[meteorite-list] Killer Asteroids: A Real But Remote Risk?

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:22:41 2004
Message-ID: <200306192044.NAA22087_at_zagami.jpl.nasa.gov>

http://news.nationalgeographic.com/news/2003/06/0619_030619_killerasteroids.html

Killer Asteroids: A Real But Remote Risk?
By John Roach
National Geographic News
June 19, 2003

It is almost certain that Earth will be hit by an asteroid large enough to
exterminate a large percentage of our planet's life, including possibly over a
billion people, according to researchers. But as such cataclysmic collisions
occur on average only once in a million years or so, are they really worth
worrying about?

At some point in the geological future a large chunk of rock and ice will
smack into Earth and destroy life as we know it. This is a cold, sober,
scientific fact, according to Andrea Milani, a researcher at the University of
Pisa in Italy.

"A future impact from, say, a 1-kilometer [0.62 mile]-diameter asteroid is,
rather than just probable, almost certain over a time span of a million years,"
he said.

Wolf Reimold, a geoscientist at the University of Witwatersrand in
Johannesburg, South Africa, said a 1-kilometer-wide asteroid would
produce an impact crater of about 12 miles (20 kilometers) in diameter and
wipe out an area the size of the United Kingdom. The human toll would
depend on where such an impact occurs.

"Estimates may range from 500,000 to 1.5 billion casualties," he said. "This
latter number certainly smells of global nuclear war. Such an event would in
all likelihood not wipe out mankind, but it would cause a global economic
crisis."

Given the real threat of impact by a so-called near Earth object (NEO) and
the consequences for human life, Milani and Reimold are urging the
worldwide scientific community, and the agencies that fund their research, to
take the field of impact mitigation seriously.

In separate papers appearing in the June 20 issue of the journal Science,
Milani and Reimold outline what is known about the impact threat and how
impacts have shaped the geologic and life history of Earth.

They agree that the developed world has made great strides over the past
few decades in NEO research, but say that more funding is required to raise
public awareness of the impact risk and to determine how to thwart an
incoming object.

"Governments have the responsibility to deal with a lot of problems afflicting
humankind. But these same governments must realize that large asteroid or
comet impact has the potential to wipe out all other problems, including
mankind," said Reimold.

Impact Science

Impacts of meteorites, asteroids, and comets are frequent events on a
geological time scale, said Milani. They have shaped the surface of the Earth
and altered the course of life that thrives upon it.

For example, 65 million years ago a 6.2-mile (10 kilometer)-diameter
asteroid impact resulted in a 100-million-megaton explosion that excavated
a 112-mile (180 kilometer)-wide crater on the Yucatán Peninsula in Mexico
and brought the dinosaur era to an end.

Events such as the impact implicated in the dinosaur extinction happen on
the order of once every 100 million years. Smaller objects collide with Earth
with greater frequency. Asteroids large enough to cause ocean-wide
tsunamis, for example, happen once every 63,000 years.

In 1998 NASA accepted the responsibility of compiling a catalog of at least
90 percent of NEOs of 1 kilometer (0.62 miles) in diameter or greater and to
assess the probability that any of them will impact Earth. Such events are
believed to happen on the order of about once every 1 million years.

To date the NASA initiative, known as Spaceguard, has identified 585
objects of 1 kilometer or greater. Most of them have no chance of impact and
those that do have only a very low probability. Scientists estimate there are
about 1,000 NEOs, so NASA is more than halfway to accomplishing its goal.

Reimold notes that this initiative and projects such as the British Taskforce
on Potentially Hazardous Near Earth Objects and the Intercontinental
Scientific Drilling Program into the Chicxulub crater in Mexico have helped
scientists understand the risks and consequences of collisions with
asteroids and comets.

The developing world, he said, is slower to catch on, but a movement by
astronomers and geoscientists in South Africa to establish a National
Working Group to assess NEO impact risk and mitigation is gaining traction.

"On the other hand, the general public in developing countries has a host of
other problems than the possibility that a large bolide could wipe out
mankind," he said. "If your first concern is to have shelter and food, if
HIV/Aids and unemployment are your daily worries, you cannot be expected
to be wary of meteorite impact."

More Mitigation Funding?

Writing in Science, Milani says that the scientific community should take on
the responsibility to investigate all objects that could potentially impact
Earth "down to the size compatible with available technology and with the
public perception of acceptable risk."

According to Milani, a reasonable goal would be to detect within the next ten
to 20 years 90 percent of the NEOs over 1,000 feet (300 meters) in diameter
and 97 percent of those greater than 1 kilometer in diameter.

To accomplish this goal, Milani says that understanding and awareness of
the impact risk must be raised amongst the public and the agencies that
provide the requisite funding to perform the work.

"If [funds] are provided, the scientists would know how to use them
efficiently," he said. "If resources dedicated to this task are not provided, the
scientists have difficulties in canceling other worthwhile basic research to
make resources available for impact risk assessment."

Reimold said that more money ought to also be made available for research
into known and potential impact sites. Currently, he said, only a few impact
sites older than 300 million years are known, but that many more should be
out there.

"Ongoing detailed geological analysis of known impact structures is a must
in order to further improve our knowledge of the impact process and its
devastating results," he said.

Robert Jedicke, an asteroid expert with the Institute for Astronomy at the
University of Hawaii, said that "it would be nice" if asteroid researchers had
more money but that current funding for the NEO impact risk assessment
programs is sufficiently supported given the available funding for all scientific
research.

"There's only so much money to go around," he said. "So if the pot gets split
there's less stew for the rest of the astronomical/scientific community."

NEO Deflection

As NEO researchers continue to search the skies for objects that pose an
impact risk, they are also beginning discussions on how to deflect an object
on a collision course with Earth.

One of the issues being explored is the interior structure of asteroids. If the
interior is weak, for example, an attempt to deflect it with a nuclear warhead
(an option under consideration) may simply breakup the asteroid into many
smaller and uncontrolled pieces.

Milani writes that such investigations are a valid extension of the NASA
and European Space Agency NEO programs and make logical sense: "We
cannot justify the effort for discovery unless we can safeguard our planet."

Jedicke said that we are not currently prepared to deflect an incoming
asteroid, but that there is no reason to be alarmed because there is little
chance that an asteroid even as small as 330 feet (100 meters) will hit Earth
within the next 100 years.

"They don't build tornado shelters in Germany. Cities don't buy snowplows
in Florida. And there's no pressing need to worry about deflection of
incoming NEOs at the moment," he said.
Received on Thu 19 Jun 2003 04:44:11 PM PDT