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CCNet-ESSAY, 2 May 2000
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     "Attempts to interpret the IAU 'adoption' of the Scale as a
     sanctification of every technical aspect of its first incarnation
     or as an iron rule on its use in scientific studies of NEOs is,
     first, misguided, and second, doomed to failure in the real world 
     of science."
        -- Johannes Andersen, General Secretary of the IAU


THE TORINO SCALE - A WORKING ALTERNATIVE

By Jonathan Tate, Spaceguard UK
   <fr77@dial.pipex.com>

The Torino Scale – a Working Alternative.
http://ds.dial.pipex.com/spaceguard/alternative2.htm

Introduction

The Torino Impact Hazard Scale was devised by Professor Richard P.
Binzel of the Department of Earth, Atmospheric, and Planetary Sciences,
at the Massachusetts Institute of Technology (MIT). It has been
described as a "Richter Scale" for describing the impact hazard
associated with newly discovered asteroids and comets, and was designed
to serve as a communication tool for astronomers to describe the
seriousness of predictions of close encounters by asteroids and comets
to the public and media.

The Torino Scale uses numbers that range from 0 to 10, where 0 
indicates that 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 Impact Hazard Scale is named after the Italian city in which
it was discussed, though not formally agreed, at the IMPACT workshop
(sponsored in part by the International Astronomical Union (IAU)) in
June 1999. Consensus was not achieved in Turin, and the IAU, while
welcoming the concept, has stated that "Attempts to interpret the IAU
'adoption' of the Scale as a sanctification of every technical aspect
of its first incarnation or as an iron rule on its use in scientific
studies of NEOs is, first, misguided, and second, doomed to failure in
the real world of science."

It is unlikely that such a scale will ever be needed in a professional
context, as those concerned are fully conversant with the subject. The
real value of an impact hazard scale comes into play when dealing with
disaster management organisations, the military, the media and the
public. To this end, any resulting scale must be simple (but not so
simple as to be misleading or confusing), easy to understand and as
accurate as possible. 

Aim

The aim of this paper is to recommend a refinement of the Torino Scale
developed in the light of experience in dealing with other interested
organisations, the public and the media.

The Problem

Since its introduction, the Torino Scale has been little used, despite
the fact that there have been at least two suitable occasions. 
Discussions with the media have involved more detailed descriptions
than provided by the Scale, but have tended to be inconsistent and
consequently confusing. A simple, easy to understand but common system
is required, that allows a full description of the hazard, in simple
terms, to be given. Such a system should allow for the amplification of
such points that seem relevant.

A scale to classify the impact threat differs from the scales used to
classify other natural disasters in one fundamental way. Other
disasters, such as earthquakes, volcanos, hurricanes and floods are not
predictable, and the scales used to classify them are retrospective. 
The impact threat is predictable, and the Torino Scale is, by
necessity, predictive.

Any scale used to describe the magnitude of a specific impact threat
must take account of three major factors:

a. Impact probability.
b. Time to probable impact.
b. The effect on the environment should the impact occur.

These are three very different factors since one is a probability,
variable with time, and the other two are determinable, given a unity
value for the first. They cannot, realistically, be combined in a
single rating. Problems have already been encountered with
non-specialists using the Torino Scale. A single number carries no
advantage if lengthy explanation is required.

Impact Probability (P).

The uncertainties involved in orbit determination make the calculation
of a definite probability of impact problematic. Any hazard rating
that includes the impact probability is liable to constant change, and,
as such, is of little value to the media or general public.  Indeed,
such a system is confusing and often misleading. Any description of
probability must be simple, avoiding the scientific complications that
often accompany the subject. The press and public are not concerned
with detail, so a maximum of five categories should be considered,
ranging from "no problem" to "very, very bad". 

In addition, any mention of the "background hazard" is irrelevant in
the context of hazard classification, as a "background" impact is just
as hazardous as any other.

Determining the probability of impact is a complex process, and the
result will always contain a substantial uncertainty. In addition, this
value will constantly change as further observations are made and the
orbit determination becomes firmer. Although it is perceived that the
lay population has some difficulty in understanding probabilities,
experience is showing that simple explanations work well in practice. 
It is therefore suggested that the following simple system, based on
that developed by R. Binzel, be used:


P Impact Likelihood (in 100 yr period) Probability
1 Almost Certain                         1:1 to 1:102
2 Likely                                 1:102 to 1:104
3 Possible                         1:104 to 1:106
4 Very Unlikely                         1:106 to 1:108
5 Almost Impossible                 Less than 1:108

Table 1 – Simplified NEO Hazard Index

(all tables of this proposal can be accessed at
http://ds.dial.pipex.com/spaceguard/alternative2.htm)

The effect on the environment should the impact occur (E).

The effects of an impact are dependant on a number of variables but
there is more certainty here than for the impact probability. 
Predictions can be made, based on the estimated mass and velocity of a
potential impactor, coupled with its composition and (if known) the
composition of the target surface. These predictions will be to a level
of accuracy sufficient for the media and general public, but may need
refinement as time passes for the emergency and disaster relief
agencies.  G. Verschuur has developed a simple classification system
that is quite adequate in this context, as shown below.

E Object Size Impact Energy (MT/TNT) Consequences
1 Very Large (>10 km) >108 Global - Mass extinctions
2 Large (2-10 km) 105 -108 Global - Some extinctions
3 Medium (0.2-2 km) 103-105 Regional -Threat to civilisation
4 Small (30-200 m) 103-105 Local - Severe
5 Very Small (10-30 m) 3-1000 Local - Minor


Table 2 - Impactor Categories (Verschuur)

Time to Probable Impact (T)

Assuming that P is determined to be near unity, then T can be
determined with some accuracy. Times can also be determined for close
approaches or potential impact solutions. It is suggested that four
standard time frames be adopted as shown below:

T Time to Predicted Impact
1 0-0.5 yr
2 0.5-2 yr
3 2-10 yr
4 10-100 yr
5 > 100 yr

Table 3 - Impact Timescale Index

Recommendation

It is recommended that a scale, similar in principle to the Torino
Scale, but including two published parameters (impact probability and
impact consequences) be adopted. This will provide customers with an
indication of the current impact probability and the consequences
should such an event occur. Only one parameter will change with time,
and, if necessary, can be described in more detail for clarity.  The
time to a predicted impact can be added, and will be an essential
factor when mitigation is planned.

Examples

a. The Tunguska impact would be described as an E4 event.

b. The K-T boundary impact would be an E1 event.

c. The 1998 XF11 affair would (before the confirmatory observations)
   have been described as an E3 P4 event, later dropping to an E3 P5
   after the precovery data was included.

d. 1999 AN10 would have started as an E3 P4 object, later dropping to
   E3 P5 after the 1955 precovery data was included.

The Next Step – a Logical Progression

While many in the astronomical community are unwilling to consider
methods by which catastrophic collisions might be prevented, there is a
clear duty incumbent upon the discipline to issue accurate and timely
warnings to governments, the media and the public should a potential
impact solution be discovered. Such warnings will be essential to allow
other agencies to prepare mitigative strategies. Without a system to
deliver such alerts, and “in progress” research and planning designed to
avoid or at least mitigate impact events, the current and planned NEO
detection and follow-up programmes will be seen by governments, the
press and public as little more than “scientific masturbation”.

The IAU WGNEO has already produced guidelines on the reporting of
potentially hazardous NEOs. However, the process described stops at the
General Secretary of the IAU. While it is hoped that there will be no
cause to involve other agencies in the foreseeable future, it would be
negligent, indeed irresponsible, not to have procedures to do so in
place. Given the stress generated by a potential catastrophe, it is
advisable to have pre-agreed and templated actions ready for use, which
are capable of flexibility if time permits. To assist observers,
researchers, the Spaceguard Foundation, the IAU WGNEO and the General
Secretary, it is suggested that a simple action matrix should be
adopted for use in the decision making cycle.

It should be noted that as it is impossible to forecast the exact
circumstances surrounding a potential impact event these action
statements constitute a guide, and may be modified, should time permit,
by agreement with all agencies concerned to deal with a specific
circumstance.

On receipt of a confirmed impact alert, the IAU WGNEO, in consultation
with the Spaceguard Foundation will place the alert into a specific
Threat Level as detailed below:

Impact Probability       Effect P5Almost Impossible P4Unlikely P3Possible P2Likely P1Almost Certain
E5Local-Minor 1 1 2 3 5
E4Local-Severe 1 2 3 4 5
E3Regional 1 2 4 5 6
E2Global 1 3 5 6 6
E1Global-Severe 1 3 6 6 6

Table 4 - Threat Level Template

The Threat Levels combine the two factors of impact probability and
effects. These must now be combined with the predicted time to impact
to produce the Action Matrix. While time will be critical for small
impacts, it is less so for larger ones, as the more time available for
mitigation, the easier the task.

A suggested Action Matrix is below:

Threat level           Time to Impact 1 2 3 4 5 6
T5(> 100 yr) 1 1 1 2 2 3
T4(10-100 yr) 1 2 2 3 4 5
T3(2-10 yr) 1 3 3 4 4 5
T2(.5-2 yr) 2 3 4 5 6 6
T1(0-.5 yr) 2 4 5 6 6 6

Table 5 – Action Matrix

Action 1 (No Action) - There is no requirement to alert the IAU WGNEO,
the Spaceguard Foundation or the other Parties to this Agreement (see
Annex A). Data may be published in professional journals, but there is
no necessity to alert outside agencies or the media.

Action 2 (Simple Alert) - The IAU WGNEO and the Spaceguard Foundation
are to be alerted.  Data is published in professional journals, and the
media may be briefed by the IAU WGNEO, the Spaceguard Foundation or the
discoverer, with a strong caveat that the specific threat is
exceedingly low or a long time in the future.

Action 3 (Reinforced Alert) - As for Action 2, but the IAU WGNEO, the
Spaceguard Foundation and other Parties to this Agreement or their
representatives will meet to decide on further precautionary measures.

Action 4 (Full Alert) - The IAU WGNEO, the Spaceguard Foundation and
other Parties to this Agreement or their representatives will formally
brief the Secretary General of the United Nations, national and
international authorities on the impact probabilities and consequences.
Spokesmen for the IAU WGNEO or the Spaceguard Foundation will alert the
media, in a managed fashion.  Planning for mitigative action should
commence.

Action 5 (Limited Global Mobilisation) - The IAU WGNEO, the Spaceguard
Foundation and other Parties to this Agreement or their representatives
will formally brief the Secretary General of the United Nations,
national and international authorities on the impact probabilities and
consequences as a matter of urgency.  Full regional emergency planning
procedures commence, and mitigation measures are considered as a
priority. The media will be briefed by spokesmen for the Secretary
General of the United Nations as to the nature of the threat and the
full consequences of the impact.

Action 6 (Full Global Mobilisation) - The IAU WGNEO, the Spaceguard
Foundation and other Parties to this Agreement or their representatives
will formally brief the Secretary General of the United Nations,
national and international authorities on the impact probabilities and
consequences as a matter of urgency.  Full global emergency planning
procedures commence, and mitigation measures are considered as a global
priority.  The media will be briefed by spokesmen for the Secretary
General of the United Nations as to the nature of the threat and the
full consequences of the impact.

The actions detailed above should be expanded and published as a series
of Standing Operating Procedures (SOPs). These SOPs would act as a
framework for national planning authorities – something that is totally
lacking at the moment. Such procedures are already in place for other
forms of natural disaster, and cut response times substantially,
without limiting flexibility in deciding on courses of action when time
is available. 

These procedures will require endorsement by the Spaceguard Foundation,
the IAU and such other organisations as deemed appropriate by the
General Secretary of the IAU. The resulting document should be
constantly updated and distributed as widely as possible. An extensive
distribution will reduce the possibility of misunderstanding and
increase the confidence of the public and media that they are being
kept fully informed of any situation that may arise.

Examples

  1998 XF11, as an E3 P4 object, would be categorised at Threat Level
   2. With a possible impact solution in 2028 it would call for Action
   2.

  For an XF11 type object, starting as an E3 P4, with a possible
   impact solution in 2028, the current (2000) Threat Level would be 2,
   and Action 2 called for. 

By 2018, assuming that the object, after careful observation, still has
an impact solution, the Threat Level will probably have risen to 4,
warranting Action 4. 

By 2023, with an impact solution probable, the object would be
classified as E3 P2, Threat Level 5 warranting Action 6. The timing of
mitigative action would be a matter for the Parties to this Agreement
to decide, but work would probably start at Action 4.

At any time, as the orbital error ellipse shrinks, the object could
drop to E3 P5, and the alert system would automatically reset to zero.

Summary

The impact hazard is becoming a subject of significant media and public
interest, and governments need guidance as to the threat and courses of
action open to them. It is the responsibility of specialists in the
field of minor planet studies and related subjects to supply the
relevant authorities with accurate and timely data, and to advise on
actions required. Recent events have demonstrated a lack of
co-ordination and cohesion within the scientific community, and the
absence of advice to governments and the media. This has led to a lack
of confidence in “scientists” amongst the general public, and a
perception that conspiracies abound.

To restore confidence, the NEO community requires a simple, accurate
method of describing the impact hazard and clear guidelines on actions
to be taken in the event of a hazard being discovered.  The systems
described above represent initial proposals that may be modified in the
light of experience, but the overarching principle should be retained.

Annex A

Parties to this Agreement


Secretary General of the United Nations.

United Nations Office of Outer Space Affairs.

International Astronomical Union.

Minor Planet Center (MPC) of the International Astronomical Union (IAU).

Spaceguard Foundation.

National and Collaborative Space Agencies.

Committee on Space Research.

International Institute of Space Law.

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