By Dean Irvine for CNN
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LONDON, England (CNN) -- What should we do if an asteroid is on a collision course with Earth? This question is being taken increasingly seriously by scientists as more is learnt about the impact a near earth object (NEO) would have on the future of civilization.
It might sound like the plot of a Hollywood movie, but one gigantic asteroid is scheduled to come within 20,000 miles of Earth in the near future -- a near miss in cosmic measurements -- and the possibility remains that it could hit our planet and cause catastrophic devastation never seen before.
"Human expansion into our solar system is fundamentally about the survival of the species. Our species hasn't been around long enough to experience a cataclysmic extinction event. But they will occur again whether we are ready for them or not," NASA Administrator Michael Griffin told an audience at Langley Research Center.
The asteroid that has made the space community sit up and take notice is nicknamed Apophis, after the Egyptian god of destruction.
Over 300 meters in diameter and weighing 25 million tons, it is set to come within 20,000 miles of Earth in 2029. And that date for the near miss? April 13, 2029, which should get the doomsday soothsayers excited.
We need not start preparing to evacuate Earth just yet. Scientists have been tracking the asteroid and with each new cache of data the chances of impact decrease. Current estimates put the chances of impact at one in 45,000.
The threat is real, however. If Apophis passes the earth at a distance of exactly 18,893 miles it will open a "gravitational keyhole" causing it to enter a new orbit that would put it on a direct collision course with earth seven years later. Current predictions are that Apophis will pass between 18,880 and 20,880 miles from earth.
Hitting the earth at 28,000 mph an asteroid the size and mass of Apophis would pack the energy of 58,000 Hiroshima nuclear bombs.
The "Tunguska Event" that flattened over 800 square miles of Siberian forest in 1908 was caused by a stony asteroid only 50 meters in diameter exploding in the lower atmosphere.
Leading the campaign for a global response to NEOs and a closer exploration of their physical make up is former astronaut Russell Schweickart, who piloted the lunar module of Apollo 9 in 1969.
He has been championing the cause to send a spacecraft onto an asteroid to study the potential mineral reserves there and also how one might be deflected if it was on a collision cause with Earth.
"The problem is nobody is responsible to protect the Earth. You might think that NASA does it, but that's not really their job. More needs to be done in terms of developing propulsion systems for spacecraft to intercept these NEOs because these are natural disasters that we can prevent," Schweickart told CNN.
"We have a good idea of what might come from Apophis and there inevitably will be other asteroids which will need different solutions and potential threats that will need new technology. Apophis was targeted because what better than to have practice at putting a transponder on an asteroid," he told CNN.
Placing a transponder on an asteroid would enable scientists to closely track the asteroid wherever it may be in its orbit via telescopes and radar from earth.
In 2005 Schweickart successfully campaigned for NASA to take the issue of NEOs seriously, the result has been a number of NASA centers developing prospective plans to land a spacecraft and even astronauts on an asteroid.
However the practicalities of landing a spacecraft to monitor, explore or deflect an asteroid still face a number of challenges. NASA is set to present the U.S. Congress with a report on how best to track and deal with the potential hazard of asteroids colliding with Earth at the end of the year and a Planetary Defense Conference will convene in March 2007, sponsored by a multi-national group including NASA, the European Space Agency and the Indian Space Research Organization.
Schweickart believes that the means to deflect an asteroid are already at our disposal and is pleased that NASA has agreed with him that action would need to be taken years before a potential impact in order to neutralize the threat.
The ways to deal with the threat include simply flying a spacecraft into an errant asteroid or either attaching one to it or parking one alongside it, like a gravity tractor, to pull it into another orbit.
The asteroid tugboat idea was developed by Schweickart and his team at Foundation B612. As a concept it's relatively straightforward. It involves the docking a small robotic spacecraft onto the surface of an asteroid and then using the same propulsion unit that got it there to push the asteroid off its course.
The alternative method of a gravity tractor spares the spacecraft the need to land. The spacecraft would be sent towards the asteroid and positioned either in front of it to speed it up or behind the NEO to slow it down. The technology is very similar to DeepSpace-1, the mission that was successfully sent to test emerging space technologies in 1999.
"There is no need for new technology in deflection spacecraft. You can just run into it as long as you get the direction correct and hit it fairly centrally. Most of the challenges are really only engineering based and certainly achievable," Schweickart told CNN.
The exploration of NEOs would be useful for NASA in the development of its Orion spacecraft that is being developed for its lunar missions.
Plans to land astronauts on an asteroid have been mooted and the technology involved in landing astronauts on the moon once again would not require too much adaptation to landing on an NEO. Valuable data could be collected with an NEO trial run, particularly testing Orion's high-speed heat shields.
Schweickart for one is an advocate of the idea and sees an NEO program as a win/win scenario:
"Public safety has to be a higher priority than exploration. It may be good to go back to the moon, but if you're going there for resources there are potentially far richer reserves on NEOs and they're easier to get to. We should be looking to use our resources to protect life on earth, plus it would cost a fraction of the proposed lunar mission.
"Even with all the plotting of asteroid orbits and tracking of them, action always will have to be taken before we know for sure whether or not an asteroid will hit earth. That is the nature of protecting the earth from impact. It happens very seldom, but when it does it is absolutely devastating."
Artist's impression of a spacecraft's rendevouz with a near earth object (NEO).