Nations spend millions on defending against their neighbors, but should they band together to create a global defense against asteroids that could hit the earth?
David Morrison, director of the Carl Sagan Center for Study of Life in the Universe at the SETI institute, thinks so.
Morrison, who is no relation to the lawyer for whom the Morrison Planetarium is named, explained the odds of an asteroid collision and the need to prepare for one during a recent Dean Lecture in the planetarium at the California Academy of Sciences.
Earlier this year, residents of Chelyabinsk , Russia awoke to see a bright object streaking across the horizon followed by an enormous explosion and hundreds of windows shattering.
An asteroid about the size of the planetarium’s dome had broken through the earth’s atmosphere and detonated 20 meters above the ground, causing the shattering shock wave minutes later.
The collision came as something of an unwelcome surprise because ground-based telescopes could not detect the asteroid before impact due to the angle of sunlight.
Smaller asteroids are not monitored regularly by NASA and that’s part of the problem, Morrision contends.
“It’s a fascinating object,” Morrison said, “And in many ways typical of the small asteroids. There’s a million of that size or larger that could hit us.”
It wasn’t the first time an unwanted heavenly body crashed into earth causing devastation. An unknown object struck Tunguska, in rural Siberia in 1908, flattening and incinerating trees for hundreds of miles.
Several million years ago, an asteroid hit the earth near the Gulf of Mexico with such force that the impact of collision and the aftermath caused the extinction of the dinosaurs, scientists believe. Ninety percent of all animal life was obliterated excepted for smaller rodent like creatures, sharks and other deep sea fish and plants with hearty seed structures that could go dormant and revive years later.
The Chelhyabinsk incident took place near a city that has been a part of the Soviet and now Russian nuclear defense program. Morrison worries that such a blast could be mistaken for a nuclear missile attack but no such panic ensued after asteroid exploded.
“We can sleep more easily at night now because what was probably the greatest danger is probably overblown, at least if it happens in the U.S. and Russia,” he said.
In case you were worried there is no immediate threat of a world ending asteroid hitting soon.
A collision the size of the Cher occurs on average every 50 to 100 years, a Tunguska level event every 100 years and the mass dinosaur extinction, now referred to as KT, every 100 million years, Morrison said.
“The calculated risk of an asteroid is pretty low,” he said.
“It’s much less risky than driving in an automobile, flying in an airplane or getting cancer, but it’s a real problem.”
Most asteroid collisions have been away from populated areas, but a crash of the magnitude of Tunguska on a city like San Francisco would obliterate the area and all its inhabitants, Morrison said.
While ground impacts are rate, Morrison and his colleagues have documented that impacts with a magnitude of the Hiroshima and Nagasaki nuclear bombs have occurred in the upper atmosphere during the past 30 years.
They confirmed their theory by checking with military sources that tracked the explosions while looking for evidence of nuclear attacks or Intercontinental Ballistic Missile launches on earth during the Cold War.
To head off a serious asteroid collision, scientists need advance warning so planetary defenses could be readied, Morrison said.
Such doomsday scenarios are common in movies were the solution is to fire a nuclear weapon at the object and destroy it in a massive explosion.
That approach is unrealistic, Morrison said. Experts believe a rocket could be sent on a collision course with the asteroid, bumping it slightly off course and away from the earth.
Since the 1990’s researchers have identified more than 90 percent of near earth asteroids of one kilometer or larger, Morrison said.
But there are still plenty of smaller asteroids that could pose a threat and the goal is to find them in time and figure out how to deal with them.
Government funding for such a project is not forthcoming but at least one group, The B612 Foundation of Menlo Park, hopes to do it with private funds.
The group is gathering donations for the Sentinel Mission, in which a deep space telescope would be launched to a spot between the Earth and Venus to look for asteroids and identify potential threats.
Morrison insists that such an early warning system is essential and is one of the few natural occurrences that mankind can control.
“We know that we can’t stop an earthquake because we all know that the big one is going to come,” he said.
“We know that a volcano will erupt, we know that there are going to be storms and hurricanes. These are events that we have no hope of stopping. But if we find an asteroid on a collision course with Earth, we could divert it,” he said.