[meteorite-list] Sceptical Inquirer article

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Sun May 8 23:45:58 2005
Message-ID: <7jnt711qtmpjim3g8oq77co54ksvjjl2tm_at_4ax.com>

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



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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.
Received on Sun 08 May 2005 11:53:24 PM PDT