Blaauw, Rhiannon

Cooke, Bill

Kingery, Aaron

McCarty, Cameron

Moorhead, Althea

Wiegert, Paul

Yoder, Will

NASA Technical Reports Server

The meteoroid fluence at Mars due to
Comet C/2013 A1 (Siding Spring)
Althea Moorhead
NASA Meteoroid Environment Office
Collaborators:
Paul Wiegert (UWO) & Bill Cooke
Rhiannon Blaauw & Aaron Kingery
Will Yoder & Cameron McCarty
May 2, 2014
https://ntrs.nasa.gov/search.jsp?R=20140010989 2019-08-31T19:27:21+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 manmade
satellites will pass through the coma and tail.
Mars will be showered with meteors and satellites will
have an increased risk of meteoroid impacts.
Comet background
Coma model
Recent observations
Outline
1 Comet background
C/2013 A1 (Siding Spring)
Mars encounter
Mars spacecraft
2 Coma model
Analytic model
Validation and simulations
Effects at Mars
3 Recent observations
Brightness monitoring
Observational constraints
Comparison with Hale-Bopp
Moorhead Siding Spring at Mars 3/ 38
Comet background
Coma model
Recent observations
C/2013 A1 (Siding Spring)
Mars encounter
Mars 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 cloud Hale-Bopp,
C/2013 A1
Sungrazers
Pass near or plunge into
the Sun
C/2012 S1 (ISON)
Moorhead Siding Spring at Mars 4/ 38
Comet background
Coma model
Recent observations
C/2013 A1 (Siding Spring)
Mars encounter
Mars spacecraft
Comet properties
Comet Hartley 2
Comets are the least
reflective objects in the
Solar System:
Halley has an albedo of
about 4%.
Asphalt has a albedo of
7%.
Long period comets
contain more volatiles, as
short period comets lose
much of these in frequent
passages around the Sun.
Moorhead Siding Spring at Mars 5/ 38
Comet background
Coma model
Recent observations
C/2013 A1 (Siding Spring)
Mars encounter
Mars spacecraft
Cometary comae
Comet Hale-Bopp, NASA
Hale-Bopp:
Discovered at 7.2 AU
Coma was 1 million km
in August 1995
Siding Spring:
Imaged at 10 AU
Already active
Moorhead Siding Spring at Mars 6/ 38
Comet background
Coma model
Recent observations
C/2013 A1 (Siding Spring)
Mars encounter
Mars spacecraft
C/2013 A1 (Siding Spring)
Discovery:
January 3, 2013
Rob McNaught
0.5 meter telescope
Siding Spring, Australia
Pre-discovery images
located in Catalina Sky
Survey
Active in earliest images
(Dec. 8, 2012)
Hyperbolic orbit
Moorhead Siding Spring at Mars 7/ 38
Im
a
g
e
cr
ed
it
:
N
A
S
A
/
JP
L
Comet background
Coma model
Recent observations
C/2013 A1 (Siding Spring)
Mars encounter
Mars spacecraft
Close encounter with mars
Movie credit: Leonid Elenin using SpaceEngine software
Moorhead Siding Spring at Mars 9/ 38
Comet background
Coma model
Recent observations
C/2013 A1 (Siding Spring)
Mars encounter
Mars spacecraft
Close encounter with mars
Comet is north of
Mars’s orbital plane at
closest approach
Close approach:
131,000 - 145,000 km
Approach distance
nominal value:
138,000 km
Coma/tail may envelop
Mars
Moorhead Siding Spring at Mars 10/ 38
Comet background
Coma model
Recent observations
C/2013 A1 (Siding Spring)
Mars encounter
Mars 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 background
Coma model
Recent observations
C/2013 A1 (Siding Spring)
Mars encounter
Mars spacecraft
Meteoroid impact risks
Impacts to critical components
Sudden attitude changes
Electrostatic/EMP effects may occur, depending on
environment and spacecraft charging state
Image courtesy of MEDUSSA
Moorhead Siding Spring at Mars 12/ 38
Comet background
Coma model
Recent observations
C/2013 A1 (Siding Spring)
Mars encounter
Mars spacecraft
Meteoroid impact risks
Encounter speed similar
to Perseids at Earth
Two spacecraft anomalies
attributed to Perseids:
Landsat 5 lost attitude
control during 2009
Perseids
OLYMPUS satellite
lost during 1993
Perseids
Image from McDonnell et al., 1993
Moorhead Siding Spring at Mars 13/ 38
Comet background
Coma model
Recent observations
C/2013 A1 (Siding Spring)
Mars encounter
Mars 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 geometry
Shower 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 background
Coma model
Recent observations
Analytic model
Validation and simulations
Effects at Mars
Particles in the coma and tail of Siding Spring
Coma and tail contains both gas
and particles
Both grow as heliocentric distance
decreases
Fluence – flux integrated over
Mars/spacecraft trajectory
Direct measure of spacecraft risk
We compute the particle fluence at
Mars using properties of Siding
Spring (magnitude, orbit),
supplementing with Halley data
(particle albedo, size distribution)
where necessary.
Moorhead Siding Spring at Mars 15/ 38
Comet background
Coma model
Recent observations
Analytic model
Validation and simulations
Effects at Mars
The Giotto flyby of 1P/Halley
We have detailed coma data for
one comet: Halley.
Giotto recorded 12,000 impacts.
Model fits to these data yield:
Particle density and albedo
Particle size distribution
Particle spatial distribution
Total number of particles
derived from Siding Spring
magnitude, not Halley.
Moorhead Siding Spring at Mars 16/ 38
Comet background
Coma model
Recent observations
Analytic model
Validation and simulations
Effects at Mars
Analytic model
Quantifying the number of ∼100 micron1 or larger particles in the
coma/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 and
material 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 fluence
estimates as comet properties are measured/constrained.
1100 micron particles are capable of cutting exposed spacecraft wires. Mass
limit is 4× 10−6 g, actual size limit depends on density
Moorhead Siding Spring at Mars 17/ 38
Comet background
Coma model
Recent observations
Analytic model
Validation and simulations
Effects at Mars
Analytic model
σ∗ =
gh−β
a
(
2
pi
) 1
3 (ρ
3
) 2
3
10−0.4(M1−m,1au) au2
×
(
3− k
1− k
)(
m
(1−k)/3
max −m(1−k)/3∗
m
(3−k)/3
max −m(3−k)/3min
)
×cos
−1(b/rc)
b rc
Moorhead Siding Spring at Mars 18/ 38
Comet background
Coma model
Recent observations
Analytic model
Validation and simulations
Effects at Mars
Analytic model
Dependence on comet/meteoroid properties
7 8 9 10
0.01
0.1
comet magnitude)
F
lu
en
ce
(m
−
2
)
0.01 0.02 0.04 0.08
0.01
0.02
0.03
0.04
albedo(
0.01 0.1 1
0
0.02
0.04
bulk density (g/cc)
F
lu
en
ce
(m
−
2
)
1 2 4
0
00.1
0.2
0.3
0.4
size index(
Moorhead Siding Spring at Mars 19/ 38
Comet background
Coma model
Recent observations
Analytic model
Validation and simulations
Effects at Mars
Analytic model
Fluence 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)
T
ot
al
fl
u
en
ce
(m
−
2
)
Coma Radius
300,000 km
250,000 km
200,000 km
150,000 km
100,000 km
50,000 km
138 000 km
0.011 m−2 fluence
at close approach
of 138 000 km
Moorhead Siding Spring at Mars 20/ 38
Comet background
Coma model
Recent observations
Analytic model
Validation and simulations
Effects at Mars
Validation #1: reproducing Giotto results
We test our model by
applying it to 1P/Halley
Using a coma radius of
200,000 km, we can
reproduce the flux
Giotto recorded
103 104 105
0.01
0.1
1
10
100
1000
r (km)
fl
u
x
(m
−
2
s−
1
)
Fulle et al. (2000) data, our model
Moorhead Siding Spring at Mars 21/ 38
Comet background
Coma model
Recent observations
Analytic model
Validation and simulations
Effects at Mars
Validation #2: reproducing Stardust results
Stardust flew 300 km
from 81P/Wild 2
Coma radius was
24,000 km at 1.7 au
We model impacts per
mass channel
1 10 100 1000
1
10
100
1000
M2
M1
m3 m2
m1
N (model)
N
(m
ea
su
re
d
)
Tuzzolino et al. (2004) data, our model
Moorhead Siding Spring at Mars 22/ 38
Comet background
Coma model
Recent observations
Analytic model
Validation and simulations
Effects at Mars
Validation #3: comparison with simulations
4× 10−6g particles
−200 0 200
−200
0
200
x (103 km)
y
(1
03
km
)
−200 0 200
x (103 km)
0.001
0.01
0.1
1
Analytical model (left) and normalized simulations (right) in
plane containing Mars (at origin), perpendicular to trajectory.
Simulations performed by Paul Wiegert, UWO.
Moorhead Siding Spring at Mars 23/ 38
Comet background
Coma model
Recent observations
Analytic model
Validation and simulations
Effects at Mars
Validation #3: comparison with simulations
4× 10−6g particles
−200 0 200
−200
0
200
x (103 km)
y
(1
03
km
)
−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 spherical
model due to coma asymmetry and tail.
Moorhead Siding Spring at Mars 23/ 38
Comet background
Coma model
Recent observations
Analytic model
Validation and simulations
Effects at Mars
Validation #3: comparison with simulations
4× 10−6g particles
−200 0 200
−200
0
200
x (103 km)
y
(1
03
km
)
−200 0 200
x (103 km)
0.001
0.01
0.1
1
Simulated coma has large radius (200, 000 km) due to early
assumed start of activity (10 AU)
Effective radius may be smaller – needs further study
Moorhead Siding Spring at Mars 23/ 38
Comet background
Coma model
Recent observations
Analytic model
Validation and simulations
Effects at Mars
Validation #3: comparison with simulations
4× 10−3g particles
−200 0 200
−200
0
200
x (103 km)
y
(1
03
km
)
−200 0 200
x (103 km)
0.001
0.01
0.1
1
Larger particles:
Have lower ejection velocity
Are less subject to radiative forces
Moorhead Siding Spring at Mars 24/ 38
Comet background
Coma model
Recent observations
Analytic model
Validation and simulations
Effects at Mars
Validation #4: comparison with independent studies
Parallel effort to model coma
particle dynamics: Vaubaillon
et al., 2014
Uses Af ρ rather than
magnitude to scale dust
production.
Results agree to within an
order of magnitude ... with the
same input parameters
Moorhead Siding Spring at Mars 25/ 38
Comet background
Coma model
Recent observations
Analytic model
Validation and simulations
Effects at Mars
Martian meteor shower
Meteor shower will
accompany Siding Spring
ZHR for 10−6 g particles
∼ 30,000,000 at Mars
Subradiant near
Opportunity at dawn
MarsExpress may see up to
1000 meteors per minute
10,704 km2 FOV
m & 3 g
Numbers from
Anastasios Margonis
Moorhead Siding Spring at Mars 26/ 38
Comet background
Coma model
Recent observations
Analytic model
Validation and simulations
Effects at Mars
Meteoroid impact risks
1966 Leonids by A. Scott Murrell
Average flux of 100 micron or
larger meteoroids in low Earth
orbit is 5× 10−6 m−2 per hour
Fluence due to Siding Spring
is 500 times higher
(5 years of LEO exposure)
There has never been an event
like this near Earth in recent
memory, with the possible
exception of the 1966 Leonids.
Moorhead Siding Spring at Mars 27/ 38
Comet background
Coma model
Recent observations
Analytic model
Validation and simulations
Effects at Mars
Effects on the Martian atmosphere
Atmospheric effects
Energy deposition:
KE =
∫
dσ
dm
m dm × v
2
2
× pir2M
1.14 megatons of TNT equivalent
0.006% of solar irradiance: insignificant
Metal deposition probably more important
(John Plane, Leeds)
Moorhead Siding Spring at Mars 28/ 38
Comet background
Coma model
Recent observations
Analytic model
Validation and simulations
Effects 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 background
Coma model
Recent observations
Brightness monitoring
Observational constraints
Comparison 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 background
Coma model
Recent observations
Brightness monitoring
Observational constraints
Comparison with Hale-Bopp
Brightness monitoring
1234567
20◦
40◦
60◦
80◦
100◦
120◦
Heliocentric distance (au)
S
-O
-T
an
gl
e
9
9.5
10
A
b
so
lu
te
m
ag
n
it
u
d
e
Asami et al., 2013
Cometas Obs
MEO
Moorhead Siding Spring at Mars 31/ 38
Comet background
Coma model
Recent observations
Brightness monitoring
Observational constraints
Comparison 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 is
influenced by gravity and
radiation pressure
“Mostly large particles” based
on curvature of tail
Low ejection velocity based on
compactness of the coma
Low ejection velocity
= compact coma
= much lower fluence at Mars
Moorhead Siding Spring at Mars 32/ 38
Comet background
Coma model
Recent observations
Brightness monitoring
Observational constraints
Comparison with Hale-Bopp
Hubble observations
Moorhead Siding Spring at Mars 33/ 38
Comet background
Coma model
Recent observations
Brightness monitoring
Observational constraints
Comparison with Hale-Bopp
Hubble observations
−20 0 20
−20
0
20
x (103 km)
y
(1
03
km
)
−20 0 20
x (103 km)
The coma does appear to be expanding slowly
Moorhead Siding Spring at Mars 34/ 38
Comet background
Coma model
Recent observations
Brightness monitoring
Observational constraints
Comparison 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 background
Coma model
Recent observations
Brightness monitoring
Observational constraints
Comparison with Hale-Bopp
Heliocentric magnitude: Hale-Bopp
123456
−2
0
2
4
6
Heliocentric distance (au)
H
el
io
ce
n
tr
ic
m
ag
n
it
u
d
e
Image credit: A. Kammerer
Moorhead Siding Spring at Mars 36/ 38
Comet background
Coma model
Recent observations
Brightness monitoring
Observational constraints
Comparison with Hale-Bopp
Heliocentric magnitude: Siding Spring
1234567
8.5
9
9.5
10
10.5
Heliocentric distance (au)
A
b
so
lu
te
m
ag
n
it
u
d
e
Asami et al., 2013
Cometas Obs
MEO
Moorhead Siding Spring at Mars 37/ 38
Comet background
Coma model
Recent observations
Summary
Comet C/2013 A1 (Siding Spring) will have close encounter
with Mars on October 19, 2014
Mars and spacecraft will pass through coma and tail
containing meteoroids
Meteoroids (4.19× 10−6 g or larger): ∼ 1% chance of impact
per square meter due to coma and tail
Continued monitoring is needed to better predict future
behavior
Moorhead Siding Spring at Mars 38/ 38


The Meteoroid Fluence at Mars Due to Comet C/2013 A1 (Siding Spring)

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