1. 6/29/20151 Session One Rapporteur Report Jim Arnold/Ames First Annual Planetary Defense Workshop July 7/8/9 NASA Ames Research Center Marian Nemec

2. Ames Integrated PD Team Tasks Task 1 Objective Question: What are the likely physical characteristics for different spectral classes of NEAs that are Potentially Hazardous Asteroids (PHAs)? Task 2 Objective Questions: What is the minimum size PHA for different spectral classes of NEAs that could damage at the surface? What is the range of damage effects and potential for casualties as a range of size and class of PHA? (Leverage NASA Entry Design Expertise) Task 3 Objective Questions: What is the range of damage effects from a surface impact and potential for casualties as a range of size and class of PHA for both land surface and ocean impacts? Task 4 Objective Questions: What is the minimum size PHA impact for which effects are severe enough that mitigation action must be taken, and therefore they must be discovered far enough in advance to enable the mitigation campaign? Versus: What is the maximum size impactor for which civil defense measures in last weeks to days such as shelter in place or evacuation can be sufficient to mitigate the impact effects?

3. Near Earth Asteroid Survey Status 6/29/20153 ? Challenge for the Future?

4. Session 1: Atmospheric Entry and Break-up Co-Chairs: Jay Melosh (Purdue) and Raj Venkatapathy (Ames) 7/7/2015

5. Paul Chodas Described funtion of JPL NEO Program office and relationship to MPC and Validation by University of Pisa Described discovery and observation of two incoming asteroids when they were in final approach to atmospheric pierce point. Question: Given reliable information on a PHA including spin based on in-situ observations could you predict its attitude at the pierce point? 6/29/20155

6. Mark Boslough 6/29/20156 Optimize Chelyabinsk model to match obs Optimize Tunguska model to match obs Include thermal radiation Couple airburst model to tsunami wave propagation code Recalculate risk with improved kill curve ================================================================== Skeptical that any amount of data will permit accurate predictions. His take is that fragmentation is inherently unpredictable. He thinks we need to be thinking of envelopes of possibility Adds to you simulation tools to make them more “predictive”?

7. Chelyabinsk event unique: large damage in the populated area (large size), huge amount of data; demonstrates that 20-m bodies are dangerous, provides a unique opportunity to calibrate models  Assumption that the energy release followed the meteor light curve satisfactory explained the butterfly-shape of the damaged area.  The SW characteristics may be described in the frame of the suggested hydrodynamical model (and simplified model for  t(z)), are in agreement with observational data (damage area, arrival times, overpressure level)  Main SW arrival is coming from the closest point of trajectory (in 3D), local shocks may be generated by energy release maxima (propagate inside ballistic cone, may reveal as separate peaks after main arrival, their number and time delays depend on parameters of maxima and location of registration) For quick rough evaluation of impact consequences for ~20-100 m bodies the point source provides a reasonable first approximation (due to similarity of SW at large distances from ground zero). Numerical simulations of impactor disruption/deceleration determine the effective height of the explosion, which is described by simple analytical formula A prototype of the information-analytical system on risk assessment and prevention of the consequences of cosmic impacts was created, which collects all possible consequences and demonstrates them visually on the geographical map (u sed simplified estimates should be refined) Olga Popova; Concluding remarks

8. Olga Popova 6/29/20158 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Thinks that more data is needed to enable improved predictive capabilities and would like to have light curves from US Government light curves.. Question: What exo-atmospheric properties of PHAs are of interest to you for Your modeling activiites?

9. Peter Brown: Future Research Luminous efficiency – calibrate from different techniques Infrasound models for validation of cylindrical line source overpressure estimates at the ground (particularly amplitude model constraints) – (Silber et al., 2015) applied to cm-sized meteoroids, need to expand to meter-sizes – Search IMS for regional IS airburst detection and apply/modify model – Adapt Whitham weak-shock theory to cylindrical hypersonic sources (eg. Haynes and Millet, 2013) 9

10. Peter Brown: General Observations Meter-sized impactors begin fragmentation under 0.1 – 1 MPa ram pressure (Popova et al 2011) – peak luminosity is reached 1-2 scale heights lower Fragmentation is complex Lightcurves are crucial to constraining atmospheric energy deposition in individual cases – Not enough meter-class LCs available to make any generalizations about fragmentation behavior Spectra very helpful, but rare Recovered meteorites provide ground-truth Multi-instrumental observations critical – each measurement technique suffers different systematic biases 10

11. Peter Brown:Need for Model validation Models have now incorporated very elaborate physics BUT we have few constraints from observations to guide choices in a very large parameter space (Fragmentation!). 1.Compare various models (particularly fragmentation characteristics) to existing published/detailed large bolide measurements (Chelyabinsk, Benesov, Sumava, Moravka, Kosice) 2.Apply models to USG data for statistical studies 3.Process/extract existing but unpublished precise large fireball data and apply models (EN – eg. EN 171101) ================================================================= Release of the USG lightcurves is the only possible transformative event which could permit statistical investigation of fragmentation Question: In your opinion, what would represent a validated Simulation tool Capable of predictive meteor entry and breakup? 11

12. Entry and Airburst Modeling Task: Leverage NASA entry vehicle design expertise and what is known about the physical characteristics for different spectral classes of NEAs to model their atmospheric entry and breakup (airburst) effects. 6/29/2015 Chelyabinsk Stardust SRC Status: NASA flow solver capability extended to 20 km/s – More work needed for 30 km/s. Material thermal response model has been developed for ordinary chondritic material. Material was tested in LHMEL at 20 kW/cm 2 radiative heating. Structural response computations cracks and voids have begun. Luminous energy estimates computed for various “regular” sizes/shapes and velocities – Shown that “Shape Matters” in producing light curves. 12 Stardust Chelyabinsk

13. Multiple Body Analysis 6/29/2015 All results shown here are for a velocity of 20 km/s and 30 bar of stag. pressure Status: Computations performed for various shapes and arrangements Extraction of luminous energy from the wake; Shape Matters. Extraction of aerodynamic/aerothermodynamic interaction forces/energies from computations. Currently no physics based model/mechanism for fragmentation. Supplemented current knowledge with computations for idealized shapes.

14. Conventional meteor physics assumes a spherical shape at entry More Realistic Shapes 6/29/2015 1/38-scale Itokawa 2x-scale NEO 2008 TC 3 Smooth“Fissured” All results shown here are for a velocity of 20 km/s and 30 bar of stag. pressure Ellipsoid (32x16x16 m) Status: Computations performed scaled versions of Asteroid Itokawa & NEO 2008 TC 3 1/38 scale Itokawa is a dumbbell shape with “weakness” at the neck 2008 TC 3 most likely oriented in flight Attempt to understand aerothermal impact of surface fissures 14

15. Dinesh Prabhu Properties of meteoritic material: Mean properties – physical, thermophysical, and thermochemical – and their variation about the mean. The intent is to build thermal, structural, and thermal-structural response models about mean properties, and the variations in these properties are for use in in bounding calculations, or in Monte Carlo simulations, if necessary. Notes: (a) we would prefer to have properties as functions of temperature; (b) variations in properties would be due to variation in composition (within a material class) and microporosity; and (c) we would prefer to focus on – (i) anhydrous silicates, (ii) metals, and (iii) metal sulfites, in that order. Opaci ties of meteoritic vapor : Construction of opacity tables based on Issue #1 above. The focus would be on silicon/silica/silicates, metals (Fe, Ni, and Mg) and their oxides, especially in the wake. The intent is to get more accurate descriptions of the aerothermal environment around a meteor (regardless of its shape or size) because the current simulations do not include material response and radiation blockage. This is our second step towards light curves (in the absence of fragmentation). Crack patterns in meteorites : Construction of unit problems for simple structural response models. This is again tied into Issue #1. Examination of meteorites, over a range of scales, could perhaps yield clues about the pre-entry state of asteroids. Structural testing of the materials, guided in part by pre-test structural response computations, would help in the construction of structural response models. 6/29/201515

16. Does Shape Matter? “Them” versus “Us” 6/29/201516 Comet 67P/Churyumov- Gerasimenko G. Lautenschlager

17. Questions/Comments Keith Holsapple (U of Washington) Leviticus Lewis (FEMA) Brian Kantsiper (APL) Guy Consolmagno (Vatican Observatory) 6/29/201517