Further development of modeling of spatial distribution of energetic electron fluxes near Europa M. V. Podzolko 1 , I. V. Getselev 1 , Yu. I. Gubar 1 , I. S. Veselovsky 1,2 - PowerPoint PPT Presentation
Further development of modeling of spatial distribution of energetic electron fluxes near Europa M. V. Podzolko 1 , I. V. Getselev 1 , Yu. I. Gubar 1 , I. S. Veselovsky 1,2 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
Transcript
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
Equatorial profiles of the integral fluxes ofE > 0.5, >2 and >10 MeV electrons and E > 2, >10 and >30 MeV protons at Jupiter.
Charged particle flux and radiation dose equatorial profiles at Jupiter
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.
2 4 6 8 10 12 14 16104
105
106
107
108
109
L, RJ
f e, 1/(c
m2
s)
> 0.5 MeV
> 2
> 10
2 4 6 8 10 12 14 15103
104
105
106
107
108
L, RJ
f p, 1/(c
m2
s)
> 2 MeV
> 10
> 30 GanymedeIoAmalthea Europa GanymedeIoAmalthea Europa
2 4 6 8 10 12 14 16102
103
104
105
106
L, RJ
Dos
e, ra
d/da
y 0.27 g/cm2
1
2.2
52.2, protons
Doses under various shielding in Europa’s (solid line) and Ganymede’s (dash line) orbits.
Calculated radiation doses in Europa’s orbit: high hazard
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
2-month doses in Europa’s and Ganymede’s orbits, rad.
Integral fluxes of electrons in Europa’s (solid line) and Ganymede’s (dash line) orbits.
10-1 100 101 102
103
104
105
106
107
108
Energy, MeV
f e, 1/(c
m2
s)
0.01 0.1 1 10101
102
103
104
105
106
Shielding, g/cm2
Dos
e, ra
d/da
y
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
0 90 180 270 360-90
-60
-30
0
30
60
90
Longitude, degrees
Latit
ude,
deg
rees
< 0.05 0.2 0.4 0.6 0.8 1 Flux, relative to maximum
5 MeV, 0 km
>30 MeV <30 MeV
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.
Distribution of differential fluxes of 5 MeV electrons on Europa’s surface taking into account only guiding center approximation.
Dependence of electron flux from their Larmor motion near the surface
2
34
1
20 40 60 80
0.1
0.2
0.3
0.4
0.5
Europa latitude, degrees
Allo
wed
flux
and
spa
ce a
ngle
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°
L parameter:L = 9.5 RJ
Magnetic fieldB/B0 = 1
Integral flux of >5 MeV electronsFe(>5 MeV) = 8.9·106
Integral flux of >10 MeV protonsFp(>10 MeV) = 1.4·105
Fluxes computed using Divine, Garrett, 1983 model.
Europa’s magnetic latitude λM = 10°
L parameter:L = 9.8 RJ
Magnetic fieldB/B0 = 1.26
Integral flux of >5 MeV electronsFe(>5 MeV) = 6.3·106
Integral flux of >10 MeV protonsFp(>10 MeV) = 8.3·104
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
< 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.
J
v
5 MeV, 0 km
Spatial distribution of relativistic electron fluxes on Europa’s surface
< 0.05 0.2 0.4 0.6 0.8 1 Flux, relative to maximum
Distribution of differential fluxes of electrons with energy 50 MeV on Europa’s surface.
Distribution of differential fluxes of electrons with energy 5 MeV on Europa’s surface.
J
v
5 MeV, 0 km
J
v
50 MeV, 0 km
Spatial distribution of relativistic electron fluxes on Europa’s surface
0 90 180 270 360 -90
-60
-30
0
30
60
90
Longitude, degrees
Latit
ude,
deg
rees
0 90 180 270 360 -90
-60
-30
0
30
60
90
Longitude, degrees
Latit
ude,
deg
rees
< 0.05 0.2 0.4 0.6 0.8 1 Flux, relative to maximum
50 MeV, 0 km
5 MeV, 0 km
0 90 180 270 360 -90
-60
-30
0
30
60
90
Longitude, degrees
Latit
ude,
deg
rees
0 90 180 270 360 -90
-60
-30
0
30
60
90
Longitude, degrees
Latit
ude,
deg
rees
Electron fluxes on Europa’s surface and at 100 km altitude
0 90 180 270 360 -90
-60
-30
0
30
60
90
Longitude, degrees
Latit
ude,
deg
rees
0 90 180 270 360 -90
-60
-30
0
30
60
90
Longitude, degrees
Latit
ude,
deg
rees
50 MeV, 100 km
5 MeV, 100 km5 MeV, 0 km
50 MeV, 0 km
< 0.05 0.2 0.4 0.6 0.8 1 Flux, relative to maximum
Spatial distribution of radiation doses on Europa’s surface
0 90 180 270 360 -90
-60
-30
0
30
60
90
Longitude, degrees
Latit
ude,
deg
rees
0 90 180 270 360 -90
-60
-30
0
30
60
90
Longitude, degrees
Latit
ude,
deg
rees
2.2 g/cm2, 0 km
5 g/cm2, 0 km
< 0.05 0.2 0.4 0.6 0.8 1 Dose, relative to maximum
0 90 180 270 360 -90
-60
-30
0
30
60
90
Longitude, degrees
Latit
ude,
deg
rees
0 90 180 270 360-90
-60
-30
0
30
60
90
Longitude, degrees
Latit
ude,
deg
rees
0 90 180 270 360 -90
-60
-30
0
30
60
90
Longitude, degrees
Latit
ude,
deg
rees
0 90 180 270 360 -90
-60
-30
0
30
60
90
Longitude, degrees
Latit
ude,
deg
rees
Radiation doses on Europa’s surface and at 100 km altitude
5 g/cm2, 100 km
2.2 g/cm2, 100 km2.2 g/cm2, 0 km
5 g/cm2, 0 km
< 0.05 0.2 0.4 0.6 0.8 1 Dose, relative to maximum
Dependence of dose at 100 km orbit around Europa from its inclination
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°.
0 30 60 90 0.1
0.2
0.3
0.4
0.5
0.6
Orbit inclination, degrees
Dos
e, re
lativ
e to
max
imum
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.
10 1002
3
57
10
20
30
5070
r, RJ
Дoз
a(E
вpoп
a), к
рад
2.2 г/cм2
5 г/cм2
10 100
10-1
100
101
r, RJ
Дoз
a(Га
ним
ед),
крад
2.2 г/cм2
5 г/cм2
Doses during gravity assists using Europa and Ganymede
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.
