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On alert for asteroids
By DAVID BALLINGRUD, Times Staff Writer If this were an old sci-fi movie, now would be the time for a somber gathering of the world's scientists to consider what to do about the approaching menace from outer space. Outlandish ideas would be suggested and rejected. A plan would emerge -- risky and with limited prospects for success -- but the only option available to a desperate world. In the real world, Earth is not menaced by anything in outer space -- at least so far as we know. But many scientists have developed an increasing sense of urgency about the threat posed by asteroids, if only in a cosmic time frame. Just last month, an asteroid the size of a football field missed earth by a mere 74,000 miles -- about one-third the distance to the moon. And we didn't even see it until it had passed us. At summer's end, NASA will conduct a workshop to try to figure out what we could do if we spotted a comet or asteroid on a collision course with our planet. "We're a little like cavemen getting together to decide what to do about a mysterious threat like forest fires," said Dan Scheeres, a professor of aerospace engineering. But before a specific plan can be developed, before decisions can be made, "we need to understand asteroids better; we need to do basic science so we can talk intelligently about what to do." Lucy McFadden, a member of the NASA team planning a mission to a comet in 2004, said scientists feel different degrees of urgency. "There's not the kind of urgency such as, I'm concerned about my daughter flying into Dallas-Fort Worth in the rain. "But we can't predict the "when' or the "if' with asteroids so we can't ignore the issue either. "We need to find out what we need to know." * * * Over the eons, the earth has had numerous run-ins with asteroids. A crater near Winslow, Ariz., caused by a relatively small asteroid, is about 4,000 feet across. In 1908, an asteroid flattened 800 acres of forest in Siberia. An asteroid crashing into Earth may have ended the reign of the dinosaurs millions of years ago. Worries about an asteroid collision with Earth have grown in part because better detection has revealed how many close calls our planet has had.
The close call June 14 with the football-field sized asteroid was not detected till three days after it passed. Named 2002 MN, the object probably was large enough to have caused the kind of devastation Siberia experienced in 1908. On March 8, asteroid 2002 EM7 passed within about 288,000 miles of Earth. Like the June asteroid, it came from the "blind spot" near the sun and was not detected until several days after it passed. This is no cause for "doom and gloom," writes NASA asteroid expert David Morrison. Both were detected long before they threatened Earth, he said. "It makes no difference if an (asteroid) is discovered on approach or departure from the vicinity of the Earth," he said. "Objects in blind spots will be missed until they move into a more favorable geometry, sometimes within a few days, otherwise usually within a few years. Both of these asteroids were successfully found." * * * Asteroids are relatively small, rocky bodies orbiting the sun like planets. There are many thousands of them in the so-called "asteroid belt" beyond the orbit of Mars. Some are enormous, hundreds of miles in diameter; some 30 feet across, or even smaller. Most asteroids stay put in the belt, but from time to time one gets loose -- perhaps jarred free by a collision with another asteroid, or pulled out by the gravitational tug from nearby Jupiter. Earth's atmosphere protects the surface from most small asteroids, also called meteorites when seen from Earth. They burn up before they strike the ground. Larger ones, though, could pose a threat. NASA researchers have found more than 350 near-Earth asteroids more than a half-mile in diameter. From this, they estimate anywhere from 500 to 1,000 similar-sized objects could be spinning around the solar system. None has an orbit that will bring it anywhere near Earth in the near future. But scientists haven't found them all. Then there are the surprise flybys, including those from March and June. If one were headed for a collision with Earth, mankind's only course would be to try to change its path somehow, or destroy it. The workshop scheduled for September, "Scientific Requirements for Mitigation of Hazardous Comets and Asteroids," mostly will deal with the science of asteroids. Some members of the military will be present. "There's a common misconception that we're going to sit around with a bunch of arms experts and discuss how to blow an asteroid up," said McFadden, a University of Maryland research professor. "But we may not ever even have to consider something like that." A smorgasbord of topics are on the agenda. Scheeres, who was on a NASA team that flew an unmanned spacecraft to an asteroid in February of last year, will talk about "Fancy maneuvers: Hovering, Hopping and Tethering." He explained: "I've been studying how to control a spacecraft when it is next to or close to an asteroid's surface." Because gravity is light and erratic, hovering near an asteroid will be difficult. Some have suggested a tether might do the trick. Putting a rover on the surface to gather soil samples will be a headache, too, because the light gravity might mean a rover's wheels would not gain traction. "So the most efficient way to move a rover would be to have it hop," Scheeres said, "to jump up and come down somewhere else to take more samples." "We'll have a lot of interests represented, a lot of mind-sets," said workshop organizer Erik Asphaug of the University of California at Santa Cruz. "It will be fun." Scheeres, from the University of Michigan, said more people are paying attention. "I think there is a change in awareness taking place. I think it began when Shoemaker-Levy hit Jupiter almost a decade ago." From July 16 through July 22, 1994, pieces of Comet Shoemaker-Levy slammed into Jupiter in a spectacular, much photographed collision -- the first between two solar bodies ever to be observed. "That single event," Scheeres said, "showed people that the solar system is a very dynamic place, that catastrophic events are still happening."
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