Wheeler, Lorien

NASA Technical Reports Server

National Aeronautics and Space Administration
www.nasa.gov 
Asteroid Impact Risk Assessment
Lorien Wheeler
Asteroid Threat Assessment Project
NASA Ames Research Center
https://ntrs.nasa.gov/search.jsp?R=20180000805 2019-08-31T16:17:38+00:00Z
Asteroid Threat Assessment Project
2
Asteroid Properties 
Entry Physics
Surface Hazards
Damage & Risk
Characterization
• Measurements
• Inference
• Data aggregation
Hazard Simulations
• 3D blast simulations
• Tsunami simulations
• Impact crater simulations
• Thermal radiation models
• Global effects
Probabilistic Risk Assessment
• Analytic physics-based entry and 
damage models 
• Probabilistic Monte Carlo simulation 
using uncertainty distributions
Entry Simulations & Testing
• Coupled aerothermodynamics
• Ablation & radiation modeling
• Arc jet testing
NASA Supercomputing
Supercomputing helps address the challenging unknowns of asteroid threat 
assessment by enabling:
• Analysis of millions of impact cases to assess risk 
probabilities, including uncertain asteroid properties, entry 
modeling, local populations, and multiple hazard sources
• High-fidelity simulations to improve understanding of key 
impact effects and refine probabilistic risk models
• Inference of asteroid properties from automated entry 
modeling of observed meteors
• Rapid-turnaround risk assessment to support mitigation and 
response planning in the event of a potential impact threat.
Probabilistic Asteroid Impact Risk (PAIR)
4
Airburst Altitude &
Surface Impact Energy
Input Parameter Distributions
Monte Carlo Sampling
Asteroid Characterization
Thermal 
Radiation
Blast 
Overpressure
Initial 
Conditions
Entry & Breakup 
Modeling 
Tsunami
Risk Assessment Results
Damage Consequence + Likelihood à Risk
x
min$ max$expected$
Global EffectsTsunami 
Inundation
Local 
Blast/Thermal
Casualties and Affected Populations
• Diameter
• Density
• Strength
• Velocity
• Entry angles
• Impact coordinates
• Uncertain modeling 
parameters
Fragment-Cloud Model (FCM)
Analytic model of energy deposited in the 
atmosphere during entry and breakup
• Represents breakup process using a combination of 
discrete fragments and aggregate debris clouds
• Can represent range of asteroid structures and 
breakup characteristics
FCM results can match observed meteor light 
curves to:
• Infer pre-entry asteroid properties
• Investigate breakup characteristics
• Guide model refinements
Energy deposition results used to estimate 
airburst altitudes and ground energies in 
probabilistic risk model
! ! !
! ! !
FCM Breakup Modeling
Varied structures
Discrete fragments
Debris clouds
*Chelyabinsk energy deposition curve from: Brown et al., 2013. A 500-kiloton airburst over 
Chelyabinsk and an enhanced hazard from small impactors. Nature 503 (7475), 238–241. 
*
FCM Modeling of Chelyabinsk Meteor
Automated Meteor Inference
Developing automated approach for matching Fragment-Cloud Model (FCM) 
energy deposition results to observed meteor light curves.
Sample evolutions of diameter, density, and velocity parameters
D
ia
m
et
er
O
bjective Value
Generation 1
Generation 25
Generation 100
Automated fit 
obtained for the 
Chelyabinsk 
meteor energy 
deposition profile
• Automates entry modeling for 
thousands of asteroid and entry 
parameter variations.
• Objective function evaluates quality 
of matches to observed data.
• Genetic algorithm approach evolves 
selection of the input parameters to 
produce the best fits.
Modeling & Image Credit: Ana Tarano, Stanford/NASA Ames
Blast Overpressure Modeling
CFD blast propagation simulations improved ground damage estimates in risk model
• Height-of-burst maps estimate the extent of ground overpressures as a 
function of airburst altitude, based on nuclear test data
• Yield-scaling based on smaller nuclear sources becomes inaccurate 
for higher impact energies due to buoyancy effects 
(KE >10-50 megatons, diameter > 50-80m)
• CFD results provided improved height-of-burst map for higher asteroid impact energies
Cart3D blast propagation simulation
Image/simulation: Michael Aftosmis, NASA Ames Image: Michael Aftosmis, Ana Tarano, NASA Ames
Simulation vs. nuclear-based (G&D) height-of-burst map
See demo “Simulating 
Atmospheric Impacts” by 
Marian Nemec
Asteroid-Generated Tsunami Simulations
• High-fidelity simulations address big unknown of whether 
asteroid impacts or airbursts of various sizes could cause 
significant tsunamis
• Recent results show asteroid impacts to pose less tsunami 
threat than previously thought
• Results used to refine analytic tsunami risk model
GeoClaw simulations of long-range 
wave propagation and inundation
(M. Berger, NYU)
à For more on asteroid tsunami 
simulation, see demo “Simulating 
Atmospheric Impacts” by Marian 
Nemec
ALE3D hydrocode simulations of water 
impact, wave generation and propagation 
(D. Robertson, NASA Ames)
Tsunami Risk Modeling Advancements
• Analytic model estimates wave run-up based on energy impacting surface of the water and propagation 
distance from impact to shore (Chesley & Ward 2006)
• Improved energy coupling estimates for airbursts and splashdowns based on ALE3D and GeoClaw
simulations of wave formation and propagation.
• Supercomputing enables risk model to include inundation of specific coastal topography for millions of 
ocean impact/airburst cases, enabling damage assessment based on local populations and flood depths.
9Image: Paul Register, NASA Ames
Comparison of analytic model scaled 
to match simulation results
Risk model inundation including local topography
Asteroid-Generated Tsunami Simulations
Simulation & movie credit: Darrel Robertson, NASA Ames
ALE3D simulation of a 1 gigaton asteroid impact 
into deep water of the Japan Trench
Asteroid-Generated Tsunami Simulations
Simulation & movie credit: Darrel Robertson, NASA Ames
ALE3D simulation of a 1 gigaton asteroid impact 
into shallow water of the Japan Trench
Ground Impact Simulations
12Simulation & movie credit: Darrel Robertson, NASA Ames
ALE3D simulation of a 1 gigaton asteroid 
ground impact
NEO Science Definition Team Study
Performed comprehensive impact risk 
assessment for the 2017 Near-Earth 
Object (NEO) Science Definition Team 
(SDT) study
• SDT convened by NASA’s Planetary Defense 
Coordination Office (PDCO) to 
reevaluate the level of threat posed by 
asteroids of various sizes
• Will guide survey systems and search criteria 
for future NEO surveys 
Risk modeling on Pleiades Supercomputer 
provided substantial advancements since 
the prior 2003 study
SDT Impact Risk Results
• 60 million impact cases analyzed on Pleiades Supercomputer
• Asteroid sizes 20m – 10km in diameter
• Assessed local damage from blast waves and thermal radiation, tsunami inundation 
from water impacts, and global effects from large-scale impacts.
Impact Response Exercises
15
100 120 140 160 180
30
32
34
36
38
40
42
1-2 psi
2-4 psi
4-10 psi
10+ psi
Probabilistic risk assessment for HYPOTHETICAL impact exercise performed at the 2017 Planetary Defense Conference in Tokyo
• Have participated hypothetical impact exercises to vet and improve assessment tools, response 
protocols,  and decision support.
• Risk model takes impact trajectory inputs from JPL orbital models and evaluates risk probabilities 
along a potential impact corridor.
• Pleiades Supercomputer enables rapid risk assessment for emergency response.


Asteroid Impact Risk Assessment

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