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Title:              Condensed O₂ on Europa and Callisto
Authors:            Spencer, John R.; Calvin, Wendy M.
Affiliation:        AA(Lowell Observatory, 1400 West Mars Hill Road, 
                    Flagstaff, AZ 86001; spencer@lowell.edu.), 
                    AB(Department of Geological Sciences, MS172, 
                    University of Nevada at Reno, Reno, NV 89557-0138.)
Journal:            The Astronomical Journal, Volume 124, Issue 6, pp. 
                    3400-3403. (AJ Homepage)
Publication Date:   12/2002
Origin:             UCP
AJ Keywords:        Planets and Satellites: General, Planets and 
                    Satellites: Individual: Callisto, Planets and 
                    Satellites: Individual: Europa, Techniques: 
                    Spectroscopic
Abstract Copyright: (c) 2002: The American Astronomical Society
Bibliographic Code: 2002AJ....124.3400S

Abstract

High signal-to-noise ratio spectra of Europa and Callisto's trailing side show a 0.3% deep 5771 Å absorption band due to condensed O₂ at the same wavelength as a stronger band previously identified on Ganymede. Excellent longitudinal coverage for Europa shows that unlike Ganymede, where the band is much stronger on the trailing side, Europa shows no significant longitudinal variation in the O₂ band strength.

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Title:              Hubble Space Telescope Space Telescope Imaging 
                    Spectrograph Search for an Atmosphere on Callisto: A 
                    Jovian Unipolar Inductor
Authors:            Strobel, Darrell F.; Saur, Joachim; Feldman, Paul D.;
                    McGrath, Melissa A.
Affiliation:        AA(Department of Earth and Planetary Sciences, Johns 
                    Hopkins University, 3400 North Charles Street, 
                    Baltimore, MD 21218; strobel@jhu.edu.; Department of 
                    Physics and Astronomy, Johns Hopkins University, 
                    3400 North Charles Street, Baltimore, MD 21218.), 
                    AB(Department of Earth and Planetary Sciences, Johns 
                    Hopkins University, 3400 North Charles Street, 
                    Baltimore, MD 21218; strobel@jhu.edu.), 
                    AC(Department of Physics and Astronomy, Johns 
                    Hopkins University, 3400 North Charles Street, 
                    Baltimore, MD 21218.), AD(Space Telescope Science 
                    Institute, 3700 San Martin Drive, Baltimore, MD 
                    21218.)
Journal:            The Astrophysical Journal, Volume 581, Issue 1, pp. 
                    L51-L54. (ApJ Homepage)
Publication Date:   12/2002
Origin:             UCP
ApJ Keywords:       Atomic Processes, Line: Identification, Planets and 
                    Satellites: Individual: Callisto, Planets and 
                    Satellites: Individual: Jupiter, Ultraviolet: Solar 
                    System
Abstract Copyright: (c) 2002: The American Astronomical Society
Bibliographic Code: 2002ApJ...581L..51S

Abstract

Hubble Space Telescope observations of Callisto with the Space Telescope Imaging Spectrograph were performed at both eastern and western elongations to search for the UV emissions diagnostic of the presence of O₂, CO₂, and/or CO atmospheres. We report upper limits of 5×10^-5 photons cm^-2 s^-1 or 15 R for a uniform disk the diameter of Callisto on emissions of O I λ1304, O I λ1356, C I λ1561, C II λ1335, and CO fourth positive bands. These upper limits yield upper bounds on O₂, CO₂, and CO atmospheres far in excess of the detected CO₂ atmosphere by R. W. Carlson. Our results are interpreted in terms of a strong electrodynamic interaction with the Jovian magnetosphere, which drives ~1.5×10⁵ A through Callisto's highly conducting (~10⁴ mho) ionosphere and generates a highly reduced ionospheric electric field, severely retarded ionospheric convection (~0.1 km s^-1), and a factor of ~1500 reduction in the net electron impact emission rate. Callisto's highly conducting ionosphere renders it the most tenable unipolar inductor of the Galilean satellites.

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Title:              Morphology and Size-Frequency Distribution of 
                    Kilometer-Scale Impact Craters on Callisto and 
                    Ganymede Derived from Galileo Data
Authors:            Ivanov, M. A.; Basilevsky, A. T.
Affiliation:        AA(Vernadsky Institute of Geochemistry and 
                    Analytical Chemistry, Russian Academy of Sciences, 
                    ul. Kosygina 19, Moscow, 117975 Russia), 
                    AB(Vernadsky Institute of Geochemistry and 
                    Analytical Chemistry, Russian Academy of Sciences, 
                    ul. Kosygina 19, Moscow, 117975 Russia)
Journal:            Solar System Research, v. 36, Issue 6, p. 447-457 
                    (2002).
Publication Date:   11/2002
Origin:             KLUWER
Abstract Copyright: (c) 2002 Kluwer Academic Publishers
Bibliographic Code: 2002SoSyR..36..447I

Abstract

Using high-resolution Galileo images, we counted the number of craters (larger than 1 km) on two of Jupiter's satellites-Callisto (outside and inside the Asgard impact basin) and Ganymede (in the dark cratered Galileo region)-and classified these craters morphologically. Based on the degree of preservation of crater rims, three morphological classes, A, B, and C (from the most preserved to the most degraded), have been identified. The A : B : C ratios, equal, respectively, to 1 : 3 : 5, 1 : 3 : 7, and 1 : 2.5 : 6.5 for fragments of the territory outside and inside the Asgard basin and within Galileo Regio, indicate that these crater populations reached a considerably high degree of maturity. The degradation of kilometer-scale craters on Callisto proceeds by the narrowing of their rims and their disintegration into chains of knobs, probably due to the sublimation of ice that composes the rim material. Comparing the density of craters of different classes in the regions inside and outside Asgard shows that class A craters on the territories examined were formed after the event that formed this impact basin. Kilometer-scale craters on Ganymede degrade through the expansion and smoothing of their rims and the dissection of them by radial furrows. This implies the involvement in the crater destruction of a downslope movement triggered by the seismic activity that accompanied the formation of tectonic grooves. It is possible that ice sublimation also took part in the destruction of craters on Ganymede, but its effect was less prominent than the effect of downslope movements.

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Title:              The Phase-Angle and Longitude Dependence of 
                    Polarization for Callisto
Authors:            Rosenbush, Vera K.
Affiliation:        AA(Main Astronomical Observatory, National Academy 
                    of Science of Ukraine, Golosiiv, Kiev-127, 03680, 
                    Ukraine)
Journal:            Icarus, Volume 159, Issue 1, p. 145-155. (Icarus 
                    Homepage)
Publication Date:   09/2002
Origin:             ELSEVIER
Abstract Copyright: (c) 2002 Elsevier Science (USA)
Bibliographic Code: 2002Icar..159..145R

Abstract

A detailed study of the linear polarization of Callisto in the UBVR filters has been carried out using the results of the author's observations and all the data available. The variations of polarization with phase angle, longitude, and wavelength have been investigated. Systematic shifts of different sets of observations have been detected, and all data have been consequently reduced to a unified system by introducing a correction to the degree of polarization. The separation of the phase-angle and orbital curves of polarization is of special interest, because the observed polarization depends on the solar phase angle as well as on the longitude of the central meridian. The amplitude of longitudinal variations of polarization depends also on the phase angle. A method of separating the solar and orbital curves of polarization has been proposed, and their analytical description is given. The major sources of uncertainty in the problem of extracting the phase-angle dependence of polarization and the longitude one from the Callisto observations have been analyzed. The results obtained show that the satellite surface is polarimetrically heterogeneous. There is a cluster of seven data points that have very small values of polarization for the leading hemisphere. In our opinion, the Valhalla ring system, which has a high-albedo palimpsest in the center (~600 km diameter), may cause this particularly low polarization.

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Title:              The Morphology of Small Craters and Knobs on the 
                    Surface of Jupiter's Satellite Callisto
Authors:            Basilevsky, A. T.; Kryuchkov, V. P.; Ivanov, M. A.;
                    Zabalueva, E. V.; Kotova, I. V.
Affiliation:        AA(Vernadsky Institute of Geochemistry and 
                    Analytical Chemistry, Russian Academy of Sciences, 
                    ul. Kosygina 19, Moscow, 119991 Russia), 
                    AB(Vernadsky Institute of Geochemistry and 
                    Analytical Chemistry, Russian Academy of Sciences, 
                    ul. Kosygina 19, Moscow, 119991 Russia), 
                    AC(Vernadsky Institute of Geochemistry and 
                    Analytical Chemistry, Russian Academy of Sciences, 
                    ul. Kosygina 19, Moscow, 119991 Russia), 
                    AD(Vernadsky Institute of Geochemistry and 
                    Analytical Chemistry, Russian Academy of Sciences, 
                    ul. Kosygina 19, Moscow, 119991 Russia), AE(Moscow 
                    State University, Vorob'evy gory, Moscow, 119899 
                    Russia)
Journal:            Solar System Research, v. 36, Issue 4, p. 322-333 
                    (2002).
Publication Date:   07/2002
Origin:             KLUWER
Abstract Copyright: (c) 2002 Kluwer Academic Publishers
Bibliographic Code: 2002SoSyR..36..322B

Abstract

Using the images of Callisto's surface acquired at 15-km resolution by the Galileo spacecraft during its C21 orbit, we studied the morphology of craters with diameters of less than 1-2 km and knobs. By analogy with other regions of Callisto that have been studied, these craters and knobs are thought to be formed by the sublimation degradation of the rims of larger craters that are also present in the region under study. The small craters closely resemble similar-sized lunar craters and, by analogy with the latter, are also divided into morphological classes. The depths of 42 craters of different morphological classes are estimated using shadow lengths visible in the craters. The fractions of the craters of different classes in the subpopulation are determined as a function of the crater diameter. Evidence has been obtained that larger craters degrade at a slower rate than smaller ones. The mean thickness of the mantle of dark material (~40 m) is estimated from the sizes of the craters ejecting the blocks of the basement ice material. The shape of the knob shadows shows that the knobs are heights of mostly conical form with slopes whose steepness is close to the angle of repose. Analysis has shown that the observed landforms and material units of the region under investigation have been formed during two successive stages of the geologic history of Callisto. Large craters, knobs, and the mantle of dark material were formed mostly at the end of the period of heavy meteorite bombardment. The leading processes of this period are impact cratering, the sublimation of Callisto's ``crustal'' ice with the accumulation of residual non-icy material, and downslope mass movement. The next stage, which continues until the present time, involved the formation of the subpopulation of small (<1-2 km) craters. This formation was accompanied by the impact reworking of the upper portion of the dark mantle. The key processes occurring at this stage are impact cratering and downslope mass movement. The mean intensity of resurfacing at this stage is much lower than at the preceding stage.

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Title:              CCD observations for the Hipparcos star 104297 
                    measured with respect to the Galilean satellite 
                    Callisto
Authors:            Peng, Q. Y.; Li, Z. L.
Journal:            Acta Astronomica Sinica, vol.43, no.1, p. 84-89
Publication Date:   02/2002
Origin:             ACASN
Keywords:           NATURAL SATELLITE, REFERENCE SYSTEM, ASTROMETRY
Bibliographic Code: 2002AcASn..43...84P

Abstract

CCD images for two Galilean satellites: Europa, Callisto and a bright star in Hipparcos Catalogue (No.104297) are obtained on 1 meter telescope at the Yunnan Observatory on the night of Nov.14, 1997. After the two satellites were measured for the scale and orientation of CCD frames, the apparent positions for the star were determined with respect to Callisto. The theoretical positions for Europa and Callisto were calculated from JPL DE405 and Sampson-Lieske theory (G5). The mean differences for the star in R.A. and Dec. between observed apparent positions and calculated ones from Hipparcos Catalogue are 0.''029+/-0.''012 and 0.''005+/-0.''011, respectively (at the mean epoch: 1997 Nov.14, 13h43m50s(UT). The result is in a good agreement with that from Casas et al. Furthermore, it also means a good agreement between the dynamical reference system from DE405 and the optical one from the Hipparcos Catalogue at the observational epoch. Our standard errors for a single observation are 0.''052 and 0.''047 in R.A. and Dec., respectively. These are as good as the most accurate observation for Galilean satellite.

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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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