A Richter Scale for Cosmic Collisions: Planetary scientists have
developed the Torino Scale, a new means of conveying the risks associated
with asteroids and comets that might collide with the Earth.
IAU Press Release
22 July 1999
"Dealing With the Impact Hazard: An International Project"
The Earth is constantly sweeping up particles of various sizes as it
travels on its orbit around the Sun. We often see some of them burning
in the atmosphere as meteors. From time to time, penetrating objects
that are many meters across may cause major explosions in the air.
Recently, public concern has been raised over much less frequent but
devastating impacts by km-sized asteroids or comets. It has now been
realized that the risk of fatality as a result of such impacts is
comparable to that of well-perceived hazards like airplane crashes.
Possibly hazardous objects in the solar system can be discovered by
astronomical observations, e.g., when they are recorded as faint
streaks of light in long telescopic exposures because of their
motions. Astronomers therefore have a special mission relating to the
impact hazard, namely, that of discovering and characterizing the
dangerous objects, and, hopefully, by verifying the expectation that
no major impact is going to occur during the next centuries.
The vast majority of these "dangerous" objects have as yet escaped
discovery and, since we do not know their orbits, they may hit at any
time. For the time being, only statistical calculations can be
made. They show that the risk of the Earth being hit by a km-sized
object during the next couple of centuries is one-in-a-thousand. The
risks are low but the consequences are large enough to cause
concern. In fact, astronomers have now put in place efficient search
programs that are already resulting in a fast stream of new
discoveries of such objects.
When the newly discovered objects are investigated with regard to
future encounters with the Earth, it is sometimes found that, due to
the necessarily imprecise, initial orbit determinations, the risk of a
collision cannot be entirely ruled out. The likelihood of such a
possible disaster may also be estimated. If it is found to be
significant when compared to the combined risk posed by all the
unknown objects, then the asteroid or comet in question will become
subject of careful monitoring. The expectation is that improved
knowledge of its orbit will sooner or later show that the impact will
not occur. This is at least the outcome of all monitoring programmes
so far.
This type of observational work is now occupying a small group of
astronomers worldwide. It is an international effort, since the impact
hazard is obviously of concern to the entire world. Possible impacting
objects are best studied by means of international observing campaigns
and there must be an efficient exchange of information among all
scientists involved. This is also why the International Astronomical
Union (IAU) has engaged itself as co-sponsor of a very well attended
workshop in Torino, Italy, on June 1-4. Among the other main
co-sponsors were NASA and ESA.
Many related issues were debated during this meeting. For instance,
how to secure a fast, efficient search such that nearly all the
potentially hazardous asteroids get discovered and safely catalogued
before too long; how to collaborate in order to measure their most
important physical properties by means of ground-based as well as
space-based observations; how to speed up and widen the data channels
for an optimal use of the world's combined observational facilities,
and, not least, how to inform both the public and political
authorities - if ever needed - about calculations that point towards
sinister events.
Even though US national agencies, i.e., NASA and the US Air Force, are
presently carrying a major part of the burden of these observations
and calculations and may possibly increase their efforts further, the
participants in the Torino meeting decided to make a strong
recommendation to all governments to establish ``National Spaceguard
Centres'' and to support these financially. In this way, a proper
sharing of responsibilities may be realised, so that this important
work can be enhanced and reach maximum efficiency. Another urgent
action item is the setting up of an expert committee, under the
auspices of the IAU, that will check impact predictions and advise
about their publication.
Perhaps the most visible and immediately practical result was the
adoption of the so-called "Torino impact scale". It was worked out by
Prof. Richard Binzel of MIT (Cambridge MA, USA) as a tool for
communicating the issues of impact prediction outside the professional
circuit. With some superficial similarities to the Richter scale for
earthquake intensity, it divides the predictions into classes 0-10.
All events that have no likely consequences belong to class 0 and
higher numbers correspond to progressively more probable, and/or more
serious impacts.
At the present time, no single asteroid is known that has been
assigned an impact prediction in a class higher than 0. This is of
course fortunate and this is expected to be the normal state of
affairs. However, it is also likely that initial uncertainties in the
calculation of an orbit of a newly discovered asteroid may temporarily
place it in a higher category. This is not a cause for immediate
concern, but merely signals the need for more accurate observations,
leading to a better determination of the orbit.
With the increased rate of discoveries of asteroids and the efficient
schemes of orbital computations now in use, the new Torino Scale will
most certainly become of great use and will be frequently cited as
reference.
Scientists Warn Of Risk From 'Doomsday' Asteroids
By Deborah Zabarenko
July 27, 1999
ITHACA, N.Y. (Reuters) - The good news: there are fewer potential
"doomsday" asteroids than previously believed that could cause an earthly
catastrophe if they struck the planet, scientists said Tuesday.
The bad news? A big one could smack into Earth in the coming century, they
said.
A "doomsday" asteroid is defined as one with a diameter greater than .6
mile (1 km), which could cause global climatic catastrophe if it collided
with Earth. Debris from such a collision would be predicted to cause
worldwide clouding and cooling, with possibly disastrous effects on crops
and animals.
Earthquakes have their Richter Scale. Tornadoes have the Fujita Scale, and
hurricanes fall into neat little categories. Now asteroids have a
measurement system all their own, one that estimates the threat of impact.
In an attempt to help scientists, the media and the public assess the
potential danger of asteroids and comets, an MIT professor created a scale,
which runs from zero to 10, to gauge the risk of a collision with Earth.
It is my pleasure to report the adoption by the International Astronomical
Union of the Torino Impact Hazard Scale, developed by Rick Binzel of MIT
and discussed in detail at the recent NEO workshop in Turino, Italia. The
Torino Scale, which is designed to classify and help communicate various
degrees of hazard from predicted asteroid and comet impacts, is described
below and can be referenced on the Internet athttp://impact.arc.nasa.gov.
Also, in a separate but related story, I have added for your information
the current draft of proposed IAU guidelines for voluntary technical review
of discoveries or predictions of possible future impacts. This review
process is recommended for any prediction that rises above level zero on
the Torino scale.
CAMBRIDGE, Mass. -- A Massachusetts Institute of Technology professor has
come up with a scale that assigns a number to the likelihood that an
asteroid will collide with the Earth. Zero or one means virtually no chance
of impact or damage; 10 means certain catastrophe.
Richard P. Binzel, professor of Earth, Atmospheric and Planetary Sciences
at MIT, created the scale to help scientists, the media and the public
assess the potential danger of asteroids. He hopes that it will assuage
concerns about a potential doomsday collision with the Earth.
Binzel's risk-assessment system is similar to the Richter scale used for
earthquakes. It is named the Torino Impact Hazard Scale for the Italian
city in which it was adopted at a workshop of the International
Astronomical Union (IAU) in June.
The IAU will announce today (July 22) at the third United Nations
conference on the exploration and peaceful uses of outer space (UNISPACE
III in Vienna, Austria) that it has officially endorsed the Torino scale to
gauge potential impacts with asteroids and comets, collectively referred to
as near-Earth objects (NEOs).
"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 Hans Rickman, IAU assistant general
secretary.
"The Torino scale is a major advance in our ability to explain the hazard
posed by a particular NEO," said Carl Pilcher, science director for solar
system exploration in the NASA Office of Space Science in Washington, D.C.
"If we ever find an object with a greater value than one, the scale will be
an effective way to communicate the resulting risk."
"Naming the newly proposed hazard scale after Torino is a highly
appreciated recognition of the Torino Astronomical Observatory's great deal
of work over the past two decades," said Alberto Cellino, astronomer at the
Torino Astronomical Observatory.
DEEP IMPACT?
Based on the orbit trajectory for a given NEO, the scale takes into account
the object's size and speed as well as the probability that it will come
into contact with the Earth. The scale can be used at different levels of
complexity by scientists, science journalists and the general public.
The scale assigns a number from zero through 10 to a predicted close
encounter by an NEO. A zero, in the white zone, means that the object has
virtually no chance of colliding with the Earth or that the object is so
small it would disintegrate into harmless bits if it passed through the
Earth's atmosphere. A red 10 means that the object will definitely hit the
Earth and have the capability to cause a "global climatic catastrophe."
Close encounters in the green, yellow and orange zones with "scores" from
one to seven are categorized as "events meriting careful monitoring" to
"threatening events." Certain collisions fall in the red zone, with values
of eight, nine or 10, depending on whether the impact energy is large
enough to be capable of causing local, regional or global devastation.
No asteroid identified to date has ever made it out of the green zone by
having a scale value greater than one. Several asteroids that had initial
hazard scale values of one have been reclassified into category zero after
additional orbit measurements showed that the chances of impact with the
Earth became zero. All currently known asteroids have scale values of zero.
A COSMIC SHOOTING GALLERY
Binzel, who has been developing the scale for five years, aims to give
scientists a consistent way to communicate about the growing number of
close-encounter asteroids being spotted. Increasingly sophisticated
equipment, partially funded by NASA, such as the Lincoln Near Earth
Asteroid Research (LINEAR) project at MIT's Lincoln Laboratory in
Lexington, Mass., is being used to detect and track a growing number of the
estimated 2,000 NEOs larger than about a half-mile (1 kilometer) in
diameter.
The LINEAR project uses technology originally developed for the
surveillance of Earth-orbiting satellites to detect and catalog NEOs. It
has detected almost 250,000 asteroids to date, more than any other source.
Of these, 228 are newly discovered NEOs.
While more asteroids than ever are being identified in the cosmic shooting
gallery inhabited by our planet, Binzel points out that there is no
increase in the number of asteroids out there -- only in our awareness of
them. Because we know about more asteroids, there is an increasing
awareness that many of them can make close passes by the Earth. "This
doesn't mean that the Earth is in any greater danger," he said.
"Fortunately, the odds favor that newly discovered objects will miss."
On the other hand, space-borne objects do hit the Earth. Tiny fragments as
big as grains of sand bombard us constantly, and objects the size of a
small car hit a few times a year. An asteroid bigger than a mile across
might hit once every 100,000 to 1 million years. The planet bears scars
from these encounters.
In the 1960s, Eugene Shoemaker of the U.S. Geological Survey proved that a
big dent in the Arizona desert is a meteor crater. Most scientists believe
that the dinosaurs were wiped out by a massive object 65 million years ago.
The well-documented collision of the Shoemaker-Levy comet with Jupiter
demonstrates that impacts are still a reality in the solar system today,
but, Binzel points out, "No one has clearly documented deaths from a
meteorite impact."
JUDGING HAZARDS
"If you tell a Californian that an earthquake registering one on the
Richter scale was going to hit tomorrow, he would say, 'So what?'" Binzel
said. "If you were talking about a six, that would be different."
So Binzel hopes it will be with asteroids. Nobody should lose sleep, he
said, over an asteroid in the zero or one category, which accounts for the
vast majority of them. He hopes to avoid sensationalism such as that
surrounding the 1997 XF11 asteroid that led to the New York Post headline
of March, 13, 1998, "Kiss your asteroid goodbye," or embarrassments such as
astronomers' announcement -- and quick retraction -- regarding the 1999
AN10 asteroid's potential impact. AN10 is now known to be a sure miss, a
zero on the Torino scale.
"Scientists haven't done a very good job of communicating to the public the
relative danger of collision with an asteroid," said Binzel, who is a
specialist on planetary astronomy. "Scientist-astronomers who are going to
be confronted with this should have some means of clearly communicating
about it so as to clearly inform but not confuse or unnecessarily alarm the
public."
Once an asteroid is detected, scientists try to use information that shows
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 NEO may be altered by gravity if it
passes close to the Earth or another planet, but "orbits generally behave
like clockwork," Binzel said.
As more information is gathered about a particular asteroid, its placement
on the scale can be adjusted accordingly, he points out. "It is hoped that
in all cases the placement will go to zero.
"What I hope the scale will accomplish is to put in perspective whether an
object merits concern," he said. "This is a case of a high-consequence but
low-probability event. It's difficult in human nature to figure out what
level of anxiety we should assign to an approaching asteroid."
The Torino Scale is a "Richter Scale" for categorizing the Earth impact
hazard associated with newly discovered asteroids and comets. It is
intended to serve as a communication tool for astronomers and the public to
assess the seriousness of predictions of close encounters by asteroids and
comets during the 21st century.
Why is the Torino Scale needed?
When a new asteroid or comet is discovered, predictions for where the
object will be months or decades in the future are naturally uncertain.
These uncertainties arise because the discovery observations typically
involve measurements over only a short orbital track and because all
measurements have some limit in their precision.
Fortunately, for the majority of objects, even the initial calculations are
sufficient to show that they will not make any close passes by the Earth
within the next century. However, for some objects, 21st century close
approaches and possible collisions with the Earth cannot be completely
ruled out.
How does the Torino Scale Work?
The Torino Scale utilizes numbers that range from 0 to 10, where 0
indicates an object has a zero or negligibly small chance of collision with
the Earth. (Zero is also used to categorize any object that is too small
to penetrate the Earth's atmosphere intact, in the event that a collision
does occur.) A 10 indicates that a collision is certain, and the
impacting object is so large that it is capable of precipitating a global
climatic disaster.
The Torino Scale is color coded from white to yellow to orange to red.
Each color code has an overall meaning:
======================================================
WHITE SHADING: "EVENTS HAVING NO LIKELY CONSEQUENCES"
======================================================
0. The likelihood of a collision is zero, or well below
the chance that a random object of the same size
will strike the Earth within the next few decades.
This designation also applies to any small object
that, in the event of a collision, is unlikely
to reach the Earth's surface intact.
====================================================
GREEN SHADING: "EVENTS MERITING CAREFUL MONITORING"
====================================================
1. The chance of collision is extremely unlikely, about
the same as a random object of the same size
striking the Earth within the next few decades.
==========================================
YELLOW SHADING: "EVENTS MERITING CONCERN"
==========================================
2. A somewhat close, but not unusual encounter.
Collision is very unlikely.
3. A close encounter, with 1% or greater chance of a
collision capable of causing localized destruction.
4. A close encounter, with 1% or greater chance of a
collision capable of causing regional devastation.
=====================================
ORANGE SHADING: "THREATENING EVENTS"
=====================================
5. A close encounter, with a significant threat of a
collision capable of causing regional devastation.
6. A close encounter, with a significant threat of a
collision capable of causing a global catastrophe.
7. A close encounter, with an extremely significant threat
of a collision capable of causing a global catastrophe.
==================================
RED SHADING: "CERTAIN COLLISIONS"
==================================
8. A collision capable of causing localized destruction.
Such events occur somewhere on Earth between
once per 50 years and once per 1000 years.
9. A collision capable of causing regional devastation.
Such events occur between once per 1000 years
and once per 100,000 years.
10. A collision capable of causing a global climatic
catastrophe. Such events occur once per
100,000 years, or less often.
==============================
How does an object get its Torino Scale number?
An object is assigned a 0 to 10 value on the Torino Scale based on its
collision probability and its kinetic energy (proportional to its mass
times the square of its encounter velocity). Categorization on the Torino
Scale is based on the placement of a close approach event within a
graphical representation of kinetic energy and collision probability
. An object that is capable of making multiple close approaches to
the Earth will have a separate Torino Scale value associated with each
approach. (An object may be summarized by the single highest value that it
attains on the Torino Scale.) There are no fractional values or decimal
values used in the Torino Scale.
Can the Torino Scale value for an object change?
Yes! It is important to note that the Torino Scale value for any object
initially categorized as 1 or greater _will_ change with time. The change
will result from improved measurements of the object's orbit showing, most
likely in all cases, that the object will indeed miss the Earth. Thus, the
most likely outcome for a newly discovered object is that it will
ultimately be re-assigned to category 0. Any object initially placed in
category 0 is unlikely to have its Torino Scale value change with time.
How did the Torino Scale get its name?
The Torino Scale was created by Professor Richard P. Binzel in the
Department of Earth, Atmospheric, and Planetary Sciences, at the
Massachusetts Institute of Technology (MIT). The first version, called "A
Near-Earth Object Hazard Index", was presented at a United Nations
conference in 1995 and was published by Binzel in the subsequent conference
proceedings (Annals of the New York Academy of Sciences, volume 822, 1997.)
A revised version of the "Hazard Index" was presented at a June 1999
international conference on near-Earth objects held in Torino (Turin)
Italy. The conference participants voted to adopt the revised version,
where the bestowed name "Torino Scale" recognizes the spirit of
international cooperation displayed at that conference toward research
efforts to understand the hazards posed by near-Earth objects. ("Torino
Scale" is the proper usage, not "Turin Scale.)
+++++++++++++++++++++++++++++++++++++++++++++++++
PROPOSED IAU REVIEW PROCEDURES FOR NEOS THAT MIGHT POSE AN IMPACT THREAT
**DRAFT***DRAFT***DRAFT**
Proposed IAU procedural guidelines in the event that a potentially
Earth threatening object is discovered (7/21/99).
The IAU Working Group on Near-Earth Objects,
RECOGNIZING
that the International Astronomical Union (IAU) has charged its Working
Group on Near-Earth Objects (WGNEO), in consultation with astronomers
worldwide, to draft a set of recommended procedures to be followed in case
asteroids or comets are discovered that lead to predictions of potential
impacts on Earth;
that the recent cases of asteroids 1997 XF11 and 1999 AN10 have
provided, at an early stage after their discovery, real examples of such
predictions;
that NEO scientists have a professional obligation to seek peer review
of their results before any public announcement of impact risk or threat;
that there is a need to identify the successive steps to be adopted by
the astronomical community in order to provide the authorities, the media
and the public with reliable information on the discovery of potentially
threatening objects;
RECOMMENDS the following procedures to be available to the members of the
astronomical community in any future case of discovery and/or theoretical
analysis leading to the prediction of impacts that fall at level 1 or
higher on the Torino Impact Hazard Scale at any apparition in the next
century.
The IAU establishes the following review procedure available on a voluntary
basis to all scientists involved in prediction of possible NEO impacts. The
information leading to such a prediction, consisting of an evaluation of
the case and all data and computational details necessary to understand and
reproduce the studies carried out by the authors, shall be transmitted for
confidential review to the chair of the WGNEO, the General Secretary of the
IAU, and the members of the WGNEO Review Team, before any announcement
and/or written document on the subject be made public on any information
media, including the World Wide Web. The membership of the standing Review
Team will be selected by the Chair of the WGNEO with the concurrence of the
IAU Division 3 President and the General Secretary, with names and e-mail
addresses posted on the IAU NEO webpage. The individual members of the NEO
Review Committee shall review the work for technical accuracy and shall
communicate within 72 hours the results of their reviews to the President
of the WGNEO and directly to the authors of the report or manuscript.
If the consensus of the above review supports the conclusion that there is
a significant impact risk, the results of this analysis will be posted on
the IAU webpage for public access. If the review disagrees with the
original analysis or if there is not a consensus among the reviewers, the
confidential results of the review will be given to the authors so they can
revise or improve their work, as they see fit. The news posted on the WGNEO
webpage shall represent the official position of the IAU; no further
information will be provided by the WGNEO, unless important updates become
necessary.
The authors of the work are encouraged to refer the media to this IAU
position if they choose to make a public release of their conclusions. If
so requested by various agencies (e.g., NASA or ESA), the IAU will also
inform the responsible officials of these agencies of the results of the
WGNEO review.
David Morrison
President, IAU Working Group on NEOs
NASA Headquarters, Washington, DC
Massachusetts Institute of Technology, Cambridge, MA
July 22, 1999
NEAR EARTH OBJECTS SCALE HELPS RISK COMMUNICATION
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.
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.
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."
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."
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