Draft 26 May 1999

    Australian Spaceguard Survey: the Australian component of an international effort to detect Earth-threatening asteroids and comets

       Prepared by Michael Paine (mpaine@tpgi.com.au) NSW Co-ordinator,
      The Planetary Society Australian Volunteer Co-ordinators
    [TPSAVC Site map]The Planetary Society (USA)Home page for the Australian Volunteer Co-ordinators  Join TPS Tribute to Carl  SaganComments on Planetary ScienceHow microbes might hitch a ride between planetsCarl Sagan's Baloney Detection KitThe Search for Extraterrestrial IntelligenceThe search for Earth-threatening comets and asteroidsProposal to revive the Australian Spaceguard ProgramTsunami (Correspondence with politiciansTPSAVC Home (of course!)

    This proposal has been prepared in consultation with the former members of the Anglo-Australian Near Earth Asteroid Survey team (Ken Russell, Gordon Garradd, Rob McNaught and Duncan Steel) and scientists involved in NEO and related work throughout the world. The views presented in this document are those of the author and do not necessarily represent the views of any other person or organisation.
     

    Contents

    Purpose
    Executive Summary
    Backgound
    The Impact Hazard
    Public Health Issues
    Current NEO Detection Programs
    Worldwide Spaceguard Goals
    Equipment Required to Achieve the Goals
    Budget
    Cost Effectiveness
    Sources of Funds
    Conclusions
    References
    Appendix A - Near Earth Objects
    Appendix B - Estimates of fatalities and damage
    Appendix C - Stakeholders
    Appendix D - Action Plan (New)
     

    Purpose

    There is no Spaceguard program in Australia - government funding stopped in 1996! This document sets out a proposal for a renewed and substantially upgraded Australian program to detect and track asteroids and comets which might impact the Earth ("Near Earth Objects" or NEOs). This will become an important component of an international effort to detect these threatening objects.

    This proposal has been prepared on a voluntary basis - the author is not associated with any organisation which might benefit financially from a NEO search program.

    Executive Summary

    The threat to Earth from impacts by asteroids and comets is very real. Impact craters have been found on much of the Earth's uneroded land surface, including the giant crater from the main impact that killed off the dinosaurs 65 million years ago. The cratering rate over the past few million years reasonably matches that predicted from the small sample of "Near Earth Objects" (NEOs) found by astronomers to date.

    A major NEO impact is an infrequent but highly destructive event. An impact by a 1 kilometre object could kill 1,500 million people. The chances of such an impact in the next 50 years are about 1 in 2000 (much "better" than the odds of four of a kind in poker). For a low-lying area on the shoreline of an ocean the risk of death from an impact is probably greater than that of an inland location due to the additional hazard of tsunami.

    A highly successful Australian search for NEOs was conducted between 1990 and 1996. The program ceased in 1996 when Australian Government funds were cut. We teach our children to look both ways before crossing the road - the decision to cut NEO funding was equivalent to saying "Don't bother looking for cars before you cross the road".

    This document proposes the re-establishment of a major Australian NEO search program, as part of the international Spaceguard Survey. The proposed full Australian Spaceguard program would cost between AU$1.3 and AU$3.9 million to implement and about AU$600,000 per annum to run. On the basis of very a conservative estimate, the annual cost works out at about $750 per human life saved (or, more selfishly, $240,000 per Australian life saved).

    Based on recent natural disasters in Australia, there is the potential for a $800 saving in direct economic losses in Australia (community, property and business losses) for every dollar spent on the Spaceguard program.

    Within a few years the annual operating costs of the Spaceguard program could be funded, at least partially, through private and corporate sponsorship/donations. Government funds (national and international) will be needed to get the program underway.

    We have the technology to both detect most of these threatening objects and to avoid or mitigate an impact, provided that sufficient warning is available. If, in a few decades, an imminent impact is detected when it is too late to do anything about it then the finger will be pointed at our generation - we had the ability to provide this gift of survival knowledge to the future but did nothing about it.

    Read on...

    Background

    It is only in the past few decades that scientists have found clear evidence that the Earth is subjected to random impacts from asteroids and comets. Exploration of the solar system by spacecraft revealed a long and continuing history of impacts with planets and moons. Spacecraft orbiting the Earth revealed the remnants of impact craters across the planet. It was not until the early 1990s that scientists found, in Mexico, the 170km diameter impact crater associated with the impact of a 15km object that marked the demise of the dinosaurs and many other species some 65 million years ago. Giant impacts have been associated with several other mass extinctions of life on this planet. There is also mounting evidence that smaller impacts have devastated regions of the Earth from time to time (Chapman 1998a, Verschuur 1998).

    During the 1980's several programs were initiated around the world to search for NEOs. These gave a better understanding of the size of the NEO population but were generally not sensitive enough to detect a major percentage of these objects. In 1992 the Spaceguard Survey was proposed, in response to a US Congress request to NASA to accelerate the discovery rate (NASA 1992). In May 1998 a US House of Representatives Committee conducted a hearing on the impact hazard. The evidence presented to the committee made a strong case for implementing a global Spaceguard program (Chapman 1998b).

    The proposal for reviving the Australian component of this important program has been under development since 1996, when the Australian Federal Government withdrew funding for the initial project (which started as the Anglo-Australian Near Earth Asteroid Survey - AANEAS). The demise of the Australian program caused great concern among the NEO scientific community as it was the only major search in the Southern Hemisphere. NEOs discovered in the Northern Hemisphere might be "lost" if they move into southern skies:
     

      'Steel notes that the Australian NEO program had particular significance: "As the only Southern Hemisphere program, there was a special responsibility to track objects discovered by the US. search programs but not accessible to them later." The Australian program supplied about 30 percent of all NEO positional measurements and made about 60 percent of recoveries (spotting NEOs on predicted visits) during its final three years. With this gaping hole in the coverage of southern skies, many if not most of the NEOs that are detected will not benefit from significant follow-up observations. After finding the needles in the haystack we throw most of them back in again, says Steel.' (Verschuur 1998)
    The Planetary Society, which is based in California and has more than 100,000 members throughout the world, has been a long-standing advocate and supporter of NEO search programs. In September 1996 the Society's Executive Director, Louis Freidman, wrote to the Australian Prime Minister seeking reconsideration of the decision to stop funding the Australian NEO search program. A copy of that letter was sent to the Society's 1,000 Australian members and that action initiated the current proposal (the first step was taken in December 1996).

    Appendix A contains further information about NEOs.
     

    The Impact Hazard

    There are an estimated 2,000 NEOs larger than 1 kilometre. As at mid-1998 about 250 of these large NEOs have been detected and tracked (some have subsequently been "lost" due to the lack of follow-up observations). None of the detected NEOs are on a collision course with Earth within the next 50 years. The chances of one of the undetected NEOs with a diameter of 1km or more colliding with Earth in the next 50 years is about 1 in 2000 (based on NASA 1995). The consequences of such an impact would be catastrophic and global: there would be years of permanent winter, a collapse of agriculture and, possibly, the end of our civilisation.

    Early detection of an impending impact by a large NEO would initiate an international effort to deflect the object (the earlier this is done the better the chance of success) and to prepare contingency plans in the event of an impact. In either case civilisation could be saved.

    There are many more smaller NEOs which also present a regional hazard on Earth. An object about 100m in diameter can devastate the landscape for a 50km radius around the point of impact (as occurred in Siberia earlier this century). The chances of such an object hitting the Earth in the next 50 years are about 1 in 10 (perhaps much higher - one purpose of Spaceguard is to refine these estimates). The proposed worldwide Spaceguard program is expected to greatly increase the detection rate of these smaller NEOs. Sufficient prior warning of a small NEO impact would enable evacuation of the affected areas and contingency preparations for possible effects on crop production.

    Public Health Issues

    The detection of NEOs can no longer be regarded solely as scientific research. The research to date has shown there is a real and predictable hazard to mankind. The issue now is prevention of loss of life through early detection and mitigation. This clearly has also become a public health issue.

    The chances of a US citizen dying from an asteroid or comet impact is about 1 in 20,000. This is compared with other causes of death in the US in the following table:

    Table 1 - Summary of Accidental Causes of Death for US Citizens

      Cause of Death                        Chances
      Motor vehicle accident             1 in 100
      Homicide                                 1 in 300
      Fire                                         1 in 800
      Firearms accident                     1 in 2,500
      Melanoma (type of skin cancer)1 in 4,000
      Electrocution                            1 in 5,000
      Asteroid/comet impact          1 in 20,000
      Passenger aircraft crash           1 in 20,000
      Flood                                       1 in 30,000
      Tornado                                   1 in 60,000
      Venomous bite or sting             1 in 100,000
      Food poisoning of botulism        1 in 3 million
    (Source Chapman 1998a based on C.R. Chapman and D. Morrison, 1994, Nature 367, 33-40. The Melanoma risk has been estimated from other data and is included because it is another example of a death which can be prevented by early detection.)

    It can be seen that asteroid/comet impact is relatively high in the list compared with other "civil disasters". Although major impacts are very rare the consequences of such impacts, in terms of loss of life, are extremely high. The significant difference is that, given an adequate detection program, a NEO impact can be predicted many years in advance and therefore the consequences can be minimised. In other words, the above table is based on current (minimal) NEO detection programs - the chances of death through NEO impact can be substantially reduced through improved NEO search programs.

    On a worldwide basis, it is conservatively estimated that, averaged over many years, the global death rate from NEO impacts would be equivalent to 3,000 deaths per year or about one death per two million of population (see Appendix B). This rate will be used in the cost-effectiveness estimates set out below. Although the value seems relatively low, compared with other causes of death around the globe, the actual deaths from any one NEO impact event could range from zero to most of the population of the Earth - it has been pointed out that the impact of a 1km asteroid could cause the death of 25% of the human population (Steel 1995). Furthermore, the fragile global economy is likely to be affected by a NEO impact in a populated, agricultural or resource rich area.

    Another factor not fully covered in this estimate are the consequences of an ocean impact. These consequences have only recently been determined through computer modelling. Tsunami and hurricanes resulting from the impact of a NEO can cause fatalities and damage equivalent to a large NEO striking land. Taking these and other factors into account Steel (1995) derives an annual expectancy of deaths from impacts in the range 3,000 to 15,000. As indicated above, the lower value will be used for cost effectiveness estimates. For comparison, the global long-term average death toll from earthquakes is about 10,000 per year.

    The NEO detection program has many parallels with public health disease prevention programs - early detection can prevent or mitigate the effects of the threat.
     

    Current NEO Detection Programs

    Currently there is no major program within Australia to detect and track NEOs. Between 1990 and 1996 the AANEAS was one of the most prolific programs of its type in the world (Steel 1998). AANEAS lead to the discovery of 38 Near-Earth asteroids, 9 comets, 63 supernovae and the delivery of a substantial proportion of all NEA astrometry (tracking) obtained worldwide (30% in 1994-95). Many other scientific advances were reported in the literature.

    The major NEO detection effort is currently within the US where there are several projects (Spacewatch, NEAT, LONEOS, LINEAR). In July 1998 NASA established a Near-Earth Object Program Office within JPL "to co-ordinate NASA-sponsored efforts to detect, track and characterise potentially hazardous asteroids and comets that could approach Earth". David Morrison from NASA recently reported on the progress of these US programs - about one tenth of the required global discovery rate.

    Japan has just allocated a budget of US$15million for NEO-related research including an optical telescope and a radar system.

    In Europe the OCA-DLR Asteroid Survey (O.D.A.S.) is located north of Nice, France. It began observing in October 1996.

    Asteroid/comet detection is also undertaken by dozens of amateur astronomers throughout the world. Although generally these people do not have access to equipment which would detect the faint objects of most concern they form a very important part of the follow-up of anticipated detections by the Spaceguard program. In addition, there will be a need, from time to time, to use other professional observatories, particularly if recovery/follow-up of an object requires larger telescopes than that used by Spaceguard.

    Co-ordination of all asteroid/comet detections (including NEOs) is carried out by Minor Planet Centre (MPC) based in the USA. It is understood that the US government intends to increase resourcing for the MPC in order to cope with an anticipated vast increase in detection rates over the next few years.
     

    Worldwide Spaceguard Goals

    This section is based on the NEO Survey Workgroup Report (NASA 1995). A realistic goal is to detect and establish the orbits of 80% of short period NEOs larger than 1km within a decade  . A great many smaller objects will also be detected and tracked (estimated 50% of NEOs 500m in diameter and 20% of NEOs 200m in diameter over the first ten years). It should be possible to exceed these goals but they will be used for planning and evaluation purposes (recently the Spaceguard detection goal was revised to 90% but the lower figure will be used in this analysis for a conservative estimate).

    With this level of NEO search there would also be a greatly increased chance of detecting longer-period comets, which spend much of their time in the dimly lit outer reaches of the solar system. However, an effective (say 80%) detection program for these objects is much more challenging, as is an effective detection program for the region-threatening small NEOs (under 200m diameter). In either case the sampling by the Spaceguard program would provide important information that would enable these more sophisticated programs to be assessed and ultimately developed.

    A key issue in setting goals is the prompt implementation of an effective program. Due to the nature of the orbits of NEOs they are generally only in favourable positions in the night sky for several days every few years. For an object that is visible today it could be several years before an opportunity arises to detect that object again. Furthermore, in order to precisely calculate the object's orbit and determine the long-term hazard to the Earth, it is necessary to have observations a year or more apart. That is why observations made today are so important - they can be used in several years time to redetect the object and make precise orbit calculations. Today's observations could provide a gift of survival information to the future.

    The Spaceguard goals are realistic and the technology exists to implement an effective program immediately.
     

    Equipment Required to Achieve the Goals

    This section is based on the assessment provided in the NEO Survey Workgroup Report. An international program utilising telescopes reaching limiting magnitude of 20 can achieve the goal of at least 80% completeness of NEOs down to a size of 1km in a 10 year survey.

    The limiting magnitude (minimum brightness of a detected object) achievable by a given telescope depends primarily on the aperture (the diameter of the main mirror), the exposure time and the method of detection (photographic plate or CCD - see below). The larger the aperture the shorter the exposure time to detect on object of a given magnitude. Excessive exposure times would mean that the telescope must be pointing at a set spot in the sky for too long and there would be insufficient telescope time to survey the whole of the sky allocated to that telescope. For longer-term follow-ups (such as detecting an object discovered a year or more previously) the exposure times can be extended in order to detect the object of interest, which might be in a less favourable position for observation the second time.

    A related issue is the observational strategy. An asteroid or comet generally moves very slowly against the background stars. If two exposures of the same portion of sky are taken 1 hour apart then the motion of the comet or asteroid should become evident. Experience has shown, however, that it is best to make a third exposure an hour later to help eliminate spurious signals (mainly from cosmic rays). This technique will show that an asteroid or comet is present in that portion of the sky. If it is not a previously catalogued object then follow-up observations will be needed over several days in order to provisionally determine the object's orbit (and the possibility of collision with Earth within a few decades). If the follow up observation is missed then there is a strong chance the object will be lost - a missed opportunity.

    The necessary exposure times and the observational strategy place limits on the minimum aperture of a Spaceguard telescope. A telescope with a 1m aperture and an advanced CCD detector will be able to detect magnitude 20 objects after exposures of 20 seconds. However, the area of sky covered during a single exposure, coupled with time needed to make the second and third exposures, mean that the telescope would have insufficient free time for follow-up observations and a second telescope would probably need to be employed for this purpose. Given the importance of the follow-up observations, a second 1m telescope would be needed on a near-fulltime basis.

    An alternative strategy, currently being implemented at the University of Arizona, is to use a 1.8m telescope, or larger. In this case magnitude 20 objects can be detected after exposures of about 10 seconds. The telescope would therefore have sufficient time to complete its own follow-up surveys of the sky.

    Most of the NEO detection efforts in the early 1990s involved the time-consuming and tedious analysis of photographic plates. There has been a recent major breakthrough in technology with the application of Charge Coupled Devices (CCD) to astronomy.  This is demonstrated by the recent success of the LINEAR project in the USA. CCDs detect faint light signals on an electronic matrix (the same type of device as that used in video cameras). The resulting electronic image can be directly processed by computer. For example, two images taken an hour apart can be automatically analysed to identify objects, such as NEOs, which have moved over that time (a fast-moving NEO might need to be slightly brighter than the magnitude 20 "target" value in order to be detected by the system).

    Once a potential NEO is detected it will need to be checked against data for previously discovered objects to determine if it is a new discovery. This will mean that the observer will need computing facilities that can perform the necessary orbital calculations and that have access to a database of known objects. In either case the resulting astrometric data will be forwarded to a central repository (currently the Minor Planet Centre) for distribution to other NEO observers. The determination of the impact threat to the Earth could be undertaken by any organisation with access to this data, although guidelines have recently been developed to cover the public announcement of the discovery of a potentially threatening object (to avoid false alarms). Computer programs are now available to analyse CCD data and calculate NEO orbits.
     

    Budget

    These are provisional cost estimates based on experience with existing observatories similar in size to the one proposed for Spaceguard. All costs are in Australian dollars.

    START-UP COSTS

    The cost of constructing a new 2m telescope with CCDs and other equipment would be around $4 million. An alternative approach is to obtain most of the equipment from redundant programs - preferably through donation. Possible sources of equipment are the Automated Patrol Telescope at Siding Spring and the US Air Force or NASA for the CCD system and computer software. There would still be substantial costs involved in providing the facilities (proposed at Siding Spring) and adapting the equipment for the Spaceguard project. Estimates of these costs are set out below.
     

      Telescope systems - possible donation (otherwise allow $2m)
      CCD systems - possible donation (otherwise allow $500,000)
      Site preparation and construction $800,000
      Support equipment $300,000
      Computer software - possible donation (otherwise allow $100,000)
      Extra staffing costs during implementation $200,000
    Total start-up costs range from $3.9 million to $1.3 million depending on donations of equipment.

    ANNUAL COSTS

      Staffing                                      $350,000
        1 Project Leader/Astronomer
        1 Software/Data Processing expert
        1 Engineer
        2 Observing Assistants
      Ongoing operational costs             $200,000
        Equipment maintenance ($30,000)
        Administration and overheads ($70,000)
        Data processing and communication ($50,000)
        Services and other operational ($50,000)
      Total operational and staffing costs $550,000 per year

      10% Contingency -                 allow $50,000 per year

    TOTAL ANNUAL COSTS                  $600,000

    It would be possible to stage the implementation to optimise the resources. For example the first phase might involve upgrading the Automated Patrol Telescope at Siding Spring for NEO search work. This telescope could then be effectively used as the main telescope in the initial years for an estimated operating cost of about $300,000 per year.  The second phase would involve the commissioning of a larger telescope for dedicated NEO search work (this would be needed for detecting fainter objects as the Spaceguard Survey progresses). The estimated costs of $600,000 per year cover the full-time operation of this telescope and the part time operation of a follow-up telescope such as the APT.

    Cost Effectiveness

    For the following estimate it is assumed that an international Spaceguard Program is 80% successful in detecting threatening NEOs with sufficient warning to fully mitigate the effects (that is, 20% of NEOs 1km or more in diameter will strike the Earth without sufficient warning). Therefore, averaged over many years, the global program will save 80% of 3,000 = 2,400 deaths per year. If it is assumed that a Spaceguard program in Australia contributes to one third of this success then a total of 800 lives per year would be saved through the Australian program. At an annual cost of $600,000, this is equivalent to $750 per life saved.

    The above calculation is based on saving lives around the globe. If the calculation is confined to Australian lives saved then it is estimated that, averaged over many years, 2.5 Australian lives would be saved each year (this is a somewhat selfish approach and ignores the grave economic, social and political consequences of a major impact). The Spaceguard program in Australia would therefore equate to $240,000 per life saved.

    This level of cost per life saved is well within the "worth doing" category for road safety initiatives, airline safety programs and medical funding. For example, averaged over the past two decades, the worldwide number of fatalities in non-sabotage commercial airliner crashes is around 700 per year (Reynolds 1992). This is one quarter of the estimated death rate from NEOs under current search efforts. The relatively low rate for commercial airline crashes is primarily due to very effective preventative measures that apply in the commercial airline industry - measures which cost hundreds of millions of dollars per year and equate to millions of dollars per life saved. (Note that the chances of a USA citizen dying in a commercial airline crash are much higher than citizens from most other countries due to higher rates of airline travel in the USA - the value for "Passenger airline crash" in Table 1 only applies to residents of the USA). The annual cost of the Australian component of Spaceguard is probably well below the annual cost of weapon detection systems (including staffing) at just Sydney domestic airport.

    These NEO cost effectiveness calculations are very conservative since they are based solely on preventing deaths from major impacts (NEOs 1km and larger). They do not include the benefits of preventing the global economic chaos which would result from a major NEO impact, the prevention or mitigation of the regional effects of smaller NEO impacts (including the potential for many additional deaths resulting from an impact above the ocean) or the protection of our satellite and communication systems through a better understanding of NEOs. Furthermore, the benefits would extend well beyond the ten year period proposed for achieving the Spaceguard goals. On the other hand, mitigation measures such as deflecting asteroids or creating global food and energy stores have not been costed but these could be expected to be much less than the potential economic losses.

    Based on recent natural disasters in Australia, it is estimated that the Australian component of an effective Spaceguard program would be associated with direct economic savings of about $500 million per year - more than eight hundred times the annual cost of the program (see Appendix B). This estimate is likely to be very conservative since the physical and economic effects of cyclones, floods and earthquakes tend to be confined to regions and, to date, they have not seriously disrupted the Australian economy.
     

    Sources of Funds

    It is proposed that funds be sought from government and private stakeholders such as those listed in Appendix C.

    Start-up costs could be shared between the Australian and US Governments (including the value of US agency-donated assets).

    In the first year the operational costs could be met by the following split:
     

      Australian government 50% (AU$300,000 per year)
      Overseas Government Agencies (mainly US) 50% (AU$300,000 per year)
    In subsequent years sponsorship and donations would be sought from the stakeholders with a realistic target of raising about $200,000 per year. Government funding of about $400,000 per year would therefore be required for the remainder of the ten year program.

     Conclusions

    Over the last decade evidence has been found that the Earth is still subject to random impacts from asteroids and comets. There is a 1 in 2000 chance that an impact with global environmental consequences will occur in the next 50 years and a 1 in 10 chance or greater that an impact with regional environmental consequences (and possibly global economic consequences) will occur in that period.

    We now have the technology to detect a significant proportion potentially threatening objects. If an object is found to be on a collision course with the Earth in the foreseeable future then we can take action to avoid the collision or to mitigate the effects of an impact. If we do not look for these objects then an impact is likely to occur without warning and the consequences will be much graver.

    There is an urgent need for a Southern Hemisphere component of the international Spaceguard program. Australia is ideally placed for this task, with a suitable location and experienced astronomers. Is is estimated that it would cost $1.3 million to establish an effective NEO search program in Australia (assuming the donation of some redundant assets) and the operating costs would be $600,000 per year, over the proposed 10 year Spaceguard program. Within a few years the annual operating costs of the Spaceguard program could be funded, at least partially, through private and corporate sponsorship/donations. Government funds (national and international) will be needed to get the program underway.

    The NEO search is clearly a public health issue. Averaged over many years, the global death rate from NEO impacts is conservatively estimated to be 3,000 per year under current (minimal) NEO search programs. This could be cut by 2,400 per year through the proposed worldwide Spaceguard program (assuming that 20% of large NEOs remain undetected). In effect, the Australian component would contribute to about one third of the lives saved or about 800 lives per year. With an annual cost of $600,000 this is equivalent to $750 per life saved - a remarkably cost-effective program. Even if the costing is confined to Australian lives then the cost of the Australian program is equivalent to $240,000 per life saved - this compares very favourably with road safety and medical prevention programs. Based on recent natural disasters in Australia, there is the potential for a $800 saving in direct economic losses in Australia (community, property and business losses) for every dollar spent on the Spaceguard program.

    Let us not wait until a catastrophic impact shocks to world into conducting a serious search for NEOs. In any case, the environmental and economic consequences of even a moderate impact could set civilisation back for decades or centuries, paradoxically making a NEO search a lower priority than the rebuilding of civilisation.

    By conducting a serious NEO search now we can provide future generations with otherwise unobtainable information which may prove crucial to their survival - a rare gift to the future from the people of the 20th Century.
     

    References

    Note: numerous World Wide Web links are available on the Australian Spaceguard Survey web site http://www1.tpgi.com.au/users/tps-seti/spacegd.html.

    Archer M (1998) 'The one-in-600-year wave', Nature Australia, The Australian Museum Trust. Vol.26, No. 1.

    Chapman (1998a) The Asteroid/Comet Impact Hazard, Originally presented at the Workshop on Prediction in the Earth Sciences, Boulder CO, 10 July 1997. Updated 22 April 1998. http://www.boulder.swri.edu/clark/index.html>

    Chapman C (1998b) The Threat of Impact by Near-Earth Asteroids, Statement before the Subcommittee on Space and Aeronautics, Committee on Science, US House of Representatives, May 21 1998. http://www.boulder.swri.edu/clark/hr.html. Also Action Plan Statement, 9 June 1998: http://www.boulder.swri.edu/clark/actnea.html

    Hodges A (1997) 'Disasters and disaster issues - the Australian Experience', Australian Insurance Law Association National Conference, 14 August 1997. http://www.ema.gov.au/insclawc.html

    Martel L (1997) Damage by Impact, Hawaii Institute of Geophysics and Planetology, http://www.soest.hawaii.edu/PSRdiscoveries/Dec97/impactBlast.html

    Morrison D (1997) 'Is the sky falling?', Skeptical Inquirer, May/June 1997. http://www.csicop.org/si/9705/asteroid.html

    NASA (1992) The Spaceguard Survey, http://ccf.arc.nasa.gov/sst/spaceguard/index.html

    NASA (1996) Responding to the potential threat of a NEO impact, AIAA Position paper. http://impact.arc.nasa.gov/reports/aiaa/index.html

    NASA (1995) The NEO Survey Workgroup Report, http://impact.arc.nasa.gov/reports/neoreport/executive.html

    NRC (1998) Impact Cratering on Earth, Natural Resources Canada, (includes maps and database) http://gdcinfo.agg.emr.ca/paper/cratering_e.html

    Reynolds T (1992) 'Aircraft Passenger Cabin Safety', Interior Safety of Passenger Transport, Institution of Mechanical Engineers, London, November 1992.

    Steel D (1995) Rogue asteroids and doomsday comets: the search for the million megaton menace that threatens life on Earth, John Wiley & Sons, ISBN 0471193380.

    Steel D, McNaught R, Garradd G, Asher D and Russell K (1998) 'AANEAS: A Valedictory Report', Australian Journal of Astronomy, June 1998. http://www1.tpgi.com.au/users/tps-seti/spacegd4.html

    Verschuur G (1998) 'Impact Hazards: Truth and Consequences', Sky and Telescope, June 1998. http://impact.skypub.com

    Verschuur G (1996) Impact! The Threat of Comets and Asteroids, Oxford University Press. ISBN 0-19-510105-7

    Young R, Bryant E, Price D and Spassov E (1995) 'The imprint of tsunami in quarternary coastal sediments of Southeastern Australia', Bulgarian Geophysical Journal, Vol.XXi, No.4.
    http://wwwrses.anu.edu.au/~edelvays/tsunami1.html
    (also http://www.uow.edu.au/science/geosciences/research/tsun.htm)

    Appendix A - Near Earth Objects

    The Solar System

    Most of the planets of the Solar System orbit the Sun in near-circular orbits with the Sun at the centre. All of the planets, except Pluto, orbit the Sun in roughly the same plane but at different radii from the Sun. Interspersed among the planets are much smaller objects - asteroids and comets ranging from ten metres to tens of kilometres in size (objects smaller than 10 metres are called meteoroids - although they pose a serious threat to spacecraft they are not a great threat to the surface of the Earth since they tend to break up and burn in our thick atmosphere). There are millions (perhaps billions) of asteroids orbiting the Sun between Mars and Jupiter (the "asteroid belt") and there are likely to be billions of comets orbiting the Sun way beyond the orbit of the outermost planet Pluto (the "Oort-Opik Cloud").

    Earth Crossing Orbits

    Occasionally some of these comets and asteroids are nudged out of orbit and some head towards the inner solar system. These objects usually have highly elliptical orbits which bring them close to the Sun and then far out into space - the most famous is probably Comet Halley which orbits the Sun every 76 years (its orbit spans from inside the Earth's orbit to beyond Neptune). It is estimated that there are several million objects greater than 10m in diameter which cross the Earth's orbit and therefore have the potential to collide with the Earth - these are the "Near Earth Objects" (NEOs). Of these it is estimated that about 2000 are large enough (diameter 1 kilometre or more) for an impact to have severe global consequences. It is only a matter of time before many of these NEOs collide with Earth - it is estimated that 40% will collide with the Earth over the next hundred million years. During this time other asteroids and comets might also be nudged into an Earth-crossing orbit so the population will remain roughly constant.

    Craters on Earth

    70% of the Earth's surface is covered by ocean where evidence of an impact is difficult to detect or quickly erased. Furthermore, about half of the land surface has changed sufficiently over geological time for evidence of craters to be erased. This leaves about 15% of the Earth's surface area over which impact craters can be expected. More than 150 have now been identified and several more are being found every year. Of these the most recent major impact of NEO with a diameter greater than 1km was probably in Kazakstan about 900,000 years ago causing a crater 15 km in diameter (NRC 1998).

    Based on the relatively small sample of the NEO population by astronomers, the expected impact rate for these large NEOs is one every 100,000 years (thus the 1 in 2000 chance of an impact in the next 50 years). On the 15% of the Earth's surface that would have retained evidence of such an impact the average interval between events would therefore be about 700,000 years which is in reasonable agreement with the independent (and incomplete) observation of cratering on Earth (3 impacts causing craters over 10km diameter in the last 4 million years - NRC 1998). However, it is wrong to think that the "next major impact" will not occur for tens of thousands of years and is therefore not of current concern. It could occur at any time - there is a 1 in 100,000 chance that it will occur next year and the same odds in any subsequent year. See Poisson Distributions for more information about interpreting impact rates.

    Craters from impacts with regional significance have been found in Algeria (100,000 years ago), Arizona (50,000 years ago), India (50,000 years ago), South Africa (200,000 years ago), Argentina (100,000 years ago) and Western Australia (300,000 years ago). Again this cratering rate is in reasonable agreement with estimates based on the known NEO population. Furthermore, as in the case of Tunguska, not all impacts with regional significance leave an impact crater.

    Ocean Impacts - Tsunami

    The waves created by a sudden disturbance in the ocean are known as tsunami. They generally travel very fast across the ocean (500km/h or more compared with 50km/h for wind-generated waves - they therefore have at least 100 times the energy of normal waves). In deep water the wave heights might not be great but the height increases dramatically (typically five times  but sometimes by 40 times or more) when the wave slows in shallow water and the energy becomes more concentrated.

    The usual causes of tsunami are earthquakes and underwater landslides but there is now evidence that giant tsunami can be caused by NEO impacts. Tsunami and hurricanes resulting from the impact of a NEO can cause fatalities and damage equivalent to a large NEO striking land.

    Research by the University of Wollongong suggests that the New South Wales South Coast has been struck by at least six large tsunami within the last 6,000 years - a typical interval of 1,000 years - perhaps much less (Archer 1998, Young et al 1995). One possible cause is giant underwater "landslides" on the edge of the continental shelf but NEO ocean impacts may have caused some (or all) of these tsunami.

    Civil Disasters

    The main differences between a major NEO impact and other severe natural disasters are:
    • The consequences of a major NEO impact are potentially much greater than any other single natural disaster in terms of lives lost, environmental impact and economic impact.
    • We now have the technology to detect most large NEOs and to predict an impact. Given the incentive of a positive detection (that is, a threat to the Earth), we can also quickly develop the technologies to deflect the object or, at the very least, evacuate the impact zone and prepare for food and energy shortages.
    • A moderate to major impact has not occurred within living memory and therefore the threat may not be immediately apparent to policy makers and government advisors - it is easy to find other priorities which seem more pressing.
    Arthur C Clarke, in his Foreword to Duncan Steel's book, points out that no one has (apparently) ever died from a thermonuclear explosion but, hopefully, mankind treats the threat of catastrophe from these weapons very seriously indeed. The same logic - prevention of a catastrophic event - should apply to the search for NEOs.

    Although we probably cannot detect most of the smaller NEOs with current technology the threat of tsunami from the smaller impacts could be mitigated by the installation of tsunami warning systems, as used in Japan and Hawaii.

    Threat to Spacecraft

    Small NEOs (meteoroids) pose a threat to our spacecraft. The operators of satellites are very concerned that, in November 1998 and 1999, the Earth will be passing through an extra-dense portion of the debris of a comet that causes the annual Leonids meteors showers. Even though most of the particles are no larger than a grain of sand the relative speeds are sufficient to knock out vital spacecraft systems. Although the proposed Spaceguard program would not directly detect such small objects it should assist scientists better understand the phenomenon.

    The explosion of a small asteroid several kilometres above the Earth's surface is likely to throw tens of thousands of tonnes of debris into near space where it would pose a threat to spacecraft.

    Appendix B - Estimates of fatalities and damage

    These estimates are based on averages over many decades. The US death rate is about 0.87% of the total population per year or approximately 2.3 million deaths/year. At a rate of 1 in 20,000 (Chapman 1998a) the number of US deaths from NEO impacts is estimated to be 115. This is equivalent to 0.5 NEO deaths per million of population. Applying this to the world population of about 6 billion gives an estimated death rate from NEO impacts of 3,000 per year. For comparison, the global long-term average death toll from earthquakes is about 10,000 per year.

    An indication of the scale of direct economic losses of an impact can be gained from Australia's recent natural disasters: "Australian citizens rightly expect prevention of, or at least protection from, disasters which affect life and property. But though our disasters have caused relatively few deaths, very substantial economic losses are often sustained. For instance [in 1996] there were 23 events nationally with individual losses exceeding $5 million causing total losses of $1.3 billion." (Hodges 1997). The 1989 Newcastle Earthquake caused 15 deaths, 150 injuries and seriously damaged 33,000 buildings. The total estimated cost of the disaster was $4 billion including insurance losses of almost $1 billion. Using these events as a very rough rule of thumb, the estimated 2.5 Australian lives saved per year through an effective Spaceguard program would be associated with direct economic savings of about $500 million per year - more than eight hundred times the annual cost of the program.

    The above analysis does not take into account the extra hazard to Australia's coastal areas from impact-generated tsunami. On the basis of the limited research into NEOs and tsunami to date, the death toll from a 10 metre tsunami striking the east coast of Australia is estimated to be at least 35,000.

    Appendix C - Stakeholders

    The following list gives an brief indication of the stakeholders in the Spaceguard Program.

    The Population of Earth - UN, WHO

      Our civilisation could be threatened by a major NEO impact. Even a minor impact to a region of economic importance could have severe worldwide economic consequences.

    National Governments

      Portfolios concerned with health, defence, science and emergency management. Concerns are regional disaster and global economic collapse. Northern Hemisphere NEO detection efforts could be in vain if a NEO moves into southern skies and there is no effective Southern Hemisphere NEO search.

    Defence forces, space agencies and emergency services

      False alarms of nuclear missile launches, threat to satellites and other spacecraft (GPS, communications), disaster planning.

    Insurers

      Threat to (insured) spacecraft. Regional disasters - for example, insurers paid for about one quarter of the AU$4 billion cost of the Newcastle Earthquake in 1989.

    Coastal populations, coastal agriculture.

      Tsunami ("tidal" waves) from ocean impacts.
      The Australian sugar cane industry is particularly vulnerable since the crop producing areas are typically in low-lying coastal areas. The industry generates an income of approximately $2 billion per year in Australia. Similarly the Australian tourist industry is very dependent on coastal attractions.

    Scientists/Astronomers

      Building on current knowledge - with the potential to make a significant discovery. A job for at least ten years with reliable funding!

    Individuals, space societies and corporations

      A gift of survival knowledge for future generations. People of the twentieth century have left very little of benefit for future generations - the century may well go down in history as the age of greed when a disproportionate amount of the Earth's resources were consumed and little attention was paid to long-term environmental consequences. A Spaceguard Program would show that at least some people in this century were thinking about the long-term future of mankind and were collecting information intended to help a future scientists accurately plot the orbit of a threatening NEO.

    Sponsorship

      It is anticipated that sponsorship and donations could be used to generate funds from the private sector - Spacewatch in Arizona is successful with this approach.

      An alternative approach could be considered for raising funds from the private sector: people and corporations could pay to have an Spaceguard-discovered asteroid named after them. This would involve a radical change to the way that asteroids are named* and would require international agreement. However, under Spaceguard there will be a huge increase in the discovery rate for "main-belt" asteroids, in addition to NEOs and comets and therefore a rethink about naming procedures will probably be necessary. The intention is that sponsored names would only apply to objects discovered through the Spaceguard program - in fact this proposal could be used to raise funds for the international Spaceguard effort.

      *Note: The current practice is to name comets after their discoverer. Discoverers of asteroids can submit a name (not their own) for consideration.

      There could be grades of sponsorship which depend on the "importance" of the object: the heirarchy might be: large NEOs, large main-belt asteroids, small NEOs, small main-belt asteroids. A possible sponsorship scenario for the Australian component of the Spaceguard program might be:

      Type of object              Est.discovery         Naming fee         Income per yr
                                          rate per yr
      Large NEO                       100                         $500                  $50,000
      Large MB Aster.               300                         $200                  $60,000
      Small NEO                        500                         $100                  $50,000
      Small MB Aster.             2,000                         $20                    $40,000
                                                                                         Total: $200,000

      Both the discovery rate and the possible naming fees are approximate at this stage but they indicate that there is potential to cover at least some of the Spaceguard annual budget through this mechanism. After all, many people pay several hundred dollars for a headstone when they die - a named asteroid would last much longer than a headstone. Care would, of course, need to be taken to ensure that any sponsored object was not going to impact the Earth, at least within the next fifty years.
       

    Appendix D Action Plan

    (This is based on Clark Chapman's Action Plan Statement to the US Government)

    The Australian Government should establish an Australian Spaceguard Working Party to address the following issues:

    Quantify the threat from Near Earth Objects

      • Develop a project plan for a major NEO search program in Australia
      • Provide technical and operational advice and oversee the implementation of the plan
      • Liaise with NASA and USAF over the provision of NEO search systems and co-ordination of international NEO search efforts
      • Liaise with international experts to gather information about the NEO threat and the status of other NEO search programs
      • Refine the estimates of the threat of NEO impacts based on the latest information

    Quantify the threat to Australian coastlines from tsunami

      • Develop a project plan for tsunami research and mitigation
      • Provide technical and operational advice and oversee the implementation of the plan
      • Conduct further research into geological evidence of tsunami along the Australian coastline
      • Conduct further research into archaeological and historical evidence of tsunami affecting coastal Aboriginal populations.
      • Liaise with international experts on the vulnerability of the Australian coastline to tsunami
      • Arrange computer simulations to determine the likely effects of tsunami on various parts of the Australian coast
      • Review tsunami warning and mitigation systems in place in Japan and the West Coast of North America.
      • Develop a proposal to implement an appropriate tsunami warning and mitgation systems in Australia.

      •  
    The Working Party should include astronomers, experts in risk management and hazard mitigation, defence personnel, geophysicists and space policy experts (including a representative from NASA). Its clear goal should be to get things done, not to debate the scientific worth of the research.
     

    Update: Dec 1999

    There has been recent progress on the Australian tsunami hazard.
     

    The Author

      Michael Paine  (email) is a Chartered Professional Engineer and runs an engineering  consultancy specialising in automotive safety . He has undertaken several studies of the cost-effectiveness of road safety initiatives for Australian government departments. He has also carried out project engineering work. His 1974 engineering thesis included the development of an early computer model of breaking ocean waves, creation of a standing breaking wave in a flume tank and a study of the motion of deep water solitary waves.

      He has an amateur interest in planetary science. He is a member of The Planetary Society (TPS) and is NSW Co-ordinator of the TPS Australian Volunteer Coordinators.
      He first became aware of the demise of the Australian NEO search program when TPS Executive Director Louis Friedman wrote to Australian TPS member in 1996. Michael then wrote to his local Member of Parliament (Bronwyn Bishop - the Minister for Defence Science) and, on receiving a poorly researched reply, subsequently  wrote to several other Australian Ministers - the saga has continued from there!

      This document has been in preparation for several months and Michael is grateful for the advice and comments provided by NEO scientists from around the globe. Several recent events have made it important to progress this issue:

      • The Federal election in Australia in October 1998 and the opportunity to seek statements from the major political parties
      • The release of the movies Deep Impact and Armageddon
      • The New Guinea tsunami
      • The US Government hearings into the threat from NEO impacts, including testimony by Clark Chapman
      • NASA's establishment of an Office for NEO Research within JPL