Margaret Galland Kivelson
6/27/2013 Margaret Kivelson- Dynamics - MoP 2011 – Boston University 1 Rotationally driven magnetospheres! (Mauk et al., (Saturn, Chapter 11) state: “while it is true that Saturn’s magnetosphere is intermediate between those of Earth and Jupiter
in terms of size (whether measured by RP; RPP, or RMP), it is not intermediate in any meaningful dynamical sense. It is clearly rotationally driven like Jupiter’s, not solar-wind–driven like Earth’s.”
Margaret Kivelson- Dynamics - MoP 6/27/2013 2011 – Boston University 2 This Vasyliunas (1983) diagram is a necessary element of any discussion of the magnetospheres of gas giants! It captures some critical features implicitly or explicitly: A significant source of heavy plasma deep within the magnetopause (Io, Enceladus) is spun up to some fraction of corotation speed by field-aligned currents coupling magnetosphere and ionosphere. Rotation dominates the dynamics – drives plasmoid releases down the tail. Solar wind shapes the boundaries but does not dominate the dynamics.
Margaret Kivelson- Dynamics - MoP 6/27/2013 2011 – Boston University 3 Thomas et al., 2004
Schneider and Trager, 1995 In the pickup process, ions acquire perp. thermal speed of local rotation speed. Energy added N m()2 pu Pickup energy is shared with background plasma. Typically heats plasma. Melin6/27/2013 et al., 2009 4 Much is well established, but puzzles remain.
Discuss a few features energy density of plasma and why it changes vs. radial distance, vs. local time, periodicities, Anomalies in regions of high dust density.
Margaret Kivelson- Dynamics - MoP 6/27/2013 2011 – Boston University 5 At Earth, temperature (more correctly Below a plot from Kane et al (1995) thermal energy per particle) decreases of Voyager data at Jupiter, modeled with but not at Jupiter or Saturn. as kappa distributions
Wing and Newell, 2002 Earth Kane et al., 1995 Jupiter
r Proton temperature remains nearly constant (20 keV) on day side. Heavy ion temperature increases with proportional to corotation energy. r WHY? Margaret Kivelson- Dynamics - MoP 6/27/2013 2011 – Boston University 6
For <6 keV ions (measured by PLS at Jupiter), temperature shown in figure changes little between 10 and 40 RJ. Pickup as heat source not ruled out. The >30 keV heavy ions shown for Jupiter in previous slide require vth >~500 km/s, which exceeds rotation speed. (Also, each new ion must share pickup energy with ambient ions). Not plausible that pickup is the primary heat source for energetic heavy ions. From Khurana et al., 2004 Voyager 1 inbound, warm plasma Margaret Kivelson- Dynamics - MoP 6/27/2013 2011 – Boston University 7
m 2 2 2 H 2 (v ) is an exact constant of the motion for observer in rotating frame if the field in that frame is static.
Data provide T vs. (axial radial distance).
T gives mean particle kinetic energy in fluid rest frame, i.e. in rotating frame.
6/27/2013 8 m 2 2 2 H 2 (v ) is constant in the corotating frame and the field is constant in that frame. Possibly this type of In the corotating frame, for a acceleration contributes to collection of particles, the bounce - observed temperature 3 averaged particle energy is 2 kT so increase of both high and 2 2 2 low energy ions with radial kT 3 (H ) distance at Jupiter. Many other processes need For simple rotation, the increases and decreases of to be considered. T cancel out over a rotation. Concern: Temperature (T ) is measured in plasma rest If flux tubes interchange, there can be net frame, which is not fully energization. corotating, but we assume that it is close enough for
the relation to be valid as it Efficient: the full seems to work for Jupiter. distribution changes energy What about Saturn? with . Margaret Kivelson- Dynamics - MoP 6/27/2013 2011 – Boston University 9 Increase ∝ 22
data from Thomsen et al., 2010
Thomsen et al., 2010
Margaret Kivelson- Dynamics - MoP 6/27/2013 2011 – Boston University 10 Outward transport of plasma in a static field occurs thru interchange: Interchange works without temporal change of field. Heavy ions move out from
source in inner magnetosphere. varies like 2 If no ∂B/∂t, they should conserve Northop/Birmingham’s “H”.
At Saturn, protons arise from Kane et al., 1995 Jupiter dissociation of water and like heavy ions participate in outward (slow) interchange. T increases. At Jupiter, protons probably come from solar wind. Maybe they move inward in narrow fingers too Thomsen et al., 2010 fast to conserve H. A puzzle. r 6/27/2013 11 I have ignored significant contributions from: Above remarks applied pickup ions, charge exchange to a static field in the Saur et al. (2004) argue that rotating frame. at Saturn, the effect of ion– neutral collisional drag may Not too bad an slow plasma as much as assumption out to does charge exchange. some critical , but . . . radiation LT dependence of Coulomb interactions boundary location Charged dust invalidates the Centrifugal forces may be modifying the plasma in ways assumption of a static that have not been fully field in the rotating analyzed. frame at larger . What then?
Margaret Kivelson- Dynamics - MoP 6/27/2013 2011 – Boston University 12 Configuration and It is likely that the magnitude change with centrifugal acceleration of rotation plasma as it rotates from phase. noon to dusk is responsible for changing the character of the plasma and of B. Flux tubes move inward from Local time variations of night to noon and outward from field and flow are noon to dusk and beyond. considerable and we At fixed position in the rotating believe link to centrifugal frame dB/dt ǂ 0. acceleration. Bouncing particles are accelerated if rotating flux tubes stretch over a bounce period. Marissa Vogt has a poster on this subject (#119). Please visit. Margaret Kivelson- Dynamics - MoP 6/27/2013 2011 – Boston University 13 Pioneer 10 inbnd, dawn; DAWN DUSK 20 Galileo G29 outbound near dusk
Br Br 0
Br -20 20 B , |B| B , |B| q B ,|B| 0
20 B Bf B 0
-20 40 50 60 70 80 90 100 40 50 60 R a di al70 distanc e ( R J) 80 90 100 LAT 9.96 9.55 9.25 9.02 8.85 8.70 8.59 LT 4.88 5.04 5.14 5.22 5.28 5.33 5.37 LAT 0.41 0.49 0.55 0.59 0.62 0.65 0.67 LT 14.93 15.34 15.65 15.89 16.10 16.26 16.41
MargaretC:\My Documents\20 11Kivelson\MOP\DAWN DUSK -com pDynamicsared w magnitude -- July 06, 2-011 1MoP5:23 6/27/2013 2011 – Boston University 14 adapted from N. Krupp Galileo/EPD flow measurements in the equatorial plane. Look INSIDE MAGNETOPAUSE On average Strong must have dependence same on LOCAL magnetic flux TIME transported across both terminators
ufBq equal at dawn and dusk, so
because uf decreases near dusk,
Bq must increase there. Margaret Kivelson- Dynamics - MoP 6/27/2013 2011 – Boston University 15 Near dawn, the north-south In the afternoon, Bq dominant component of B is very small. and |B| variable. B r 0400Callisto 9 (s3 rh(C9) inbound 0 40inbnd0-0500 LT ) Br 1600 LTG29 o(G29utbound nea r outbnd16 LT ) |B| 20 |B| 10 B Br r |B| 0 |B| 0
B -20 -10 q Bq 30 Bq >0.5|B| <------B ------> B 20 |B| 20 magnetosheath Btheta |B| |B| -----Bq <0.25 |B| ----- |B| 10 0
20 Bf B B 20 f 10 |B| Bphi 62 RJ 102 RJ |B| |B| |B| 0 0 DOY: 365001-00 003-00 005-00 007-00 009-00 011-00 2000-Dec-30 1600 1997-Jun-22 Jun-23 Jun-24 Jun-25 DOY: 173 time R 37 54 69 81 92 103 R 46.39 Ulysses (s3rh) inbound from39.35 >100 RJ 31.35 loctim 14.78 15.48 15.87 16.12 16.30 16.45 local time 3.90 4.33 4.97 pls sheet boundary C:\GALILEO\JupIite3r g2lob aol\duynatmbicso\pulotsn pldasm an loessa\Gr29 1out3 clo0se0 m gpL --T December 11, 2004 14:20 1000 (ULLGalileo MAG Team (UinbndCLA): Revised July 3, 2001 ) ~1400 LT (I32 inbnd) Br 20 20 B B r r |B| Br |B| 0 0 |B||B | Bq <0.25 |B| -20 20 B 20 B >0.5|B| q B q BqB 0 |B| 0 |B| THICK, UNSTABLE PLASMA - B > ~6 nT 60 69 RJ 20 30 B B B f B |B| 0 0 f |B| -30 1992-Feb-2 Feb-03 Feb-04 Feb-05 Feb-06 Feb-07 DOY: 33 time |B| 2001-Oct-17 08:00 18:00 04:00 14:00 00:00 10:00 20:00 06:00 16:00 02:00 12:00 22:00
R 108.11 90.18 71.99 53.41 34.18 DOY: 290 LAT 5.36 6.14 7.31 9.27 13.33 R 23 27 31 35 39 43 46 50 53 56 59 62 loctim 10.29 10.22 10.12 9.95 9.60 l octim 12.15 12.50 12.82 13.07 13.26 13.41 13.55 13.66 13.76 13.85 13.93 14.00 Galileo MAG Team (UCLA): April 8, 2002 Galileo MAG Team -- April 8, 2002 Margaret Kivelson- Dynamics - MoP 40 ≤ 60 RJ 6/27/2013 2011 – Boston University 16 Heating the plasma? Time evolution of a model In rotating frame, include field line starting at 50 RJ and stretching radially outward centrifugal force; take B t 0 over 2.5 hours. dv 2 0 min 1.5 h m qE v B m r 30 min. 2 h dt A where B A; E t
The flux tube expands during rotation from noon from Vogt et al. poster to dusk because the Bounce motion is not magnetopause lies longer conservative. increasingly far from planet. Margaret Kivelson- Dynamics - MoP 6/27/2013 2011 – Boston University 17 Bounce Times, 1 keV ion (20 mp) As ion 1 moves towards equator, Radial Equatorial Bounce the equatorial point of field line distance at pitch Period recedes; ion keeps gaining equator angle (hours) energy with increase of . As ion (RJ) (degrees) 2 moves up the field line, it is 30 20 20.8 also carried outward by the field 30 80 6.4 stretching. More energy is gained than lost in the ion 40 20 27.4 distribution. 1 40 80 5.6 50 20 36.0 This model 2 needs 50 80 5.7 60 20 46.5 to be made 60 80 6.1 quantitative. Vogt et al., poster Margaret Kivelson- Dynamics - MoP 6/27/2013 2011 – Boston University 18 Maybe a hint in Bq, but the magnetospheric scale is far too small for this process to be significant.
Saturn: OUTBOUND DAWN ORBIT 8 10 INBOUND DUSK ORBIT 133
5 Br 0 Br -5
-10 16
8 B |B| B |B| 0
-8 6 4
B 2 0 -2 -4 15 20 25 30 35 40 RADIAL DISTANCE, RS lat dawn 5 1 -2 -5 -7 -11 lat dusk -2 -1 -1 -1 -1 -1
C:\My Documents\2011\MOP\saturn dawn dusk -- July 08, 2011 14:37 Velocities from Thomsen et al., 2010
Margaret Kivelson- Dynamics - MoP 6/27/2013 2011 – Boston University 19 Well established at Saturn. For Jupiter seasonal effects System IV (different slow drift of period from System III rotation period) different north and south periodicities have Models have attributed been reported from periodicity to several types of convective instability in the observations. magnetosphere, Is System IV (period to periodic disconnections, 3% longer than to FACs driven by System III) the Jovian ionospheric flows. equivalent of the SKR periodicity at Saturn? We will hear lots about this matter for Saturn during the meeting. Margaret Kivelson- Dynamics - MoP 6/27/2013 2011 – Boston University 20 Margaret Kivelson- Dynamics - MoP 6/27/2013 2011 – Boston University 21 2 3 4 5 RS
Saturn Dust distribution. E ring is quite diffuse.
Dust complicates the plasma
Margaret Kivelson- Dynamics - MoP 6/27/2013 2011 – Boston University 22 Whereas ion motions are Through most of dominated by Jupiter’s and electromagnetic Saturn’s forces, more magnetospheres, massive dust grains Keplerian speeds are controlled by are slower than gravitational forces corotation. Keplerian orbits. Anomalous rotation has been attributed to the effect of dust.
Margaret Kivelson- Dynamics - MoP 6/27/2013 2011 – Boston University 23 E.g. for Saturn, near the E-ring, there are multiple populations (Wahlund et al, 2009). Hot ions ~corotate; Dust grains move at ~Keplerian speed.
Colder ions (Ti a few eV) and electrons can interact with the electrical potential cavities of the negatively charged (~Volt neg.) water- rich dust grains in the E-ring (Wahlund et al., 2009). Margaret Kivelson- Dynamics - MoP 6/27/2013 2011 – Boston University 24 Touched on vary few matters.
I hope I leave you with the sense that there is a good deal more to learn about the dynamics of the magnetospheres of Jupiter and Saturn.
JUNO is coming.
Cassini is continuing.
MOP 2013 should be fun too.
Margaret Kivelson- Dynamics - MoP 6/27/2013 2011 – Boston University 25