Connecting Morphology

1
Connecting Morphology Energetics in the Io
Plasma Torus

• Nick Schneider
• Laboratory for Atmospheric Space Physics
  University of Colorado

2
Connecting Morphology Energetics in the Io
Plasma Torus

• Overview of the Io Torus and Neutral Clouds
• Measuring the torus 3-D structure
• Interpreting the structure morphology reveals
  energy flows
• The torus-aurora connection Cassini results

3
Torus at auroral workshopwhy should we care?

• Torus is major source of precipitating particles
• Aurora may affect atmosphere/ionosphere, thereby
  affecting torus
• Aurora reflect whats happening in magnetosphere
  torus shows directly
• Make your predictions how should auroral
  events be related to torus events?

4
The Jupiter-Io System The Big Picture

• The Jupiter-Io system is a complex interconnected
  system...
• although the phenomena shown here have been well
  studied individually, the cause- and-effect
  relationships between them have not been
  established.

5
The Io Torus Neutral Clouds

• Escaping neutrals form vast clouds
• Electron impact ionization charge exchange
  create a ring of plasma encircling Jupiter near
  Ios orbit
• Plasma re-impacts Io in a positive feedback loop

6
Composition of the torus

• 1973 Na discovered near Io (R.A. Brown)
• 1975 S discovered in torus (Kupo), K found in
  neutral clouds (Trafton)
• 1979 Voyager and groundbased telescopes identify
  O ions, SO2 on Io
• 1990s SO2, SO, S2 from groundbased telescopes
  HST (Lellouch, McGrath)
• 1999 Cl in torus (groundbased, FUSE)
• 2002 NaCl in Io atmosphere (Lellouch)

7
Spectroscopy provides composition and plasma
diagnostics

• .

8
Spectroscopy provides composition and plasma
diagnostics

• .

9
.

• The torus exhibits a complex 3-D structure, much
  of which is unexplained
• Warm torus, ribbon cold torus are persistent
  features
• Relative bright-nesses vary cause unknown

10
The plasma oscillates along field lines about the
centrifugal equator

• An electric field imposed across the system
  shifts the torus eastward...

11
Jupiters Rotation...

• Creates the confining dipole field
• Creates the centrifugal force which compresses
  the plasma to the equator
• Enforces corotation of the plasma
• Creates pickup energy (280-560eV/ion)
• Returns plasma to Io to sputter off more
• Allows remote sensing to determine the 3-D
  structure

12
Groundbased torus movie

• .

13
.

• Torus radial structure reveals interplay of
  transport energetics
• Torus longitudinal structure is the next
  challenge...

Groundbased S images (one rotation)
14
Deciphering Longitudinal Variations

• Longitudinal intensity variations (at optical
  wavelengths) must be local density variations ...

15
but the longitudinal brightness asymmetry seems
to be mainly an ion temperature effect

• Ions are cooler,
• less extended, and denser around ?III200º

16
Deciphering Longitudinal Variations

• Ion density is anticorrelated with ion
  temperature...

17
Deciphering Longitudinal Variations

• such that S flux tube content is actually
  fairly constant

18
Three Dimensions of Torus Structure

• Vertical (latitudinal) structure is a measure of
  ion temperature
• Radial structure is largely a map of transport
  processes
• Longitudinal structure is prominent but
  unexplained relationship to oval structure?
• Finding the cause of longitudinal structure is a
  key issue in the field

19
Energy Flows in the Io Torus

• Neutral Cloud Theory Other Energy Sources?
• Jupiters Rotation
• Energetic ions from
• Pickup Ions (400eV) outer magnetosphere
• Thermal ions (100eV)
• Thermal electrons (5eV)
• Excited states (1-20eV)
• EUV, UV, Visible photons (terrawatts!)

20
The Energy Crisis in the Io Plasma Torus

• Dynamic equilibrium models use energy transfer
  rates, ion chemistry, transport processes
• Studies show that the pickup ion energy can only
  maintain 3eV electrons too cool for S/Slt1
  (Shemansky 1988 several independent
  confirmations)
• Extra energy sources required we cannot explain
  the luminosity of the brightest magnetosphere
• Identifying and locating the extra energy source
  is a key question in the field

21
A new approach to torus models

• The long-standing questions on torus structure
  and energetics may have a single solution. Two
  advances are needed
• cubic centimeter models miss the fundamental
  link between ni and Ti
• ?Models of the whole flux tube are required
• Longitudinal variations are indicators of
  non-uniform energy flows
• ?diagnostic observations at short wavelengths are
  essential

22
Conclusions on Morphology Energetics

• Torus morphology may hold the key to finding the
  mystery energy source(s?) in the torus
• Evidence so far suggests that energy is supplied
  to electrons around ?III20º and to ions in the
  outer regions of the torus
• Future observations should target these regions
  to identify the heating mechanisms
• Definitive answers are held up by the lack of
  simultaneous multiwavelength data

23
Torus Visible vs. EUV Observations

• To date

24
Cassini Torus Observations
-6Rj 6Rj
60nm Wavelength?
120nm

• The Cassini UVIS instrument confirmed the
  prodigious EUV flux from the torus, detected
  longitudinal variations and recorded substantial
  temporal variations over the months of
  observation
• Preliminary analysis by Stewart, Pryor and Steffl

25
Cassini UVIS spectra

• .

26
Cassini/UVIS torus movie

• .

27
The torus-aurora connection

• Cassini UV Imaging Spectrometer (UVIS) measured
  torus EUV and auroral emissions
• Slit parked on Jupiter, wider than planet
  diameter Spatial resolution 1Rj
• Power summed over whole torus and whole planet

28
.

• .

29
.

• During stable pointing period
• Each auroral event coincides with torus event
• Some torus events not connected with observed
  auroral event

30
Torus-aurora connection a closer look

• .

31
Torus-aurora connection a closer look

• .

32
Torus-aurora connection conclusions

• Cassini detects multiple connected events -
  unexpected exciting result!
• Torus auroral events each last 1 rotations
• Torus events appear to lag auroral events by 1-2
  rotations,
• Spatial resolution too low to identify which type
  of aurora is affected, or what part of torus
• Sampling gaps severely limit usefulness of data

33
Taking jovian magnetosphere studies to the next
level

• Many dynamic processes observed briefly by HST,
  Voyager, Galileo and Cassini, but more remote
  sensing from Earth orbit is the next logical
  step.
• Each of the key phenomena is readily observed
  with UV telescopes in Earth orbit.
• Progress has been fundamentally hindered by
• Insufficient temporal coverage
• Non-simultaneity of observations
• Our understanding of the jovian system is no
  better than that of any variable Earth phenomena
  studied sporadically from one or two locations.

34
.

• .

35
.

• .

36
The plasma oscillates along field lines about the
centrifugal equator

• but this isnt the whole story...

37
.

• .