http://www.csicop.org/si/2005-03/asteroids.html
Hyperbole in Media Reports on Asteroids and Impacts News releases and media reporting on asteroid impact-related science frequently exaggerate the uniqueness and significance of new research. We should be skeptical of all claims of scientific revolutions. David Morrison -------------------------------------------------------------------------------- Many observers of the science press have noted an increasing tendency for both news releases and printed stories to exaggerate the uniqueness and significance of new research. The writer of a news release does this to increase the probability that the media will cover the story, and the media reporter will go along with this hyperbole or perhaps expand it further to get the story approved for publication by editors or other gatekeepers. The field of impacts (and impact hazards) is not immune to these trends. In my NASA-supported Web page http://impact.arc.nasa.gov, I try to apply a filter to reduce the noise level in media reports, which would otherwise overwhelm much of the real science. This is not intended as a general criticism of science reporting. There are many excellent science journalists who understand the issues and provide well-reasoned discussions of context for news stories. Overall, the reporting by science journalists of impact-related stories has been excellent. But a hyperbolic headline added without their knowledge can sometimes catch even the best writers. Background on Asteroids and Impacts In his excellent book Mysteries of Terra Firma (Free Press, 2001), geologist James Powell discusses three revolutions in our understanding of Earth history. The first, responding primarily to the discovery of radioactivity at the end of the nineteenth century, was the concept of deep time-measurement of the age of Earth and dating of the primary geological and evolutionary events in its history. The second revolution dealt with the discovery of plate tectonics, first suggested (as "continental drift") but subsequently rejected early in the twentieth century. Plate tectonics was accepted only in the 1960s (when a wide range of strong new evidence was obtained) and has become the fundamental theory for understanding the dynamics and history of the Earth's crust. The third revolution was the space-age recognition of the role of cosmic impacts on geology and evolution. Scientists are still exploring many implications of this third revolution. Space exploration missions to other worlds and careful scrutiny of impact landforms on Earth have revealed that cratering is a universal process in the solar system. The pioneering work by Walter Alvarez and colleagues on the end-Cretaceous mass extinction further showed that cosmic impacts can have profound influences on the evolution of life. Whether other mass extinctions are also due to impacts remains an open question. My own interest in impacts includes the contemporary danger from asteroids colliding with Earth. Although the probabilities are low, a devastating impact capable of killing hundreds of millions of people could happen at any time. The NASA Spaceguard program, which seeks to find any threatening asteroid in time to mitigate the impact (preferably by deflecting the asteroid away from Earth), is one response to a growing awareness of the impact problem. Did the KT Impact Cause the Extinction of the Dinosaurs? The KT (Cretaceous/Tertiary, 65 million years ago) extinction is by now an old story, but sometimes the news media still report dramatically opposed conclusions as if a major debate existed to this day. Certainly the issue was contentious when impact extinction was first proposed by the Alvarez team twenty-five years ago, but a scientific consensus had emerged by the early 1990s. This progress of the Alvarez theory, increasingly supported by new evidence (such as the discovery of the Chicxulub Crater in Mexico), has been chronicled in several excellent books, such as Night Comes to the Cretaceous by James Powell, T. Rex and the Crater of Doom by Walter Alvarez, The End of the Dinosaurs by Charles Frankel, and When Life Nearly Died by Michael Benton. In spite of the scientific consensus, there was substantial media coverage in 2004 of alternative hypotheses of dinosaur extinction. Major stories have arisen from the work of paleontologist Gerta Keller at Princeton, who has been challenging the impact theory for more than two decades. Recently she has decided that impacts may indeed be implicated, but probably not the Chicxulub impact (just off the coast of the Yucatan peninsula, the impact most earth scientists think is primarily responsible). One hypothesis she has suggested is that while the 100-million-megaton energy Chicxulub impact was insufficient to kill the dinosaurs, a smaller impact 300,000 years later may have done so. Princeton University frequently issues news releases on her work, and sometimes the publicity gets out of hand, with bold headlines such as "KT Mass Extinction Debate Wide Open and in Full Swing," "The Space Rock Was Framed: Asteroid Cleared in Dinosaurs' Death," and "Asteroid Couldn't Have Wiped Out Dinos." One characteristic of media hype is to suggest that all science dealing with the KT extinction is about dinosaurs. Dinosaurs are popular. But dinosaur fossils, which are relatively rare, do not define the mass extinction boundary, which is precisely marked in the marine fossil record by changes in single-celled protists, as well as by the global layer of extraterrestrial material and shocked quartz from the impact. On the other hand, some scientists discuss the dinosaur extinction without reference to the simultaneous global mass extinction in which more than half of all biological families were lost. This attitude is reflected in the remark by paleontologist David Penny that "We agree completely with the geophysicists that an extraterrestrial impact marks the end of the Cretaceous. But after twenty-five years [scientists] have still not provided a single piece of evidence that this was the primary reason for the decline of the dinosaurs." [1] Most scientists consider it to be exceedingly unlikely that the dinosaur extinction was unrelated to the global KT event. In addition to the coincidence in time and increasing evidence that the dinosaur extinction was abrupt, we think we understand how the Chicxulub impact killed large land animals by a combination of brief global firestorm followed by months of cold. Neglecting this relationship is one fatal flaw in this year's widely reported hypothesis that dinosaurs went extinct because of disparity in the numbers of males and females born. Perhaps in this case the publicity was stimulated by the word sex, as in the Washington Times headline "Why Dinosaurs Died-It's All about Sex." An Impact-caused Extinction 250 Million Years Ago? Was the end-Permian mass extinction caused by an impact? No one knows, even though the PT event (Permian/Triassic, 252.6 million years ago, a newly published, more precise date for the prime extinction) was the greatest of all mass extinctions, with more than 90 percent of families becoming extinct. The past year has seen several new scientific results, many associated with claims and counter-claims concerning the submarine Bedout impact (or non-impact) structure that might (or might not) be the "smoking gun" crater. Also widely reported have been evidence of extraterrestrial material (but not iridium or shocked quartz, so far) at the PT boundary, and recent indications that the PT extinction may have been two sharp events separated by several million years. I have no quarrel with the media coverage of these issues, except where news releases claim that the question has been definitively solved. There is no consensus concerning the cause of the PT extinction, and hence every reason to follow the debates as they happen. For example, I will be interested in results from a blind test for evidence of an impact that is being conducted by a team of scientists using new samples from China, where an excellent cross- section of PT rocks is accessible. Meteorites and Fires Meteorites do not cause fires. Yet it is common to find news reports that a bright meteor fell and started a fire. Often the existence of a fire is quoted as evidence that the meteor struck the ground (thus making it a meteorite). In 2003, the old idea that both the Great Chicago Fire of 1871 and another conflagration more than a hundred miles north in Wisconsin were started by hot stones falling from the sky was revived. This coincidence seems striking, with two of the most destructive fires in U.S. history happening at the same time-but the coincidence might also be related to extreme dryness and high winds across the upper Midwest. In the cases where we have been able to estimate the surface temperature of just-fallen meteorites (such as where they land on snow or ice), the data indicate that they are cool. Nor should this be surprising: the violent heating of the stone's surface by atmospheric friction lasts only a few seconds, followed by several minutes of free-fall through the cold stratosphere. I follow the rule of thumb that if a meteor or meteorite is reported to have started a fire, the claim is probably mistaken. These are "meteorwrongs," not meteorites. The Recent Impact Rate A common assertion in the tabloid press and on some Web sites is that we are at great risk from impacts, because impacts happen much more frequently than the scientists claim. Usually the argument is related to supposed evidence for recent large impacts. One report (from The Guardian, on August 19, 2004) concerned huge craters under the Antarctic ice sheet said to be caused by an asteroid as big as the one that wiped out the dinosaurs, but striking about 780,000 years ago. The newspaper reported that an asteroid measuring three to seven miles across broke up in the atmosphere with five large pieces creating multiple craters over an area measuring 1,300 by 2,400 miles. Supposedly this impact caused a reversal in Earth's magnetic field (a highly suspect claim) but little other damage. Obviously the description of this event is inconsistent with what is known about cosmic impacts, yet this "discovery" was reported seriously. The "Sirente crater," a lake near Abruzzi, Italy, has also been widely speculated to be an impact from the Roman period. If this were true, Sirente would be one of the most recent craters on Earth, falling right next door to the capital of the Roman Empire. However, no meteoritic material has yet been recovered from the lake. In 2004, an article in Tumbling Stone magazine suggests that this is an anthropogenic feature and not the result of an impact. The Web site of Astronomy magazine published a report in October 2004 on identification of a field of meteorites and impact craters near Lake Chiemsee in southeastern Bavaria, Germany. This crater field, which falls within an ellipse 58 by 27 km, is said to hold at least eighty-one impact craters ranging from 3 to 370 meters in size. The authors, using historical and archeological evidence, conclude that an asteroid or comet fragment exploded above southeastern Germany in the Celtic-Roman period, probably around 200 b.c. They estimate that the projectile had a diameter of about 1 km. Since the authors are primarily amateur scientists and their work has not been published in a refereed journal, it is difficult for me to judge these conclusions, in terms of either the identification of impact craters or their probable date of formation. Another report, discussed below, suggests that there are many very dark, unseen comets that constitute a previously unrecognized threat. In assessing the reliability of such stories, we should note that even one of these recent mega-impacts is unexpected from known impact rates, which are based on both astronomical observations and the long-term cratering history of Earth and Moon. (These impact rates might be off by a factor of two, but certainly not by a factor of ten or more.) For example, the Lake Chiemsee impactor is claimed to have been about 1 km in diameter and to have struck within the past 2,500 years, whereas on average an asteroid or comet this large hits Earth only once in about 500,000 years. While any one impact might be true (as a statistical fluke), it is hard to believe that several of these stories are correct. I remain skeptical. Super-dark "Stealth" Comets A new report in Monthly Notices of the Royal Astronomical Society by W.M. Napier, J.T. Wickramasinghe, and N.C. Wickramasinghe is titled "Extreme albedo comets and the impact hazard." Based on a dynamical argument, they conclude that there should be more than 1,000 times more Halley-type comets than are actually observed. They therefore suggest that the comets become invisible, and that the impactor population is dominated by bodies too dark to be seen with current astronomical surveys. One should be skeptical of a theoretical result that has no data to support it. One should be even more skeptical if it seems inconsistent with the data we do have, resolved (in this case) only by postulating a new class of "invisible" comets. But further, the idea that our astronomical surveys might miss huge numbers of such "stealth" objects is largely beside the point. We know about the low comet cratering rates from the dearth of small craters on Jupiter's Galilean satellites, especially Europa. From this perspective it seems clear that there is not a large population of stealth comets to worry us. Proposed Rain of Mini-comets In the late 1980s, the proposal of a tremendous flux of tiny comets (each no bigger than a bus) was widely discussed in the science media. The discoverer was a well-respected space scientist from the University of Iowa, Lou Frank, who was attempting to interpret very small, transient dark patches in NASA spacecraft images of Earth's atmosphere. Frank hit upon the idea that these dark spots were due to bursts of water vapor liberated in the upper atmosphere by disintegrating small comets, a hypothesis that he advocated at meetings of the American Geophysical Union, in published papers, and directly to many science journalists. In spite of the excellent reputation of their advocate and invocation of NASA satellite data, an intense rain of such mini-comets was quickly recognized by most scientists as inconsistent with a wide range of other observations. The numbers of impactors proposed by Frank were a million times higher than the known flux of objects with their proposed mass. They would have to be so black that they were invisible to telescopes. Since their atmospheric impacts were also not being seen as meteors or flashes of light, they must also carry little energy. (The absence of a flash was later confirmed when data were released from sensitive surveillance satellites that constantly scan Earth from above.) They also evidently did not make craters when they struck the Moon. Finally, the amount of water vapor they would dump in the upper atmosphere was inconsistent with the known dry conditions in the stratosphere. Although many scientists assumed that the dark spots were just noise in the spacecraft detector, they were unable to work with the raw data to verify this speculation. The media story persisted, aided by NASA news releases supporting the mini-comets. While they shook their heads in wonderment, few of Frank's colleagues wanted to challenge him personally. His advocacy of mini-comets became an obsession-he even wrote a book called The Big Splash to market his ideas directly to the public. There seemed to be no polite way to make the story go away. One scientist tried, however, to counter with humor, when he proposed that the mini-comets be called Louis A. Frank Objects, or LAFOs. Impact News in Great Britain Based on the large sampling of press reports from both sides of the Atlantic collected by anthropologist Benny Peiser of Liverpool John Moores University, there seem to be significant differences in the press treatment of impact science stories between the United States and the United Kingdom. Many British science reporters like to play such stories for their humorous possibilities, as opposed to the straight science reporting that is standard in America. Ridiculing the "boffins" seems to be a popular way to treat scientific controversy. Another approach is to start off a story in a hyperbolic vein, only tempering the initial overstatements several paragraphs down. For example, an opening assertion might be made that an asteroid is on a collision course with Earth, but a few paragraphs later it is revealed the the probability of the impact is only one in 100,000. My impression is that the British reading public does not take this very seriously, and that their news reporting in general is intended to be more entertaining. A problem can occur, however, when such stories are picked up in other countries, where this tongue-in-cheek tone might be taken seriously. Let the reader beware. Space science research dealing with impacts often makes a good story, especially when it is controversial. The public is likely to find science more interesting if they realize that research is carried out by real people working in a competitive environment. The controversy is very real in some cases, such as finding the cause (or causes) of the great PT mass extinction. In other cases, such as the KT mass extinction and the contemporary rate of impacts on Earth, a consensus exists based on multiple lines of evidence. While there are still many media-worthy stories, we should be skeptical of reports that the consensus has been overthrown by a single new result. As Carl Sagan often said, "extraordinary claims require extraordinary evidence." A similar admonition might be that before revolutionary theories are widely publicized, they need to be given a reality check. This is best done by the scientists deciding whether to issue a news release. But if the scientists are not self-policing, the burden falls upon the journalists to filter the signal from the noise, or upon the skeptical attitude of the reader. ______________________________________________ Meteorite-list mailing list [email protected] http://six.pairlist.net/mailman/listinfo/meteorite-list
