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article imageKiller nuclear-level asteroids from space — but help is at hand

By Robert Myles     Apr 24, 2014 in Science
Seattle - How often do asteroids hit Earth? You may suppose such events occur more often in movies than real life, but you’d be wrong. This week, three astronauts revealed that Earth’s been pummelled 26 times by asteroids since the turn of the millennium.
Maybe it’s some sort of cosmic comfort blanket that causes us to believe that events such as the 2013 Chelyabinsk meteor that exploded above Russia are once-in-a-century potential Armageddons. In reality, Chelyabinsk was just one of numerous asteroids to have peppered Earth so far this century. On average asteroids, each a potential “killer asteroid,” have been hitting Earth at a rate of about two a year. Some of these impacts ranged in explosive power up to 40 times more powerful than the atomic bomb dropped on Hiroshima in 1945.
These startling figures, showing just how much Earth is threatened by passing space-rocks, were revealed earlier this week at a presentation at the Museum of Flight in Seattle given by three astronauts in support of the B612 Foundation as part of events marking Earth Day 2014.
Set up in 2002, B612 is a private foundation with the object of protecting Earth from asteroid impacts. Founder member Ed Lu, now B612’s CEO, is a former US shuttle and Soyuz astronaut. Along with former NASA astronaut Tom Jones and Apollo 8 astronaut William “Bill” Anders, Lu presented “Saving the Earth by Keeping Big Asteroids Away,” Tuesday past.
The three space-farers discussed recently released findings of the Comprehensive Nuclear Test-Ban Treaty Organization (CTBTO) on asteroid impacts. Among its other functions, the CTBTO operates a network of sensors across the globe that monitor day and night listening for the infra-sound signature of nuclear detonations. But the same sensors can also detect the explosive force of asteroids hitting Earth.
It was particularly fitting that Apollo 8 veteran Bill Anders should join the presentation. Anders was one of three astronauts aboard the Apollo 8 mission in 1968, the first to take astronauts beyond low Earth orbit, looping round the Moon and paving the way for the first lunar landing in 1969. Anders is credited with taking the iconic “Earthrise” photograph that, possibly more than any space photograph to date, has changed humanity’s perception of its place in the cosmos.
After retiring from NASA, Anders, who holds a Master of Science degree in nuclear engineering, was appointed to the Atomic Energy Commission in 1973. Subsequently, he became the first chairman of the Nuclear Regulatory Commission established by President Ford in 1975.
So why the nuclear connection? The reason is that, in considering the potential of asteroids to cause mayhem on Earth, the nearest Earthbound equivalent is the devastating force unleashed by nuclear devices.
Just like nuclear bombs, the “yield” of asteroids that collide with Earth is measured in kilotons or megatons of TNT and the same CTBTO sensors that detect nuclear explosions also pinpoint asteroid impacts.
Between 2000 and 2013, the sensor network detected 26 explosions on Earth ranging in energy output from 1 to 600 kilotons that were put down to asteroid impacts and not nuclear tests. Putting that in perspective, the first atomic bomb used in wartime, the “Little Boy” air-burst over Hiroshima on Aug. 6, 1945, had an explosive yield of 15 kilotons.
Most of this century’s asteroid impacts have, so far, exploded too high in the atmosphere to cause serious damage. Such was the case with 2013’s Chelyabinsk meteor in Russia, a 600 kiloton fireball that broke up into billions of smaller fragments that mostly burned up harmlessly in the atmosphere.
Nonetheless, the data that B612 gathers is important from the standpoint of assessing the frequency of a potential “city-killer-size” asteroid.
An illustration of just how close humanity came to facing such an apocalyptic event came in the early 20th century when the Tunguska meteor exploded over remote Siberian forests. The 1908 Tunguska event had an estimated energy impact of between 5 and 15 megatons — equivalent to 1000 Hiroshima detonations. Fortunately, it was trees that bore the brunt of the casualties back in 1908 with an estimated 2,000 square kilometers (770 square miles) of Siberian forests flattened.
More recently, a number of asteroid impacts exceeding 20 kilotons force have received little publicity: at South Sulawesi, Indonesia 2009, in the Southern Ocean 2004, and in the Mediterranean Sea 2002.
Significantly, in not one of these cases, despite the asteroid being on a collision trajectory with Earth, was the threat detected or tracked in advance by any existing space-based or terrestrial observatory.
Do you feel lucky?
That civilization, somewhere on Earth, has not yet been cauterized by a cosmic catastrophe is remarkable since less than one percent of potential “killer asteroids” have, so far, been detected.
As B612’s Ed Lu explained, “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.”
“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,” Lu added.
So how can humanity avert a scenario, such as that portrayed in the movie “Deep Impact”, being played out for real? Well, the B612 Foundation may have the answer. It’s aiming to construct the Sentinel Space Telescope Mission, an early warning infrared space telescope that would track asteroids.
In so doing, the Sentinel would provide many years warning in anticipation that preparations could be laid to deflect an asteroid millions of miles distant from Earth, long before it became an imminent threat to life on Earth.
Sentinel’s task is as ambitious as it is gargantuan. The privately funded mission, the first deep space mission that doesn’t rely on a national government funding, will provide astronomers and scientists with the first comprehensive, dynamic map of our inner solar system. The Sentinel will also identify the current and future locations and trajectories of Earth crossing asteroids. Planned for launch in 2018, mission scientists project the Sentinel space telescope will detect and track more than 200,000 asteroids — and that just in the first year of operation.
Until 2018, humanity will just have to ride its luck.
Author's note: Since the above article was published, the B612 Foundation has since made available a video of the Earth Day 2014 presentation at Seattle's Museum of Flight.
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