The Experts below are selected from a list of 102 Experts worldwide ranked by ideXlab platform
Anthony Mallama - One of the best experts on this subject based on the ideXlab platform.
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assessment of the resonant perturbation errors in Galilean Satellite ephemerides using precisely measured eclipse times
Icarus, 2010Co-Authors: Anthony Mallama, Christopher Stockdale, Bruce A Krobusek, Peter F NelsonAbstract:Astrometric Satellite positions are derived from timings of their eclipses in the shadow of Jupiter. The 548 data points span 20 years and are accurate to about 0.006 arcsec for Io and Europa and about 0.015 arcsec or better for Ganymede and Callisto. The precision of the data set and its nearly continuous distribution in time allows measurement of regular oscillations with an accuracy of 0.001 arcsec. This level of sensitivity permits detailed evaluation of modern ephemerides and reveals anomalies at the 1.3 year period of the resonant perturbations between Io, Europa and Ganymede. The E5 ephemeris shows large errors at that period for all three Satellites as well as other significant anomalies. The L1 ephemeris fits the observations much more closely than E5 but discrepancies for the resonant Satellites are still apparent and the measured positions of Io are drifting away from the predictions. The JUP230 ephemeris fits the observations more accurately than L1 although there is still a measurable discordance between the predictions and observations for Europa at the resonance period.
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precise timings of Galilean Satellite eclipses and assessment of the e 3 ephemeris
Icarus, 1994Co-Authors: Anthony Mallama, Douglas S Caprette, Peter Nelson, James L Park, Donald F Collins, Michal VojtiseklomAbstract:Abstract Astrometric positions for the Galilean Satellites are derived from high-precision timings of their jovian eclipses observed with CCD cameras between 1990 to 1993, and the positions are compared to Lieske's E-3 ephemeris. The root-mean-square (rms) ephemeris residuals for Io and Callisto were only 80 and 89 km, respectively; the rms residuals for Europa and Ganymede were larger, 185 km and 142 km, with maximum residuals of 340 km and 244 km, respectively.
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photometric models for Galilean Satellite astronomy
Journal of Geophysical Research, 1993Co-Authors: Anthony MallamaAbstract:Models for the Galilean Satellites have been used to determine the distribution of brightness on their surfaces. The results indicate that the distance between a Satellite's photocenter and its center-of-figure can reach 209 km for Io, 221 km for Europa, 303 km for Ganymede, and 255 km for Callisto. Astrometry of the Satellites can achieve much greater precision than this, so a correction for the photocentric offset should be applied. This paper presents tables of photocentric offsets for the Galilean Satellites as functions of orbital longitude and solar phase angle. The estimated accuracy of these corrections is 32 km for Io, 45 km for Europa, 49 km for Ganymede, and 40 km for Callisto, but the latter two may be optimistic. The Satellite ephemerides derived from astrometry are essential for interpreting observations of variable phenomena on Io, such as volcanic activity inferred from IR observations taken during occultations of the Satellite. Accurate ephemerides are also critical to spacecraft navigation.
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light curve model for the Galilean Satellites during jovian eclipse
Icarus, 1991Co-Authors: Anthony MallamaAbstract:Abstract A model for the light curve of a Galilean Satellite eclipsed by Jupiter's shadow is developed. This model allows center-of-figure information on the Satellite's position to be derived from photometric eclipse data. The major features of the model are the Satellite-Jupiter-Sun-Earth geometry, limb-darkening and albedo features of the Satellite, and refraction of light in the Jovian atmosphere. Sample output from the model reveals that tens of seconds may elapse between the time of half-phase in the eclipse and that of half-luminosity of the Satellite. The model fits eclipse photometry to less than 1% rms luminosity. Furthermore, much of the scatter in O − C (observed minus calculated) residuals, for eclipse times compared to modern ephemeris predictions, is reduced when the model is used to correct the times of half-luminosity to half-phase.
Shigeru Ida - One of the best experts on this subject based on the ideXlab platform.
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n body simulations of Satellite formation around giant planets origin of orbital configuration of the Galilean moons
The Astrophysical Journal, 2012Co-Authors: Masahiro Ogihara, Shigeru IdaAbstract:As the number of discovered extrasolar planets has been increasing, diversity of planetary systems requires studies of new formation scenarios. It is important to study Satellite formation in circumplanetary disks, which is often viewed as analogous to formation of rocky planets in protoplanetary disks. We investigated Satellite formation from Satellitesimals around giant planets through N-body simulations that include gravitational interactions with a circumplanetary gas disk. Our main aim is to reproduce the observable properties of the Galilean Satellites around Jupiter through numerical simulations, as previous N-body simulations have not explained the origin of the resonant configuration. We performed accretion simulations based on the work of Sasaki et al., in which an inner cavity is added to the model of Canup & Ward. We found that several Satellites are formed and captured in mutual mean motion resonances outside the disk inner edge and are stable after rapid disk gas dissipation, which explains the characteristics of the Galilean Satellites. In addition, owing to the existence of the disk edge, a radial compositional gradient of the Galilean Satellites can also be reproduced. An additional objective of this study is to discuss orbital properties of formed Satellites for a wide range of conditions by considering large uncertainties in model parameters. Through numerical experiments and semianalytical arguments, we determined that if the inner edge of a disk is introduced, a Galilean-like configuration in which several Satellites are captured into a 2:1 resonance outside the disk inner cavity is almost universal. In fact, such a configuration is produced even for a massive disk 104 g cm–2 and rapid type I migration. This result implies the inevitability of a Galilean Satellite formation in addition to providing theoretical predictions for extrasolar Satellites. That is, we can predict a substantial number of exomoon systems in the 2:1 mean motion resonance close to their host planets awaiting discovery.
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n body simulations of Satellite formation around giant planets origin of orbital configuration of the Galilean moons
arXiv: Earth and Planetary Astrophysics, 2012Co-Authors: Masahiro Ogihara, Shigeru IdaAbstract:As the number of discovered extrasolar planets has been increasing, diversity of planetary systems requires studies of new formation scenarios. It is important to study Satellite formation in circumplanetary disks, which is often viewed as analogous to formation of rocky planets in protoplanetary disks. We investigated Satellite formation from Satellitesimals around giant planets through N-body simulations that include gravitational interactions with a circumplanetary gas disk. Our main aim is to reproduce the observable properties of the Galilean Satellites around Jupiter through numerical simulations, as previous N-body simulations have not explained the origin of the resonant configuration. We performed accretion simulations based on the work of Sasaki et al. (2010), in which an inner cavity is added to the model of Canup & Ward (2002, 2006). We found that several Satellites are formed and captured in mutual mean motion resonances outside the disk inner edge and are stable after rapid disk gas dissipation, which explains the characteristics of the Galilean Satellites. In addition, owing to the existence of the disk edge, a radial compositional gradient of the Galilean Satellites can also be reproduced. An additional objective of this study is to discuss orbital properties of formed Satellites for a wide range of conditions by considering large uncertainties in model parameters. Through numerical experiments and semianalytical arguments, we determined that if the inner edge of a disk is introduced, a Galilean-like configuration in which several Satellites are captured into a 2:1 resonance outside the disk inner cavity is almost universal. In fact, such a configuration is produced even for a massive disk and rapid type I migration. This result implies the inevitability of a Galilean Satellite formation in addition to providing theoretical predictions for extrasolar Satellites.
W B Moore - One of the best experts on this subject based on the ideXlab platform.
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an adjunct Galilean Satellite orbiter using a small radioisotope power source
Space Technology and Applications International Forum (STAIF-2005), 2005Co-Authors: Robert D. Abelson, James E Randolph, Leon Alkalai, D Collins, W B MooreAbstract:This is a conceptual mission study intended to demonstrate the range of possible missions and applications that could be enabled were a new generation of Small Radioisotope Power Systems to be developed by NASA and DOE. While such systems are currently being considered by NASA and DOE, they do not currently exist. This study is one of several small RPS-enabled mission concepts that were studied and presented in the NASA/JPL document "Enabling Exploration with Small Radioisotope Power Systems" available at: http://solarsystem.nasa.gov/multimedia/download-detail.cfm?DL_ID=82
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shape mean radius gravity field and interior structure of callisto
Icarus, 2001Co-Authors: John D Anderson, G Schubert, R A Jacobson, W B Moore, T P Mcelrath, P C ThomasAbstract:Radio Doppler data generated by the Deep Space Network (DSN) from five encounters of the Galileo spacecraft with Callisto, Jupiter's outermost Galilean Satellite, have been used to determine the mass (GM) and unnormalized quadrupole gravity coefficients in Callisto's external gravitational field. The results are GM=(7179.292±0.009) km3 s−2, J2=(32.7±0.8)×10−6, C22=(10.2±0.3)×10−6, S22=(−1.1±0.3)×10−6, C21=(0.0±0.3)×10−6, and S21=(0.0±1.6)×10−6. Also, four spacecraft images of Callisto have been used to determine its mean radius. The result is R=(2410.3±1.5) km, with no detectable deviation from sphericity. Derived parameters are Callisto's mean density of (1834.4±3.4) kg m−3 and axial moment of inertia C/MR2=0.3549±0.0042. While the mean density indicates that Callisto is a mixture of rock and ice, the moment of inertia is too small for a homogeneous mixture. Accordingly, we present a suite of possible two- and three-layer interior models that satisfy the given constraints for radius, density, and moment of inertia. While not unique, these models show that Callisto cannot be entirely differentiated, and that there must exist a region of mixed ice and rock–metal, possibly extending to the center of the Satellite.
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gravitational evidence for an undifferentiated callisto
Nature, 1997Co-Authors: John D Anderson, G Schubert, Eunice L Lau, W L Sjogren, W B MooreAbstract:Before the arrival of the Galileo spacecraft at Jupiter, models for the interior structure of the four Galilean Satellites-lo, Europa, Ganymede and Callisto-ranged from uniform mixtures of rock and ice (that is, undifferentiated objects) or rocky cores surrounded by a mantle of water ice. Now it appears that lo has a large metallic core and that Ganymede is strongly differentiated, most probably into a three-layer structure consisting of a metallic core, a silicate mantle and a deep outer layer of ice. Direct information on the interior structure of Callisto determined from previous spacecraft fly-bys was essentially limited to an estimate of the mean density being intermediate between pure ice and pure rock. Here we report measurements of Callisto's gravitational field which reveal that, in contrast to lo and Ganymede, this Galilean Satellite is most probably a homogeneous object consisting of a solar mixture of 40% compressed ice and 60% rock (including iron and iron sulphide). Callisto's undifferentiated state is consistent with the apparent lack of an intrinsic magnetic field, and indicates that the outermost Galilean Satellite has not experienced a heating phase sufficiently high to separate its rock and metal components from the lighter ices.
Marc Bretton - One of the best experts on this subject based on the ideXlab platform.
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the phemu15 catalogue and astrometric results of the jupiter s Galilean Satellite mutual occultation and eclipse observations made in 2014 2015
Monthly Notices of the Royal Astronomical Society, 2018Co-Authors: Eleonore Saquet, N V Emelyanov, V Robert, J E Arlot, P Anbazhagan, Kevin Baillie, J Bardecker, A A Berezhnoy, Marc BrettonAbstract:During the 2014-2015 mutual events season, the Institut de Mecanique Celeste et de Calcul desEphemerides (IMCCE), Paris, France, and the Sternberg Astronomical Institute (SAI), Moscow, Russia, led an international observation campaign to record ground-based photomet-ric observations of Galilean moon mutual occultations and eclipses. We focused on processing the complete photometric observations data base to compute new accurate astrometric positions. We used our method to derive astrometric positions from the light curves of the events.
V Robert - One of the best experts on this subject based on the ideXlab platform.
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the phemu15 catalogue and astrometric results of the jupiter s Galilean Satellite mutual occultation and eclipse observations made in 2014 2015
Monthly Notices of the Royal Astronomical Society, 2018Co-Authors: Eleonore Saquet, N V Emelyanov, V Robert, J E Arlot, P Anbazhagan, Kevin Baillie, J Bardecker, A A Berezhnoy, Marc BrettonAbstract:During the 2014-2015 mutual events season, the Institut de Mecanique Celeste et de Calcul desEphemerides (IMCCE), Paris, France, and the Sternberg Astronomical Institute (SAI), Moscow, Russia, led an international observation campaign to record ground-based photomet-ric observations of Galilean moon mutual occultations and eclipses. We focused on processing the complete photometric observations data base to compute new accurate astrometric positions. We used our method to derive astrometric positions from the light curves of the events.
