So says a new report by the National Research Council of the National Academy of Sciences. The accompanying press release notes:
The report says the $4 million the U.S. spends annually to search for NEOs [Near Earth Objects] is insufficient to meet a congressionally mandated requirement to detect NEOs that could threaten Earth.
Congress mandated in 2005 that NASA discover 90 percent of NEOs whose diameter is 140 meters or greater by 2020, and asked the National Research Council in 2008 to form a committee to determine the optimum approach to doing so. In an interim report released last year, the committee concluded that it was impossible for NASA to meet that goal, since Congress has not appropriated new funds for the survey nor has the administration asked for them.
In its final report, the committee lays out two approaches that would allow NASA to complete its goal soon after the 2020 deadline; the approach chosen would depend on the priority policymakers attach to spotting NEOs. If finishing NASA's survey as close as possible to the original 2020 deadline is considered most important, a mission using a space-based telescope conducted in concert with observations from a suitable ground-based telescope is the best approach, the report says. If conserving costs is deemed most important, the use of a ground-based telescope only is preferable.
The report also recommends that NASA monitor for smaller objects – those down to 30 to 50 meters in diameter—which recent research suggests can be highly destructive. However, the report stresses that searching for smaller objects should not interfere with first fulfilling the mandate from Congress. Beyond completion of that mandate, the report notes the need for constant vigilance in monitoring the skies, so as to detect all dangerous NEOs. …
Near-Earth objects are asteroids and comets that orbit the sun and approach or cross Earth's orbit. An asteroid or comet about 10 kilometers in diameter struck the Yucatan peninsula 65 million years ago and caused global devastation, probably wiping out large numbers of plant and animal species including the dinosaurs. Objects as large as this one strike Earth only about once every 100 million years on average, the report notes. NASA has been highly successful at detecting and tracking objects 1 kilometer in diameter or larger, and continues to search for these large objects. Objects down to sizes of about 140 meters in diameter—which NASA has been mandated to survey for—would cause regional damage; such impacts happen on average every 30,000 years, the report says.
While impacts by large NEOs are rare, a single impact could inflict extreme damage, raising the classic problem of how to confront a possibility that is both very rare and very important. Far more likely are those impacts that cause only moderate damage and few fatalities. Conducting surveys for NEOs and detailed studies of ways to mitigate collisions is best viewed as a form of insurance, the report says.