The Experts below are selected from a list of 174 Experts worldwide ranked by ideXlab platform
R Vasundhara - One of the best experts on this subject based on the ideXlab platform.
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astrometry from mutual events of Jovian Satellites in 1997
Astronomy and Astrophysics, 2003Co-Authors: R Vasundhara, J E Arlot, V Lainey, W ThuillotAbstract:Astrometric results of observations of the mutual events of the Galilean Satellites of Jupiter of the PHEMU97 campaign by the Institut de Mecanique Celeste et de Calcul des Ephemerides are presented. These astrometric positions can be directly utilized in the construction of future ephemerides. We attempt here to compare the residuals of the relative astrometric positions of Satellites with respect to the E3, G5, E5 and L1 ephemerides. The model to fit the observed light curves includes the intensity variations on the surface of Satellites using the mosaics constructed by the teams at the US Geological Survey from Voyager and Galileo imagery.
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astrometry from ccd photometry of mutual events of Jovian Satellites from vbo during 1997
Astronomy and Astrophysics, 2002Co-Authors: R VasundharaAbstract:Astrometric results of CCD observations of the mutual events of the Galilean Satellites of Jupiter from the Vainu Bappu Observatory are presented. The shifts in the photo-centers on the disks of Io and Europa due to albedo variations inferred from the available mosaics of Galileo imagery are determined. The estimated shifts from ≈ 90 km East to ≈ 50 km West on Io and from ≈ 50 km East to ≈ 30 km West for Europa during one orbital period are comparable to the accuracies provided by the present-day ephemerides. In a given mutual event series, the mutual events involving a given satellite pair dominate in number and occur nearly at the same orbital longitude within ± ; all the events are therefore delayed or all of them advanced depending on the direction of the shift of the photo-center. The implications of including these cumulative and sustained longitude residuals on the constructed ephemerides are discussed.
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mutual phenomena of Jovian Satellites
Journal of Astrophysics and Astronomy, 1991Co-Authors: R VasundharaAbstract:Results of the observations of mutual eclipses of Galilean Satellites observed from the Vainu Bappu Observatory during 1985 are presented. Theoretical models assuming a uniform disc, Lambert’s law and Lommel-Seeliger’s law describing the scattering characteristics of the surface of the eclipsed satellite were used to fit the observations. Light curves of the 1E2 event on 1985 September 24 and the 3E1 event on 1985 October 24 observed from VBO and published light curves of the 1E2 event on 1985 September 14, the 3E1 event on 1985 September 26 and the 2E1 event on 1985 October 28 (Arlotet al 1989) were fitted with theoretical light curves using Marquardt’s algorithm. The best fitting was obtained using Lommel-Seeliger’s law to describe the scattering over the surface of Io and Europa. During the fitting, a parameterδxshift which shifts the theoretical light curve along the direction of relative motion of the eclipsed satellite with respect to the shadow centre, on the sky plane (as seen from the Sun) was determined along with the impact parameter. In absence of other sources like prominent surface features or non perfect sky conditions which could lead to asymmetric light curves,δxshift would be a measure of the phase correction (Aksnes, Franklin & Magnusson 1986) with an accuracy as that of the midtime. Heliocentric Δα cos (δ) and gDδ at mid times derived from fitted impact parameters are reported
R A Jacobson - One of the best experts on this subject based on the ideXlab platform.
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the orbits of jupiter s irregular Satellites
The Astronomical Journal, 2017Co-Authors: Marina Brozovic, R A JacobsonAbstract:We report on the improved ephemerides for the irregular Jovian Satellites. We used a combination of numerically integrated equations of motion and a weighted least-squares algorithm to fit the astrometric measurements. The orbital fits for 59 Satellites are summarized in terms of state vectors, post-fit residuals, and mean orbital elements. The current data set appears to be sensitive to the mass of Himalia, which is constrained to the range of GM = 0.13–0.28 km3 s−2. Here, GM is the product of the Newtonian constant of gravitation, G and the body's mass, M. Our analysis of the orbital uncertainties indicates that 11 out of 59 Satellites are lost owing to short data arcs. The lost Satellites hold provisional International Astronomical Union (IAU) designations and will likely need to be rediscovered.
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the orbits of the outer Jovian Satellites
The Astronomical Journal, 2000Co-Authors: R A JacobsonAbstract:We report on the numerically integrated orbits for the nine outer Uranian Satellites. The orbits are calculated based on fits to the astrometric observations for the period from 1984 to 2006. The results include the state vectors, post-fit residuals, and mean orbital elements. We also assess the accuracy of the orbital fits and discuss the need for future measurements.
Giuliano Vannaroni - One of the best experts on this subject based on the ideXlab platform.
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Dielectric Measurements of Saline Ices: Implication for Jovian Satellites Radar Exploration
Remote Sensing 2012, 2012Co-Authors: Barbara Cosciotti, M. De Santis, Sebastian Lauro, Elisabetta Mattei, Elena Pettinelli, Giuliano VannaroniAbstract:of Jupiter’s moon Ganimede. Recently, Marsis and Sharad missions on Mars showed the capability of orbiting radar sounder, to detect the subsurface features of the planet .Therefore, the use of such techniques could prove the presence of a subsurface Ganimede ocean. The achievement of such an objective depends on the electromagnetic properties of Ganimede ice shell, which in turn will depend on the ice’s purity and temperature gradient, as well as on the radar wavelength. In this scenario, we have performed measurements of dielectric properties of pure and saline ice (mixing MgSO4 or Na2SO4 with bidistilled water) both in time and frequency domain. Both methods set show the capability of TDR and LCR techniques to estimate the electromagnetic properties of salty ice.
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Dielectric measurements of saline ices: Implications for Jovian Satellites radar exploration
2011 6th International Workshop on Advanced Ground Penetrating Radar (IWAGPR), 2011Co-Authors: M. De Santis, Barbara Cosciotti, Elisabetta Mattei, Elena Pettinelli, S. E. Lauro, Giuliano VannaroniAbstract:A spacecraft in orbit around Jupiter's moon Ganimede can use ice penetrating radar to probe for a possible liquid water ocean beneath Ganimede's surface ice. The success of such a mission is constrained to the electromagnetic properties of ice, possible subsurface temperature gradients, and possible impurities in the ice. Several saline ice samples were analyzed using Time Domain Reflectometry technique to extract the electrical permittivity and conductivity as function of temperature, from 20°C to -30°C.
Reggie L Hudson - One of the best experts on this subject based on the ideXlab platform.
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what is eating ozone thermal reactions between so2 and o3 implications for icy environments
The Astrophysical Journal, 2016Co-Authors: M J Loeffler, Reggie L HudsonAbstract:Laboratory studies are presented, showing for the first time that thermally driven reactions in solid H2O + SO2 + O3 mixtures can occur below 150 K, with the main sulfur-containing product being bisulfate (). Using a technique not previously applied to the low-temperature kinetics of either interstellar or solar-system ice analogs, we estimate an activation energy of 32 kJ mol−1 for formation. These results show that at the temperatures of the Jovian Satellites, SO2 and O3 will efficiently react making detection of these molecules in the same vicinity unlikely. Our results also explain why O3 has not been detected on Callisto and why the SO2 concentration on Callisto appears to be highest on that world's leading hemisphere. Furthermore, our results predict that the SO2 concentration on Ganymede will be lowest in the trailing hemisphere, where the concentration of O3 is the highest. Our work suggests that thermal reactions in ices play a much more important role in surface and sub-surface chemistry than generally appreciated, possibly explaining the low abundance of sulfur-containing molecules and the lack of ozone observed in comets and interstellar ices.
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o atom production in water ice implications for o2 formation on icy Satellites
Journal of Geophysical Research, 2010Co-Authors: Paul D Cooper, M H Moore, Reggie L HudsonAbstract:[1] We have found that O atoms are a primary product in the irradiation of water-ice with 0.8 MeV protons. This observation has implications in understanding the chemical reactions that occur to produce molecular oxygen (O2) in such laboratory ices, as well as ices found on the surfaces of Ganymede and Europa, and the ice particles present in Saturn's rings. We estimate that in irradiated water-ice, O2 can be formed at a lower limit of 0.07% by number relative to water and is in agreement with observations of the icy Jovian Satellites.
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the radiolysis of so2 and h2s in water ice implications for the icy Jovian Satellites
Icarus, 2007Co-Authors: M H Moore, Reggie L Hudson, R W CarlsonAbstract:Abstract Spectra of Europa, Ganymede, and Callisto reveal surfaces dominated by frozen water, hydrated materials, and minor amounts of SO 2 , CO 2 , and H 2 O 2 . These icy moons undergo significant bombardment by Jovian magnetospheric radiation (protons, electrons, and sulfur and oxygen ions) which alters their surface compositions. In order to understand radiation-induced changes on icy moons, we have measured the mid-infrared spectra of 0.8 MeV proton-irradiated SO 2 , H 2 S, and H 2 O-ice mixtures containing either SO 2 or H 2 S. Samples with H 2 O/SO 2 or H 2 O/H 2 S ratios in the 3–30 range have been irradiated at 86, 110, and 132 K, and the radiation half-lives of SO 2 and H 2 S have been determined. New radiation products include the H 2 S 2 molecule and HSO − 3 , HSO − 4 , and SO 2− 4 ions, all with spectral features that make them candidates for future laboratory work and, perhaps, astronomical observations. Spectra of both unirradiated and irradiated ices have been recorded as a function of temperature, to examine thermal stability and phase changes. The formation of hydrated sulfuric acid in irradiated ice mixtures has been observed, along with the thermal evolution of hydrates to form pure sulfuric acid. These laboratory studies provide fundamental information on likely processes affecting the outer icy shells of Europa, Ganymede, and Callisto.
Irina Kulyk - One of the best experts on this subject based on the ideXlab platform.
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astrometry of the inner Jovian moons thebe amalthea and metis
Planetary and Space Science, 2008Co-Authors: Irina KulykAbstract:Abstract The paper presents the results of the astrometric observations of the inner Jovian Satellites Thebe, Amalthea, and Metis obtained with 2-m Zeiss RCC Telescope located at Peak Terskol Observatory. The 268 inter-satellite positions were gathered during the five-year period between 1998 and 2002. Comparison of the observed positions with those of JPL JUP203 ephemerides demonstrates high quality of the collected observations. The RMS errors of the differences between the observed and the theoretical positions are about 0.10, 0.15, and 0.30 arcsec for Amalthea, Thebe, and Metis, respectively. Thebe and Amalthea's mean residuals are about zero. The dispertion of the mean residuals derived from the data sets obtained in the different years does not exceed 0.04 arcsec. The brief description of the technique for the scattered light subtraction may be useful as an experience of the image processing of a faint object near the bright planet.
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ground based photometric observations of jupiter s inner Satellites thebe amalthea and metis at small phase angles
Icarus, 2004Co-Authors: Irina Kulyk, Klaus JockersAbstract:Abstract We present the results of photometric measurements of the inner Jovian Satellites Thebe, Amalthea and Metis based on extensive optical observations taken from October 1999 to January 2002. The observations were made in the phase angle range from 8.1° to 0.3°. The Two-Channel Focal Reducer of the Max-Planck Institute for Aeronomy attached to the 2-m RCC telescope at Terskol Observatory (Pik Terskol, Northern Caucasus) was used in coronagraph mode. The observations were performed at a wavelength of 0.887 μm. Mean observational uncertainties corresponding to 1 σ rms errors were 3% for the leading and trailing sides of Amalthea, 7 and 9% for the leading and trailing sides of Thebe and 9% for the leading side of Metis after taking into account the longitude brightness variations. Photometric data calibrated on an absolute scale were used to evaluate the near-opposition behavior of satellite brightness. All three Satellites exhibit significant opposition brightening, but the strength of this effect, measured as the ratios of intensities at α 1 =1.6° and α 2 =6.7° does not vary significantly among these Satellites. In order to measure the opposition surge parameters the empirical law proposed by Karkoschka and Hapke's model were used. The parameters of the satellite opposition effects are presented and discussed. The values of geometric albedos calculated with best-fit Hapke parameters are 0.096, 0.157, and 0.24 for Thebe, Amalthea, and Metis respectively. We found that the average leading/trailing ratios of surface reflectance at the measured phase angles are 1.53±0.05, 1.25±0.04, 1.04±0.08 for Amalthea, Thebe, and Metis.
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Astrometric CCD observations of the inner Jovian Satellites in 1999-2000
Astronomy and Astrophysics, 2002Co-Authors: Irina Kulyk, Klaus Jockers, N. Karpov, A. SergeevAbstract:This paper presents the results of observations of the inner Jovian Satellites Thebe, Amalthea, Adrastea and Metis made in October–November 1999 and in November 2000. We provide $\Delta\alpha$ and $\Delta\delta$ of Thebe and Amalthea with respect to the Galilean Satellites, while the positions of Adrastea and Metis are referred to either the Galilean moons or to Thebe or to Amalthea. All observed positions are compared with theoretical ones. Residual statistics show an inner accuracy of our observations in the range from about 0.1 to 0.9 arcsec. The dependence of the differences of the observed and calculated positions on the orbital longitude is presented for our observations of Adrastea and Metis.
