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FROM A NASA HQ PRESS RELEASE
 July 22, 1999: Planetary scientists have developed a new means of conveying
the risks associated with asteroids and comets that might collide
with the Earth.
A risk-assessment scale, similar to the Richter scale used
for earthquakes, will assign values to celestial objects moving
near Earth. The scale will run from zero to 10. An object with a
value of zero or one will have virtually no chance of causing
damage on Earth; a 10 means a certain global climatic catastrophe.
Above: Artist Don Davis's concept of a
catastrophic asteroid impact with the Earth. Life
near the impact would be instantly wiped out from the effects of high
temperatures and pressures. Injection of huge masses of dust (and gases)
into the atmosphere would effectively block out sunlight for long periods
of time to the point that most life could not be sustained ("Nuclear
Winter"). Credit: NASA Ames.
The scale was created by Dr. Richard P. Binzel, professor of
Earth, Atmospheric and Planetary Sciences at the Massachusetts
Institute of Technology (MIT) in Cambridge, MA. It is named the
Torino Impact Hazard Scale after the Italian city in which the
scale was initially adopted by the International Astronomical
Union (IAU) in June 1999.
"These events have a small probability of occurring, but if
they happen they can have severe consequences," said Binzel. "It
is difficult to figure out what level of anxiety we should have
about an approaching asteroid or comet. I hope the Torino scale
will put in perspective whether a Near-Earth Object merits public
concern, just as the Richter Scale does with earthquakes."
The scale is being endorsed officially today by the IAU in an
announcement at the United Nations' UNISPACE III conference in
Vienna, Austria.
"What I find especially important about the Torino impact
scale is that it comes in time to meet future needs as the rate of
discoveries of Near-Earth Objects continues to increase," said Dr.
Hans Rickman, IAU Assistant General Secretary.
Right: The Torino Impact Hazard Scale. Click for a larger
image.
The scale takes into account the object's size and speed, as
well as the probability that it will collide with Earth. The
scale can be used at different levels of complexity by scientists,
science journalists and the public.
Close encounters, assigned Torino-scale values from two to
seven, could be categorized as ranging from "events meriting
concern" to "threatening events." Certain collisions would merit
values of eight, nine or 10, depending on whether the impact
energy is large enough to cause local, regional or global
devastation.
No asteroid identified to date has ever had a value greater
than one, noted Binzel, who has been working on the scale for five
years. Several asteroids that had initial hazard scale values of
one have been reclassified to zero after additional orbit
measurements showed that the chances of impact with the Earth were
essentially zero.
"Nobody should lose sleep over an asteroid in the zero or one
category," Binzel said. "Scientists haven't done a very good job
of communicating to the public the relative danger of collision
with an asteroid. The Torino Scale should help us clearly inform
but not confuse the public."
Left: a 996 kB MPEG
animation of the Peekskill meteorite from the NASA/Ames cosmic
impact picture gallery.
The events surrounding the fall of the Peekskill meteorite on October 9, 1992 were quite unique. It was observed by many
people who were attending a football game, being photographed and videotaped by over a dozen people. The meteorite was
found crashed into the trunk of a parked car. [more information]
Increasingly sophisticated equipment, partially funded by
NASA, such as the Lincoln Near Earth Asteroid Research project at
MIT's Lincoln Laboratory in Lexington, MA, is used to detect and
track a growing number of an estimated 2,000 Near-Earth Objects
larger than about a half-mile (one kilometer) in diameter. The
project uses technology originally developed for the surveillance
of Earth-orbiting satellites. It has detected almost 250,000
asteroids to date, more than any other source. Of these, 228 are
newly discovered Near-Earth Objects.
Large asteroids are rarely a threat to the Earth. An
asteroid bigger than a mile across might hit once every 100,000 to
one million years on average. On the other hand, tiny meteorite
fragments as big as grains of sand bombard Earth constantly, and
objects the size of a small car hit a few times a year.
Once an asteroid is detected, scientists use tracking data
from a tiny section of its orbit to calculate where it will be in
10, 15 or 100 years. There is some uncertainty in this prediction
because the orbit measurements are not perfect and the path of an
object may be altered by gravity if it passes close to Earth or
another planet. As more information is gathered about a
particular asteroid, its placement on the scale can be adjusted.
"The Torino scale is a major advance in our ability to
explain the hazard posed by a particular object," said Dr. Carl
Pilcher, science director for Solar System exploration in NASA's
Office of Space Science, Washington, DC. "If we ever find an
object with a value greater than one, the scale will be an
effective way to communicate the resulting risk."
A more detailed explanation of the points on the Torino scale
and related graphics are available on the Internet at
http://impact.arc.nasa.gov
Left:
On the way to visiting the near-Earth asteroid 433 Eros, the Near Earth
Asteroid Rendezvous (NEAR) spacecraft flew right by another asteroid: 253 Mathilde in June 1997. Shown above is one picture
from the encounter. Mathilde is a large chunk of rock roughly 60 kilometers across that orbits the Sun between Mars and Jupiter
in the main asteroid belt. Mathilde's surface is very dark and heavily cratered. The NEAR pictures of Mathilde received so far
indicate that the asteroid has undergone spectacular collisions, one of which created the huge impact basin in the center, which is
estimated to be about 10 kilometers deep. Credit: Astronomy Picture of the Day [more information]
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