[FPSPACE] FW: NEO News (05/22/08) Is the Sky Falling?

[LARRY KLAES]

>From: David Morrison <david.morrison at nasa.gov>
>To: David Morrison <david.morrison at nasa.gov>
>Subject: NEO News (05/22/08) Is the Sky Falling?
>Date: Thu, 22 May 2008 13:18:56 -0700
>
>NEO News (05/22/08) Is the Sky Falling?
>
>The June issue of The Atlantic features a long article on the impact threat 
>and how to defend against asteroids, called "The Sky is Falling". The 
>author is Gregg Easterbrook, a contributing editor to both The Atlantic and 
>The New Republic. This is one of the most visible and potentially 
>influential articles on NEO impact issues to be published in several years.
>
>Easterbrook has written an advocacy article, not an objective discussion of 
>this topic. His primary thesis (which I will not discuss further here) is 
>that NASA should make asteroid defense a major part of its mission, perhaps 
>replacing current emphasis on human flight to the Moon. To support this 
>thesis, Easterbrook has painted the impact hazard as severe and has chosen 
>examples that suggest that that the risk is much greater, by factors of up 
>to a thousand, than in the "conventional wisdom". I will comment briefly on 
>some of this evidence. I thank Bill Bottke, Mark Boslough, Clark Chapman, 
>Al Harris, Michael Paine, Rusty Schweickart, and other colleagues for their 
>email comments on this article.
>
>Here are some of the rhetorical techniques used by Easterbrook to dramatize 
>the threat.
>
>The article repeatedly states that perception of the threat is increasing, 
>but it does not indicate the baseline against which to measure this 
>supposed increase. While it is certainly true that we are much more aware 
>of the impact threat than we were a century ago, or even 50 years, it is 
>not true that the scientific perception of the threat has increased in the 
>past decade. In fact, current risk estimates are a factor or 2-3 lower than 
>the frequently-quoted values published by Chapman and Morrison in 1994 and 
>described in the NASA Spaceguard Report. The science threat estimate, which 
>is primarily what Easterbrook is discussing, has thus been stable and even 
>decreased over the past 15 years. However, it is true that the public 
>perception has been increasing.
>
>Of the various ways that the population and impact rate of NEAs are 
>calculated, Easterbrook mentions only estimates based on the number of 
>craters on land areas of Earth. There is no reference to the astronomical 
>surveys that today provide the best population estimates. He asserts that 
>until very recently the estimates of impact frequency, based on land 
>craters, neglected impacts into the ocean or airbursts like Tunguska; when 
>ocean impacts and airbursts are considered, the impact frequency jumps at 
>least a factor of ten. This is wrong. Gene Shoemaker and others, who began 
>in the 1980s to use terrestrial craters to estimate impact rates, counted 
>craters per unit area (thus correcting for unobserved areas such as the 
>ocean) and also allowed for airbursts that do not produce craters. Since 
>the early 1990s, impact rates derived from terrestrial craters, lunar 
>craters, and astronomical surveys have been consistent.
>
>There is one reference to survey results: Easterbrook writes "in 1980, only 
>86 [NEOs] were known to exist. By 1990, the figure had risen to 170; by 
>2000, it was 921, as of this writing, it was 5388." He apparently takes 
>these numbers as an indication that "near-Earth space rocks are more 
>numerous than once was thought." An analogy illustrates the flaws in this 
>logic: You move to a town of 50,000 and initially know only a handful of 
>your neighbors. After a decade the number of your acquaintances has 
>increased to several thousand. But this does not mean that the town has 
>grown; indeed, its population may have fallen from 50,000 to 40,000.
>
>Here is another paragraph that raises questions. He writes "A generation 
>ago, the standard assumption was that a dangerous object would strike the 
>Earth perhaps once in million years. By the mid-1990s, researchers began to 
>say that the threat was greater: perhaps a strike every 300,000 years. This 
>winter I asked William Ailor Š what he thought the risk was. Ailor's 
>answer: a one-in-ten chance per century of a dangerous 
>space-object-strike." Most readers of "NEO News" will recognize 
>one-in-a-million-years as the estimate for a civilization-threatening 
>impact, by a NEA 1-2 km across (energy a million megatons). The 
>one-in-a-thousand-year number quoted by Ailor is for a Tunguska class 
>airburst of 10 megatons, ten thousand times smaller. If we compare impacts 
>of the same size, then the current estimate for the million-megaton impact 
>is once in 2 million years, and the earlier (1994) estimate for Tunguska is 
>once in a couple of centuries. Both calculated frequencies are consistent 
>with each other, and both have gone down with our increasing knowledge, not 
>up.
>
>One could make many more criticisms, but these give the flavor of 
>Easterbrook's rhetorical style. You can judge for yourself in reading his 
>article, below.
>
>David Morrison
>
>=======================
>
>THE SKY IS FALLING
>
>Gregg Easterbrook
>The Atlantic, June 2008, pp 74-84
>
>Breakthrough ideas have a way of seeming obvious in retrospect, and about a 
>decade ago, a Columbia University geophysicist named Dallas Abbott had a 
>breakthrough idea. She had been pondering the craters left by comets and 
>asteroids that smashed into Earth. Geologists had counted them and 
>concluded that space strikes are rare events and had occurred mainly during 
>the era of primordial mists. But, Abbott realized, this deduction was based 
>on the number of craters found on land-and because 70 percent of Earth's 
>surface is water, wouldn't most space objects hit the sea? So she began 
>searching for underwater craters caused by impacts rather than by other 
>forces, such as volcanoes. What she has found is spine-chilling: evidence 
>that several enormous asteroids or comets have slammed into our planet 
>quite recently, in geologic terms. If Abbott is right, then you may be here 
>today, reading this magazine, only because by sheer chance those objects 
>struck the ocean rather than land.
>
>Abbott believes that a space object about 300 meters in diameter hit the 
>Gulf of Carpentaria, north of Australia, in 536 A.D. An object that size, 
>striking at up to 50,000 miles per hour, could release as much energy as 
>1,000 nuclear bombs. Debris, dust, and gases thrown into the atmosphere by 
>the impact would have blocked sunlight, temporarily cooling the planet-and 
>indeed, contemporaneous accounts describe dim skies, cold summers, and poor 
>harvests in 536 and 537. "A most dread portent took place," the Byzantine 
>historian Procopius wrote of 536; the sun "gave forth its light without 
>brightness." Frost reportedly covered China in the summertime. Still, the 
>harm was mitigated by the ocean impact. When a space object strikes land, 
>it kicks up more dust and debris, increasing the global-cooling effect; at 
>the same time, the combination of shock waves and extreme heating at the 
>point of impact generates nitric and nitrous acids, producing rain as 
>corrosive as battery acid. If the Gulf of Carpentaria object were to strike 
>Miami today, most of the city would be leveled, and the atmospheric effects 
>could trigger crop failures around the world.
>
>What's more, the Gulf of Carpentaria object was a skipping stone compared 
>with an object that Abbott thinks whammed into the Indian Ocean near 
>Madagascar some 4,800 years ago, or about 2,800 B.C. Researchers generally 
>assume that a space object a kilometer or more across would cause 
>significant global harm: widespread destruction, severe acid rain, and dust 
>storms that would darken the world's skies for decades. The object that hit 
>the Indian Ocean was three to five kilometers across, Abbott believes, and 
>caused a tsunami in the Pacific 600 feet high-many times higher than the 
>2004 tsunami that struck Southeast Asia. Ancient texts such as Genesis and 
>the Epic of Gilgamesh support her conjecture, describing an unspeakable 
>planetary flood in roughly the same time period. If the Indian Ocean object 
>were to hit the sea now, many of the world's coastal cities could be 
>flattened. If it were to hit land, much of a continent would be leveled; 
>years of winter and mass starvation would ensue.
>
>At the start of her research, which has sparked much debate among 
>specialists, Abbott reasoned that if colossal asteroids or comets strike 
>the sea with about the same frequency as they strike land, then given the 
>number of known land craters, perhaps 100 large impact craters might lie 
>beneath the oceans. In less than a decade of searching, she and a few 
>colleagues have already found what appear to be 14 large underwater impact 
>sites. That they've found so many so rapidly is hardly reassuring.
>
>Other scientists are making equally unsettling discoveries. Only in the 
>past few decades have astronomers begun to search the nearby skies for 
>objects such as asteroids and comets (for convenience, let's call them 
>"space rocks"). What they are finding suggests that near-Earth space rocks 
>are more numerous than was once thought, and that their orbits may not be 
>as stable as has been assumed. There is also reason to think that space 
>rocks may not even need to reach Earth's surface to cause cataclysmic 
>damage. Our solar system appears to be a far more dangerous place than was 
>previously believed.
>
>The received wisdom about the origins of the solar system goes something 
>like this: the sun and planets formed about 4.5 billion years ago from a 
>swirling nebula containing huge amounts of gas and dust, as well as 
>relatively small amounts of metals and other dense substances released by 
>ancient supernova explosions. The sun is at the center; the denser planets, 
>including Earth, formed in the middle region, along with many asteroids-the 
>small rocky bodies made of material that failed to incorporate into a 
>planet. Farther out are the gas-giant planets, such as Jupiter, plus vast 
>amounts of light elements, which formed comets on the boundary of the solar 
>system. Early on, asteroids existed by the millions; the planets and their 
>satellites were bombarded by constant, furious strikes. The heat and shock 
>waves generated by these impacts regularly sterilized the young Earth. Only 
>after the rain of space objects ceased could life begin; by then, most 
>asteroids had already either hit something or found stable orbits that do 
>not lead toward planets or moons. Asteroids still exist, but most were 
>assumed to be in the asteroid belt, which lies between Mars and Jupiter, 
>far from our blue world.
>
>As for comets, conventional wisdom held that they also bombarded the 
>planets during the early eons. Comets are mostly frozen water mixed with 
>dirt. An ancient deluge of comets may have helped create our oceans; lots 
>of comets hit the moon, too, but there the light elements they were 
>composed of evaporated. As with asteroids, most comets were thought to have 
>smashed into something long ago; and, because the solar system is largely 
>void, researchers deemed it statistically improbable that those remaining 
>would cross the paths of planets.
>
>These standard assumptions-that remaining space rocks are few, and that 
>encounters with planets were mainly confined to the past-are being upended. 
>On March 18, 2004, for instance, a 30-meter asteroid designated 2004 FH-a 
>hunk potentially large enough to obliterate a city-shot past Earth, not far 
>above the orbit occupied by telecommunications satellites. (Enter "2004 FH" 
>in the search box at Wikipedia and you can watch film of that asteroid 
>passing through the night sky.) Looking at the broader picture, in 1992 the 
>astronomers David Jewitt, of the University of Hawaii, and Jane Luu, of the 
>Massachusetts Institute of Technology, discovered the Kuiper Belt, a region 
>of asteroids and comets that starts near the orbit of Neptune and extends 
>for immense distances outward. At least 1,000 objects big enough to be seen 
>from Earth have already been located there. These objects are 100 
>kilometers across or larger, much bigger than whatever dispatched the 
>dinosaurs; space rocks this size are referred to as "planet killers" 
>because their impact would likely end life on Earth. Investigation of the 
>Kuiper Belt has just begun, but there appear to be substantially more 
>asteroids in this region than in the asteroid belt, which may need a new 
>name.
>
>Beyond the Kuiper Belt may lie the hypothesized Oort Cloud, thought to 
>contain as many as trillions of comets. If the Oort Cloud does exist, the 
>number of extant comets is far greater than was once believed. Some 
>astronomers now think that short-period comets, which swing past the sun 
>frequently, hail from the relatively nearby Kuiper Belt, whereas comets 
>whose return periods are longer originate in the Oort Cloud.
>
>But if large numbers of comets and asteroids are still around, several 
>billion years after the formation of the solar system, wouldn't they by now 
>be in stable orbits-ones that rarely intersect those of the planets? Maybe 
>not. During the past few decades, some astronomers have theorized that the 
>movement of the solar system within the Milky Way varies the gravitational 
>stresses to which the sun, and everything that revolves around it, is 
>exposed. The solar system may periodically pass close to stars or groups of 
>stars whose gravitational pull affects the Oort Cloud, shaking comets and 
>asteroids loose from their orbital moorings and sending them downward, 
>toward the inner planets.
>
>Consider objects that are already near Earth, and the picture gets even 
>bleaker. Astronomers traditionally spent little time looking for asteroids, 
>regarding them as a lesser class of celestial bodies, lacking the beauty of 
>comets or the significance of planets and stars. Plus, asteroids are hard 
>to spot-they move rapidly, compared with the rest of the heavens, and even 
>the nearby ones are fainter than other objects in space. Not until the 
>1980s did scientists begin systematically searching for asteroids near 
>Earth. They have been finding them in disconcerting abundance.
>
>In 1980, only 86 near-Earth asteroids and comets were known to exist. By 
>1990, the figure had risen to 170; by 2000, it was 921; as of this writing, 
>it is 5,388. The Jet Propulsion Laboratory, part of NASA, keeps a running 
>tally at www.neo.jpl.nasa.gov/stats. Ten years ago, 244 near-Earth space 
>rocks one kilometer across or more-the size that would cause global 
>calamity-were known to exist; now 741 are. Of the recently discovered 
>nearby space objects, NASA has classified 186 as "impact risks" (details 
>about these rocks are at www.neo.jpl.nasa.gov/risk). And because most 
>space-rock searches to date have been low-budget affairs, conducted with 
>equipment designed to look deep into the heavens, not at nearby space, the 
>actual number of impact risks is undoubtedly much higher. Extrapolating 
>from recent discoveries, NASA estimates that there are perhaps 20,000 
>potentially hazardous asteroids and comets in the general vicinity of 
>Earth.
>
>There's still more bad news. Earth has experienced several mass 
>extinctions-the dinosaurs died about 65 million years ago, and something 
>killed off some 96 percent of the world's marine species about 250 million 
>years ago. Scientists have generally assumed that whatever caused those 
>long-ago mass extinctions-comet impacts, extreme volcanic activity-arose 
>from conditions that have changed and no longer pose much threat. It's a 
>comforting notion-but what about the mass extinction that occurred close to 
>our era?
>
>About 12,000 years ago, many large animals of North America started 
>disappearing-woolly mammoths, saber-toothed cats, mastodons, and others. 
>Some scientists have speculated that Paleo-Indians may have hunted some of 
>the creatures to extinction. A millennia-long mini-Ice Age also may have 
>been a factor. But if that's the case, what explains the disappearance of 
>the Clovis People, the best-documented Paleo-Indian culture, at about the 
>same time? Their population stretched as far south as Mexico, so the 
>mini-Ice Age probably was not solely responsible for their extinction.
>
>A team of researchers led by Richard Firestone, of the Lawrence Berkeley 
>National Laboratory, in California, recently announced the discovery of 
>evidence that one or two huge space rocks, each perhaps several kilometers 
>across, exploded high above Canada 12,900 years ago. The detonation, they 
>believe, caused widespread fires and dust clouds, and disrupted climate 
>patterns so severely that it triggered a prolonged period of global 
>cooling. Mammoths and other species might have been killed either by the 
>impact itself or by starvation after their food supply was disrupted. These 
>conclusions, though hotly disputed by other researchers, were based on 
>extensive examinations of soil samples from across the continent; in strata 
>from that era, scientists found widely distributed soot and also magnetic 
>grains of iridium, an element that is rare on Earth but common in space. 
>Iridium is the meteor-hunter's lodestar: the discovery of iridium dating 
>back 65 million years is what started the geologist Walter Alvarez on his 
>path-breaking theory about the dinosaurs' demise.
>
>A more recent event gives further cause for concern. As buffs of the 
>television show The X Files will recall, just a century ago, in 1908, a 
>huge explosion occurred above Tunguska, Siberia. The cause was not a 
>malfunctioning alien star-cruiser but a small asteroid or comet that 
>detonated as it approached the ground. The blast had hundreds of times the 
>force of the Hiroshima bomb and devastated an area of several hundred 
>square miles. Had the explosion occurred above London or Paris, the city 
>would no longer exist. Mark Boslough, a researcher at the Sandia National 
>Laboratory, in New Mexico, recently concluded that the Tunguska object was 
>surprisingly small, perhaps only 30 meters across. Right now, astronomers 
>are nervously tracking 99942 Apophis, an asteroid with a slight chance of 
>striking Earth in April 2036. Apophis is also small by asteroid standards, 
>perhaps 300 meters across, but it could hit with about 60,000 times the 
>force of the Hiroshima bomb-enough to destroy an area the size of France. 
>In other words, small asteroids may be more dangerous than we used to 
>think-and may do considerable damage even if they don't reach Earth's 
>surface.
>
>Until recently, nearly all the thinking about the risks of space-rock 
>strikes has focused on counting craters. But what if most impacts don't 
>leave craters? This is the prospect that troubles Boslough. Exploding in 
>the air, the Tunguska rock did plenty of damage, but if people had not seen 
>the flashes, heard the detonation, and traveled to the remote area to 
>photograph the scorched, flattened wasteland, we'd never know the Tunguska 
>event had happened. Perhaps a comet or two exploding above Canada 12,900 
>years ago spelled the end for saber-toothed cats and Clovis society. But no 
>obvious crater resulted; clues to the calamity were subtle and hard to come 
>by.
>
>Comets, asteroids, and the little meteors that form pleasant shooting stars 
>approach Earth at great speeds-at least 25,000 miles per hour. As they 
>enter the atmosphere they heat up, from friction, and compress, because 
>they decelerate rapidly. Many space rocks explode under this stress, 
>especially small ones; large objects are more likely to reach Earth's 
>surface. The angle at which objects enter the atmosphere also matters: an 
>asteroid or comet approaching straight down has a better chance of hitting 
>the surface than one entering the atmosphere at a shallow angle, as the 
>latter would have to plow through more air, heating up and compressing as 
>it descended. The object or objects that may have detonated above Canada 
>12,900 years ago would probably have approached at a shallow angle.
>
>If, as Boslough thinks, most asteroids and comets explode before reaching 
>the ground, then this is another reason to fear that the conventional 
>thinking seriously underestimates the frequency of space-rock strikes-the 
>small number of craters may be lulling us into complacency. After all, if a 
>space rock were hurtling toward a city, whether it would leave a crater 
>would not be the issue-the explosion would be the issue.
>
>A generation ago, the standard assumption was that a dangerous object would 
>strike Earth perhaps once in a million years. By the mid-1990s, researchers 
>began to say that the threat was greater: perhaps a strike every 300,000 
>years. This winter, I asked William Ailor, an asteroid specialist at The 
>Aerospace Corporation, a think tank for the Air Force, what he thought the 
>risk was. Ailor's answer: a one-in-10 chance per century of a dangerous 
>space-object strike.
>
>Regardless of which estimate is correct, the likelihood of an event is, of 
>course, no predictor. Even if space strikes are likely only once every 
>million years, that doesn't mean a million years will pass before the next 
>impact-the sky could suddenly darken tomorrow. Equally important, 
>improbable but cataclysmic dangers ought to command attention because of 
>their scope. A tornado is far more likely than an asteroid strike, but 
>humanity is sure to survive the former. The chances that any one person 
>will die in an airline crash are minute, but this does not prevent us from 
>caring about aviation safety. And as Nathan Myhrvold, the former chief 
>technology officer of Microsoft, put it, "The odds of a space-object strike 
>during your lifetime may be no more than the odds you will die in a plane 
>crash-but with space rocks, it's like the entire human race is riding on 
>the plane."
>
>Given the scientific findings, shouldn't space rocks be one of NASA's 
>priorities? You'd think so, but Dallas Abbott says NASA has shown no 
>interest in her group's work: "The NASA people don't want to believe me. 
>They won't even listen."
>
>NASA supports some astronomy to search for near-Earth objects, but the 
>agency's efforts have been piecemeal and underfunded, backed by less than a 
>tenth of a percent of the NASA budget. And though altering the course of 
>space objects approaching Earth appears technically feasible, NASA 
>possesses no hardware specifically for this purpose, has nearly nothing in 
>development, and has resisted calls to begin work on protection against 
>space strikes. Instead, NASA is enthusiastically preparing to spend 
>hundreds of billions of taxpayers' dollars on a manned moon base that has 
>little apparent justification. "What is in the best interest of the country 
>is never even mentioned in current NASA planning," says Russell 
>Schweick-art, one of the Apollo astronauts who went into space in 1969, who 
>is leading a campaign to raise awareness of the threat posed by space 
>rocks. "Are we going to let a space strike kill millions of people before 
>we get serious about this?" he asks.
>
>In January, I attended an internal NASA conference, held at agency 
>headquarters, during which NASA's core goals were presented in a PowerPoint 
>slideshow. Nothing was said about protecting Earth from space strikes-not 
>even researching what sorts of spacecraft might be used in an 
>approaching-rock emergency. Goals that were listed included "sustained 
>human presence on the moon for national preeminence" and "extend the human 
>presence across the solar system and beyond." Achieving national 
>preeminence-isn't the United States pretty well-known already? As for 
>extending our presence, a manned mission to Mars is at least decades away, 
>and human travel to the outer planets is not seriously discussed by even 
>the most zealous advocates of space exploration. Sending people "beyond" 
>the solar system is inconceivable with any technology that can reasonably 
>be foreseen; an interstellar spaceship traveling at the fastest speed ever 
>achieved in space flight would take 60,000 years to reach the next-closest 
>star system.
>
>After the presentation, NASA's administrator, Michael Griffin, came into 
>the room. I asked him why there had been no discussion of space rocks. He 
>said, "We don't make up our goals. Congress has not instructed us to 
>provide Earth defense. I administer the policy set by Congress and the 
>White House, and that policy calls for a focus on return to the moon. 
>Congress and the White House do not ask me what I think." I asked what 
>NASA's priorities would be if he did set the goals. "The same. Our 
>priorities are correct now," he answered. "We are on the right path. We 
>need to go back to the moon. We don't need a near-Earth-objects program." 
>In a public address about a month later, Griffin said that the moon-base 
>plan was "the finest policy framework for United States civil space 
>activities that I have seen in 40 years."
>
>Actually, Congress has asked NASA to pay more attention to space rocks. In 
>2005, Congress instructed the agency to mount a sophisticated search of the 
>proximate heavens for asteroids and comets, specifically requesting that 
>NASA locate all near-Earth objects 140 meters or larger that are less than 
>1.3 astronomical units from the sun-roughly out to the orbit of Mars. Last 
>year, NASA gave Congress its reply: an advanced search of the sort Congress 
>was requesting would cost about $1 billion, and the agency had no intention 
>of diverting funds from existing projects, especially the moon-base 
>initiative.
>
>How did the moon-base idea arise? In 2003, after the shuttle Columbia was 
>lost, manned space operations were temporarily shut down, and the White 
>House spent a year studying possible new missions for NASA. George W. Bush 
>wanted to announce a voyage to Mars. Every Oval Office occupant since John 
>F. Kennedy knows how warmly history has praised him for the success of his 
>pledge to put men on the moon; it's only natural that subsequent presidents 
>would dream about securing their own place in history by sending people to 
>the Red Planet. But the technical barriers and even the most optimistic 
>cost projections for a manned mission to Mars are prohibitive. So in 2004, 
>Bush unveiled a compromise plan: a permanent moon base that would be 
>promoted as a stepping-stone for a Mars mission at some unspecified future 
>date. As anyone with an aerospace engineering background well knows, 
>stopping at the moon, as Bush was suggesting, actually would be an 
>impediment to Mars travel, because huge amounts of fuel would be wasted 
>landing on the moon and then blasting off again. Perhaps something useful 
>to a Mars expedition would be learned in the course of building a moon 
>base; but if the goal is the Red Planet, then spending vast sums on lunar 
>living would only divert that money from the research and development 
>needed for Mars hardware. However, saying that a moon base would one day 
>support a Mars mission allowed Bush to create the impression that his plan 
>would not merely be restaging an effort that had already been completed 
>more than 30 years before. For NASA, a decades-long project to build a moon 
>base would ensure a continuing flow of money to its favorite contractors 
>and to the congressional districts where manned-space-program centers are 
>located. So NASA signed on to the proposal, which Congress approved the 
>following year.
>
>It is instructive, in this context, to consider the agency's rhetoric about 
>China. The Chinese manned space program has been improving and is now about 
>where the U.S. program was in the mid-1960s. Stung by criticism that the 
>moon-base project has no real justification-37 years ago, President Richard 
>Nixon cancelled the final planned Apollo moon missions because the program 
>was accomplishing little at great expense; as early as 1964, the 
>communitarian theorist Amitai Etzioni was calling lunar obsession a 
>"moondoggle"-NASA is selling the new plan as a second moon race, this time 
>against Beijing. "I'll be surprised if the Chinese don't reach the moon 
>before we return," Griffin said. "China is now a strategic peer competitor 
>to the United States in space. China is drawing national prestige from 
>achievements in space, and there will be a tremendous shift in national 
>prestige toward Beijing if the Chinese are operating on the moon and we are 
>not. Great nations have always operated on the frontiers of their era. The 
>moon is the frontier of our era, and we must outperform the Chinese there."
>
>Wouldn't shifting NASA's focus away from wasting money on the moon and 
>toward something of clear benefit for the entire world-identifying and 
>deflecting dangerous space objects-be a surer route to enhancing national 
>prestige? But NASA's institutional instinct is not to ask, "What can we do 
>in space that makes sense?" Rather, it is to ask, "What can we do in space 
>that requires lots of astronauts?" That finding and stopping space rocks 
>would be an expensive mission with little role for the astronaut corps is, 
>in all likelihood, the principal reason NASA doesn't want to talk about the 
>asteroid threat.
>
>NASA's lack of interest in defending against space objects leaves a void 
>the Air Force seems eager to fill. The Air Force has the world's 
>second-largest space program, with a budget of about $11 billion-$6 billion 
>less than NASA's. The tension between the two entities is long-standing. 
>Many in the Air Force believe the service could achieve U.S. space 
>objectives faster and more effectively than NASA. And the Air Force simply 
>wants flyboys in orbit: several times in the past, it has asked Congress to 
>fund its own space station, its own space plane, and its own space-shuttle 
>program. Now, with NASA all but ignoring the space-object threat, the Air 
>Force appears to be seizing an opportunity.
>
>All known space rocks have been discovered using telescopes designed for 
>traditional "soda straw" astronomy-that is, focusing on a small patch of 
>sky. Now the Air Force is funding the first research installation designed 
>to conduct panoramic scans of the sky, a telescope complex called 
>Pan-STARRS, being built by the University of Hawaii. By continuously 
>panning the entire sky, Pan-STARRS should be able to spot many near-Earth 
>objects that so far have gone undetected. The telescope also will have 
>substantially better resolving power and sensitivity than existing survey 
>instruments, enabling it to find small space rocks that have gone 
>undetected because of their faintness.
>
>The Pan-STARRS project has no military utility, so why is the Air Force the 
>sponsor? One speculation is that Pan-STARRS is the Air Force's foot in the 
>door for the Earth-defense mission. If the Air Force won funding to build 
>high-tech devices to fire at asteroids, this would be a major milestone in 
>its goal of an expanded space presence. But space rocks are a natural 
>hazard, not a military threat, and an Air Force Earth-protection 
>initiative, however gallant, would probably cause intense international 
>opposition. Imagine how other governments would react if the Pentagon 
>announced, "Don't worry about those explosions in space-we're protecting 
>you."
>
>Thus, the task of defending Earth from objects falling from the skies seems 
>most fitting for NASA, or perhaps for a multinational civilian agency that 
>might be created. Which raises the question: What could NASA, or anyone 
>else, actually do to provide a defense?
>
>Russell Schweickart, the former Apollo astronaut, runs the B612 Foundation 
>(B612 is the asteroid home of Saint-Exupéry's Little Prince). The 
>foundation's goal is to get NASA officials, Congress, and ultimately the 
>international community to take the space-rock threat seriously; it 
>advocates testing a means of precise asteroid tracking, then trying to 
>change the course of a near-Earth object.
>
>Current telescopes cannot track asteroids or comets accurately enough for 
>researchers to be sure of their courses. When 99942 Apophis was spotted, 
>for example, some calculations suggested it would strike Earth in April 
>2029, but further study indicates it won't-instead, Apophis should pass 
>between Earth and the moon, during which time it may be visible to the 
>naked eye. The Pan-STARRS telescope complex will greatly improve 
>astronomers' ability to find and track space rocks, and it may be joined by 
>the Large Synoptic Survey Telescope, which would similarly scan the entire 
>sky. Earlier this year, the software billionaires Bill Gates and Charles 
>Simonyi pledged $30 million for work on the LSST, which proponents hope to 
>erect in the mountains of Chile. If it is built, it will be the first major 
>telescope to broadcast its data live over the Web, allowing countless 
>professional and amateur astronomers to look for undiscovered asteroids.
>
>Schweickart thinks, however, that even these instruments will not be able 
>to plot the courses of space rocks with absolute precision. NASA has said 
>that an infrared telescope launched into an orbit near Venus could provide 
>detailed information on the exact courses of space rocks. Such a telescope 
>would look outward from the inner solar system toward Earth, detect the 
>slight warmth of asteroids and comets against the cold background of the 
>cosmos, and track their movements with precision. Congress would need to 
>fund a near-Venus telescope, though, and NASA would need to build 
>it-neither of which is happening.
>
>Another means of gathering data about a potentially threatening near-Earth 
>object would be to launch a space probe toward it and attach a transponder, 
>similar to the transponders used by civilian airliners to report their 
>exact locations and speed; this could give researchers extremely precise 
>information on the object's course. There is no doubt that a probe can 
>rendezvous with a space rock: in 2005, NASA smashed a probe called Deep 
>Impact into the nucleus of comet 9P/Tempel in order to vaporize some of the 
>material on the comet's surface and make a detailed analysis of it. 
>Schweickart estimates that a mission to attach a transponder to an 
>impact-risk asteroid could be staged for about $400 million-far less than 
>the $11.7 billion cost to NASA of the 2003 Columbia disaster.
>
>Then what? In the movies, nuclear bombs are used to destroy space rocks. In 
>NASA's 2007 report to Congress, the agency suggested a similar approach. 
>But nukes are a brute-force solution, and because an international treaty 
>bans nuclear warheads in space, any proposal to use them against an 
>asteroid would require complex diplomatic agreements. Fortunately, it's 
>likely that just causing a slight change in course would avert a strike. 
>The reason is the mechanics of orbits. Many people think of a planet as a 
>vacuum cleaner whose gravity sucks in everything in its vicinity. It's true 
>that a free-falling body will plummet toward the nearest source of 
>gravity-but in space, free-falling bodies are rare. Earth does not plummet 
>into the sun, because the angular momentum of Earth's orbit is in 
>equilibrium with the sun's gravity. And asteroids and comets swirl around 
>the sun with tremendous angular momentum, which prevents them from falling 
>toward most of the bodies they pass, including Earth.
>
>For any space object approaching a planet, there exists a "keyhole"-a patch 
>in space where the planet's gravity and the object's momentum align, 
>causing the asteroid or comet to hurtle toward the planet. Researchers have 
>calculated the keyholes for a few space objects and found that they are 
>tiny, only a few hundred meters across-pinpoints in the immensity of the 
>solar system. You might think of a keyhole as the win-a-free-game opening 
>on the 18th tee of a cheesy, incredibly elaborate miniature-golf course. 
>All around the opening are rotating windmills, giants stomping their feet, 
>dragons walking past, and other obstacles. If your golf ball hits the 
>opening precisely, it will roll down a pipe for a hole in one. Miss by even 
>a bit, and the ball caroms away.
>
>Tiny alterations might be enough to deflect a space rock headed toward a 
>keyhole. "The reason I am optimistic about stopping near-Earth-object 
>impacts is that it looks like we won't need to use fantastic levels of 
>force," Schweickart says. He envisions a "gravitational tractor," a 
>spacecraft weighing only a few tons-enough to have a slight gravitational 
>field. If an asteroid's movements were precisely understood, placing a 
>gravitational tractor in exactly the right place should, ever so slowly, 
>alter the rock's course, because low levels of gravity from the tractor 
>would tug at the asteroid. The rock's course would change only by a 
>minuscule amount, but it would miss the hole-in-one pipe to Earth.
>
>Will the gravitational-tractor idea work? The B612 Foundation recommends 
>testing the technology on an asteroid that has no chance of approaching 
>Earth. If the gravitational tractor should prove impractical or 
>ineffective, other solutions could be considered. Attaching a rocket motor 
>to the side of an asteroid might change its course. So might firing a 
>laser: as materials boiled off the asteroid, the expanding gases would 
>serve as a natural jet engine, pushing it in the opposite direction.
>
>But when it comes to killer comets, you'll just have to lose sleep over the 
>possibility of their approach; there are no proposals for what to do about 
>them. Comets are easy to see when they are near the sun and glowing but are 
>difficult to detect at other times. Many have "eccentric" orbits, spending 
>centuries at tremendous distances from the sun, then falling toward the 
>inner solar system, then slingshotting away again. If you were to add 
>comets to one of those classroom models of the solar system, many would 
>need to come from other floors of the building, or from another school 
>district, in order to be to scale. Advanced telescopes will probably do a 
>good job of detecting most asteroids that pass near Earth, but an unknown 
>comet suddenly headed our way would be a nasty surprise. And because many 
>comets change course when the sun heats their sides and causes their frozen 
>gases to expand, deflecting or destroying them poses technical problems to 
>which there are no ready solutions. The logical first step, then, seems to 
>be to determine how to prevent an asteroid from striking Earth and hope 
>that some future advance, perhaps one building on the asteroid work, proves 
>useful against comets.
>
>None of this will be easy, of course. Unlike in the movies, where 
>impossibly good-looking, wisecracking men and women grab space suits and 
>race to the launchpad immediately after receiving a warning that something 
>is approaching from space, in real life preparations to defend against a 
>space object would take many years. First the necessary hardware must be 
>built-quite possibly a range of space probes and rockets. An asteroid that 
>appeared to pose a serious risk would require extensive study, and a 
>transponder mission could take years to reach it. International debate and 
>consensus would be needed: the possibility of one nation acting alone 
>against a space threat or of, say, competing U.S. and Chinese missions to 
>the same object, is more than a little worrisome. And suppose Asteroid X 
>appeared to threaten Earth. A mission by, say, the United States to deflect 
>or destroy it might fail, or even backfire, by nudging the rock toward a 
>gravitational keyhole rather than away from it. Asteroid X then hits Costa 
>Rica; is the U.S. to blame? In all likelihood, researchers will be unable 
>to estimate where on Earth a space rock will hit. Effectively, then, 
>everyone would be threatened, another reason nations would need to act 
>cooperatively-and achieving international cooperation could be a greater 
>impediment than designing the technology.
>
>We will soon have a new president, and thus an opportunity to reassess 
>NASA's priorities. Whoever takes office will decide whether the nation 
>commits to spending hundreds of billions of dollars on a motel on the moon, 
>or invests in space projects of tangible benefit-space science, 
>environmental studies of Earth, and readying the world for protection 
>against a space-object strike. Although the moon-base initiative has been 
>NASA's focus for four years, almost nothing has yet been built for the 
>project, and comparatively little money has been spent; current plans don't 
>call for substantial funding until the space-shuttle program ends, in 2010. 
>This suggests that NASA could back off from the moon base without having 
>wasted many resources. Further, the new Ares rocket NASA is designing for 
>moon missions might be just the ticket for an asteroid-deflection 
>initiative.
>
>Congress, too, ought to look more sensibly at space priorities. Because it 
>controls federal funding, Congress holds the trump cards. In 2005, it 
>passively approved the moon-base idea, seemingly just as budgetary 
>log-rolling to maintain spending in the congressional districts favored 
>under NASA's current budget hierarchy. The House and Senate ought to demand 
>that the space program have as its first priority returning benefits to 
>taxpayers. It's hard to imagine how taxpayers could benefit from a moon 
>base. It's easy to imagine them benefiting from an effort to protect our 
>world from the ultimate calamity.
>
>--
>+++++++++++++++++++++++++++++++++++++++++++
>
>NEO News (now in its fourteenth year of distribution) is an informal 
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>their impacts. These opinions are the responsibility of the individual 
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