Reconnection at Ganymede:Work in Progress

Bill Paterson & Glyn CollinsonNASA GSFC

Neubauer, 1998

Ganymede

Most complex of the plasma interactions because of its magnetic moment.

Ganymede has both an oxygen atmosphere [Hall et al., 1998], and a hydrogen exosphere [Barth et al., 1997].

The equatorial region of the atmosphere is shielded from the external plasma sheet. Thus, atmosphere and ionosphere may be quite different in equatorial and polar regions.

Ganymede exhibits auroral emissions which are not longitudinally symmetric [Feldman et al., 2000].

Galileo - Hot electrons are found near the magnetopause, especially on the upstream side of the interaction. Complex streams of cold ions are found in the downstream region.

Feldman et al., 2000

Ganymede orbit

Corotation – Jupiter’s plasma rotates with the planet

CLOCKWORK MOONS (INTELLIGENT DESIGN?)

Io Volcanoes

Europa Oceans

Flow

BG

BJ

The Perfect Reconnection Machine

Galileo Near Encounters With Ganymede

Magnetic Fields and Dipole Superposition During 4 Encounters

Jovian Plasma Ganymede Plasma

IONS

ELECTRONS

G02 Downstream Encounter

Paty, Paterson and Winglee, JGR 2008

No Cold Ions?

No Illumination

Jovian Plasma

Ganymede PlasmaNo Cold Ions?

Atmosphere Not Illuminated

IONS

ELECTRONS

Jovian Plasma

Magnetopause Electrons

G08 Ganymede Flyby

Measured and Simulated MagnetosphereJia et al., JGR, 2010

NO RESPONSE BELOW ~ 1KEV

SENSORS E1, E2, E4, E5, E6, E7

NO RESPONSE AT ALLSENSOR E3

E2, E4, E6

WELL MATCHED SENSITIVITY ABOVE ~ 1 KEV

PROVIDE SYMMETRIC COVERAGE

Key QuestionsWhat are the origins of the BeamsWhat is the topology of the Field

Io – Heart of the Jovian Magnetosphere

A chunk of iron, covered with silicates, laced with volatiles.

5.9 RJ from Jupiter.

Stressed by tidal forces, Io spews SO2.

Ionization feeds the magnetosphere at a rate ~1 ton/s.

The plasma is entrained by Jupiter’s magnetic field and rotates with the planet.

It diffuses outward and fills the magnetosphere.

It sweeps past the moons, overtaking them from behind due to rotation of planet and magnetic field.

SO2 plume on Io. Io radius = 1815 km.

The Io Plasma Torus inside Jupiter’s magnetosphere

NASA is considering two possible future missions to Jupiter. Both are in accord with recent recommendations of the NRC-SSB Decadal Survey.

1) The Jupiter Polar Orbiter, a New Frontiers mission, would placed in a close orbit to determine high-order moments of the gravity field and of the magnetic field, and to observe plasmas near the auroral region and make remote observations of the atmosphere.

2) The Jupiter Icy Moons Orbiter, a flagship-class mission, would visit Callisto, Ganymede, and Europa with multiple goals, but foremost to search for evidence of oceans beneath the ice that might foster life.

Jupiter itself is inhospitable.

The moons have but thin atmospheres, and are immersed in an extreme radiation environment.

There is little hope for life in this system, unless it is hiding deep beneath the surface of a moon.

Europa is the primary candidate. Surface fissures suggest a layer of something soft or liquid beneath a crust of hard ice.

Magnetic field measurements from Galileo provide an important piece of evidence that seems to corroborate the liquid water scenario.