Further development of modeling of spatial
distribution of energetic electron fluxes near Europa
M. V. Podzolko1, I. V. Getselev1, Yu. I. Gubar1, I. S. Veselovsky1,2
1 Skobeltsyn
Institute of Nuclear Physics, Lomonosov Moscow State University, Russia
2 Space Research Institute (IKI), Russian Academy of Sciences, Moscow, Russia
– Charged particle flux and radiation dose equatorial profiles at Jupiter
– Radiation doses in Europa’s orbit: high hazard
– Factors which determine charged particle flux reduction near Europa
– Relativistic electron fluxes on Europa’s surface and at 100 km altitude
– Radiation doses on Europa’s surface and at 100 km orbit around Europa
– Doses during gravity assists using Jupiter’s moons
– Conclusions, discussion
Charged particle flux and radiation dose equatorial profiles at Jupiter
109
> 0.5 MeV
8
10
7
10
6
> 10
105
4
f p, 1/(cm2s)
10
8
10
10
7
10
6
10
6
10
5
0.27 g/cm
10
4
1
10
3
>2
2
4
6
8
10
12
14
16
L, RJ
Dose, rad/day
f e, 1/(cm2s)
10
2
2.2
2.2, protons
5
> 2 MeV
102
2
4
6
> 10
10
10
12
14
16
L, RJ
105
Amalthea
> 30
104
8
Io
Europa
Ganymede
3
2
4
6
8
10
12
14
L, RJ
Equatorial profiles of the integral fluxes of
E > 0.5, >2 and >10 MeV electrons and E > 2,
>10 and >30 MeV protons at Jupiter.
15
Equatorial profiles of radiation doses under 0.27, 1,
2.2 and 5 g/cm2 shielding, and separately dose under
2.2 g/cm2 from protons only near Jupiter.
f e, 1/(cm2s)
10
8
10
7
Dose, rad/day
Calculated radiation doses in Europa’s orbit: high hazard
10
6
10
5
10
4
10
3
102
106
10
101
0.01
5
10
4
10
3
0.1
1
10
Shielding, g/cm
2
Doses under various shielding in Europa’s (solid line)
and Ganymede’s (dash line) orbits.
10-1
100
101
102
Energy, MeV
Integral fluxes of electrons in Europa’s (solid
line) and Ganymede’s (dash line) orbits.
2-month doses in Europa’s and Ganymede’s
orbits, rad.
g/cm2
E
G
1.0
2.2·106
3.5·104
2.2
8.8·105
9.0·103
5.0
2.4·105
2.0·103
10.0
4.5·104
5.2·102
Factors which determine charged particle flux reduction near Europa
1. Particle drift speed relative to Europa.
2. Larmor motion of the particles near the surface.
3. Difference of Europa’s orbital plane from Jupiter’s geomagnetic equator plane.
4. Disturbance of Jupiter’s magnetic field in vicinity of Europa.
5. Presence of the electric fields, which can accelerate particles in the magnetosphere.
6. Interaction of particles with Europa’s tenuous atmosphere.
7. Particle diffusion.
8. Thickness and configuration of spacecraft’s shielding.
Dependence of electron flux from their drift speed relative to Europa
>30 MeV
<30 MeV
90
5 MeV, 0 km
60
Latitude, degrees
Fluxes of Electrons with energies a) 42–65 keV, b) 527–
884 keV from the Galileo EPD data during flyby near
Europa. Directions of the longitudinal drift of electrons with
energies <30 and >30 MeV relative to Europa are shown.
30
0
-30
-60
-90
Distribution of differential fluxes of 5 MeV electrons
on Europa’s surface taking into account only
guiding center approximation.
0
90
180
270
360
Longitude, degrees
< 0.05
0.2
0.4
0.6
0.8
Flux, relative to maximum
1
3
4
Allowed flux and space angle
Dependence of electron flux from their Larmor motion near the surface
0.5
0.4
0.3
0.2
0.1
20
40
60
80
Europa latitude, degrees
1
2
Dependency of the allowed range of space
angles (upper curve) and flux of electrons of
energies 500 keV (middle curve) and 5 MeV
(lower curve) from point’s latitude,.taking into
account their Larmor motion near the surface.
Dependence of electron flux parameters from Europa’s magnetic latitude
Europa’s magnetic latitude λM = 0°
Europa’s magnetic latitude λM = 10°
L parameter:
L = 9.5 RJ
L parameter:
L = 9.8 RJ
Magnetic field
B/B0 = 1
Magnetic field
B/B0 = 1.26
Integral flux of >5 MeV electrons
Fe(>5 MeV) = 8.9·106
Integral flux of >5 MeV electrons
Fe(>5 MeV) = 6.3·106
Integral flux of >10 MeV protons
Fp(>10 MeV) = 1.4·105
Integral flux of >10 MeV protons
Fp(>10 MeV) = 8.3·104
Fluxes computed using Divine, Garrett, 1983
model.
The period of particle drift speed relative to
Europa can be up to 2 times higher.
Spatial distribution of relativistic electron fluxes on Europa’s surface
5 MeV, 0 km
v
J
< 0.05
0.2
0.4
0.6
0.8
1
Flux, relative to maximum
Distribution of differential fluxes of electrons
with energy 5 MeV on Europa’s surface.
Spatial distribution of relativistic electron fluxes on Europa’s surface
5 MeV, 0 km
50 MeV, 0 km
v
v
J
J
< 0.05
0.2
0.4
0.6
0.8
1
Flux, relative to maximum
Distribution of differential fluxes of electrons
with energy 5 MeV on Europa’s surface.
Distribution of differential fluxes of electrons
with energy 50 MeV on Europa’s surface.
Spatial distribution of relativistic electron fluxes on Europa’s surface
90
5 MeV, 0 km
Latitude, degrees
60
30
0
-30
-60
-90
90 0
90
270
360
50 MeV, 0 km
Longitude, degrees
60
Latitude, degrees
180
30
0
-30
-60
-90
0
90
180
270
360
Longitude, degrees
< 0.05
0.2
0.4
0.6
0.8
Flux, relative to maximum
1
Electron fluxes on Europa’s surface and at 100 km altitude
90
90
5 MeV, 0 km
5 MeV, 100 km
60
Latitude, degrees
Latitude, degrees
60
30
0
-30
-60
90
180
270
-30
-90
90 0
360
50 MeV, 0 km
Longitude, degrees
90
30
0
-30
180
270
360
50 MeV, 100 km
Longitude, degrees
60
Latitude, degrees
60
Latitude, degrees
0
-60
-90
90 0
30
0
-30
-60
-60
-90
30
0
90
180
270
-90
360
0
90
270
Longitude, degrees
Longitude, degrees
< 0.05
180
0.2
0.4
0.6
0.8
Flux, relative to maximum
1
360
Spatial distribution of radiation doses on Europa’s surface
90
2.2 g/cm2, 0 km
Latitude, degrees
60
30
0
-30
-60
-90
90 0
90
270
360
5 g/cm2, 0 km
Longitude, degrees
60
Latitude, degrees
180
30
0
-30
-60
-90
0
90
180
270
360
Longitude, degrees
< 0.05
0.2
0.4
0.6
0.8
Dose, relative to maximum
1
Radiation doses on Europa’s surface and at 100 km altitude
90
90
2.2
g/cm2,
2.2 g/cm2, 100 km
0 km
60
Latitude, degrees
Latitude, degrees
60
30
0
-30
-60
90
180
270
-30
-90
90 0
360
5 g/cm2, 0 km
Longitude, degrees
90
30
0
-30
-60
180
270
360
5 g/cm2, 100 km
Longitude, degrees
60
Latitude, degrees
60
Latitude, degrees
0
-60
-90
90 0
-90
30
30
0
-30
-60
0
90
180
270
360
Longitude, degrees
< 0.05
0.2
0.4
0.6
-90
0
90
180
270
Longitude, degrees
0.8
Dose, relative to maximum
1
360
Dependence of dose at 100 km orbit around Europa from its inclination
Dose, relative to maximum
0.6
0.5
0.4
0.3
0.2
0.1
0
30
60
90
Orbit inclination, degrees
Dependence of the dose under 2.2 (solid line)
and 5 g/cm2 (dash line) at 100 km orbit around
Europa. Optimal orbits have inclination >60°.
Doses during gravity assists using Europa and Ganymede
70
Дoзa(Eвpoпa), крад
50
30
2.2 г/cм2
20
10
7
5
5 г/cм2
3
2
Дoзa(Ганимед), крад
10
10
10
10
100
1
r, RJ
2.2 г/cм2
0
5 г/cм2
-1
10
100
r, RJ
Doses behind 2.2 (upper curves on each plot) and 5 g/cm2 (lower curves) for one orbital circuit during
gravity assists using Europa and Ganimide, depending on the distance of the opposite orbit’s node.
Conclusions, discussion
– In Jupiter’s radiation belts and in particular in Europa’s orbit very intensive fluxes of
relativistic electrons are present, which will represent the main hazard for spacecraft’s
electronic equipment behind the shielding of ≥1 g/cm2. The radiation hazard in Europa’s
orbit is sufficiently higher, than in vicinity of Ganymede.
– But near Europa part of the flux is shaded by the moon. This reduction of fluxes is
nonuniform and differs for various particle energies and pitch-angles, and for the
surface and the low-altitude orbit. Factors, which determine this particle flux reduction
have been revealed. They were put in a basis of the model of spatial distribution of
energetic particle fluxes near Europa, which is being developed by the authors.
– Distribution of relativistic electron fluxes taking into account several of mentioned
above factors has been computed.
– These computations have shown, that the most intensive fluxes of relativistic electrons
of energies <30 MeV precipitate on Europa’s trailing side along its orbital motion. But
their fluxes on the surface are several times lower, than at 100 km altitude, and decrease
from middle latitudes to equator.
– The least hazardous low-altitude orbits around Europa are those with inclination >60°.
– Each gravity assist using Europa adds a dose of ≥10 krad behind 2.2 g/cm2.
– Further development of the model is appropriate.