"Gravity Tractor," Super Telescopes Enlisted to Battle Killer Asteroids - National Geographics
Elizabeth Svoboda in
for National Geographic News
February 17, 2007
A giant asteroid named Apophis could be on a trajectory to careen into Earth in 2036. That was the prediction NASA scientists made in 2004, suggesting a 1 in 37 chance that the space rock would hit our planet.
The danger has since receded—the revised likelihood that Apophis will hit Earth is 1 in 45,000. But the close call has galvanized efforts among scientists to predict and hopefully prevent a potentially apocalyptic impact.
The aim, researchers said, is to defend the planet from an asteroid strike such as the one that slammed into
"There are 127 near-Earth objects we know about that have some chance of hitting us," said Russell Schweickart, a former Apollo astronaut and founder of the Houston, Texas-based Association of Space Explorers.
"You have to act when it looks like things are going to happen. If you wait until you're certain, it's going to be too late."
"Gravity Tractor," Super Scopes
Edward Lu, an astronaut and physicist at NASA, has developed a novel way to nudge off course any asteroids that appear to be headed for Earth.
Lu's proposed "gravitational tractor" is a spacecraft so massive—up to 20 tons (18 metric tons)—that it could divert an asteroid's path just by thrusting its engines in a specific direction while in the asteroid's vicinity.
"You don't aim your engines at the asteroids, you aim them to the side," he said. "That enables you to tow the asteroid just by the force of gravity."
In order for the gravitational tractor to work effectively, Lu said, international authorities would have to decide to use it long before an anticipated impact.
"You want many years or even decades of notice," he said. "It's like billiards—when you make a slight change before the bank shot, it creates a big change [in where the ball goes]."
Lu thinks other proposed interventions, such as detonating a nuclear bomb near an asteroid, would create more danger for Earth than they would avert.
- "There's a possibility of breaking chunks off, and even small chunks could cause tremendously bad effects," he said.
(See an interactive feature on asteroid impacts on Earth.)
Scientists also described two massive new survey-telescope projects to detect would-be killer asteroids.
One, dubbed Pan-STARRS, is slated to begin operation later this year. The project will use an array of four 6-foot-wide (1.8-meter-wide) telescopes in
The other program, the Large Synoptic Survey Telescope in
(Related news: "Google Partners With High-Tech Telescope to Map Universe" [January 10, 2007].)
When both of these new telescope projects go online, they will be able to detect objects much fainter than anything today's scopes pick up, the scientists said.
David Morrison, an astronomer at NASA's
"You can expect asteroids like Apophis [to be found] every month."
The influx of new discoveries will likely increase public anxieties about the asteroid threat, which makes a concrete scientific plan of action all the more necessary, the experts said.
In the wake of the Apophis incident, many lawmakers have become convinced of the importance of devoting more attention to asteroid searches.
In 2005 the U.S. Congress amended the Space Act to entrust NASA with the specific responsibility to "detect, track, catalog and characterize" asteroids and other near-Earth objects.
But to some scientists, these efforts aren't enough.
Schweickart, the former astronaut, thinks the United Nations needs to draft a treaty detailing standardized international measures that will be carried out in response to any asteroid threat.
His group, the Association of Space Explorers, has started building a team of scientists, risk specialists, and policymakers to draft such a treaty, which will be submitted to the UN for consideration in 2009.
Schweickart believes the uncertainty involved in predicting the path of an incoming asteroid makes a coordinated global response essential.
"When you look at where something like Apophis is going to hit, it's not going to be a single point, it's going to be a line of potential points," he said. "Therefore this is going to be inherently an international decision.
"We can't prevent a hurricane or a tornado," he continued. "But we can prevent an asteroid impact, and we can do it by slightly reshaping the solar system to enhance the survival of life on Earth.
"If we don't do that, we're not that far past the dinosaurs."