NASA should be assigned to lead a new research program to better determine the population and physical diversity of near-Earth objects that may collide with our planet, down to a size of 200 meters, according to the final report of a workshop on the scientific requirements for the mitigation of hazardous comets and asteroids.

The workshop's report also recommends that the U.S. Department of Defense (DoD) work to more rapidly communicate surveillance data on natural airbursts of smaller rocky bodies, and it concludes that governmental policy makers must "formulate a chain of responsibility" to be better prepared in the event that a threat to Earth becomes known.

"As our discussions proceeded, it became clear that the prime impediment to further advances in this field is the lack of assigned responsibility to any national or international governmental organization," said planetary scientist Michael Belton, organizer of the September 2002 workshop. "Since it is part of NASA's newly stated mission to 'understand and protect our home planet,' it seems obvious that this responsibility should reside in NASA."

Belton presented the findings of the workshop in Washington, DC, to officials at NASA, the National Science Foundation, and the Office of Management and Budget, and the report was delivered to the U.S. Congress.

About 2,225 near-Earth objects (NEOs) have been detected, primarily by ground- based optical searches, in the size range between 10 meters and 30 kilometers, out of a total estimated population of about one million; some information about the physical size and composition of these NEOs is available for only 300 objects.

The total number of objects a kilometer in diameter or larger, a size that could cause global catastrophe upon Earth impact, is now estimated to range between 900 and 1,230. The NASA-led Spaceguard Survey has a congressional mandate to detect 90% of these kilometer-sized objects by 2008, and it is making "excellent progress" on this goal, the report says.

However, a full survey of objects that could cause significant damage on Earth should reach down to NEOs at least as small as 200 meters, the report says, which should be within the capability of proposed ground-based facilities such as the Large Synoptic Survey Telescope and the PanStarrs telescope system. Ground-based radar systems will remain a "critical contributor" to obtaining the most accurate possible data on the orbits of many hazardous objects, the report says.

The workshop report discusses a preliminary roadmap based on five themes: more complete and accurate surveys of the orbits of potentially hazardous objects; improved public education about the risk; characterizing the physical properties of a range of asteroids and comets; more extensive laboratory research; and initial physical experiments toward a realistic plan to intercept and divert a future incoming object.

In order to keep maximum annual expenses on the order of a typical spacecraft mission (approximately $300 million), the report estimates that it would take about 25 years to accomplish this roadmap.

The workshop was attended by 77 scientists from the United States, Europe and Japan. It was co-sponsored by Ball Aerospace, Science Applications International Corp., Lockheed Martin Corp., the National Optical Astronomy Observatory and the University of Maryland.