2018 launch.

The study shows that most of the kiloton-range explosions recorded this century resulted in very little debris striking the planet's surface. Asteroids are ablated by the earth's thick atmosphere and heat up to the point of explosion – most of the time – but sooner or later, probability suggests, one will hit and cause major damage. ®

Bootnote

The curious name of the B612 Foundation stems from the popular French book The Little Prince, by Antoine de Saint-Exupéry.

In the fable, the author meets a small man after crash-landing his plane in the desert, who explained he lived on an asteroid named B612. The foundation used this name because, it says, the moral of the prince's tale was that what is essential in life is often invisible to the human eye.