Voyager Results Revisited

By

Ed Sittler

NASA/GSFC

CAPS Team Meeting #28

Marseille, France

July 26-28, 2004

Voyager Encounter Geometry

Saturn Encounter Trajectories

Saturn’s Magnetospheric Plasma

Voyager 1 Plasma Electrons

Voyager 2 Plasma Electrons

Voyager 1 Electron Spectrum

Voyager 2 Electron Spectrum

Voyager Ion Measurements

Voyager 1 Ions at Ring Plane

Saturn’s Radiation Belts

Saturn’s Ring Current

Saturn’s Outer Magnetosphere

Saturn’s Outer Magnetosphere Energetic Ion and Electron Events

OH Cloud with Saturn’s Inner Magnetosphere (HST Observations)

Titan’s Nitrogen Torus

Mimas

Enceladus

Tethys

Dione

Rhea

Neutral N Cloud

Saturn

Particle Density(per cm3)

Titan

(Sputtered from Titan atmosphere at U/(E+U)2)

(Source Rate: 4.5 x 1025 /s)

Radius (Saturn Radii)

Height(Saturn

Radii)

0 5 10 15 20 25 30-12

-10

-8

-6

-4

-2

0

2

4

6

8

10

12

2.52.32.12.01.81.61.51.31.21.00.80.70.50.30.20.0

Frame 001 22 Mar 2004 Converted Excel DataFrame 001 22 Mar 2004 Converted Excel Data

Enrichment of Nitrogen Ion’s within Saturn’s Inner Magnetosphere?

• Solar wind source of keV protons and alphas• Titan Torus as source of keV Nitrogen Ions• Ions energized as they diffuse inward to form

radiation belts within inner magnetosphere.– Radial diffusion and Convection

• Charged particle sinks– Wave scattering by MHD waves– Satellite sweeping– Loss due to dust particles– Charge exchange losses with neutral clouds

800 keV Electrons Starting at L = 7 Static Solar Wind (V = 400 km/s)

Dawn

Dusk

Energy Spectrum of Ions and Electrons within Titan’s Neutral

Torus

Satellite Sweeping by Rhea

Energy Spectrum of Ions and Electrons at Dione’s L Shell

Summary• Voyager plasma data showed presence of light ion component (H+) and

heavy ion component (N+,O+,W+). Did not see evidence of H2+.

• Data consistent with heavy ions dominating near equator and light ions dominating at high latitudes.

• Electron observations show plasma sheet within inner magnetosphere inside L ~ 15 and time dependent region in outer magnetosphere.

• Electron data shows keV electrons confined near equatorial plane (T/Tll >> 1). Same is true for energetic electrons (LECP).

• Expect energetic heavy ions to be confined to equatorial plane, while protons more isotropic and at all latitudes (LECP).

• PLS observed hot keV ion component (N+/O+) confined to equatorial plane in Titan torus region (T/Tll >> 1). Hot keV ion component (N+, O+, W+) also observed at Dione’s L shell ring plane crossing.

• Ions typically sub-corotate in outer magnetosphere at ~ 50% of co-rotation. Ionospheric pederson height conductivity ~ 0.2 mho.

• Saturn’s magnetosphere falls in the category of a fast rotator where neutral clouds can dominate the plasma environment by number.