Europa's Oxygen Exosphere and Its Magnetospheric Interaction

Ip, W. H.

doi:10.1006/icar.1996.0052

Cited by 62 publications

(51 citation statements)

References 11 publications

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“…Assuming a neutral atmospheric scale height of 150 km favored by the numerical simulation of Saur et al (1998) (and not very different from the preferred 175 km of the MHD model by Kabin et al 1999), this yields a maximum O 2 density of about 10 14 m −3 . With an average O 2 ionization time of 6.7 × 10 5 s (Ip 1996), we obtaiṅ ρ < 5 × 10 9 amu m −3 s −1 and a pick-up Pedersen conductivity <5 × 10 −2 mS/m, almost two orders of magnitude less than the required value derived above, even if a cloud of this conductivity extended up to the altitude of the spacecraft during encounter E4. At Callisto, ions may be injected into the surrounding medium by photoionization of the thin CO 2 atmosphere recently discovered with the Galileo near-infrared mapping spectrometer (Carlson 1999).…”

Section: Influence Of An Ionosphere/pick-up Cloudmentioning

confidence: 54%

Subsurface Oceans on Europa and Callisto: Constraints from Galileo Magnetometer Observations

Zimmer

Khurana

Kivelson

2000

Icarus

341

361

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Magnetic field perturbations measured during Galileo flybys of Europa and Callisto are consistent with dipole fields induced by the temporal variations of the ambient jovian magnetospheric field. These fields are close to those expected for perfectly conducting moons. We investigate the implications of these observations for the electrical structure of the moon's interiors using a simple shell model. It is found that Europa and Callisto must possess regions where the conductivity exceeds 0.06 and 0.02 S/m at a depth of less than 200 and 300 km below the surface, respectively. This conductivity is unattainable in ice or silicates, unless the ice layer is at least partially molten or very large temperature gradients can be maintained below the ice. An ionosphere or a cloud of pick-up ions are probably also insufficiently conductive. Global Earth-like oceans under the surface of both moons could account for the observations provided they are at least a few kilometers thick.

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Section: Influence Of An Ionosphere/pick-up Cloudmentioning

confidence: 54%

Subsurface Oceans on Europa and Callisto: Constraints from Galileo Magnetometer Observations

Zimmer

Khurana

Kivelson

2000

Icarus

341

361

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“…Initial modeling by Ip (1996) showed that the oxygen atmosphere could form from sputtering of water ice on the surface of Europa, as originally suggested by Johnson (1990), and that a tenuous extended atmosphere should also form in the process. Brown and Hill (1996) first detected this extended atmosphere through observations of sodium emission at distances of up to 20 Europa radii (1 R E = 1569 km) from the satellite surface.…”

Section: Introductionmentioning

confidence: 83%

Potassium in Europa's Atmosphere

Brown

2001

Icarus

105

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Trace element abundances in the sputtered extended atmospheres of the Galilean satellites reflect the surface abundances of these trace elements and can thus serve as signatures of surface processes on these satellites. We have measured sodium and potassium abundances in the extended atmospheres of Europa and Io, and derive sodium-to-potassium ratios of 25 ± 2 and 10 ± 3. The large difference between the values of Na/K in these atmospheres is difficult to explain if the dominant source of sodium for Europa's surface is implantation of Io sodium, as suggested earlier. The three remaining likely sources for trace elements on the surface of Europametals brought in from meteoritic impact, trace elements native to the surface ices, and salts deposited in liquid water resurfacing events-are all broadly consistent with the measured sodium-topotassium ratio at Europa. Observations of additional trace elements are required to further discriminate among these possible sources.

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“…Ip (1996) modeled the atmosphere using the sputtering rates estimated by Shi et a1. (1995) and a simple model for the plasma interaction.…”

Section: Introductionmentioning

confidence: 99%