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The meteoroid fluence at Mars due toComet C/2013 A1 (Siding Spring)
Althea MoorheadNASA Meteoroid Environment Office
Collaborators:Paul Wiegert (UWO) & Bill CookeRhiannon Blaauw & Aaron Kingery
Will Yoder & Cameron McCarty
May 2, 2014
https://ntrs.nasa.gov/search.jsp?R=20140010989 2018-06-06T19:57:06+00:00Z
On October 19, 2014, Comet C/2013 A1 (Siding Spring)will pass within 150,000 km of Mars.
This is closer than all known Earth-comet encounters.
A collision has been ruled out, but Mars and its manmadesatellites will pass through the coma and tail.
Mars will be showered with meteors and satellites willhave an increased risk of meteoroid impacts.
Comet backgroundComa model
Recent observations
Outline
1 Comet backgroundC/2013 A1 (Siding Spring)Mars encounterMars spacecraft
2 Coma modelAnalytic modelValidation and simulationsEffects at Mars
3 Recent observationsBrightness monitoringObservational constraintsComparison with Hale-Bopp
Moorhead Siding Spring at Mars 3/ 38
Comet backgroundComa model
Recent observations
C/2013 A1 (Siding Spring)Mars encounterMars spacecraft
Comet types: classed by orbit
Type Orbit Origin Examples
Short period P < 200 yrs Kuiper Belt Halley
Long period(Oort cloud)
P ∼ 1000s yrs Oort cloudHale-Bopp,C/2013 A1
SungrazersPass near or plunge intothe Sun
C/2012 S1 (ISON)
Moorhead Siding Spring at Mars 4/ 38
Comet backgroundComa model
Recent observations
C/2013 A1 (Siding Spring)Mars encounterMars spacecraft
Comet properties
Comet Hartley 2
Comets are the leastreflective objects in theSolar System:
Halley has an albedo ofabout 4%.Asphalt has a albedo of7%.
Long period cometscontain more volatiles, asshort period comets losemuch of these in frequentpassages around the Sun.
Moorhead Siding Spring at Mars 5/ 38
Comet backgroundComa model
Recent observations
C/2013 A1 (Siding Spring)Mars encounterMars spacecraft
Cometary comae
Comet Hale-Bopp, NASA
Hale-Bopp:
Discovered at 7.2 AUComa was 1 million kmin August 1995
Siding Spring:
Imaged at 10 AUAlready active
Moorhead Siding Spring at Mars 6/ 38
Comet backgroundComa model
Recent observations
C/2013 A1 (Siding Spring)Mars encounterMars spacecraft
C/2013 A1 (Siding Spring)
Discovery:
January 3, 2013Rob McNaught0.5 meter telescopeSiding Spring, Australia
Pre-discovery imageslocated in Catalina SkySurvey
Active in earliest images(Dec. 8, 2012)
Hyperbolic orbit
Moorhead Siding Spring at Mars 7/ 38
Ima
ge
cred
it:
NA
SA
/JP
L
Comet backgroundComa model
Recent observations
C/2013 A1 (Siding Spring)Mars encounterMars spacecraft
Close encounter with mars
Movie credit: Leonid Elenin using SpaceEngine software
Moorhead Siding Spring at Mars 9/ 38
Comet backgroundComa model
Recent observations
C/2013 A1 (Siding Spring)Mars encounterMars spacecraft
Close encounter with mars
Comet is north ofMars’s orbital plane atclosest approach
Close approach:131,000 - 145,000 km
Approach distancenominal value:138,000 km
Coma/tail may envelopMars
Moorhead Siding Spring at Mars 10/ 38
Comet backgroundComa model
Recent observations
C/2013 A1 (Siding Spring)Mars encounterMars spacecraft
Mars satellites
Odyssey (NASA)400 km, 2 hr orbit
MRO (NASA)300 km, 2 hr orbit
Mars Express (ESA)300 - 10,000 km
7.5 hr orbit
MAVEN (NASA)150 - 6,200 km, 4.5 hr orbit
Arrives September 2014
MOM (ISRO)365 - 80,000 km, 76.7 hr orbit
Arrives September 2014
Moorhead Siding Spring at Mars 11/ 38
Comet backgroundComa model
Recent observations
C/2013 A1 (Siding Spring)Mars encounterMars spacecraft
Meteoroid impact risks
Impacts to critical components
Sudden attitude changes
Electrostatic/EMP effects may occur, depending onenvironment and spacecraft charging state
Image courtesy of MEDUSSA
Moorhead Siding Spring at Mars 12/ 38
Comet backgroundComa model
Recent observations
C/2013 A1 (Siding Spring)Mars encounterMars spacecraft
Meteoroid impact risks
Encounter speed similarto Perseids at Earth
Two spacecraft anomaliesattributed to Perseids:
Landsat 5 lost attitudecontrol during 2009PerseidsOLYMPUS satellitelost during 1993Perseids
Image from McDonnell et al., 1993
Moorhead Siding Spring at Mars 13/ 38
Comet backgroundComa model
Recent observations
C/2013 A1 (Siding Spring)Mars encounterMars spacecraft
Possible mitigation strategies
Align solar arrays sunward, edge-on to meteor shower
Sun-Mars-comet angle is 90.2◦
Present hard side to radiant
Phase orbit to use Mars as a partial shield:
Depends on orbit geometryShower will last a few hours, dependent on coma size(30 min per 100,000 km of coma/tail)Odyssey and MRO have 2 hour orbits
Moorhead Siding Spring at Mars 14/ 38
Comet backgroundComa model
Recent observations
Analytic modelValidation and simulationsEffects at Mars
Particles in the coma and tail of Siding Spring
Coma and tail contains both gasand particles
Both grow as heliocentric distancedecreases
Fluence – flux integrated overMars/spacecraft trajectory
Direct measure of spacecraft risk
We compute the particle fluence atMars using properties of SidingSpring (magnitude, orbit),supplementing with Halley data(particle albedo, size distribution)where necessary.
Moorhead Siding Spring at Mars 15/ 38
Comet backgroundComa model
Recent observations
Analytic modelValidation and simulationsEffects at Mars
The Giotto flyby of 1P/Halley
We have detailed coma data forone comet: Halley.
Giotto recorded 12,000 impacts.
Model fits to these data yield:
Particle density and albedoParticle size distributionParticle spatial distribution
Total number of particlesderived from Siding Springmagnitude, not Halley.
Moorhead Siding Spring at Mars 16/ 38
Comet backgroundComa model
Recent observations
Analytic modelValidation and simulationsEffects at Mars
Analytic model
Quantifying the number of ∼100 micron1 or larger particles in thecoma/tail:
1 Determine the brightness at the time of the encounter.
2 Use particle albedo to compute the total particle surface area.
3 Combine with Halley-like particle size distribution andmaterial density to compute number of particles.
4 Use r−2 spatial distribution to compute the number density.
5 Integrate along the trajectory to get fluence.
Our analytic model can be used to quickly calculate new fluenceestimates as comet properties are measured/constrained.
1100 micron particles are capable of cutting exposed spacecraft wires. Masslimit is 4× 10−6 g, actual size limit depends on density
Moorhead Siding Spring at Mars 17/ 38
Comet backgroundComa model
Recent observations
Analytic modelValidation and simulationsEffects at Mars
Analytic model
σ∗ =gh−β
a
(2
π
) 13 (ρ
3
) 23
10−0.4(M1−m�,1au) au2
×(
3− k
1− k
)(m
(1−k)/3max −m
(1−k)/3∗
m(3−k)/3max −m
(3−k)/3min
)
×cos−1(b/rc)
b rc
Moorhead Siding Spring at Mars 18/ 38
Comet backgroundComa model
Recent observations
Analytic modelValidation and simulationsEffects at Mars
Analytic modelDependence on comet/meteoroid properties
7 8 9 10
0.01
0.1
comet magnitude)
Flu
ence
(m−
2)
0.01 0.02 0.04 0.08
0.01
0.02
0.03
0.04
albedo(
0.01 0.1 10
0.02
0.04
bulk density (g/cc)
Flu
ence
(m−
2)
1 2 4
0
00.1
0.2
0.3
0.4
size index(
Moorhead Siding Spring at Mars 19/ 38
Comet backgroundComa model
Recent observations
Analytic modelValidation and simulationsEffects at Mars
Analytic modelFluence depends strongly on close approach distance
0 50 100 150 200 250 300
0.001
0.01
0.1
1
10
Close approach distance (103 km)
Tot
alfl
uen
ce(m
−2)
Coma Radius300,000 km250,000 km200,000 km150,000 km100,000 km
50,000 km
138 000 km
0.011 m−2 fluenceat close approachof 138 000 km
Moorhead Siding Spring at Mars 20/ 38
Comet backgroundComa model
Recent observations
Analytic modelValidation and simulationsEffects at Mars
Validation #1: reproducing Giotto results
We test our model byapplying it to 1P/Halley
Using a coma radius of200,000 km, we canreproduce the fluxGiotto recorded
103 104 1050.01
0.1
1
10
100
1000
r (km)
flu
x(m
−2
s−1)
Fulle et al. (2000) data, our model
Moorhead Siding Spring at Mars 21/ 38
Comet backgroundComa model
Recent observations
Analytic modelValidation and simulationsEffects at Mars
Validation #2: reproducing Stardust results
Stardust flew 300 kmfrom 81P/Wild 2
Coma radius was24,000 km at 1.7 au
We model impacts permass channel
1 10 100 1000
1
10
100
1000
M2
M1
m3 m2
m1
N (model)
N(m
easu
red
)
Tuzzolino et al. (2004) data, our model
Moorhead Siding Spring at Mars 22/ 38
Comet backgroundComa model
Recent observations
Analytic modelValidation and simulationsEffects at Mars
Validation #3: comparison with simulations4× 10−6g particles
−200 0 200
−200
0
200
x (103 km)
y(1
03km
)
−200 0 200
x (103 km)
0.001
0.01
0.1
1
Analytical model (left) and normalized simulations (right) inplane containing Mars (at origin), perpendicular to trajectory.
Simulations performed by Paul Wiegert, UWO.
Moorhead Siding Spring at Mars 23/ 38
Comet backgroundComa model
Recent observations
Analytic modelValidation and simulationsEffects at Mars
Validation #3: comparison with simulations4× 10−6g particles
−200 0 200
−200
0
200
x (103 km)
y(1
03km
)
−200 0 200
x (103 km)
0.001
0.01
0.1
1
Small scale simulations do not predict number of particles;fluence on right is multiplied by Ntheory/Nsim.
Simulations do illustrate (modest) deviance from sphericalmodel due to coma asymmetry and tail.
Moorhead Siding Spring at Mars 23/ 38
Comet backgroundComa model
Recent observations
Analytic modelValidation and simulationsEffects at Mars
Validation #3: comparison with simulations4× 10−6g particles
−200 0 200
−200
0
200
x (103 km)
y(1
03km
)
−200 0 200
x (103 km)
0.001
0.01
0.1
1
Simulated coma has large radius (200, 000 km) due to earlyassumed start of activity (10 AU)
Effective radius may be smaller – needs further study
Moorhead Siding Spring at Mars 23/ 38
Comet backgroundComa model
Recent observations
Analytic modelValidation and simulationsEffects at Mars
Validation #3: comparison with simulations4× 10−3g particles
−200 0 200
−200
0
200
x (103 km)
y(1
03km
)
−200 0 200
x (103 km)
0.001
0.01
0.1
1
Larger particles:
Have lower ejection velocityAre less subject to radiative forces
Moorhead Siding Spring at Mars 24/ 38
Comet backgroundComa model
Recent observations
Analytic modelValidation and simulationsEffects at Mars
Validation #4: comparison with independent studies
Parallel effort to model comaparticle dynamics: Vaubaillonet al., 2014
Uses Af ρ rather thanmagnitude to scale dustproduction.
Results agree to within anorder of magnitude ... with thesame input parameters
Moorhead Siding Spring at Mars 25/ 38
Comet backgroundComa model
Recent observations
Analytic modelValidation and simulationsEffects at Mars
Martian meteor shower
Meteor shower willaccompany Siding Spring
ZHR for 10−6 g particles∼ 30,000,000 at Mars
Subradiant nearOpportunity at dawn
MarsExpress may see up to1000 meteors per minute
10,704 km2 FOVm & 3 gNumbers fromAnastasios Margonis
Moorhead Siding Spring at Mars 26/ 38
Comet backgroundComa model
Recent observations
Analytic modelValidation and simulationsEffects at Mars
Meteoroid impact risks
1966 Leonids by A. Scott Murrell
Average flux of 100 micron orlarger meteoroids in low Earthorbit is 5× 10−6 m−2 per hour
Fluence due to Siding Springis 500 times higher(5 years of LEO exposure)
There has never been an eventlike this near Earth in recentmemory, with the possibleexception of the 1966 Leonids.
Moorhead Siding Spring at Mars 27/ 38
Comet backgroundComa model
Recent observations
Analytic modelValidation and simulationsEffects at Mars
Effects on the Martian atmosphere
Atmospheric effects
Energy deposition:
KE =
∫dσ
dmm dm × v2
2× πr2
M
1.14 megatons of TNT equivalent0.006% of solar irradiance: insignificant
Metal deposition probably more important(John Plane, Leeds)
Moorhead Siding Spring at Mars 28/ 38
Comet backgroundComa model
Recent observations
Analytic modelValidation and simulationsEffects at Mars
Effects on the Martian system
Impact ejecta from the moons could last months or years(Apostolos Christou, Armagh)
Moorhead Siding Spring at Mars 29/ 38
Comet backgroundComa model
Recent observations
Brightness monitoringObservational constraintsComparison with Hale-Bopp
Brightness monitoring
1 m at Siding Spring
Hubble
Multiple efforts to monitor Siding Spring:
NMSkies, 0.5m (MEO)
Siding Spring, 1m (MEO)
Siding Spring, 2m (Christou, Armagh)
NEOWISE
Hubble (PI: Jian-Yang Li)
Moorhead Siding Spring at Mars 30/ 38
Comet backgroundComa model
Recent observations
Brightness monitoringObservational constraintsComparison with Hale-Bopp
Brightness monitoring
1234567
20◦
40◦
60◦
80◦
100◦
120◦
Heliocentric distance (au)
S-O
-Tan
gle
1234567
9
9.5
10
Heliocentric distance (au)
Ab
solu
tem
agn
itu
de
Asami et al., 2013
Cometas Obs
MEO
Moorhead Siding Spring at Mars 31/ 38
Comet backgroundComa model
Recent observations
Brightness monitoringObservational constraintsComparison with Hale-Bopp
Syndyne calculations
– 25 –
Fig. 6.— Syndyne-synchrone computation for the master frames. North is up and east is
left.
Ye & Hui, 2014
Ye & Hui, 2014:
Shape of cometary tail isinfluenced by gravity andradiation pressure“Mostly large particles” basedon curvature of tailLow ejection velocity based oncompactness of the coma
Low ejection velocity= compact coma= much lower fluence at Mars
Moorhead Siding Spring at Mars 32/ 38
Comet backgroundComa model
Recent observations
Brightness monitoringObservational constraintsComparison with Hale-Bopp
Hubble observations
Moorhead Siding Spring at Mars 33/ 38
Comet backgroundComa model
Recent observations
Brightness monitoringObservational constraintsComparison with Hale-Bopp
Hubble observations
−20 0 20
−20
0
20
x (103 km)
y(1
03km
)
−20 0 20
x (103 km)
The coma does appear to be expanding slowly
Moorhead Siding Spring at Mars 34/ 38
Comet backgroundComa model
Recent observations
Brightness monitoringObservational constraintsComparison with Hale-Bopp
Heliocentric magnitude: Hale-Bopp
Hale-Bopp had three phases of activity pre-perihelion (Kidger,1997)
∝ r−5 at large distances
∝ r−1 around 4 au (a “standstill”)
∝ r−3.5 at smaller heliocentric distances
Kidger notes that ice sublimation begins around 4 au
Moorhead Siding Spring at Mars 35/ 38
Comet backgroundComa model
Recent observations
Brightness monitoringObservational constraintsComparison with Hale-Bopp
Heliocentric magnitude: Hale-Bopp
123456
−2
0
2
4
6
Heliocentric distance (au)
Hel
ioce
ntr
icm
agn
itu
de
Image credit: A. Kammerer
Moorhead Siding Spring at Mars 36/ 38
Comet backgroundComa model
Recent observations
Brightness monitoringObservational constraintsComparison with Hale-Bopp
Heliocentric magnitude: Siding Spring
1234567
8.5
9
9.5
10
10.5
Heliocentric distance (au)
Ab
solu
tem
agn
itu
de
Asami et al., 2013
Cometas Obs
MEO
Moorhead Siding Spring at Mars 37/ 38
Comet backgroundComa model
Recent observations
Summary
Comet C/2013 A1 (Siding Spring) will have close encounterwith Mars on October 19, 2014
Mars and spacecraft will pass through coma and tailcontaining meteoroids
Meteoroids (4.19× 10−6 g or larger): ∼ 1% chance of impactper square meter due to coma and tail
Continued monitoring is needed to better predict futurebehavior
Moorhead Siding Spring at Mars 38/ 38