Unsolved Problems in Saturn’s Magnetosphere Michelle F. Thomsen Planetary Science Ins>tute UPMP, Scarborough, 6-12 Sep 2015 If you’ve seen one magnetosphere, you’ve seen one magnetosphere! Saturn’s magnetospheric Features: • Radiaon belts • Plasmasphere • Plasma sheet • Magnetospheric tail • Aurorae • Bow shock • Magnetopause • Magnetospheric dynamics (convec>on, reconnec>on, wave-par>cle interac>ons, etc.) But each oF these is significantly different From the corresponding Features at Earth! Factors Affec>ng Planetary Magnetospheres Saturn rel. to Earth • Size of the planet 10x • Strength of its magnetic field 500x • Presence of satellites and rings Earth has none • plasma sources ✓ • plasma sinks ✓ • dynamic interactions ✓ • imbedded magnetospheres! ✓ • Rotational period 2.5x faster • Tilt of magnetic dipole rel. to rotational axis ~0 • Properties of external plasma (solar wind) n~0.02x; B~0.1x merged stream regions; high MA Factors Affec>ng Planetary Magnetospheres Saturn rel. to Earth • Size of the planet 10x • Strength of its magnetic field 500x • Presence of satellites and rings Earth has none • plasma sources ✓ • plasma sinks ✓ • dynamic interactions ✓ • imbedded magnetospheres! ✓ • Rotational period 2.5x faster • Tilt of magnetic dipole rel. to rotational axis ~0 • Properties of external plasma (solar wind) n~0.02x; B~0.1x merged stream regions Some interes>ng aspects oF Saturn’s magnetosphere Plasma sources, transport, sinks, global dynamics… 3.6x106 km Credit: NASA/JPL/Space Science Ins>tute Credit: Univ. oF Michigan 504 km Saturn’s Magnetospheric Imperave • Dominant source oF plasma in Saturn’s magnetosphere is at low L (ionizaon oF gas From Enceladus) • Recombinaon is too slow to maintain a steady state • All this plasma must ul>mately be shed to the solar wind • How and where does that happen? Convec>on at Saturn is dominated by corotaon • Weaker interplanetary field • Rapid rotaon Therefore, no convecon plasmapause is expected. Brice and Ioannidis, The magnetospheres oF Jupiter and Earth, Icarus, 1970 Plasma Shedding at Saturn: A Two-Step Process 1. CentriFugally-driven interchange • Inner to middle magnetosphere 2. Tail reconnec>on/Plasmoid release • Middle/outer magnetosphere Step One: Centrifugally-Driven Interchange Instability Rayleigh-Taylor Instability Liu et al., 2010 High- Heavy fluid density plasma Light fluid Low- density plasma Centrifugal force Gravity Ion Energy (eV) UT r 3.9 4.7 5.5 6.3 7.0 7.7 8.3 Rs Interchange- unstable when ∂η < 0 ∂L where η = ndV ∫V Sittler et al., 2007 Southwood & Kivelson (1987) Step Two: Magne>c Reconnec>on oF Loaded Flux Tubes CentriFugal Force -> stretched flux tubes -> B unable to confine Vasyliunas, V. M., Phys. Jov. Msp., 1983 Stretched flux tubes reconnect Step Two: Magne>c Reconnec>on oF Loaded Flux Tubes CentriFugal Force -> stretched flux tubes -> B unable to confine “Vasyliunas-type reconnecon” Dipolarizaon oF returning closed flux Depar>ng plasmoid Strong tailward flows Dipolarizaon View From above the dusk meridian View From above the noon meridian X. Jia et al., JGR, 2012 PP Lobe 1# 2# Outer 3# Inner 25#Jun#2009# 2# 104# a# 103# )# eV 2# # #( 10 Ei • Hot, low-density 101# accum 100# • Significant energe>c O+ 4# CAPS 10 b# )# 103# fluxes eV Log#counts/ #( 2# Ee 10 • “Leading field”=>evidence 101# 0# For supercorotaon 100# # )# '30 c# • nT '50# SKR enhancement and #( r B '70# )# expansion to lower d# 40# nT # #( 38 θ B MAG 36# frequencies 4# )# 0# nT # #( φ '4 B '8# e# CHEMS H+ CHEMS H+ 55# 5 25# 2 4 '1# 4 )# 10 f# Freshly injected plasma H+ ) 3 eV 3 Energy (kev) keV Energy (kev) 1 # 1 2 4# 2 EH#( 10 sr units 1 / ( cm^2 ster keV sec ) From tail reconnec>on oF 1 # units 1 / ( cm^2 ster keV sec ) Time (UTC) 06:00:00 07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00:00 #s# 1 1 2009/176 CHEMS W+ 2009/176 2 CHEMS W+ Time (UTC) Dipole06:00:00 L (RS) 10.67 07:009.83 9.17 08:008.69 09:008.35 8.13 10:008.03 8.0311:00 8.12 12:00 13:00 14:00:00 Radial Dist2009/176 (RS) 7.22 7.24 7.29 7.36 7.46 7.59 7.73 7.9 8.08 2009/176 DipoleSZS L (RS) Local Time10.67 (hrs) 7.62 9.837.96 8.26 9.17 8.54 8.698.8 9.04 8.359.26 9.478.13 9.66 8.03 8.03 8.12 Radial Dist (RS) 7.22 7.24 7.29 7.36 7.46 7.59 7.73 3 # 7.9 8.08 3 )# 5# 2 SZS Local Time (hrs) 1027.62 g# 7.96 8.26 8.54 8.8 9.04 9.26 3 9.47 previously-closed field 9.66 eV CHEMS 2 2 Energy (kev) O+ Energy (kev) EO#( log#flux(cm 11# units 1 / ( cm^2 ster keV sec ) 1 lines. Time (UTC) 06:00:00 07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00:00 units 1 / ( cm^2 ster keV sec ) 2009/176 2009/176 Dipole L (RS) 10.67 9.83 9.17 8.69 8.35 8.13 8.03 8.03 8.12 Time (UTC) Radial Dist06:00:00 (RS) 7.22 07:007.24 7.29 08:007.36 09:007.46 7.59 10:007.73 11:007.9 8.08 12:00 13:00 14:00:00 SZS Local Time2009/176 7#(hrs) 7.62 7.96 8.26 8.54 8.8 9.04 9.26 9.47 9.66 2009/176 Dipole L (RS) 1010.67 9.83 9.17 8.69 8.35 8.13 8.03 8.03 8.12 Radial Dist (RS) 7.22 7.24 7.29 7.36 7.46 7.59 7.73 # # 7.9 8.08 SZS Local Time (hrs) 7.62 7.96 8.26 8.54 8.8 9.04 9.26 30 9.47 9.66⇒ “Vasyliunas cycle” 105# bkg 20# #(Hz)# h# 103# RPWS Freq # dB#above# 10 101# 0# UT# 0600# 0700# 0800# 0900# 1000# 1100# 1200# L# 10.67# 9.83# 9.17# 8.69# 8.35# 8.13# 8.03# LT# 7.62# 7.96# 8.26# 8.54# 8.80# 9.04# 9.26# Thomsen et al., 2015 Lat# '34.6# '30.9# '27.0# '23.0# '19.0# '15.0# '11.2# 1# 2# 3# 25#Jun#2009# 2# 104# a# 103# )# eV 2# # #( 10 Ei 101# accum 100# 104# b# )# 103# eV Log#counts/ #( 2# Ee 10 101# 0# 100# # )# '30 c# nT '50# #( r B '70# d# 40# )# nT # #( 38 θ 36# B 4# )# 0# nT # #( φ '4 B '8# e# CHEMS H+ CHEMS H+ 55# 5 25# 2 4 '1# 4 )# 10 f# ) 3 eV 3 Energy (kev) # keV Energy (kev) 1# 2# 3# 1 25#Jun#2009 # 1 2 4# 2 EH#( 10 sr # units 1 / ( cm^2 ster keV sec ) 1 2# 4# units 1 / ( cm^2 ster keV sec ) Time (UTC) 06:00:00 07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00:00 #s# 1 1 10 2 2009/176 CHEMS W+ 2009/176 CHEMS W+ Dipole06:00:00 L (RS) 10.67a# 07:009.83 9.17 08:008.69 09:008.35 8.13 10:008.03 8.0311:00 8.12 12:00 13:00 14:00:00 Time (UTC) Radial Dist2009/176 (RS) 7.22 7.24 7.29 7.36 7.46 7.59 7.73 7.9 8.08 2009/176 DipoleSZS L (RS) Local Time10.67 (hrs) 7.62 9.837.96 8.26 9.17 8.54 8.698.8 9.04 8.359.26 9.478.13 9.66 8.03 8.03 8.12 Radial Dist (RS) 7.223# 7.24 7.29 7.36 7.46 7.59 7.73 3 # 7.9 8.08 3 SZS Local Time (hrs))# 1027.625# 2 7.96 8.26 8.54 8.8 9.04 9.26 9.47 9.66 )# 10 g# 3 eV eV 2# 2 # 2 #( 10 Energy (kev) Energy (kev) Ei EO#( 1# log#flux(cm 11# 10 units 1 / ( cm^2 ster keV sec ) 1 Time (UTC) 06:00:00 07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00:00 units 1 / ( cm^2 ster keV sec ) 2009/176 2009/176 accum Dipole L (RS) 10.67 9.83 9.17 8.69 8.35 8.13 8.03 8.03 8.12 Time (UTC) Radial Dist06:00:00 7#(RS)0# 7.22 07:007.24 7.29 08:007.36 09:007.46 7.59 10:007.73 11:007.9 8.08 12:00 13:00 14:00:00 SZS Local Time2009/17610 (hrs) 7.62 7.96 8.26 8.54 8.8 9.04 9.26 9.47 9.66 2009/176 Dipole L (RS) 1010.674# 9.83 9.17 8.69 8.35 8.13 8.03 8.03 8.12 Radial Dist (RS) 107.22 7.24 7.29 7.36 7.46 7.59 7.73 # # 7.9 8.08 SZS Local Time (hrs) 7.62 b# 7.96 8.26 8.54 8.8 9.04 9.26 30 9.47 9.66 bkg )# 5# 10103# eV 20# Log#counts/ #(Hz)# #( 3#2# h# Ee 1010 Freq # dB#above# 10 101# 101# 0# 100# 0# # UT#)# '300600#c# 0700# 0800# 0900# 1000# 1100# 1200# L#nT '5010.67## 9.83# 9.17# 8.69# 8.35# 8.13# 8.03# #( PP r LT#B 7.62# 7.96# 8.26# 8.54# 8.80# 9.04# 9.26# '70# L~9 Lat# '34.6# '30.9# '27.0# '23.0# '19.0# '15.0# '11.2# )# d# 40# Tail reconnec>on oF loaded flux tubes nT # #( 38 θ 36# B • sheds inner magnetospheric mass 4# )# 0# nT # #( • creates a sharp boundary between the dense inner-φ '4 B '8# e# CHEMS H+ CHEMS H+ 55# 5 magnetospheric plasma that has escaped reconnec>on, 25# 2 4 '1# 4 )# 10 f# ) 3 eV 3 Energy (kev) keV and the injected hot tenuous plasma oF the reconnected Energy (kev) 1 # 1 2 4# 2 EH#( 10 sr units 1 / ( cm^2 ster keV sec ) 1 # units 1 / ( cm^2 ster keV sec ) Time (UTC) 06:00:00 07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00:00 #s# 1 1 2009/176 CHEMS W+ 2009/176 2 flux region: Plasmapause CHEMS W+ Time (UTC) Dipole06:00:00 L (RS) 10.67 07:009.83 9.17 08:008.69 09:008.35 8.13 10:008.03 8.0311:00 8.12 12:00 13:00 14:00:00 Radial Dist2009/176 (RS) 7.22 7.24 7.29 7.36 7.46 7.59 7.73 7.9 8.08 2009/176 DipoleSZS L (RS) Local Time10.67 (hrs) 7.62 9.837.96 8.26 9.17 8.54 8.698.8 9.04 8.359.26 9.478.13 9.66 8.03 8.03 8.12 Radial Dist (RS) 7.22 7.24 7.29 7.36 7.46 7.59 7.73 3 # 7.9 8.08 3 )# 5# 2 SZS Local Time (hrs) 1027.62 g# 7.96 8.26 8.54 8.8 9.04 9.26 3 9.47 9.66 eV 2 2 Energy (kev) Energy (kev) EO#( => Unstable to centriFugal interchange log#flux(cm 11# units 1 / ( cm^2 ster keV sec ) 1 Time (UTC) 06:00:00 07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00:00 units 1 / ( cm^2 ster keV sec ) 2009/176 2009/176 Dipole L (RS) 10.67 9.83 9.17 8.69 8.35 8.13 8.03 8.03 8.12 Time (UTC) Radial Dist06:00:00 (RS) 7.22 07:007.24 7.29 08:007.36 09:007.46 7.59 10:007.73 11:007.9 8.08 12:00 13:00 14:00:00 SZS Local Time2009/176 7#(hrs) 7.62 7.96 8.26 8.54 8.8 9.04 9.26 9.47 9.66 2009/176 Dipole L (RS) 1010.67 9.83 9.17 8.69 8.35 8.13 8.03 8.03 8.12 Radial Dist (RS) 7.22 7.24 7.29 7.36 7.46 7.59 7.73 # # 7.9 8.08 SZS Local Time (hrs) 7.62 7.96 8.26 8.54 8.8 9.04 9.26 30 9.47 9.66 105# bkg 20# #(Hz)# h# 103# Freq # dB#above# 10 101# 0# UT# 0600# 0700# 0800# 0900# 1000# 1100# 1200# L# 10.67# 9.83# 9.17# 8.69# 8.35# 8.13# 8.03# LT# 7.62# 7.96# 8.26# 8.54# 8.80# 9.04# 9.26# Lat# '34.6# '30.9# '27.0# '23.0# '19.0# '15.0# '11.2# Major Open Ques>ons • How important is the solar wind? – Magnetopause reconnec>on is inhibited but does occur => flux return is another imperave, which can’t be accomplished with Vasyliunas reconnecon.