Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.cosmos.ru/conf/2009elw/presentations/presentations_pdf/session3/petrukovich_ELW.pdf Дата изменения: Mon Mar 2 19:59:08 2009 Дата индексирования: Mon Apr 6 23:54:51 2009 Кодировка: Поисковые слова: m 27

Plasma environment of Europa
A. A. Petrukovich
Space Research Institute

a review of plasma conditions and effects near Europa of interest to prime tasks of a landing mission

Acknowledgements to used publications: K.Khurana et al, Russell et al, Frank et al., Paranicas et al., Kivelson et al., Johnson et al., Krupp et al., etc

ELW-2009

Space Research Institute


Jupiter specifics
weak solar wind: strong magnetic field & fast rotation: Io outflow: internal effects dominate powerful energizing environment strong outflow of cold heavy ions Space Research Institute

ELW-2009


rotating magnetosphere
electric potential of rotation at Jupiter is 400 MV, solar wind "only" 1 MV at Earth both are ~ 100 kV

Europa location

ELW-2009

Space Research Institute


particle populations

magnetic flux tubes with cold plasma (100 eV) diffuse out and heated most of plasma is lost flux tubes with hot rarefied plasma 10's of keV return back to Jupiter Outer radiation belts ~ 1-100 MeV are accelerated tails of hot plasma balance of hot and cold populations powers instabilities

ELW-2009

Space Research Institute


ELW-2009

Space Research Institute


variability
cold plasma diffuse outside + up and down motion relative to Europa orbit bursty iward radial transport of hot plasma: three time scales interchange: relatively empty flux tubes penetrate inside minutes, 100 km/s injections: drifting hot plasma regions hours substorms: global unloading, a bunch of injections days cold plasma: 10-200 cm-3 pressure 2-10 nPa energetic plasma (> 20 keV): pressure ?-10 nPa
interchange

ELW-2009

Space Research Institute


particle motion
Europa orbital motion 14 km/s
gyration

corotation velocity 117 km/s
bounce drifts

Europa is standing in plasma flow ~100 km/s
electric field drift ~ 40 mV/m energetic plasma has gradient drifts ions drift in direction of corotation Europa moves ~5000 km per bounce electrons drift against corotation < 20 MeV can not overcome corotation > 20 MeV faster than corotation Europa moves ~300 km per bounce

ELW-2009

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plasma effects-1
high abundance of heavy ions: sulfur: SchwefelaufnahmevermЖgen fast pick-up of fresh ions by corotation: ions acquire velocity ~ 100 km/s and run away analysis of neutrals by ionization might be a problem (Phobos-type experiment)

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plasma effects-2
Secondary electrons photoelectrons Plasma electrons

surface charging objects in plasma acquire floating potential so that total current is zero floating potential is of the order of temperature of dominating flux

Plasma ions

J(V

float

)=0

in solar wind (Phobos, asteroids) photoelectrons dominate V ~ +1-5 V at Europa photocurrent is weak, if cold electrons dominate V ~ -100 V if hot electrons (>keV) V ~ - some keV

spacecraft are equipotential (by conducting layer) but ice, regolith, moving elements may be differentially charged

ELW-2009

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energetic plasmas
10
9

Electron flux, 1/(cm2s)

Proton flux, 1/(cm2s)

10

8

electrons

10 10 10 10 10 10 10

8

Courtesy Podzolko et al protons

7

6

10

7

5

10

6

4

10

5

Earth

3

2

Earth
10
0

10

4

10

-1

10

0

10

1

10

2

Energy, MeV

10

1

10

2

Energy, MeV

total dose amounts to megarad - a killing quantity for a near-Earth satellites Galileo survived 650 krad (estimate), 3 times above nominal, thanks to a very conservative design for various instruments and conditions doses might be substantially different dose is "global climate", while "regional climate" and "weather" are also important

ELW-2009

Space Research Institute


plasma effects-3
dose behind 1 cm of Al is dominated be electrons: dose with no shielding is dominated by ions: 1 Mrad for 2 months 0.2 Grad for 2 months

ions penetrate to sub-mm depths important for open sensitive elements (like CCD's) total dose single event upsets electrons pass ~0.5 cm of unit density per MeV important for electronics total dose internal charging bremsstrahlung gamma rays from electrons (>10 MeV) can pass 10's of cm

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Space Research Institute


plasma effects-4
radiation affects the spacecraft as well as ... Europa surface tomorrow's talk by Patterson et al. 1 rad = 100 erg/g ~ 10-10 eV/nuclon * mega/gigarads * millions of years

what organics can survive ? How deep to dig ? detailed calculations + surface formation +differential rotation electrons orbit High-energy electrons (+bremsstrahlung)

Moderate and polar latitudes might be less affected by penetrating radiation

ELW-2009

Space Research Institute


conclusions
Jupiter has powerful magnetosphere a lot of heavy ions fast acceleration of new ions surface charging radiation effects on spacecraft radiation effects on surface ELW-2009
Space Research Institute