Io Observations During The Galileo Europa Mission

Thanks in part to the amazing discoveries on Europa, NASA approved an extended mission for Galileo through January 2000 called the Galileo Europa mission (GEM). The extended mission tacked on 13 additional fly-bys to the end of the nominal mission. The first 8 orbits, 12 through 19, focused on Europa with continued distant observations of Io. The next 4 orbits, 20 through 23, were designed to reduce the perijove distance using repeated fly-bys of Callisto. This sequence included the closest...

Eruption styles

One of the primary advantages of repeated imaging of the anti-Jovian hemisphere during the Galileo mission was obtaining the potential to catch volcanoes in various parts of their eruption cycles, to identify both the types of eruptions occurring, and how those eruptions evolved. Through correlation of the SSI, NIMS, and PPR observations during each orbital fly-by with those of previous fly-bys, a set of three primary types of eruption styles were identified flow-dominated volcanism Figure 7.2....

Early Evolution Of Io

It is fitting, in this penultimate section, to briefly discuss one of the more interesting applications of the slow-inflow accretion disk model for the formation of Io and the Galilean satellites. Io's special place in the geophysical pantheon is owed to the tidal heating that follows from the satellite's resonant orbital configuration with Europa and Ganymede - the Laplace resonance. A subject of much research, the Laplace relation has long been thought to have been a by-product of the outward...

Gas

Plumes are also prominent at night and during eclipses, when they display an ethereal glow produced by the stimulation of the gases by charged particles, similar to terrestrial aurorae (Figure 8.4). The plumes can be seen at visible wavelengths as distinct knots or bubbles within an assortment of auroral glows that are present even when no plumes are active, including limb glows and equatorial emissions that periodically shift locations with the changing orientation of Jupiter's magnetic field....

Preface

This book is a community effort that grew largely out of the informal Io workshops that have happened since the early 1990s. In the first few years, the purpose of the workshops was to determine which Galileo observations would be key to further our understanding of this exotic moon. Since Galileo's main antenna did not open, the number of observations taken by the spacecraft was exceedingly small compared with other missions it was therefore imperative to decide which observations would be the...

Summary And Outstanding Questions

With the end of the Galileo mission, future studies of Io will rely upon the increasingly sophisticated observations possible from newly developed techniques at large ground-based observatories. Advanced speckle techniques (Marchis et al., 2000, 2001) and adaptive optics systems (Marchis et al., 2002 de Pater, 2004) are now producing infrared images of Io comparable with those obtained by the Galileo NIMS instrument during the early (non-Io-targeted) fly-bys. These techniques are also now being...

Thermal And Orbital Evolution

Io is unique in the Solar System in that its primary source of internal heat is not radioactive decay but tidal dissipation (Peale et al., 1979). The tidal heat source is not only capable of much greater heating rates, it evolves with the orbit of Io, since it depends on both the distance of Io from Jupiter (the semi-major axis) and the eccentricity of Io's orbit. Tidal heating is also very sensitive to the rheology of Io's interior. The heat source is therefore coupled to both the orbit and...

The Circumjovian Accretion Disk

Sunyaev Disk Model

As discussed above, Io and Galilean satellites most likely formed in a circum-Jovian accretion disk supplied by inflow from the solar nebula after Jupiter formed (Coradini et al. 1989 Canup and Ward, 2002 Alibert et al., 2005b cf. Mosqueira and Estrada, 2003a). Figure 4.3 illustrates several key aspects of this picture. Solids and gas are delivered to circum-planetary orbit with a range of specific angular momenta such that they achieve orbit in the satellite-forming region, out to rC (Canup...

Sulfur on lo

Wamsteker et al.'s (1973) suggestion for sulfur on Io was based on the similarity of the 350-500-nm absorption edge, prominent in Io's spectrum, to laboratory reflectance spectra measured by Sill (1973). Sulfur was also thought to be consistent with the Figure 9.2. Spectra of sulfur with pyrite at various concentrations. Figure 9.2. Spectra of sulfur with pyrite at various concentrations. I i i i I I i i i I I i i I i I i i I Pure reagent sulfur powder Pure reagent sulfur powder Figure 9.3....

Context Terrestrial Effusive Volcanism

Effusive volcanism, exemplified by lava flows and lava lakes, is ubiquitous on Earth, and evidence of effusive volcanism is found throughout the geologic record, dating as far back as the Archean (e.g., De Witt and Ashwal, 1997). As on other planets, the products and emplacement styles of lava flows on Earth are dependent upon the volume and flow rate of the lava, the eruption environment in which the flows are emplaced (subaerial, subaqueous, or subglacial), and the chemical composition...

H2o

H2S ( ), CI2SO2 ( ) S8, S02, S03, S2O rings Neutral Na, K, Cl, S, SO and ions of O, S, CI S02, SO, H2S, Cl, S ions Primarily S02 S8(P) Hkely S4 most likely No olivine Ubiquitous feature, enhanced in southern polar region, depleted in Pele plume deposit Ubiquitous frost Production rate extremely small compared with resurfacing rate Enhanced concentration in bright equatorial S02 snowfields Localized feature H2S unstable on Io Detailed analysis unpublished. See Figure 9.4. Powerful method for Io...