Death from the skies? Ho-hum.by Jeff Foust
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| The report found that achieving the asteroid detection goal in the 2005 authorization bill simply isn’t possible, given the lack of funding to date. |
Such meteorite falls are, of course, not that uncommon, but it’s one of a series of recent events that have raised interest, if only slightly, in the threats posed by near Earth objects (NEOs). Earlier this month a newly discovered asteroid, 2010 AL30, passed less than 125,000 kilometers—roughly one-third the Moon’s distance—from the Earth. While there was some speculation that the object was a spent rocket stage, astronomers believe the object is a small asteroid, no more than 10–15 meters across; objects that size pass closer to the Earth than the Moon every week. Meanwhile, NASA’s Wide-field Infrared Survey Explorer (WISE), launched last month to perform a full-sky survey at infrared wavelengths, has detected the first of what scientists expect to be hundreds of NEOs.
Then there are the curious comments of Anatoly Perminov, head of Roskosmos, the Russian space agency. Interviewed on Russian radio in late December, Perminov said that he would convene a meeting of Russian space researchers to study what to do about the asteroid Apophis. The asteroid poses a tiny chance—1 in 233,000—of colliding with the Earth in 2036, after making a close pass by the planet in 2029. Perminov, though, claimed that an unnamed scientist told him the asteroid “will surely collide with the Earth in the 2030s” and thus it was time to begin planning a project to alter the asteroid’s trajectory to prevent that impact. Why Perminov would pay so much attention to an asteroid that poses so little near-term risk to the Earth isn’t clear; some speculate it might be an effort to gain attention to Roskosmos, particularly within Russia, and win additional funding.
It is in this atmosphere that the Space Studies Board of the National Research Council issued Friday the report “Defending Planet Earth: Near-Earth Object Surveys and Hazard Mitigation Strategies”. The report, requested by Congress in the fiscal year 2008 appropriations bill that funded NASA, examined how to meet the goal set in the 2005 NASA authorization bill of detecting 90 percent of NEOs 140 meters in diameter or larger by 2020, as well as strategies for deflecting asteroids that would be on a collision course with us.
The report found that achieving the asteroid detection goal in the 2005 authorization bill simply isn’t possible: the funding needed to support the survey programs needed for it has neither been requested by the White House nor appropriated by Congress. If money were no object—an unlikely scenario—it would be possible to complete the survey as early as 2022 using a combination of groundbased telescopes and a space mission. Relying on groundbased telescopes alone would conserve costs but make it unlikely the detection goal could be achieved until about 2030.
| A table in the report notes that the expected average annual deaths from asteroids worldwide is just 91. That is orders of magnitude lower than other causes of death that many people rarely think about on a daily basis, from firearms accidents to malaria (1 million) to air pollution. |
However, the focus on this specific goal raises two issues. The first is that objects smaller than 140 meters across still pose a threat to the Earth. According to the report, “It is highly probable that the next destructive NEO event will be an airburst from a <50-meter object, not a crater-forming impact.” An object 140 meters across could produce damage on a regional scale, but such impacts are estimated to take place, on average, once every 30,000 years. An object 50 meters across can still cause local devastation—equivalent to a 10-megaton bomb—and occur about one every 2,000 years. The report recommends that NEO surveys, besides trying to fulfill the previous survey goal, “attempt to detect as many 30- to 50-meter objects as possible.”
The second issue is the funding needed to achieve these survey goals. The report includes three funding scenarios and what could be achieved under each. A budget of $250 million a year could support a number of ground- and space-based surveys as well as research into characterizing NEOs and studying mitigation techniques. For $50 million a year a groundbased survey could achieve the 140-meter NEO detection goal by 2030. At just $10 million a year some NEO surveys could be continued, but could not achieve the detection goals “on any timescale.” The problem with these scenarios? Currently NASA spends only about $4 million a year on NEO search efforts, with no indication that will change in the upcoming fiscal year 2011 budget proposal.
So are we all doomed? The report acknowledges that the infrequent but disastrous nature of asteroid impacts makes it difficult to communicate the risks to the general public. “This risk must therefore be communicated effectively to the community at large in the context of other natural disasters, particularly those that the local community is likely to encounter,” the report recommends, without going into further detail about how to accomplish that.
Even if those risks were effectively communicated to the public in some manner, though, it’s not clear it would increase support for more active NEO searches. A table in the report notes that the expected average annual deaths from asteroids worldwide is just 91. (That doesn’t mean that 91 people are killed every year by asteroid impacts—there have been no “significant” deaths in recorded history, the report notes—but that is the average when the potential deaths from infrequent but catastrophic impacts are taken into account.) That is orders of magnitude lower than other causes of death that many people rarely think about on a daily basis, from firearms accidents (25,000 per year) to malaria (1 million) to air pollution (2 million).
Much of that estimated death rate comes not from smaller objects but instead larger NEOs greater than one kilometer across, big enough to cause a global catastrophe. So far about 85 percent of the predicted population of such larger NEOs has been detected, and none of them pose an impact threat to the Earth for at least the next century. (When that isn’t taken into account, the average annual death toll jumps to over 1,000.) The other bump in the mortality curve comes from very small objects, less than 100 meters across: less energetic but more frequent, and whose populations hasn’t been well characterized.
| Perhaps the best prospect for bolstering NEO surveys is to make the hazards of such impact just one rationale among several for performing them. |
Thus the challenge facing NEO search advocates in their quest for additional funding: how to get the public, as well as legislators, to support expanded searches when the threat posed by them appears relatively modest compared to other causes, natural or manmade. A 50-meter NEO might kill a few hundred thousand people every couple of millenia, using the estimated rates in the report, yet in the last decade we have seen several natural disasters that have killed tens or hundreds of thousands of people, including this month’s Haiti earthquake, whose death toll has now exceeded 150,000. While those disasters could not have been prevented, the death tolls could have been greatly reduced through preventative measures ranging from stricter building codes to tsunami early warning systems. If we, as a society, are unwilling to spend the money to address those risks, why would we be willing to spend tens or hundreds of millions a year studying a much lower risk?
There are cases where the attention given to a particular risk far outweighs its actual threat to human life, be it for social, geopolitical, or other reasons. A classic example tangentially mentioned in the report is shark attacks. The media attention such attacks get is greatly outsized compared to their incidence: a fatality rate of just three to seven people per year worldwide. Sensationalizing asteroid impacts—already done to some degree thanks to movies like Armageddon and Deep Impact—might bolster attention to the threat, even if it is small, but even that may not translate into additional funding.
Perhaps the best prospect for bolstering NEO surveys is to make the hazards of such impact just one rationale among several for performing them. Such surveys can contribute to the science of such objects, and the solar system in general. Surveys can also identify NEOs that could be good destinations for future human expeditions, particularly if the White House adopts something like the “Flexible Path” option in last year’s Augustine Committee report, which included human NEO missions as one destination among several for that option. Finally, surveys and characterizing NEOs is a necessary first step towards eventual exploitation of their resources—ranging from water ice and other volatiles to metals—by a future spacefaring civilization.
None of these reasons alone may be sufficient to justify increased spending on NEO surveys, particularly if the federal budget environment becomes more austere in coming years to combat huge deficits, as some fear. Scientific studies would have to compete on their merits with other missions and studies elsewhere in the solar system. Also, even the staunchest advocate of space settlement and commercialization will admit it’s likely decades before we start mining NEOs. However, an amalgam of those rationales, perhaps led (and funded) by a new space exploration architecture, might be sufficient to win at least modest additional support for NEO studies.
In the meantime, existing surveys will continue, and astronomers will keep an eye out for objects of varying sizes that might some day be headed our way. However, despite what happened to Dr. Ciampi’s office last week, the risk of getting beaned by an asteroid while sitting in a doctor’s office is still far lower than the risk of getting killed in an auto accident on the way to or from the office.