A new federal report on space rock detection and hazard mitigation strategies paints a disquieting picture of the current state of knowledge about how to protect the planet from a "near-Earth object" (NEO) impact that could potentially cause far more regional damage than the 2004 Indian Ocean earthquake and tsunami, or the recent quake in Haiti.
The bad news in the report from the National Research Council is that the $4 million in annual funding that several major NEO detection programs receive is nowhere near enough to meet a 2020 deadline set by Congress in 2005 for scientists to find 90 percent of near-Earth objects greater than 140-meters in diameter—space rocks of this size are likely to cause regional, rather than global, damage, though global damage is still possible. The mandate has yet to receive any funding. One of these regional-threat objects strikes Earth on average every 30,000 years, the report states.
Even $10 million in annual funds "would not allow completion on any timescale" of the Congressionally mandated survey of the threats, according to the report. Meeting Congress's goal would take at least $50 million in annual funding; even better would be $250 million in annual funding, with the latter allowing for completion of the survey and support for a space mission to test a mitigation plan.
Near-Earth objects are defined in the report as asteroids or comets with orbits approaching Earth's to within about one-third the average distance of Earth from the sun (0.33 AU, which is equivalent to150 million kilometers).
The two-part study and report, focused on NEO detection and NEO hazard mitigation, was sponsored by NASA at the request of Congress. Faith Vilas of the MMT Observatory at Mount Hopkins, Ariz., headed up the former effort, and Michael A'Hearn of the University of Maryland, College Park, headed up the latter.
The best way to come close to meeting the 2020 deadline is to combine a space-based telescope with a ground-based one to complete a survey by 2022 in the best-funded, best-case scenario, the report states. Alternatively, a ground-based survey alone could find the target objects "well before 2030" under a less aggressive funding approach. One candidate for the ground-based survey would be the Large Synoptic Survey Telescope (LSST), set to be constructed in Chile and designed for various science missions.
Along with a U.S.-led international "targeted research program" on impact hazard and mitigation of NEOs, the report also calls for continued funding of the Minor Planet Center at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., as well as the current federally funded NEO search projects. Continued operation of the radar systems at Arecibo Observatory in Puerto Rico and the Goldstone Deep Space Communications Complex (the former requires about $12 million annually) would also help scientists obtain highly accurate data on detected objects that would help in assessing their threat level, as well as their surface properties, mineralogy and rotation properties.
Mitigation methods assessed in the report are considered "relatively new and immature." They include simply evacuating residents from a threatened area, a tugboat-like spacecraft to nudge an object just far enough off its trajectory to avoid an Earth collision, smashing a spacecraft into an object to change its direction, or detonating a nuclear warhead on an object. Any violent blasting or impacting of a space rock heading toward Earth carries the risk that one of the fragments could still collide with the planet. None of these protection approaches could be readied on short notice, although the civil defense and impacting spacecraft are the closest to ready, the report states.
The survey to meet the 2005 mandate could be completed in 10 years with sufficient funding, A'Hearn says, and then it would take five years to work up a space mission to deflect any rock discovered to be on route to an Earth impact.
The report also notes newer research which shows that objects as small as 30 to 50 meters across could also be very destructive if they struck Earth, so the report authors recommend that surveys should try to find objects this small too, without compromising the effort to find the objects 140-meters in diameter and larger.
"The smaller events are far more frequent," A'Hearn says, adding that they are preventable.
Scientific and public awareness of the threat of space rocks has dawned slowly over the past several decades. Wake-up calls have included the late 1970s discovery of a crater near the Yucatan that was later linked by many with the extinction event that snuffed out non-avian dinosaurs, plesiosaurs, pterosaurs and many plant and invertebrate animal species. The 1994 collision of pieces of comet Shoemaker-Levy 9, some of them up to two kilometers in diameter, with Jupiter raised awareness that our solar system is still the site of some huge, violent impacts, even though the solar system's "late heavy bombardment " ended about four billion years ago (look at the moon for naked-eye evidence of that). In the past couple of years, the media has focused on various close NEO approaches, including a 350-meter asteroid called Apophis, which is swinging close in 2029 and again in 2036. An Apophis impact is now ruled out for 2029 and is "quite unlikely" in 2036, according to the report.
Still, planetary scientists haven't been asleep at the wheel and have continued searches with available funds and telescopes. In the past 10 years, 85 percent of the 940 or so largest space rocks (with diameters of one kilometer or more and that would cause global devastation, not just regional damage) that could smash into Earth have been found. None of them is expected to impact Earth in the next century, and scientists expect to find most of the rest of these asteroids and comets in the next few years.
Image: meteor crater via NASA Near Earth Object Program