Aust 090604 Steel

The NEO Impact Hazard:Cometary Component, and Recent Developments in Mitigation Strategies Duncan Steel*Ball Solutions Group†, Canberra, ACT*Also Vice-President, The Spaceguard Foundation, Rome, Italy†BSG is the Australian subsidiary of Ball Aerospace & Technologies Corp, the manufacturer of the Deep Impact spacecraft : 

The NEO Impact Hazard: Cometary Component, and Recent Developments in Mitigation Strategies   Duncan Steel* Ball Solutions Group†, Canberra, ACT *Also Vice-President, The Spaceguard Foundation, Rome, Italy †BSG is the Australian subsidiary of Ball Aerospace & Technologies Corp, the manufacturer of the Deep Impact spacecraft Deep Impact Workshop Australian Centre for Astrobiology Macquarie University 2004 September 6

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Gradual recognition of the hazard posed by asteroids & comets; examples: Edmond Halley (1690s) – comets Benjamin Franklin (1757): “Should a comet in its course strike the Earth, it might instantly beat it to pieces. But our comfort is, the same great Power that made the Universe, governs it by his providence. And such terrible catastrophes will not happen till 'tis best they should…” William Herschel (1802) – asteroids Lord Byron (1822)…

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Was Byron the inventor of cosmic impact mitigation studies?

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Discovery of Eros (1898) Discovery of Aten, Apollo & Adonis (1930s) Recognition of terrestrial impact craters (1930s-) Lunar landings Mass extinctions linked to impacts (e.g. Nininger, 1941; Urey, 1973; Napier & Clube, 1979; Alvarez et al., 1980)

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Comet ‘dangers’ in the mass media… Punch, 1907 (Comet Halley due in 1910)

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Tunguska event (1908) – an asteroid (devolatilised comet?) ca.60m in size Not recognised until 1927 (& still argued about)

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Brazilian ‘Tunguska’ in 1930

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Terrestrial impact craters… Aorounga (Chad) – 3  10 km Manicouagan (Canada) – 100 km Gosses Bluff (Australia) – 6 km central uplift, 22 km ring Silverpit (North Sea, UK) – 3 km

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The SL9 impacts on Jupiter in 1994 led to much modelling of effects of impacts on that planet and Earth Atlantic impact south of Long Island

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Tsunamis from oceanic impacts… An ‘actual’ event: A hypothetical event: Courtesy Steve Ward, UC Santa Cruz

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From the New Yorker An impact killing the dinosaurs has become part of public consciousness…

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Media stories and public interest (and alarm) have led to the development of various reference scales for communicating the level and nature of specific feasible events. Note that a comet could not become a red (level 8,9,10) object until very soon before an impact

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…and of course…

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The true level of activity on NEOs is becoming apparent to some in the media…

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Map from Orbits of all known near-Earth asteroids as at January 2000

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Asteroid trajectories (impacts) are predictable

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While asteroid trajectories/impacts are predictable… …comet impacts are not, due to non-gravitational forces What about comets?

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There is a relatively small number of short- or intermediate-period comets cf. NEA map: Are asteroids or comets the more dangerous? Prograde Retrograde

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What fraction of the NEO impact hazard is due to comets? Problem tackled by various researchers (Shoemaker, Weissman, Steel). Major uncertainty is the relation between apparent comet brightness and nucleus mass Answers range from 2% to 40% (for 1-2 km objects producing 10-30 km craters) Suitable baseline would be 15% (10% from SP/IP comets, 5% from LP/parabolic comets) An implication is that once the NASA Spaceguard goal is reached (90% of cis-jovian NEAs larger than 1 km), comets become the major hazard! Higher energy impacts (causing mass extinctions) predominantly due to big comets Lower energy impacts (causing local effects) predominantly due to small asteroids

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From B.G.Marsden & D.I.Steel, in Hazards Due to Comets and Asteroids, ed. T. Gehrels (1994) Mean impact probability is 2.2 x 10-9 for a spherical Oort cloud & uniform q-distribution

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From B.G.Marsden & D.I.Steel, in Hazards Due to Comets and Asteroids, ed. T. Gehrels (1994)

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Open Questions: How many NEAs are actually extinct/dormant comets? Are there many asteroids in IP/LP/retrograde orbits? Role of Centaurs & other outer planetary system objects unclear: What would be the effect of a 100-km ‘minor planet’ entering an inner solar system orbit? (Time-scale is ca.105 years) Finding objects in the outer planetary region: LP/parabolic comet impacts not only unpredictable, but also the comets are not easily discoverable until 1-2 years prior to event

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From B.G.Marsden & D.I.Steel, in Hazards Due to Comets and Asteroids, ed. T. Gehrels (1994)

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From B.G.Marsden & D.I.Steel, in Hazards Due to Comets and Asteroids, ed. T. Gehrels (1994)

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From the New Yorker But what could we do if we did find an object on a collision course with Earth?

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Techniques for asteroid impact mitigation?

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A variety of techniques have been suggested for pushing asteroids off a collision course with Earth, but all acknowledge that a far better knowledge of the physical characteristics of such bodies is needed first (cf. Erice meeting, August 2004) Sci Am, November 2003

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PREPARING FOR PLANETARY DEFENSE: Detection and Interception of Asteroids on Collision Course with Earth Available from: http://www.au.af.mil/Spacecast/Spacecast.html US DoD: Clementine 2 mission cancelled in 1997. Spacecast 2020 report in 1998:

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United Nations NEO conference (1995), and ongoing policy issues:

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AIAA Seville workshop in 2001 highlighted need for mitigation studies:

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UK Government report, 2001 No real action (yet), but led to developments within the OECD Global Science Forum…

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OECD Global Science Forum workshop, 2003:

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Legal implications of mitigation attempts:

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ICSU proposal, 2003

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Arlington meeting, September 2002 Papers presented available at: http://www.noao.edu/meetings/mitigation/eav.html

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SCIENTIFIC REQUIREMENTS FOR THE MITIGATION OF HAZARDOUS COMETS AND ASTEROIDS (Cambridge University Press, 2004) Chapter 16:   IMPACTS AND THE PUBLIC: COMMUNICATING THE NATURE OF THE IMPACT HAZARD  David Morrison, Clark R. Chapman, Duncan Steel & Richard Binzel   ABSTRACT Public support is required for both asteroid survey programs and eventual hazard mitigation (if an impact is predicted). Yet the impact hazard is difficult to understand, because of its relative unfamiliarity and the extremely long intervals between impacts. At the same time, any prediction of an impact makes excellent press and generates widespread public interest. Over the past few years asteroid scientists have been coping with varying success with the twin challenges of explaining the general nature of the impact hazard and of responding to sometimes exaggerated media reports of impending disaster. We must balance between the poles of complacency and alarmist reactions. This chapter explores a variety of facets of the communications challenge, including a history of early ideas, the development of the Torino scale, lessons that can be learned from media “flaps” during the past five years, and scenarios that can be expected for the future.   Book resulting from the meeting is also now available:

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Belton (2003):   Towards a National Program to Remove the Threat of Hazardous NEOs Michael J.S. Belton Belton Space Exploration Initiatives, LLC   I consider issues associated with the establishment of a national program in the United States to prevent asteroidal collisions with the Earth. I take the position that costs associated with future damage to social infrastructure rather than potential loss of life will stimulate public representatives to begin work on a system to mitigate the possibility of an asteroidal collision. With some uncertainty, there is a 0.3 percent chance of a 50-meter, or larger, sized asteroid impacting United States territory in the lifetime of its current population (~100 years). I show how a probable lack of concern for this small probability might be offset by the cost of the damage that could be caused by the large energy release (>10 Megatons of TNT) on impact. I outline four conditions, focused on the interests of United States citizens, that I believe will need to be met before the start of a national mitigation program is viable. These reflect issues of public concern, feasibility, cost, timing, and security. Establishment of a public consensus on how well these conditions have been met and some modestly detailed preplanning are probably prerequisites for the initiation of a national program. I outline a planning roadmap that indicates what a national program might look like up to the point where work on a practical mitigation project directed at a specific target could begin. I also indicate how responsibilities for the task might be divided up between different government agencies. Rough estimates of the time to complete these preliminary activities (~25 yr), and a rough estimate of the cost (~$5B) are given.  

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Michael Belton (Sept 2003), Towards a National Program to Remove the Threat of Hazardous NEOs

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Mike A’Hearn (U MD), Deep Impact PI The Deep Impact mission might be thought of as the vanguard of (comet) target characterization…

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From U of Maryland/JPL Deep Impact web site Note that P/Tempel 1 is not an NEO, formally-speaking Deep Impact after launch

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Asteroid & comet impacts: a spectrum of implications… Individual death probabilities; Downfall of national/global economic systems; Downfall of civilisation (new Dark Age); Extinction of the human species; and Termination of the potential to spread DNA throughout the galaxy.