In the race to find all the interplanetary bodies that threaten Earth, astronomers have tallied more than 600 asteroids with estimated diameters of at least 1 kilometer. However, as several participants noted during a "space roundtable" held July 10th in Washington, D.C., governments should be doing more to find these and other near-Earth objects (NEOs). Titled "The Asteroid Threat: Identification and Mitigation Strategies," the roundtable was organized by ProSpace and the Space Frontier Foundation.
Colleen N. Hartman, NASA's director of solar-system exploration, noted that the space agency funds ground-based searches at roughly $4 million annually toward its goal of finding 90 percent of large near-Earth asteroids by 2008. But Brian G. Marsden (Minor Planet Center) expressed concern that the projected total of such objects currently near 1,200 may be higher than thought. He explains that when the telescopic census nears completion the discovery rate should start to tail off. Yet astronomers continue to find about 100 kilometer-size objects per year, with no sign of letting up.
Several participants noted the danger posed by smaller asteroids, such as the close-call object 2002 MN, and argued that it may be time to expand detection efforts to include bodies less than 1 km across. Gen. Simon P. Worden (U.S. Space Command) cautioned that strikes by skyscraper-size objects like 2002 MN could trigger tsunamis capable of killing millions. "I don't think we're being alarmist at all," commented Rick Tumlinson, president of the Space Frontier Foundation. "We're just trying to lay out the facts."
While the existing telescopic surveys would be ill equipped to systematically hunt for smaller objects, more aggressive search strategies have been proposed. Wide-field telescopes like the Large-aperture Synoptic Survey Telescope and Panoramic Optical Imager could record the sky nightly to 24th magnitude, faint enough to sweep up 300-meter asteroids in Earth's vicinity. Worden suggested that variants of orbiting defense satellites could be pressed into service, and Hartman volunteered that NASA has started looking into expanding its search strategy to smaller diameters.
However, the issue then becomes what do to with all these observations. Currently the staff of the Minor Planet Center, under Marsden's direction, is nearly overwhelmed with the glut of findings from existing surveys. Worden suggests that an NEO warning center, with a staff of five to 10, could easily be added to the existing U.S. Space Command, though he cautions that the Defense Department will not take on a major NEO role unless assigned to do so by the National Security Council. In the long term, Worden personally advocates that the military coordinate all cataloging and response activities, leaving NASA to focus on deducing the makeup of asteroids and comets.
"We're at the point of needing to move away from an ad hoc response," says aerospace engineer Warren Greczyn. He notes that the American Institute of Aeronautics and Astronautics recommends the formation of a top-level interagency group to advise the government on planetary-defense issues. Tumlinson adds that such oversight might well be integrated into proposals for a U.S. Department of Homeland Defense. Congressman Dana Rohrabacher, who chairs the House Subcommittee on Space and Aeronautics, likes the idea of utilizing military-derived technology to hunt down threatening NEOs. "The potential danger from global warming," he submits, "is nothing compared to the potential danger from near-Earth objects."