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"Killer Asteroids . . . and what we can do about them"

by Louise Good

At the January Frontiers of Astronomy Community Lecture in Manoa (left to right), Ed Lu explains why we must be able to deflect asteroids, David Tholen defines the properties of asteroids, Robert Jedicke shows computer simulations, and Nick Kaiser explains how the Pan-STARRS project "will find killer asteroids before they find us." Photos by Karen Teramura.

"The chance of any one of us dying in an asteroid impact is roughly similar to the chances of you dying in a plane crash, but there is one big difference. Everyone of us is riding in the same airplane at the same time." So said Ed Lu, the former IfA solar physicist who is now a NASA astronaut in explaining why we must be prepared to deflect a large asteroid headed toward Earth. He participated in a Frontiers of Astronomy Community Lecture, "Killer Asteroids . . . and what we can do about them" on January 19 at UH Hilo and on January 22 at UH Manoa. Three IfA astronomers, David Tholen, Robert Jedicke, and Nicholas Kaiser, also spoke.

Lu compared an asteroid headed for a collision with Earth with two vehicles entering an intersection at the same time. If one speeds up or slows down even slightly so that they are not in the intersection at the same time, they will miss each other. Lu proposed building a gravity tractor--a spaceship that would hover over the asteroid headed for Earth. Such a spaceship would have enough gravity to change the speed of the asteroid by 0.001 mph, and if this were done over a long enough period of time, it could delay or speed up the asteroid just enough to miss Earth.

Lu explained why it would not be wise to blow up an asteroid: It would mean that the pieces would probably still hit Earth, doing considerable damage. He cited the case of Comet Shoemaker-Levy 9, which broke up into several pieces, all of which hit Jupiter. Lu further explained that trying to land on an asteroid or attach something to it might not work because many asteroids are essentially rubble piles held together by gravity. They are not very solid.

Lu advocates a mission to test the gravity tractor before we know an asteroid is headed our way. He pointed out that, though rare, major disasters do occur, and that being prepared is better than cleaning up the mess afterward. Much of the destruction wrought by Hurricane Katrina could have been prevented if the levees had been strengthened, and many of the lives lost in the December 2004 tsunami in Asia could have been saved if a tsunami warning system had been in place. He declared, "If we are wiped out by an asteroid, it will be our own fault," because unlike people living in earlier eras, "we do have a space program."

Astronomer Antoinette Cowie (center) examines a meteorite (piece of an asteroid that made it to Earth) after Ed Lu (lower right) spoke about gravity tractors at IfA in January. Photo by Karen Teramura.

Speaking first, Tholen told the audience all about asteroids--where they are and what they are made of. Tholen is a co-discoverer of the asteroid Apophis, which will miss Earth by only about 24,000 miles in 2029. This close encounter could change the asteroid's orbit, so that on its next close encounter with Earth in 2036, it will hit us. Tholen continues to observe Apophis with the UH telescope on Mauna Kea, "one of the few observatories in the world where we can still track it because it is so close to the Sun right now." He said we should know by 2013 whether we will be on a collision course in 2036.

Jedicke described how laboratory and computer simulations are used to determine what kind of threat asteroids pose to our planet. It is those larger than the size of a football field (about 100 yards in diameter) that we must worry about, since smaller ones burn up in the atmosphere, he said. (Apophis is about 425 yards in diameter.)

Kaiser likened our current condition to driving down the highway with our eyes closed because we don't know if there are any asteroids headed our way. Fortunately, the Pan-STARRS project, which he heads, will detect at least 90 percent of near-Earth asteroids that are large enough to pose a threat. He noted that people in Hawaii are playing key roles in developing the technology for this project. "The technology is happening fast, the technology is happening here," Kaiser stated.