Io on the eve of the galileo mission
01 May 1996-Annual Review of Earth and Planetary Sciences (Annual Reviews 4139 El Camino Way, P.O. Box 10139, Palo Alto, CA 94303-0139, USA)-Vol. 24, Iss: 1, pp 125-190
TL;DR: Io, the innermost of Jupiter's large moons, is one of the most unusual objects in the Solar System as discussed by the authors, which produces a global heat flux 40 times the terrestrial value, producing intense volcanic activity and a global resurfacing rate averaging perhaps 1 cm yr−1.
Abstract: ▪ Abstract Io, innermost of Jupiter's large moons, is one of the most unusual objects in the Solar System. Tidal heating of the interior produces a global heat flux 40 times the terrestrial value, producing intense volcanic activity and a global resurfacing rate averaging perhaps 1 cm yr−1. The volcanoes may erupt mostly silicate lavas, but the uppermost surface is dominated by sulfur compounds including SO2 frost. The volcanoes and frost support a thin, patchy SO2 atmosphere with peak pressure near 10−8 bars. Self-sustaining bombardment of the surface and atmosphere by Io-derived plasma trapped in Jupiter's magnetosphere causes escape of material from Io (predominantly sulfur, oxygen, and sodium atoms, ions, and molecules) at a rate of about 103 kg s−1. The resulting Jupiter-encircling torus of ionized sulfur and oxygen dominates the Jovian magnetosphere and, together with an extended cloud of neutral sodium, is readily observable from Earth.
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TL;DR: This work presents Earthshine observations from Apache Point Observatory to emphasize that time variability is key to detecting weak surface biosignatures such as the vegetation red edge, and implies that future terrestrial-planet-characterizing space missions should obtain data that allow time-varying, sharp spectral features at unknown wavelengths to be identified.
Abstract: Earth's deciduous plants have a sharp order-of-magnitude increase in leaf reflectance between approximately 700 and 750 nm wavelength. This strong reflectance of Earth's vegetation suggests that surface biosignatures with sharp spectral features might be detectable in the spectrum of scattered light from a spatially unresolved extrasolar terrestrial planet. We assess the potential of Earth's step-function-like spectroscopic feature, referred to as the "red edge," as a tool for astrobiology. We review the basic characteristics and physical origin of the red edge and summarize its use in astronomy: early spectroscopic efforts to search for vegetation on Mars and recent reports of detection of the red edge in the spectrum of Earthshine (i.e., the spatially integrated scattered light spectrum of Earth). We present Earthshine observations from Apache Point Observatory (New Mexico) to emphasize that time variability is key to detecting weak surface biosignatures such as the vegetation red edge. We briefly discu...
334 citations
TL;DR: In this article, it was shown that the sub-Alfvenic, low-beta interaction can be described by an anisotropic conducting atmosphere joined to an Alfven wing as one extreme case and the Jovian ionosphere as the other extreme case.
Abstract: Recent observations by the Galileo spacecraft and Earth-based techniques have motivated us to reconsider the sub-Alfvenic interaction between the Galilean satellites of Jupiter and the magnetosphere. (1) We show that the atomic processes causing the interaction between the magnetoplasma and a neutral atmosphere can be described by generalized collision frequencies with contributions from elastic collisions, ion pickup, etc. Thus there is no fundamental difference in the effect of these processes on the plasma dynamics claimed in the recent literature. For a magnetic field configuration including possible internal fields, we show that the sub-Alfvenic, low-beta interaction can be described by an anisotropically conducting atmosphere joined to an Alfven wing as one extreme case and the Jovian ionosphere as the other extreme case. (2) The addition of a small magnetic field of internal origin does not modify the general Alfven wing model qualitatively but only quantitatively. All magnetic moments discussed in the literature for In are small in this sense. For an aligned internal dipole and ambient Jovian magnetic field the interaction will be enhanced by focusing of the electric field. (3) A qualitative change occurs by the additional occurrence of closed magnetic field lines for larger internal magnetic fields as in the case of Ganymede. Here the focusing is even enhanced. (4) The first discussion of nonstationary plasma flows at the satellites shows that electromagnetically induced magnetic fields may play an important role if the satellite interiors are highly conducting. From the point of view of the external excitation, induction effects may be strong for Callisto, In, Europa, and Ganymede in order of decreasing importance. The magnetic field observations at the first Callisto encounter can be explained by these effects.
249 citations
TL;DR: Io has been monitored during the nominal Galileo satellite tour from mid 1996 through late 1997 by the Solid State Imaging (SSI) experiment, which was able to observe many manifestations of active volcanism, including changes in the color and albedo of the surface, active airborne plumes, and glowing vents seen in eclipse as discussed by the authors.
197 citations
01 Jan 2014
TL;DR: The Comparative Climatology of Terrestrial Planets (CCP) as discussed by the authors is a collection of more than sixty leading experts in the field that sets forth the foundations for this emerging new science and brings the reader to the forefront of our current understanding of atmospheric formation and climate evolution.
Abstract: The early development of life, a fundamental question for humankind, requires the presence of a suitable planetary climate. Our understanding of how habitable planets come to be begins with the worlds closest to home. Venus, Earth, and Mars differ only modestly in their mass and distance from the Sun, yet their current climates could scarcely be more divergent. Only Earth has abundant liquid water, Venus has a runaway greenhouse, and evidence for life-supporting conditions on Mars points to a bygone era. In addition, an Earth-like hydrologic cycle has been revealed in a surprising place: Saturn's cloud-covered satellite Titan has liquid hydrocarbon rain, lakes, and river networks. Deducing the initial conditions for these diverse worlds and unravelling how and why they diverged to their current climates is a challenge at the forefront of planetary science. Through the contributions of more than sixty leading experts in the field, Comparative Climatology of Terrestrial Planets sets forth the foundations for this emerging new science and brings the reader to the forefront of our current understanding of atmospheric formation and climate evolution. Particular emphasis is given to surface-atmosphere interactions, evolving stellar flux, mantle processes, photochemistry, and interactions with the interplanetary environment, all of which influence the climatology of terrestrial planets. From this cornerstone, both current professionals and most especially new students are brought to the threshold, enabling the next generation of new advances in our own solar system and beyond.
172 citations
TL;DR: Spectra for a 5-micrometer hot spot on Jupiter are consistent with the absence of a significant water cloud above 8 bars and with a depletion of water compared to that predicted for solar composition, corroborating results from the Galileo probe.
Abstract: The Near Infrared Mapping Spectrometer performed spectral studies of Jupiter and the Galilean satellites during the June 1996 perijove pass of the Galileo spacecraft. Spectra for a 5-micrometer hot spot on Jupiter are consistent with the absence of a significant water cloud above 8 bars and with a depletion of water compared to that predicted for solar composition, corroborating results from the Galileo probe. Great Red Spot (GRS) spectral images show that parts of this feature extend upward to 240 millibars, although considerable altitude-dependent structure is found within it. A ring of dense clouds surrounds the GRS and is lower than it by 3 to 7 kilometers. Spectra of Callisto and Ganymede reveal a feature at 4.25 micrometers, attributed to the presence of hydrated minerals or possibly carbon dioxide on their surfaces. Spectra of Europa's high latitudes imply that fine-grained water frost overlies larger grains. Several active volcanic regions were found on Io, with temperatures of 420 to 620 kelvin and projected areas of 5 to 70 square kilometers.
170 citations
References
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Kitt Peak National Observatory1, University of Southern California2, Planetary Science Institute3, Jet Propulsion Laboratory4, University of Michigan5, Johns Hopkins University6, Centre national de la recherche scientifique7, United States Naval Research Laboratory8, York University9, Harvard University10
TL;DR: The observed resonance scattering of solar hydrogen Lyman α by the atmosphere of Jupiter and the solar occultation experiment suggest a hot thermosphere (≥ 1000 K) wvith a large atomic hydrogen abundance.
Abstract: The global hydrogen Lyman alpha, helium (584 angstroms), and molecular hydrogen band emissions from Saturn are qualitatively similar to those of Jupiter, but the Saturn observations emphasize that the H(2) band excitation mechanism is closely related to the solar flux. Auroras occur near 80 degrees latitude, suggesting Earth-like magnetotail activity, quite different from the dominant Io plasma torus mechanism at Jupiter. No ion emissions have been detected from the magnetosphere of Saturn, but the rings have a hydrogen atmosphere; atomic hydrogen is also present in a torus between 8 and 25 Saturn radii. Nitrogen emission excited by particles has been detected in the Titan dayglow and bright limb scans. Enhancement of the nitrogen emission is observed in the region of interaction between Titan's atmosphere and the corotating plasma in Saturn's plasmasphere. No particle-excited emission has been detected from the dark atmosphere of Titan. The absorption profile of the atmosphere determined by the solar occultation experiment, combined with constraints from the dayglow observations and temperature information, indicate that N(2) is the dominant species. A double layer structure has been detected above Titan's limb. One of the layers may be related to visible layers in the images of Titan.
755 citations
TL;DR: The dissipation of tidal energy in Jupiter's satellite Io is likely to have melted a major fraction of the mass, and consequences of a largely molten interior may be evident in pictures of Io's surface returned by Voyager I.
Abstract: The dissipation of tidal energy in Jupiter's satellite Io is likely to have melted a major fraction of the mass. Consequences of a largely molten interior may be evident in pictures of Io's surface returned by Voyager I.
532 citations
TL;DR: In this article, the inertial corotation lag is calculated as a function of radial distance in the magnetosphere, the solution being parameterized in terms of the Pedersen conductivity of the atmosphere and the rate at which plasma mass is produced and transported outward.
Abstract: Corotation of a planetary magnetosphere with the rotation frequency of the planet is maintained by the viscous torque exerted by ion-neutral collisions in the planetary atmosphere, this torque being transmitted to the magnetosphere by Birkeland currents. In a steady state this torque balances the inertial drag associated with the production and/or outward transport of magnetospheric plasma. The viscous torque in the atmosphere requires some departure from rigid corotation, i.e., some difference between the average rotation velocities of the ionospheric plasma and of the un-ionized atmosphere. In this paper we calculate the inertial corotation lag as a function of radial distance in the magnetosphere, the solution being parameterized in terms of the Pedersen conductivity of the atmosphere and the rate at which plasma mass is produced and transported outward in the magnetosphere. Although insignificant in the case of earth's magnetosphere, the calculated inertial corotation lag is significant in the case of Jupiter’s magnetosphere, where the rotation frequency may decrease by a factor of the order of 2 between the planetary surface and the magnetopause. One interesting consequence is that the active sector of Jupiter's magnetosphere (which is associated with a longitudinally restricted sector of enhanced ionospheric conductivity) should rotate faster, at a given distance, than adjacent longitude sectors and should therefore sweep up plasma from adjacent longitudes, thus amplifying the preexisting enhancement of plasma concentration in the active longitude sector.
504 citations
TL;DR: In this paper, the authors considered the physics of magnetospheric radio emissions, plasma waves in the Jovian magnetosphere, theories of radio emissions and plasma waves, and magnetosphere models.
Abstract: Jupiter's magnetic field and magnetosphere are considered along with the ionosphere, the low-energy plasma in the Jovian magnetosphere, the low-energy particle population, high-energy particles, and spectrophotometric studies of the Io torus. Other topics explored are related to the phenomenology of magnetospheric radio emissions, plasma waves in the Jovian magnetosphere, theories of radio emissions and plasma waves, and magnetospheric models. Attention is also given to aspects of plasma distribution and flow, microscopic plasma processes in the Jovian magnetosphere, symbols and acronyms, coordinate systems, and selected physical parameters of Jupiter and Io.
380 citations
348 citations