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Title:              High-Resolution Keck Adaptive Optics Imaging of 
                    Violent Volcanic Activity on Io
Authors:            Marchis, F.; de Pater, I.; Davies, A. G.; Roe, H. G.;
                    Fusco, T.; Mignant, D. Le; Descamps, P.; Macintosh, B. A.;
                    Prangé, R.
Affiliation:        AA(), AB(), AC(), AD(), AE(ONERA, DOTA-E, BP 72, 
                    Chatillon, F-92322 France), AF(), AG(Institut de 
                    Mécanique Céleste et de Calcul des Ephémerides, 
                    UMR-CNRS 8028, Observatoire de Paris 77, avenue 
                    Denfert-Rochereau, Paris, F-75014 France), AH(), 
                    AI(Institut d'Astrophysique Spatiale, bat. 121, 
                    Université Paris Sud, Orsay Cedex, 91405, France)
Journal:            Icarus, Volume 160, Issue 1, p. 124-131. (Icarus 
                    Homepage)
Publication Date:   11/2002
Origin:             ELSEVIER
Abstract Copyright: (c) 2002 Elsevier Science (USA)
Bibliographic Code: 2002Icar..160..124M

Abstract

Io, the innermost Galilean satellite of Jupiter, is a fascinating world. Data taken by Voyager and Galileo instruments have established that it is by far the most volcanic body in the Solar System and suggest that the nature of this volcanism could radically differ from volcanism on Earth. We report on near-IR observations taken in February 2001 from the Earth-based 10-m W. M. Keck II telescope using its adaptive optics system. After application of an appropriate deconvolution technique (MISTRAL), the resolution, ~100 km on Io's disk, compares well with the best Galileo/NIMS resolution for global imaging and allows us for the first time to investigate the very nature of individual eruptions. On 19 February, we detected two volcanoes, Amirani and Tvashtar, with temperatures differing from the Galileo observations. On 20 February, we noticed a slight brightening near the Surt volcano. Two days later it had turned into an extremely bright volcanic outburst. The hot spot temperatures (>1400 K) are consistent with a basaltic eruption and, being lower limits, do not exclude an ultramafic eruption. These outburst data have been fitted with a silicate-cooling model, which indicates that this is a highly vigorous eruption with a highly dynamic emplacement mechanism, akin to fire-fountaining. Its integrated thermal output was close to the total estimated output of Io, making this the largest ionian thermal outburst yet witnessed.

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Title:              Dynamics and Evolution of SO₂ Gas Condensation 
                    around Prometheus-like Volcanic Plumes on Io as Seen 
                    by the Near Infrared Mapping Spectrometer
Authors:            The Galileo NIMS Team; Douté, Sylvain; Lopes, Rosaly;
                    Kamp, Lucas W.; Carlson, Robert; Schmitt, Bernard
Affiliation:        AA(Laboratoire de Planétologie de Grenoble, Bât. D de 
                    Physique, B.P. 53, Grenoble Cedex 9, 38041, France), 
                    AB(), AC(), AD(), AE(Laboratoire de Planétologie de 
                    Grenoble, Bât. D de Physique, B.P. 53, Grenoble Cedex 
                    9, 38041 France)
Journal:            Icarus, Volume 158, Issue 2, p. 460-482. (Icarus 
                    Homepage)
Publication Date:   08/2002
Origin:             ELSEVIER
Abstract Copyright: (c) 2002 Elsevier Science (USA)
Bibliographic Code: 2002Icar..158..460T

Abstract

We analyze a series of spectral image cubes acquired by the Galileo Near Infrared Mapping Spectrometer (NIMS) over the Prometheus region of Io. We use SO₂ frost, a volatile compound ubiquitous on the surface, as a tracer to understand various thermodynamic and volcanic processes acting in this equatorial region. Here we develop a new method to derive, from the 12-wavelength NIMS products, the distribution and physical properties of solid SO₂. This method is based on the inversion of a bidirectional reflectance model on two observed spectral ratios sensitive to (1) the areal abundance of SO₂ and (2) its mean grain size. As a result, reliable and consistent maps of SO₂ abundance and granularity are obtained which can be correlated to distinguish four different physical units. The distribution of these SO₂ units indicates zones of condensation, metamorphism, and sublimation linked with the thermodynamic and volcanic processes of interest. Our maps depict equatorial plains undisturbed by any kind of vigorous volcanic activity over 35-40% of their surface. Elsewhere, 10-20% of the equatorial plains display abnormally low frost coverage which may imply the recent presence of positive thermal anomalies with temperatures in the range 110-200 K. Hot-spots such as Prometheus, Culann, Surya, and Tupan (to mention the most persistent) emit a great variety of gases, some of which will condense at Io's surface near their source regions. Associated fields of freshly condensed SO₂ are easily observed, and deposits of more refractory compounds with higher (e.g., S₈) or lower (e.g., NaCl) molecular weight must also be present (although their exact nature is unknown). Three different mechanisms of emission are proposed for the volatile compounds and supported by the distribution maps. These are (a) the interaction between flowing lava and preexisting volatile deposits on the surface, (b) direct degassing from the lava, an d (c) the eruption of a liquid aquifer from underground. The geometric elongation of the Prometheus SO₂ deposition ring being related to the development of a 95-km-long lava field is the best illustration of mechanism (a). Details of the progressive emplacement of the SO₂ ring by the associated plume are examined by the development of a semiempirical model of material deposition based on a ballistic transfer from the sources to the surface. This model shows that lava emission may have been occuring at Prometheus at a fairly constant rate since Voyager. Mechanism (b) may operate at the hot-spot Surya, which presents a noticeable field of fresh SO₂ frost but no extended lava flow. Finally, we have noted on the northwestern flank of the volcanic edifice Emakong the existence of an extremely deep ν₁+ν₃ SO₂ absorption which is indicative of abundant, pure, and perhaps icy SO₂ deposits. These could be the result of the eruption of an SO₂ liquid aquifer (mechanism (c)).

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Title:              Discovery of Soft X-Ray Emission from Io, Europa, 
                    and the Io Plasma Torus
Authors:            Elsner, Ronald F.; Gladstone, G. Randall;
                    Waite, J. Hunter; Crary, Frank J.; Howell, Robert R.;
                    Johnson, Robert E.; Ford, Peter G.; Metzger, Albert E.;
                    Hurley, Kevin C.; Feigelson, Eric D.; Garmire, Gordon P.;
                    Bhardwaj, Anil; Grodent, Denis C.; Majeed, Tariq;
                    Tennant, Allyn F.; Weisskopf, Martin C.
Affiliation:        AA(Space Science Department, NASA Marshall Space 
                    Flight Center, SD50, Huntsville, AL 35812.), 
                    AB(Department of Space Science, Southwest Research 
                    Institute, P.O. Drawer 28510, San Antonio, TX 
                    78228.), AC(Department of Atmospheric, Oceanic and 
                    Space Sciences, University of Michigan, Ann Arbor, 
                    MI 48109.), AD(Department of Atmospheric, Oceanic 
                    and Space Sciences, University of Michigan, Ann 
                    Arbor, MI 48109.), AE(Department of Physics and 
                    Astronomy, University of Wyoming, P.O. Box 3905, 
                    University Station, Laramie, WY 82071.), 
                    AF(Department of Engineering Physics, Thornton Hall, 
                    University of Virginia, Charlottesville, VA 22903.), 
                    AG(Center for Space Research, Massachusetts 
                    Institute of Technology, Cambridge, MA 02139.), 
                    AH(Jet Propulsion Laboratory, Pasadena, CA 91109.), 
                    AI(Space Science Laboratory, University of 
                    California, Berkeley, CA 94720.), AJ(Department of 
                    Astronomy and Astrophysics, 525 Davey Laboratory, 
                    Pennsylvania State University, State College, PA 
                    16802.), AK(Department of Astronomy and 
                    Astrophysics, 525 Davey Laboratory, Pennsylvania 
                    State University, State College, PA 16802.), 
                    AL(Space Physics Laboratory, Vikram Sarabhai Space 
                    Centre, Trivandrum, India.), AM(Department of 
                    Atmospheric, Oceanic and Space Sciences, University 
                    of Michigan, Ann Arbor, MI 48109.), AN(Department of 
                    Space Science, Southwest Research Institute, P.O. 
                    Drawer 28510, San Antonio, TX 78228.), AO(Space 
                    Science Department, NASA Marshall Space Flight 
                    Center, SD50, Huntsville, AL 35812.), AP(Space 
                    Science Department, NASA Marshall Space Flight 
                    Center, SD50, Huntsville, AL 35812.)
Journal:            The Astrophysical Journal, Volume 572, Issue 2, pp. 
                    1077-1082. (ApJ Homepage)
Publication Date:   06/2002
Origin:             UCP
ApJ Keywords:       Planets and Satellites: Individual: Io, Planets and 
                    Satellites: Individual: Europa, Planets and 
                    Satellites: Individual: Jupiter, X-Rays: General
Abstract Copyright: (c) 2002: The American Astronomical Society
Bibliographic Code: 2002ApJ...572.1077E

Abstract

We report the discovery of soft (0.25-2 keV) X-ray emission from the Galilean satellites Io and Europa, probably Ganymede, and from the Io Plasma Torus (IPT). Bombardment by energetic (greater than 10 keV) H, O, and S ions from the region of the IPT seems to be the likely source of the X-ray emission from the Galilean satellites. According to our estimates, fluorescent X-ray emission excited by solar X-rays, even during flares from the active Sun, charge-exchange processes, previously invoked to explain Jupiter's X-ray aurora and cometary X-ray emission, and ion stripping by dust grains fail to account for the observed emission. On the other hand, bremsstrahlung emission of soft X-rays from nonthermal electrons in the few hundred to few thousand eV range may account for a substantial fraction of the observed X-ray flux from the IPT.

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Title:              The Abundance of Atomic Sulfur in the Atmosphere of 
                    Io
Authors:            Feaga, Lori M.; McGrath, Melissa A.;
                    Feldman, Paul D.
Affiliation:        AA(Department of Physics and Astronomy, Johns 
                    Hopkins University, 3400 North Charles Street, 
                    Baltimore, MD 21218; lanier@pha.jhu.edu, 
                    pdf@pha.jhu.edu.), AB(Space Telescope Science 
                    Institute, 3700 San Martin Drive, Baltimore, MD 
                    21218; mcgrath@stsci.edu.), AC(Department of Physics 
                    and Astronomy, Johns Hopkins University, 3400 North 
                    Charles Street, Baltimore, MD 21218; 
                    lanier@pha.jhu.edu, pdf@pha.jhu.edu.)
Journal:            The Astrophysical Journal, Volume 570, Issue 1, pp. 
                    439-446. (ApJ Homepage)
Publication Date:   05/2002
Origin:             UCP
ApJ Keywords:       Atomic Data, Planets and Satellites: Individual: Io, 
                    Ultraviolet: Solar System
Abstract Copyright: (c) 2002: The American Astronomical Society
Bibliographic Code: 2002ApJ...570..439F

Abstract

Observations with the Space Telescope Imaging Spectrograph aboard the Hubble Space Telescope have been used to constrain the atomic sulfur column density in Io's atmosphere. The S I λ1479 dipole allowed and forbidden transition multiplets have been resolved for the first time at Io, enabling the study of both optically thick and thin transitions from a single atomic species. The allowed transitions contribute 62%+/-8% and the forbidden transitions 38%+/-8%, on average, to the total signal of the S I λ1479 multiplets. Using the optically thick and thin transitions of S I λ1479 observed near the limbs of Io, we derive a tangential atmospheric sulfur column abundance of 3.6×10¹²cm^-
2<N_S<1.7×10¹³ cm^-2, which is independent of electron temperature and density. A low-density SO₂ atmosphere, N_SO₂~(5-10)×10¹⁵ cm^-2, consistent with that inferred from other recent observations, is most consistent with these bounds.

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Title:              Search for decametric occultations of Io flux tube 
                    by Ganymede
Authors:            Arkiypov, A. V.
Affiliation:        Institute of Radio Astronomy, Nat. Acad. Sc. of 
                    Ukraine, Chervonopraporna 4, 61002 Kharkiv, Ukraine
Journal:            Astronomy and Astrophysics, v.387, p.L25-L28 (2002) 
                    (A&A Homepage)
Publication Date:   05/2002
Origin:             A&A
A&A Keywords:       planets and satellites: individual, occultations, 
                    magnetic fields, radiation mechanisms: non-thermal
Abstract Copyright: (c) 2002: Astronomy & Astrophysics
Bibliographic Code: 2002A&A...387L..25A

Abstract

The satellite Ganymede sometimes occults the sources of the Jovian decameter radiation (DAM) associated with Io magnetic field line. The basic parameters of Ganymede occultations are calculated for 1990-2010. One of these events is found to coincide with a Io-A radio storm, which has been recorded in Nancay Observatory on 17 April 1994. In spite of the difficulty to identify the satellite shadow on sporadic DAM, the ratio of frequency emitted to calculated gyromagnetic frequency of electrons in the source is tentatively estimated as f / f_c >= 1.11 +/- 0.02. Formally, this limit contradicts the present generation theories where f_{c} in the DAM source is much closer to 1. Hence, improvements to the magnetic model (VIP4) or of the distortion of the Io flux tube are needed. Two possible shadows of the satellite are tentatively identified on the DAM frequency-time spectrogram. Multiple occultations are indeed possible in the Alfven wave model of Io-DAM interaction, and the lead angle of the emitting field line is not well known. That is why the tentative location of the radio source is made for both variants.

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Title:              NOTE: Detection of the Forbidden SO 
                    a¹Δ-->X³Σ^- Rovibronic Transition on Io at 1.7 μm
Authors:            de Pater, Imke; Roe, Henry; Graham, James R.;
                    Strobel, Darrell F.; Bernath, Peter
Affiliation:        AA(Department of Astronomy and Department of Earth 
                    and Planetary Sciences, University of California, 
                    Berkeley, California. imke@floris.berkeley.edu), 
                    AB(Department of Astronomy, University of 
                    California, Berkeley, California), AC(Department of 
                    Astronomy, University of California, Berkeley, 
                    California), AD(Department of Earth and Planetary 
                    Sciences and Department of Physics and Astronomy, 
                    Johns Hopkins University, Baltimore, Maryland), 
                    AE(Department of Chemistry, University of Waterloo, 
                    Waterloo, Ontario, Canada)
Journal:            Icarus, Volume 156, Issue 1, pp. 296-301 (2002). 
                    (Icarus Homepage)
Publication Date:   03/2002
Origin:             AP
Abstract Copyright: (c) 2002: Academic Press
Bibliographic Code: 2002Icar..156..296D

Abstract

We report the discovery of the forbidden electronic a¹Δ-->X³Σ^- transition of the SO radical on Io at 1.7 μm with the W. M. Keck II telescope on 24 September 1999 (UT), while the satellite was eclipsed by Jupiter. The shape of the SO emission band suggests a rotational temperature of ~1000 K; i.e., the gas is extremely hot. We interpret the observed emission rate of ~2×10²⁷ photons s^-1 to be caused by SO molecules in the excited a¹Δ state being directly ejected from the vent at a thermodynamic quenching temperature of ~1500 K, assuming a SO/SO₂ abundance ratio of ~0.1 and a total venting rate of ~10³¹ molecules s^-1 (Strobel and Wolven 2001, Astrophys. Space Sci. 277, 1-17). The shape of our complete (1.6-2.5 μm) spectrum suggests that the volcano Loki contains a small (~2 km²) hot spot at 960+/-12 K, as well as a larger (~50 km²) area at 640+/-5 K. .

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Title:              Alkali and Chlorine Photochemistry in a Volcanically 
                    Driven Atmosphere on Io
Authors:            Moses, Julianne I.; Zolotov, Mikhail Yu.;
                    Fegley, Bruce
Affiliation:        AA(Lunar and Planetary Institute, Houston, Texas. 
                    moses@lpi.usra.edu), AB(Department of Earth and 
                    Planetary Sciences, Washington University CB1169, 
                    St. Louis, Missouri), AC(Department of Earth and 
                    Planetary Sciences, Planetary Chemistry Laboratory, 
                    McDonnell Center for the Space Sciences, Washington 
                    University CB1169, St. Louis, Missouri)
Journal:            Icarus, Volume 156, Issue 1, pp. 107-135 (2002). 
                    (Icarus Homepage)
Publication Date:   03/2002
Origin:             AP
Abstract Copyright: (c) 2002: Academic Press
Bibliographic Code: 2002Icar..156..107M

Abstract

Observations of the Io plasma torus and neutral clouds indicate that the extended ionian atmosphere must contain sodium, potassium, and chlorine in atomic and/or molecular form. Models that consider sublimation of pure sulfur dioxide frost as the sole mechanism for generating an atmosphere on Io cannot explain the presence of alkali and halogen species in the atmosphere-active volcanoes or surface sputtering must also be considered, or the alkali and halide species must be discharged along with the SO₂ as the frost sublimates. To determine how volcanic outgassing can affect the chemistry of Io's atmosphere, we have developed a one-dimensional photochemical model in which active volcanoes release a rich suite of S-, O-, Na-, K-, and Cl-bearing vapor and in which photolysis, chemical reactions, condensation, and vertical eddy and molecular diffusion affect the subsequent evolution of the volcanic gases. Observations of Pele plume constituents, along with thermochemical equilibrium calculations of the composition of volcanic gases exsolved from high-temperature silicate magmas on Io, are used to constrain the composition of the volcanic vapor. We find that NaCl, Na, Cl, KCl, and K will be the dominant alkali and chlorine gases in atmospheres generated from Pele-like plume eruptions on Io. Although the relative abundances of these species will depend on uncertain model parameters and initial conditions, these five species remain dominant for a wide variety of realistic conditions. Other sodium and chlorine molecules such as NaS, NaO, Na₂, NaS₂, NaO₂, NaOS, NaSO₂, SCl, ClO, Cl₂, S₂Cl, and SO₂Cl₂ will be only minor constituents in the ionian atmosphere because of their low volcanic emission rates and their efficient photochemical destruction mechanisms. Our modeling has implications for the general appearance, properties, and variability of the neutral sodium clouds and jets observed near Io. The neutral NaCl molecules present at high altitudes in atmosph eres generated by active volcanoes might provide the NaX⁺ ion needed to help explain the morphology of the high-velocity sodium ``stream'' feature observed near Io. .

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Title:              Photochemistry of a Volcanically Driven Atmosphere 
                    on Io: Sulfur and Oxygen Species from a Pele-Type 
                    Eruption
Authors:            Moses, Julianne I.; Zolotov, Mikhail Yu.;
                    Fegley, Bruce
Affiliation:        AA(Lunar and Planetary Institute, Houston, Texas. 
                    moses@lpi.usra.edu), AB(Department of Earth and 
                    Planetary Sciences, Washington University CB1169, 
                    St. Louis, Missouri), AC(Department of Earth and 
                    Planetary Sciences, Planetary Chemistry Laboratory, 
                    McDonnell Center for the Space Sciences, Washington 
                    University CB1169, St. Louis, Missouri)
Journal:            Icarus, Volume 156, Issue 1, pp. 76-106 (2002). 
                    (Icarus Homepage)
Publication Date:   03/2002
Origin:             AP
Abstract Copyright: (c) 2002: Academic Press
Bibliographic Code: 2002Icar..156...76M

Abstract

To determine how active volcanism might affect the standard picture of sulfur dioxide photochemistry on Io, we have developed a one-dimensional atmospheric model in which a variety of sulfur-, oxygen-, sodium-, potassium-, and chlorine-bearing volatiles are volcanically outgassed at Io's surface and then evolve due to photolysis, chemical kinetics, and diffusion. Thermochemical equilibrium calculations in combination with recent observations of gases in the Pele plume are used to help constrain the composition and physical properties of the exsolved volcanic vapors. Both thermochemical equilibrium calculations (Zolotov and Fegley 1999, Icarus 141, 40-52) and the Pele plume observations of Spencer et al. (2000; Science 288, 1208-1210) suggest that S₂ may be a common gas emitted in volcanic eruptions on Io. If so, our photochemical models indicate that the composition of Io's atmosphere could differ significantly from the case of an atmosphere in equilibrium with SO₂ frost. The major differences as they relate to oxygen and sulfur species are an increased abundance of S, S₂, S₃, S₄, SO, and S₂O and a decreased abundance of O and O₂ in the Pele-type volcanic models as compared with frost sublimation models. The high observed SO/SO₂ ratio on Io might reflect the importance of a contribution from volcanic SO rather than indicate low eddy diffusion coefficients in Io's atmosphere or low SO ``sticking'' probabilities at Io's surface; in that case, the SO/SO₂ ratio could be temporally and/or spatially variable as volcanic activity fluctuates. Many of the interesting volcanic species (e.g., S₂, S₃, S₄, and S₂O) are short lived and will be rapidly destroyed once the volcanic plumes shut off; condensation of these species near the source vent is also likely. The diffuse red deposits associated with active volcanic centers on Io may be caused by S₄ radicals that are created and temporarily preserved when sulfur vapor (predominantly S₂) condenses around the volcanic vent. Condensation of SO across the surface and, in particular, in the polar regions might also affect the surface spectral properties. We predict that the S/O ratio in the torus and neutral clouds might be correlated with volcanic activity-during periods when volcanic outgassing of S₂ (or other molecular sulfur vapors) is prevalent, we would expect the escape of sulfur to be enhanced relative to that of oxygen, and the S/O ratio in the torus and neutral clouds could be correspondingly increased. .

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Title:              Ultraviolet emissions from the magnetic footprints 
                    of Io, Ganymede and Europa on Jupiter
Authors:            Clarke, J. T.; Ajello, J.; Ballester, G.; Ben Jaffel, L.;
                    Connerney, J.; Gérard, J.-C.; Gladstone, G. R.;
                    Grodent, D.; Pryor, W.; Trauger, J.; Waite, J. H.
Affiliation:        AA(), AB(), AC(), AD(), AE(), AF(), AG(), AH(), 
                    AI(), AJ(), AK()
Journal:            Nature, Volume 415, Issue 6875, pp. 997-1000 (2002).
Publication Date:   02/2002
Origin:             NATURE
Abstract Copyright: (c) 2002: Nature
Bibliographic Code: 2002Natur.415..997C

Abstract

Io leaves a magnetic footprint on Jupiter's upper atmosphere that appears as a spot of ultraviolet emission that remains fixed underneath Io as Jupiter rotates. The specific physical mechanisms responsible for generating those emissions are not well understood, but in general the spot seems to arise because of an electromagnetic interaction between Jupiter's magnetic field and the plasma surrounding Io, driving currents of around 1 million amperes down through Jupiter's ionosphere. The other galilean satellites may also leave footprints, and the presence or absence of such footprints should illuminate the underlying physical mechanism by revealing the strengths of the currents linking the satellites to Jupiter. Here we report persistent, faint, far-ultraviolet emission from the jovian footprints of Ganymede and Europa. We also show that Io's magnetic footprint extends well beyond the immediate vicinity of Io's flux-tube interaction with Jupiter, and much farther than predicted theoretically; the emission persists for several hours downstream. We infer from these data that Ganymede and Europa have persistent interactions with Jupiter's magnetic field despite their thin atmospheres.

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Title:              A nebula of gases from Io surrounding Jupiter
Authors:            Krimigis, Stamatios M.; Mitchell, Donald G.;
                    Hamilton, Douglas C.; Dandouras, Jannis;
                    Armstrong, Thomas P.; Bolton, Scott J.; Cheng, Andrew F.;
                    Gloeckler, George; Hsieh, K. C.; Keath, Edwin P.;
                    Krupp, Norbert; Lagg, Andreas; Lanzerotti, Louis J.;
                    Livi, Stefano; Mauk, Barry H.; McEntire, Richard W.;
                    Roelof, Edmond C.; Wilken, Berend;
                    Williams, Donald J.
Affiliation:        AA(), AB(), AC(), AD(), AE(), AF(), AG(), AH(), 
                    AI(), AJ(), AK(), AL(), AM(), AN(), AO(), AP(), 
                    AQ(), AR(), AS()
Journal:            Nature, Volume 415, Issue 6875, pp. 994-996 (2002).
Publication Date:   02/2002
Origin:             NATURE
Abstract Copyright: (c) 2002: Nature
Bibliographic Code: 2002Natur.415..994K

Abstract

Several planetary missions have reported the presence of substantial numbers of energetic ions and electrons surrounding Jupiter; relativistic electrons are observable up to several astronomical units (AU) from the planet. A population of energetic (>30keV) neutral particles also has been reported, but the instrumentation was not able to determine the mass or charge state of the particles, which were subsequently labelled energetic neutral atoms. Although images showing the presence of the trace element sodium were obtained, the source and identity of the neutral atoms-and their overall significance relative to the loss of charged particles from Jupiter's magnetosphere-were unknown. Here we report the discovery by the Cassini spacecraft of a fast (>10³kms^-1) and hot magnetospheric neutral wind extending more than 0.5AU from Jupiter, and the presence of energetic neutral atoms (both hot and cold) that have been accelerated by the electric field in the solar wind. We suggest that these atoms originate in volcanic gases from Io, undergo significant evolution through various electromagnetic interactions, escape Jupiter's magnetosphere and then populate the environment around the planet. Thus a `nebula' is created that extends outwards over hundreds of jovian radii.

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Title:              Observations of planetary satellites with ISO
Authors:            Coustenis, A.; Encrenaz, Th.; Lellouch, E.; Salama, A.;
                    Müller, Th.; Burgdorf, M. J.; Schmitt, B.;
                    Feuchtgruber, H.; Schulz, B.; Ott, S.; de Graauw, Th.;
                    Griffin, M. J.; Kessler, M. F.
Affiliation:        AA(DESPA, Paris-Meudon Observatory, 92195 Meudon 
                    Cedex, France), AB(DESPA, Paris-Meudon Observatory, 
                    92195 Meudon Cedex, France), AC(DESPA, Paris-Meudon 
                    Observatory, 92195 Meudon Cedex, France), AD(DESPA, 
                    Paris-Meudon Observatory, 92195 Meudon Cedex, 
                    France), AE(DESPA, Paris-Meudon Observatory, 92195 
                    Meudon Cedex, France), AF(DESPA, Paris-Meudon 
                    Observatory, 92195 Meudon Cedex, France), AG(DESPA, 
                    Paris-Meudon Observatory, 92195 Meudon Cedex, 
                    France), AH(DESPA, Paris-Meudon Observatory, 92195 
                    Meudon Cedex, France), AI(DESPA, Paris-Meudon 
                    Observatory, 92195 Meudon Cedex, France), AJ(DESPA, 
                    Paris-Meudon Observatory, 92195 Meudon Cedex, 
                    France), AK(DESPA, Paris-Meudon Observatory, 92195 
                    Meudon Cedex, France), AL(DESPA, Paris-Meudon 
                    Observatory, 92195 Meudon Cedex, France), AM(DESPA, 
                    Paris-Meudon Observatory, 92195 Meudon Cedex, 
                    France)
Journal:            Advances in Space Research, Volume 30, Issue 9, p. 
                    1971-1977. (AdSpR Homepage)
Publication Date:   00/2002
Origin:             ELSEVIER
Abstract Copyright: (c) 2002 Elsevier Science B.V. All rights reserved.
Bibliographic Code: 2002AdSpR..30.1971C

Abstract

Several observational programmes were conducted with ISO (Kessler et al., 1996) aiming at the investigation of the near- and far- infrared spectrum of the satellites of the giant planets. Thus, Jupiter's satellites Callisto, Io and Ganymede were explored mainly with the spectrometers, while the spectrum of Titan, Saturn's largest satellite, was investigated thoroughly by all the instruments. The analysis of the data has provided original and precious information on the satellites' surfaces and Titan's atmosphere in particular.

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