Next week, the Earth's residents can once again play the popular game of "What if?" What if a hunk of cosmic rock is out there on a collision course with Earth? At the moment, an asteroid labeled "(433) Eros" is rushing toward our planet on a course that will bring it relatively close, at least on a cosmic scale.
On the one hand, the chunk of rock -- measuring 30 by 13 by 13 kilometers (19 by 8 by 8 miles) -- is approaching Earth closer than any asteroid of this size has for a long time. But on the other, it is currently following a circular path far beyond the moon's orbit.
Many people might shudder to think of these silent giants. But then they will go on about their daily business, forgetting all about (433) Eros and others. After all, in statistical terms, the chances of an asteroid that size hitting the Earth are still rather slim.
Nevertheless, there are still some people who remain focused on this threat. Among them are Alan Harris and his colleagues at a newly formed consortium working on behalf of the European Union to develop "mitigation" strategies against potential cosmic killers. Harris, a planetary scientist at the German Aerospace Center's Berlin-based Institute of Planetary Research, is leading the three-year NEOShield project, with "NEO" being the acronym for "near-Earth object."
The scientists know that Earth has suffered asteroid strikes over the course of its history. A number of gigantic craters attest to these impacts, including the Barringer Crater in Arizona, the Nördlinger Ries in southern Germany and the Manicouagan Reservoir in Canada.
Many Asteroids Still Unknown
But how can we protect ourselves against such a massive asteroid? From studying images taken by the "Wise" infrared telescope, NASA estimates there are over 980 asteroids with diameters of at least one kilometer in length. In addition, there are around 19,500 mid-sized examples, with diameters between 100-meters and one-kilometer long, most of which are still undiscovered.
Of course, that's not to mention the countless smaller rocks that could still cause devastation on a more local scale. In the coming years, experts say, asteroid databases will be bursting with new observational data. And some of these space rocks, they warn, might one day pose a danger to us.
In response to these worries, the European Commission recently decided to invest 4 million ($5.3 million) in the NEOShield project. An additional 1.8 million will come from scientific institutions and industry partners. Within three years' time, the experts hope to draw up a blueprint for a test mission. If it can find a financial backer, such as the European Space Agency (ESA), the mission could be launched as early as 2020.
In reality, however, a host of ideas have already been proposed for how to deal with an approaching asteroid. For example, there's the "kinetic impactor" idea, which envisions using a massive projectile to knock an asteroid off course. And there's the "gravity tractor" idea, which entails having a small probe hover near the asteroid and use its gravitational traction to deflect it from its Earth-bound course. Some have even proposed an approach to the problem that would involve launching an all-out attack with nuclear missiles.
"Of course, a lot of things have already been proposed," Harris says. "But, so far, most of them have come from a single institution, perhaps even from a single person. So it has been hard to pursue them." The new project aims to systematically investigate all of the mitigation methods that have already been proposed. "That will take place on paper and in lab experiments, since we don't have the money to do more than that," says Wolfram Lork, who handles the involvement of Astrium, a subsidiary of the European aerospace giant EADS, in the project.
Funding Low for the "Don Quijote" Program
Astrium has two teams working on potential designs for a "kinetic impactor." Company experts have already tinkered with ideas for this kind of spacecraft on behalf of the ESA. But, owing to funding shortfalls, the so-called "Don Quijote" mission study program has never made it past the drawing-board phase.
While the Europeans are back to working on a plan for a cosmic silver bullet of last resort, a team from the Carl Sagan Center of the SETI Institute, based in Mountain View, California, are exploring the concept of the "gravity tractor." In this case, a small probe would be brought into precise position to hover near the asteroid. Its mass would gradually provide "gravity traction to produce the required deflection" that would take the asteroid out of its collision course with Earth. However, the whole process could last years, if not perhaps even decades.
On the other hand, it could be quicker -- though a bit more rudimentary -- to use another option under consideration: warding off an asteroid with targeted explosive charges. Harris, the project head, calls this so-called "blast deflection" alternative the "final, desperate approach." Russian experts at TsNIIMash, the engineering division of the Russian Federal Space Agency (Roskosmos) that develops things such as long-range ballistic missiles and air defense missiles, will also be involved in researching this idea as part of the larger NEOShield project.
"We would like to present plans for a feasible, affordable mission. We want to show the world it can be done," Harris says. He adds, however, that it has yet to be determined whether the ultimate proposal will be for a gravity tractor or a kinetic impactor. It could even turn out to be a combination of the two, he says. But one thing is clear: There will be no tests using nuclear explosives.
Indeed, a number of international bodies will have to deal with the issue of potentially using nuclear devices to keep an asteroid from slamming into Earth. "That's not a matter that Europe can decide on for itself. In this case, the world has to be sitting at the table," says Lork, the Astrium official. Even the United Nations has already put the matter on its agenda, but nobody is counting on seeing an agreement made anytime soon.
In the meantime, researchers are working hard to find out whatever they can about our cosmic escorts. For example, NASA plans to launch its "OSIRIS-REx" probe in 2016 to pay a visit to the asteroid "1999 RQ36." If everything goes according to plan, the probe will return to Earth seven years later with up to two kilograms (4.4 pounds) of sample material in its hold.
Researchers at the German Aerospace Center (DLR) are also toying with the idea of launching an asteroid mission, even though it only entails observation. But the "AsteroidFinder" mission currently lacks an affordable launcher for the undertaking.
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