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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: Orbital Evolution of Impact Ejecta from Ganymede
Authors: Alvarellos, Jose Luis; Zahnle, Kevin J.;
Dobrovolskis, Anthony R.; Hamill, Patrick
Journal: Icarus, Volume 160, Issue 1, p. 108-123. (Icarus
Homepage)
Publication Date: 11/2002
Origin: ELSEVIER
Abstract Copyright: (c) 2002 Elsevier Science (USA)
Bibliographic Code: 2002Icar..160..108A
Abstract
We have numerically computed the orbital evolution of ~103
particles representing high-speed ejecta from Gilgamesh, the largest
impact basin on Ganymede. The integration includes the four Galilean
satellites, Jupiter (including J2 and J4), Saturn,
and the Sun. The integrations last 100,000 years. The particles are
ejected at a variety of speeds and directions, with the fastest
particles ejected at 1.4 times the escape speed
vesc≡&sqrt;2GMG/RG of Ganymede.
Ejecta with speeds v<0.96vesc follow suborbital
trajectories. At v~0.96vesc there is a transition
characterized by complex behavior suggestive of chaos. For
v>0.96vesc, most particles escape Ganymede and achieve
orbits about Jupiter. Eventually most (~71%) of the jovicentric
particles hit Ganymede, with 92% of these hitting within 1000 years. The
accretion rate scales as 1/t. Their impact sites are randomly
distributed, as expected for planetocentric debris. We estimate that
most of the resulting impact craters are a few kilometers across and
smaller. The rest of the escaping ejecta are partitioned as follows: ~3%
hit Io; ~10% hit Europa; ~13% hit Callisto; 2% reach heliocentric space;
and less than ~1% hit Jupiter. Only two particles survived the entire
105-year integration. Ejecta from large impact events do not
appear to be a plausible source of large craters on the Galilean
satellites; however, such ejecta may account for the majority of small
craters.
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Title: The Permanent and Inductive Magnetic Moments of
Ganymede
Authors: Kivelson, M. G.; Khurana, K. K.; Volwerk, M.
Journal: Icarus, Volume 157, Issue 2, p. 507-522. (Icarus
Homepage)
Publication Date: 06/2002
Origin: ELSEVIER
Abstract Copyright: (c) 2002 Elsevier Science (USA)
Bibliographic Code: 2002Icar..157..507K
Abstract
Data acquired by the Galileo magnetometer on five passes by Ganymede
have been used to characterize Ganymede's internal magnetic moments.
Three of the five passes were useful for determination of the internal
moments through quadrupole order. Models representing the internal field
as the sum of dipole and quadrupole terms or as the sum of a permanent
dipole field upon which is superimposed an induced magnetic dipole
driven by the time varying component of the externally imposed magnetic
field of Jupiter's magnetosphere give equally satisfactory fits to the
data. The permanent dipole moment has an equatorial field magnitude 719
nT. It is tilted by 176° from the spin axis with the pole in the
southern hemisphere rotated by 24° from the Jupiter-facing meridian
plane toward the trailing hemisphere. The data are consistent with an
inductive response of a good electrical conductor of radius
approximately 1 Ganymede radius. Although the data do not enable us to
establish the presence of an inductive response beyond doubt, we favor
the inductive response model because it gives a good fit to the data
using only four parameters to describe the internal sources of fields,
whereas the equally good dipole plus quadrupole fit requires eight
parameters. An inductive response is consistent with a buried conducting
shell, probably liquid water with dissolved electrolytes, somewhere in
the first few hundred km below Ganymede's surface. The depth at which
the ocean is buried beneath the surface is somewhat uncertain, but our
favored model suggests a depth of the order of 150 km. As both
temperature and pressure increase with depth and the melting temperature
of pure ice decreases to a minimum at ~170 km depth, it seems possible
that near this location, a layer of water would be sandwiched between
layers of ice.
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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 / fc
>= 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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Abstract
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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Abstract
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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