NEO NEWS 7/22/99: TORINO IMPACT HAZARD SCALE
From David Morrison <email@example.com>
NEO News (7/22/99) Torino Impact Hazard Scale
Dear friends and students of NEOs:
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 at (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.
INTERNATIONAL ASTRONOMICAL UNION AND MIT ANNOUNCE NEW
"TORINO SCALE" TO MEASURE IMPACT HAZARDS
MIT News Office
Massachusetts Institute of Technology
Cambridge, MA 02139-4307
More information on asteroid hazards available at:
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
"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.
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
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
"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 [see note below -bobk]-- 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
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
"Assessing Asteroid and Comet Impact Hazard Predictions in the 21st Century"
NOTE: FULL DESCRIPTION WITH COLOR GRAPHICS CAN BE FOUND ON THE NASA IMPACT
HAZARD WEBSITE (IMPACT.ARC.NASA.GOV)
The Torino Scale (by Richard Binzel)
What is it for?
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
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
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
<link>. 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
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,
- 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
- 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
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
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
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
President, IAU Working Group on NEOs
David Morrison, NASA Ames Research Center
Tel 650 604 5094; Fax 650 604 1165
firstname.lastname@example.org or email@example.com
APOLOGY TO ANDREA MILANI
From Richard P. Binzel <rpb@MIT.EDU>
Andrea Milani has correctly pointed out that the MIT Press release
gives an unfair description of 1999 AN10 -- especially implying that
the results concerning 1999 AN had to be "retracted."
Indeed I apologize that the word "retracted" is a poor choice here,
since it has a negative connotation (especially among scientists).
Reality, of course, is that the 1999 AN10 predictions were revised
in the face of new data.
Unlike writing by most journalists, I did have a chance to review this
text, but did not sense the unfair negative perception. Thus, the
problem is my own fault. I apologize -- it was never my intention to
have any unfair perception directed toward Andrea or his work on 1999
AN10 -- especially since his work and public communication on this
object were exemplary!
The purpose of the Torino Scale is to help bring us together, and I
most especially apologize if this problem moved us apart in any way.
Torino Scale values will change with time and we must all be careful to
emphasize this is a normal scientific process and does not imply that
previous calculations were necessarily wrong.
Richard P. Binzel
CCCMENU CCC for 1999