NASA Space Science News for July 22, 1999

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.

Full story here.

By Robert Roy Britt,

July 22, 1999

New Torino Scale Measures Asteroid Threat

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.

Full story here.

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

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.

David Morrison



MIT News Office
Massachusetts Institute of Technology
Cambridge, MA 02139-4307

More information on asteroid hazards

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.


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.


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."


"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."



"Assessing Asteroid and Comet Impact Hazard Predictions in the 21st Century"


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 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:


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.


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.


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.


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.


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 procedural guidelines in the event that a potentially Earth threatening object is discovered (7/21/99).

The IAU Working Group on Near-Earth Objects,