141 results on '"Cassini"'
Search Results
2. Conductivities of Titan's Dusty Ionosphere
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Oleg Shebanits, J. H. Waite, Michele Dougherty, and Jan-Erik Wahlund
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Physics ,Solar System ,ionosphere ,Plasma ,Fusion, Plasma and Space Physics ,Physics::Geophysics ,Astrobiology ,symbols.namesake ,Fusion, plasma och rymdfysik ,Geophysics ,Physics::Plasma Physics ,Space and Planetary Science ,dusty plasma ,Physics::Space Physics ,symbols ,Astrophysics::Solar and Stellar Astrophysics ,Cassini ,Astrophysics::Earth and Planetary Astrophysics ,conductivity ,Ionosphere ,Titan (rocket family) ,Titan - Abstract
Titan's ionosphere hosts a globally distributed non-trivial dusty ion-ion plasma, providing an environment for studies of dusty ionospheres that is in many aspects unique in our solar system. Thanks to the Cassini mission, Titan's ionosphere also features one of the largest dusty plasma data sets from 126 flybys of the moon over 13 years, from 2004 to 2017. Recent studies have shown that negatively charged dust dramatically alters the electric properties of plasmas, in particular planetary ionospheres. Utilizing the full plasma content of the moon's ionosphere (electrons, positive ions, and negative ions/dust grains), we derive the electric conductivities and define the conductive dynamo region. Our results show that using the full plasma content increases the Pedersen conductivities at similar to 1,100-1,200 km altitude by up to 35% compared to the estimates using only electron densities. The Hall conductivities are in general not affected but several cases indicate a reverse Hall effect at similar to 900 km altitude (closest approach) and below. The dayside conductivities are shown to be factor similar to 7-9 larger than on the nightside, owing to higher dayside plasma densities.
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- 2022
3. A New Enceladus Global Control Network, Image Mosaic, and Updated Pointing Kernels From Cassini's 13-Year Mission
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K. L. Edmundson, D. Cook, Tammy L. Becker, Michael T. Bland, Brent A. Archinal, Robert T. Pappalardo, Geoffrey C. Collins, Thomas Roatsch, D. Takir, Paul M. Schenk, and G. W. Patterson
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Cartography ,010504 meteorology & atmospheric sciences ,Pixel ,Geodetic datum ,Bundle adjustment ,Environmental Science (miscellaneous) ,01 natural sciences ,Planetary Data System ,Enceladus ,Photogrammetry ,Saturn ,0103 physical sciences ,General Earth and Planetary Sciences ,Cassini ,Imaging science ,010303 astronomy & astrophysics ,Geology ,0105 earth and related environmental sciences ,Remote sensing - Abstract
NASA’s Cassini spacecraft spent 13 years exploring the Saturn system, including 23 targeted flybys of the small, geologically active moon Enceladus. These flybys provided a wealth of image data from Cassini’s Imaging Science Subsystem. To improve the usability of the Enceladus data set, we created a new, global photogrammetric control network for Enceladus that enabled compilation of a versatile cartographic package to support geologic mapping and other investigations. The network used 586 images in four image filters with a pixel scale generally between 50 and 500 m per pixel and a phase angle less than 120° and consisted of 10,362 tie points and 173,704 individual image measures, averaging nearly 17 measures per tie point. Least squares bundle adjustment resulted in a root-mean-square residual of 0.45 pixel, corresponding to root-mean-square ground point uncertainties of 66, 51, and 46 m in latitude, longitude, and radius, respectively. Using our geodetic control network, we created new global image mosaics, coregistered flyby mosaics to support geologic mapping, and updated pointing kernels for every image used in the solution. These products, including the updated pointing kernels, are available to the community through NASA’s Planetary Data System Imaging Annex. The bundle adjustment solution also yielded independently determined shape information, resulting in radii within the stated uncertainty of International Astronomical Union values. The challenges of the data set, and the technical methodology described here are applicable to bodies imaged during multiple flybys with variable viewing and illumination geometry, including other midsized satellites of Saturn, and the Europa Clipper mission.
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- 2018
4. Cassini Exploration of the Planet Saturn: A Comprehensive Review
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Ingersoll, Andrew P.
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Atmosphere ,Gas giant ,Giant planet ,Astronomy ,Astronomy and Astrophysics ,Article ,Jupiter ,Saturn ,Interior ,Planetary science ,Space and Planetary Science ,Planet ,Physics::Space Physics ,Cassini ,Astrophysics::Earth and Planetary Astrophysics ,Stratosphere ,Physics::Atmospheric and Oceanic Physics ,Geology - Abstract
Before Cassini, scientists viewed Saturn’s unique features only from Earth and from three spacecraft flying by. During more than a decade orbiting the gas giant, Cassini studied the planet from its interior to the top of the atmosphere. It observed the changing seasons, provided up-close observations of Saturn’s exotic storms and jet streams, and heard Saturn’s lightning, which cannot be detected from Earth. During the Grand Finale orbits, it dove through the gap between the planet and its rings and gathered valuable data on Saturn’s interior structure and rotation. Key discoveries and events include: watching the eruption of a planet-encircling storm, which is a 20- or 30-year event, detection of gravity perturbations from winds 9000 km below the tops of the clouds, demonstration that eddies are supplying energy to the zonal jets, which are remarkably steady over the 25-year interval since the Voyager encounters, re-discovery of the north polar hexagon after 25 years, determination of elemental abundance ratios He/H, C/H, N/H, P/H, and As/H, which are clues to planet formation and evolution, characterization of the semiannual oscillation of the equatorial stratosphere, documentation of the mysteriously high temperatures of the thermosphere outside the auroral zone, and seeing the strange intermittency of lightning, which typically ceases to exist on the planet between outbursts every 1–2 years. These results and results from the Jupiter flyby are all discussed in this review.
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- 2020
5. Models of Saturn's Equatorial Ionosphere Based on In Situ Data From Cassini's Grand Finale
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A. F. Nagy, Luke Moore, Jan-Erik Wahlund, J. H. Waite, Ingo Müller-Wodarg, Donald G. Mitchell, Thomas E. Cravens, A. M. Persoon, Rebecca Perryman, Mark E. Perry, and Michiko Morooka
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In situ ,THERMOSPHERE ,INFLUX ,010504 meteorology & atmospheric sciences ,ionosphere ,Mass spectrometry ,01 natural sciences ,Ion ,Atmosphere ,CHEMISTRY ,Saturn ,0103 physical sciences ,WATER ,Meteorology & Atmospheric Sciences ,Astrophysics::Solar and Stellar Astrophysics ,Geosciences, Multidisciplinary ,ION ,010303 astronomy & astrophysics ,Physics::Atmospheric and Oceanic Physics ,0105 earth and related environmental sciences ,Physics ,Science & Technology ,Astronomy ,Geology ,ATMOSPHERE ,Geophysics ,Physical Sciences ,Physics::Space Physics ,General Earth and Planetary Sciences ,Cassini ,Astrophysics::Earth and Planetary Astrophysics ,Ionosphere ,SYSTEM - Abstract
We present new models of Saturn's equatorial ionosphere based on the first in situ measurements of its upper atmosphere. The neutral spectrum measured by Cassini's Ion and Neutral Mass Spectrometer, which includes substantial methane, ammonia, and organics in addition to the anticipated molecular hydrogen, helium, and water, serves as input for unexpectedly complex ionospheric chemistry. Heavy molecular ions are found to dominate Saturn's equatorial low‐altitude ionosphere, with a mean ion mass of 11 Da. Key molecular ions include H3O+ and HCO+; other abundant heavy ions depend upon the makeup of the mass 28 neutral species, which cannot be uniquely determined. Ion and Neutral Mass Spectrometer neutral species lead to generally good agreement between modeled and observed plasma densities, though poor reproduction of measured H+ and H3+ variability and an overabundance of modeled H3+ potentially hint at missing physical processes in the model, including a loss process that affects H3+ but not H+.
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- 2018
6. Mapping Saturn's Nightside Plasma Sheet Using Cassini's Proximal Orbits
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Nicholas Achilleos, Donald G. Mitchell, Stamatios M. Krimigis, Nick Sergis, Elias Roussos, Arianna Sorba, Chris Paranicas, Norbert Krupp, Omiros Giannakis, Chris S. Arridge, Georgios Balasis, Patrick Guio, Michele K. Dougherty, and D. C. Hamilton
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IONS ,010504 meteorology & atmospheric sciences ,Plasma parameters ,Equator ,Magnetosphere ,Context (language use) ,Astrophysics ,MAGNETODISC ,PRESSURE ,01 natural sciences ,FORCE ,MAGNETOSPHERE ,Saturn ,MD Multidisciplinary ,0103 physical sciences ,Meteorology & Atmospheric Sciences ,Geosciences, Multidisciplinary ,magnetospheres ,010303 astronomy & astrophysics ,Ring current ,0105 earth and related environmental sciences ,Physics ,Science & Technology ,Plasma sheet ,Geology ,Plasma ,MODEL ,Geophysics ,Physical Sciences ,Physics::Space Physics ,General Earth and Planetary Sciences ,Cassini ,Astrophysics::Earth and Planetary Astrophysics - Abstract
Between April and the end of its mission on 15 September, Cassini executed a series of 22 very similar 6.5‐day‐period proximal orbits, covering the mid‐latitude region of the nightside magnetosphere. These passes provided us with the opportunity to examine the variability of the nightside plasma sheet within this time scale for the first time. We use Cassini particle and magnetic field data to quantify the magnetospheric dynamics along these orbits, as reflected in the variability of certain relevant plasma parameters, including the energetic ion pressure and partial (hot) plasma beta. We use the University College London/Achilleos‐Guio‐Arridge magnetodisk model to map these quantities to the conjugate magnetospheric equator, thus providing an equivalent equatorial radial profile for these parameters. By quantifying the variation in the plasma parameters, we further identify the different states of the nightside ring current (quiescent and disturbed) in order to confirm and add to the context previously established by analogous studies based on long‐term, near‐equatorial measurements.
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- 2018
7. Planetary Period Oscillations in Saturn's Magnetosphere: Cassini Magnetic Field Observations Over the Northern Summer Solstice Interval
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Stanley W. H. Cowley, T. J. Bradley, Michele K. Dougherty, Emma J. Bunce, G. Provan, and G. J. Hunt
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010504 meteorology & atmospheric sciences ,PHASE ,Magnetosphere ,Equinox ,Astronomy & Astrophysics ,01 natural sciences ,Jet propulsion ,PERIODICITIES ,Saturn ,0103 physical sciences ,Solstice ,010303 astronomy & astrophysics ,Physics::Atmospheric and Oceanic Physics ,planetary period oscillations ,0105 earth and related environmental sciences ,Science & Technology ,EQUINOX ,Astronomy ,Planetary Data System ,Magnetic field ,Geophysics ,Space and Planetary Science ,Physics::Space Physics ,Physical Sciences ,magnetosphere ,ROTATION ,SHEET ,Cassini ,Astrophysics::Earth and Planetary Astrophysics ,Geology - Abstract
We determine properties of Saturn's planetary period oscillations from Cassini magnetic measurements over the ~2‐year interval from September 2015 to end of mission in September 2017, spanning Saturn northern summer solstice in May 2017. Phases of the northern system oscillations are derived over the whole interval, while those of the southern system are not discerned in initial equatorial data due to too low amplitude relative to the northern, but are determined once southern polar data become available from inclined orbits beginning May 2016. Planetary period oscillation periods are shown to be almost constant over these intervals at ~10.79 hr for the northern system and ~10.68 hr for the southern, essentially unchanged from values previously determined after the periods reversed in 2014. High cadence phase and amplitude data obtained from the short‐period Cassini orbits during the mission's last 10 months newly reveal the presence of dual modulated oscillations varying at the beat period of the two systems (~42 days) on nightside polar field lines in the vicinity (likely either side) of the open‐closed field boundary. The modulations differ from those observed previously in the equatorial region, indicative of a reversal in sign of the radial component oscillations, but not of the colatitudinal component oscillations. Brief discussion is given of a possible theoretical scenario. While weak equatorial beat modulations indicate a north/south amplitude ratio >5 early in the study interval, polar and equatorial region modulations suggest a ratio ~1.4 during the later interval, indicating a significant recovery of the southern system.
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- 2018
8. Validation of posterior corneal curvature measurements with color light-emitting diode topography
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Vicent J. Camps, María Teresa Caballero Caballero, Celia García, Dolores de Fez, David P. Piñero, Universidad de Alicante. Departamento de Óptica, Farmacología y Anatomía, and Grupo de Óptica y Percepción Visual (GOPV)
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Adult ,Male ,Materials science ,Adolescent ,Astigmatism ,Posterior corneal astigmatism ,law.invention ,Cornea ,03 medical and health sciences ,Young Adult ,0302 clinical medicine ,Optics ,law ,medicine ,Humans ,Prospective Studies ,Pentacam ,Diode ,Óptica ,Aged ,Corneal curvature ,medicine.diagnostic_test ,business.industry ,Corneal Topography ,Reproducibility of Results ,General Medicine ,Repeatability ,Color light-emitting diode reflection topography ,Equipment Design ,Middle Aged ,Corneal topography ,medicine.disease ,Ophthalmology ,030221 ophthalmology & optometry ,Reflection (physics) ,Cassini ,Female ,Posterior corneal curvature ,business ,030217 neurology & neurosurgery ,Light-emitting diode - Abstract
Purpose: To evaluate the intrasession repeatability and validity of posterior corneal curvature and astigmatism measurements provided by a color light-emitting diode reflection topography system in healthy eyes. Methods: A total of 40 healthy eyes of 40 patients (age, 16–66 years) were enrolled. A complete eye examination was performed in all cases including posterior topographic analysis with two systems: the Scheimpflug-based system (Pentacam; Oculus Optikgeräte GmbH, Wetzlar, Germany) and the Cassini system (i-Optics; Ophthec, The Hague, The Netherlands). With this last system, three consecutive measurements were taken to assess the level of intrasession repeatability (within-subject standard deviation, Sw; intraclass correlation coefficient). The Bland & Altman analysis was used to evaluate the interchangeability of both devices. Results: The Sw was ⩽0.06 mm for all posterior corneal radius measurements, with intraclass correlation coefficient of ⩾0.960. The Sw for the magnitude of astigmatism, J0, and J45 were 0.15, 0.04, and 0.04 D, respectively, with intraclass correlation coefficient values of 0.876, 0.897, and 0.840, respectively. Statistically significant differences between devices were found in all parameters evaluated (p ⩽ 0.025). The interchangeability analysis revealed the presence of clinically relevant limits of agreement for the flattest (0.03 to 0.50 mm) and steepest posterior corneal radii (–0.01 to 0.39 mm). In contrast, limits of agreements were not clinically relevant for the magnitude of posterior astigmatism (–0.17 to 0.27 D) and their power vector components (–0.11 to 0.15 D). Conclusion: The Cassini system provides consistent measures of posterior corneal curvature and astigmatism in healthy eyes, but only measures of posterior astigmatism can be considered as interchangeable with those provided by the Pentacam.
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- 2019
9. Comparative analysis of anterior corneal curvature and astigmatism measurements obtained with three different devices
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David P. Piñero, Dolores de Fez, Ainhoa Molina-Martín, Vicent J. Camps, María Teresa Caballero Caballero, Universidad de Alicante. Departamento de Óptica, Farmacología y Anatomía, and Grupo de Óptica y Percepción Visual (GOPV)
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Adult ,Male ,medicine.medical_specialty ,Biometry ,genetic structures ,Adolescent ,Astigmatism ,Cornea ,03 medical and health sciences ,Young Adult ,0302 clinical medicine ,Ophthalmology ,medicine ,Humans ,Prospective Studies ,Pentacam ,IOL master ,Mathematics ,Óptica ,Corneal curvature ,Corneal Topography ,Reproducibility of Results ,Equipment Design ,Middle Aged ,medicine.disease ,eye diseases ,Colour light-emitting diode reflection topography ,030221 ophthalmology & optometry ,Cassini ,Female ,sense organs ,Corneal topography ,030217 neurology & neurosurgery ,Keratometry ,Optometry - Abstract
Background: The objective of this study was to compare the central corneal curvature and astigmatism measurements obtained with three different systems in healthy eyes and to assess the level of interchangeability between them. Methods: This was a comparative study examining 30 healthy eyes of 30 patients (age 15–53 years). A complete eye examination was performed in all cases including analysis of anterior corneal curvature and astigmatism with three devices: the colour‐LED topography system Cassini (i‐Optics) (CAS), the Scheimpflug‐based system Pentacam (Oculus Optikgeräte) (PTC) and the optical biometer IOL‐Master 500 (Carl Zeiss Meditec) (IOLM). Differences between devices in terms of curvature in the flattest (flat K) and steepest meridians (steep K) as well as in the magnitude (AST) and power vector components of astigmatism (J0 and J45) were evaluated. The interchangeability between devices was evaluated with the Bland–Altman method. Results: Statistically significant differences between devices were found in steep K and flat K (p
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- 2019
10. Validation of corneal topographic and aberrometric measurements obtained by color light-emitting diode reflection topography in healthy eyes
- Author
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David P. Piñero, Vicent J. Camps, María Teresa Caballero Caballero, Dolores de Fez, Ainhoa Molina-Martín, Universidad de Alicante. Departamento de Óptica, Farmacología y Anatomía, and Grupo de Óptica y Percepción Visual (GOPV)
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Adult ,Male ,medicine.medical_specialty ,genetic structures ,Adolescent ,Intraclass correlation ,Scheimpflug principle ,Standard deviation ,Cornea ,03 medical and health sciences ,Cellular and Molecular Neuroscience ,Young Adult ,0302 clinical medicine ,Ophthalmology ,medicine ,Humans ,Prospective Studies ,Pentacam ,Anterior corneal curvature ,Mathematics ,Óptica ,Aged ,medicine.diagnostic_test ,Aberrometry ,Corneal Topography ,Reproducibility of Results ,Repeatability ,Color light-emitting diode reflection topography ,Middle Aged ,Corneal topography ,Sensory Systems ,Healthy Volunteers ,Corneal diameter ,030221 ophthalmology & optometry ,Cassini ,Female ,Posterior corneal curvature ,030217 neurology & neurosurgery - Abstract
Purpose To evaluate the intrasession repeatability of anterior corneal topographic and aberrometric measurements provided by a color-LED topographer as well as their interchangeability with those provided by a Scheimpflug-based system in healthy eyes. Methods Thirty-five healthy eyes of 35 patients (age, 16–66 years) were enrolled. A complete eye examination was performed in all cases including a complete corneal analysis with the Scheimpflug-based system Pentacam (Oculus Optikgeräte) (one measurement) and the Cassini system (i-Optics) (three consecutive measurements). Intrasession repeatability of the Cassini measurements was assessed with the within-subject standard deviation (Sw) and the intraclass correlation coefficient (ICC). The Bland-Altman analysis was used to evaluate the agreement between both devices. Results Mean Sw for keratometric readings was 0.02 mm (ICC ≥ 0.992), ranging between 0.16 and 0.05 D (ICC 0.930–0.978) for anterior and total astigmatic measurements. Mean Sw for asphericity and corneal diameter were 0.06 (ICC 0.926) and 0.03 mm (IC 0.997), respectively. Aberrometric parameters showed ICCs ≥ 0.816, except for Z42 (ICC 0.741) and Z44 (ICC 0.544). When comparing devices, statistically significant differences were found for most of topographic and aberrometric data (p ≤ 0.044). Likewise, ranges of agreement between devices were clinically relevant (keratometry > 0.06 mm; total astigmatic components > 0.69 D; asphericity 0.35; second-, third-, and fourth-order Zernike terms, more than 0.20, 0.13, and 0.01 μm, respectively). Conclusions Consistent anterior corneal topographic, total corneal astigmatic, and aberrometric measurements are obtained with color-LED topography in healthy eyes, which are not interchangeable with those provided by the Scheimpflug-based topography. The author David P Piñero has been supported by the Ministry of Economy, Industry and Competitiveness of Spain within the program Ramón y Cajal, RYC-2016-20471.
- Published
- 2019
11. Comparison of the deep atmospheric dynamics of Jupiter and Saturn in light of the Juno and Cassini gravity measurements
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Adam P. Showman, Tristan Guillot, Luciano Iess, Eli Galanti, Yohai Kaspi, David J. Stevenson, Scott Bolton, Joseph Louis LAGRANGE (LAGRANGE), Université Côte d'Azur (UCA)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Observatoire de la Côte d'Azur, and COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
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Juno ,Gravity (chemistry) ,010504 meteorology & atmospheric sciences ,Gas giant ,[SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP] ,FOS: Physical sciences ,Zonal and meridional ,01 natural sciences ,Exploration of Jupiter ,Planet ,Saturn ,0103 physical sciences ,010303 astronomy & astrophysics ,ComputingMilieux_MISCELLANEOUS ,0105 earth and related environmental sciences ,Earth and Planetary Astrophysics (astro-ph.EP) ,[SDU.ASTR.SR]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Solar and Stellar Astrophysics [astro-ph.SR] ,Fluid Dynamics (physics.flu-dyn) ,Astronomy ,Astronomy and Astrophysics ,Physics - Fluid Dynamics ,Physics - Atmospheric and Oceanic Physics ,Planetary science ,Cassini ,Gravity science ,Jupiter ,Planetary atmospheres ,Space and Planetary Science ,13. Climate action ,Physics::Space Physics ,Atmospheric and Oceanic Physics (physics.ao-ph) ,Great conjunction ,Astrophysics::Earth and Planetary Astrophysics ,Geology ,Astrophysics - Earth and Planetary Astrophysics - Abstract
The nature and structure of the observed east-west flows on Jupiter and Saturn has been one of the longest-lasting mysteries in planetary science. This mystery has been recently unraveled due to the accurate gravity measurements provided by the Juno mission to Jupiter and the Grand Finale of the Cassini mission to Saturn. These two experiments, which coincidentally happened around the same time, allowed determination of the vertical and meridional profiles of the zonal flows on both planets. This paper reviews the topic of zonal jets on the gas giants in light of the new data from these two experiments. The gravity measurements not only allow the depth of the jets to be constrained, yielding the inference that the jets extend roughly 3000 and 9000 km below the observed clouds on Jupiter and Saturn, respectively, but also provide insights into the mechanisms controlling these zonal flows. Specifically, for both planets this depth corresponds to the depth where electrical conductivity is within an order of magnitude of 1 S/m, implying that the magnetic field likely plays a key role in damping the zonal flows., Comment: Submitted to Space Science Reviews. Part of ISSI special collection on Diversity of Atmospheres
- Published
- 2019
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12. Photometrically-corrected global infrared mosaics of Enceladus: New implications for its spectral diversity and geological activity
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Gabriel Tobie, Marion Massé, Sebastien Rodriguez, S. Le Mouélic, R. Robidel, Christophe Sotin, Benoît Seignovert, Laboratoire de Planétologie et Géodynamique [UMR 6112] (LPG), Université d'Angers (UA)-Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Université de Nantes (UN)-Université de Nantes (UN)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), Institut de Physique du Globe de Paris (IPGP), and Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP)
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010504 meteorology & atmospheric sciences ,Infrared ,[SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP] ,FOS: Physical sciences ,Terrain ,01 natural sciences ,Enceladus ,Image processing ,0103 physical sciences ,VIMS ,Instrumentation and Methods for Astrophysics (astro-ph.IM) ,010303 astronomy & astrophysics ,Image resolution ,0105 earth and related environmental sciences ,Remote sensing ,Earth and Planetary Astrophysics (astro-ph.EP) ,[SDU.ASTR]Sciences of the Universe [physics]/Astrophysics [astro-ph] ,Spectrometer ,Northern Hemisphere ,Hyperspectral imaging ,Astronomy and Astrophysics ,Seafloor spreading ,Spectrophotometry ,Space and Planetary Science ,Cassini ,Astrophysics - Instrumentation and Methods for Astrophysics ,Geology ,Astrophysics - Earth and Planetary Astrophysics - Abstract
Between 2004 and 2017, spectral observations have been gathered by the Visual and Infrared Mapping Spectrometer (VIMS) on-board Cassini (Brown et al., 2004) during 23 Enceladus close encounters, in addition to more distant surveys. The objective of the present study is to produce a global hyperspectral mosaic of the complete VIMS data set of Enceladus in order to highlight spectral variations among the different geological units. This requires the selection of the best observations in terms of spatial resolution and illumination conditions. We have carried out a detailed investigation of the photometric behavior at several key wavelengths (1.35, 1.5, 1.65, 1.8, 2.0, 2.25, 2.55 and 3.6 ${\mu}$m), characteristics of the infrared spectra of water ice. We propose a new photometric function, based on the model of Shkuratov et al. (2011). When combined, corrected mosaics at different wavelengths reveal heterogeneous areas, in particular in the terrains surrounding the Tiger Stripes on the South Pole and in the northern hemisphere around 30{\deg}N, 90{\deg}W. Those areas appear mainly correlated to tectonized units, indicating an endogenous origin, potentially driven by seafloor hotspots., Comment: Erratum: Fix south polar grid longitudes in Figures 9 and 11
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- 2020
13. Field‐aligned currents in Saturn's magnetosphere: Local time dependence of southern summer currents in the dawn sector between midnight and noon
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Vladimir Kalegaev, Igor Alexeev, Gabrielle Provan, G. J. Hunt, Emma J. Bunce, Andrew J. Coates, Michele K. Dougherty, Elena Belenkaya, Stanley W. H. Cowley, Imperial College Trust, Science and Technology Facilities Council (STFC), The Royal Society, and Science and Technology Facilities Council
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NORTHERN ,010504 meteorology & atmospheric sciences ,media_common.quotation_subject ,Magnetosphere ,Astrophysics ,Astronomy & Astrophysics ,Noon ,Atmospheric sciences ,01 natural sciences ,Asymmetry ,FLOWS ,Midnight ,Saturn ,0103 physical sciences ,010303 astronomy & astrophysics ,0105 earth and related environmental sciences ,media_common ,AURORAL OVAL ,Physics ,Science & Technology ,POLAR IONOSPHERE ,HST ,CURRENT SYSTEMS ,CASSINI ,Magnetic field ,MODEL ,BOUNDARY ,Geophysics ,Space and Planetary Science ,Local time ,Magnetosphere of Saturn ,Physical Sciences - Abstract
We examine and compare the magnetic field perturbations associated with field-aligned ionosphere-magnetosphere coupling currents at Saturn, observed by the Cassini spacecraft during two sequences of highly inclined orbits in 2006/2007 and 2008 under late southern summer conditions. These sequences explore the southern currents in the dawn-noon and midnight sectors, respectively, thus allowing investigation of possible origins of the local time (LT) asymmetry in auroral Saturn kilometric radiation (SKR) emissions, which peak in power at ~8 h LT in the dawn-noon sector. We first show that the dawn-noon field data generally have the same four-sheet current structure as found previously in the midnight data and that both are similarly modulated by “planetary period oscillation” (PPO) currents. We then separate the averaged PPO-independent (e.g., subcorotation) and PPO-related currents for both LT sectors by using the current system symmetry properties. Surprisingly, we find that the PPO-independent currents are essentially identical within uncertainties in the dawn-dusk and midnight sectors, thus providing no explanation for the LT dependence of the SKR emissions. The main PPO-related currents are, however, found to be slightly stronger and narrower in latitudinal width at dawn-noon than at midnight, leading to estimated precipitating electron powers, and hence emissions, that are on average a factor of ~1.3 larger at dawn-noon than at midnight, inadequate to account for the observed LT asymmetry in SKR power by a factor of ~2.7. Some other factors must also be involved, such as a LT asymmetry in the hot magnetospheric auroral source electron population.
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- 2016
14. Nature, distribution, and origin of Titan’s Undifferentiated Plains
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Alexander G. Hayes, Kenneth J. Lawrence, Athena Coustenis, Michael Malaska, A. Le Gall, M. A. Janssen, A. Solomonidou, Ellen R. Stofan, Samuel Birch, Jani Radebaugh, Bryan Stiles, Catherine D. Neish, R. L. Kirk, Elizabeth P. Turtle, K. L. Mitchell, Ashley Schoenfeld, Rosaly M. C. Lopes, Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), PLANETO - LATMOS, Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Department of Physics and Space Sciences [FIT], Florida Institute of Technology [Melbourne], Johns Hopkins University Applied Physics Laboratory [Laurel, MD] (APL), Department of Astronomy [Ithaca], Cornell University [New York], Department of Geological Sciences [BYU], Brigham Young University (BYU), Astrogeology Science Center [Flagstaff], United States Geological Survey [Reston] (USGS), Department of Earth and Planetary Sciences [UCL/Birkbeck], Birkbeck College [University of London], and California Institute of Technology (CALTECH)-NASA
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Synthetic aperture radar ,010504 meteorology & atmospheric sciences ,[SDU.ASTR.EP]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP] ,Fluvial ,01 natural sciences ,Astrobiology ,law.invention ,Sedimentary depositional environment ,Paleontology ,symbols.namesake ,Impact crater ,law ,0103 physical sciences ,Radar ,010303 astronomy & astrophysics ,0105 earth and related environmental sciences ,Astronomy and Astrophysics ,15. Life on land ,Radar observations ,[SDU.ASTR.IM]Sciences of the Universe [physics]/Astrophysics [astro-ph]/Instrumentation and Methods for Astrophysic [astro-ph.IM] ,13. Climate action ,Space and Planetary Science ,symbols ,Aeolian processes ,Cassini ,Sedimentary rock ,Geological processes ,Titan ,Titan (rocket family) ,Geology - Abstract
The Undifferentiated Plains on Titan, first mapped by Lopes et al. (Lopes, R.M.C. et al., 2010. Icarus, 205, 540–588), are vast expanses of terrains that appear radar-dark and fairly uniform in Cassini Synthetic Aperture Radar (SAR) images. As a result, these terrains are often referred to as “blandlands”. While the interpretation of several other geologic units on Titan – such as dunes, lakes, and well-preserved impact craters – has been relatively straightforward, the origin of the Undifferentiated Plains has remained elusive. SAR images show that these “blandlands” are mostly found at mid-latitudes and appear relatively featureless at radar wavelengths, with no major topographic features. Their gradational boundaries and paucity of recognizable features in SAR data make geologic interpretation particularly challenging. We have mapped the distribution of these terrains using SAR swaths up to flyby T92 (July 2013), which cover >50% of Titan’s surface. We compared SAR images with other data sets where available, including topography derived from the SARTopo method and stereo DEMs, the response from RADAR radiometry, hyperspectral imaging data from Cassini’s Visual and Infrared Mapping Spectrometer (VIMS), and near infrared imaging from the Imaging Science Subsystem (ISS). We examined and evaluated different formation mechanisms, including (i) cryovolcanic origin, consisting of overlapping flows of low relief or (ii) sedimentary origins, resulting from fluvial/lacustrine or aeolian deposition, or accumulation of photolysis products created in the atmosphere. Our analysis indicates that the Undifferentiated Plains unit is consistent with a composition predominantly containing organic rather than icy materials and formed by depositional and/or sedimentary processes. We conclude that aeolian processes played a major part in the formation of the Undifferentiated Plains; however, other processes (fluvial, deposition of photolysis products) are likely to have contributed, possibly in differing proportions depending on location.
- Published
- 2016
15. Hybrid simulation of Titan's interaction with the supersonic solar wind during Cassini's T96 flyby
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Sven Simon, Fritz M. Neubauer, Niklas J. T. Edberg, M. Feyerabend, Cesar Bertucci, William S. Kurth, George Hospodarsky, and Uwe Motschmann
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010504 meteorology & atmospheric sciences ,Ciencias Físicas ,Magnetosphere ,01 natural sciences ,purl.org/becyt/ford/1 [https] ,symbols.namesake ,0103 physical sciences ,Supersonic speed ,010303 astronomy & astrophysics ,MOON-PLASMA INTERACTION ,0105 earth and related environmental sciences ,Physics ,T96 FLYBY ,Astronomy ,CASSINI ,purl.org/becyt/ford/1.3 [https] ,Plasma ,Magnetic field ,Astronomía ,Solar wind ,Geophysics ,TITAN ,Magnetosphere of Saturn ,Physics::Space Physics ,symbols ,General Earth and Planetary Sciences ,Astrophysics::Earth and Planetary Astrophysics ,Ionosphere ,Titan (rocket family) ,CIENCIAS NATURALES Y EXACTAS - Abstract
By applying a hybrid (kinetic ions and fluid electrons) simulation code, we study the plasma environment of Saturn´s largest moon Titan during Cassini´s T96 flyby on 1 December 2013. The T96 encounter marks the only observed event of the entire Cassini mission where Titan was located in the supersonic solar wind in front of Saturn´s bow shock. Our simulations can quantitatively reproduce the key features of Cassini magnetic field and electron density observations during this encounter. We demonstrate that the large-scale features of Titan´s induced magnetosphere during T96 can be described in terms of a steady state interaction with a high-pressure solar wind flow. About 40 min before the encounter, Cassini observed a rotation of the incident solar wind magnetic field by almost 90°. We provide strong evidence that this rotation left a bundle of fossilized magnetic field lines in Titan´s ionosphere that was subsequently detected by the spacecraft. Fil: Feyerabend, Moritz. Georgia Institute Of Techology; Estados Unidos Fil: Simon, Sven. Georgia Institute Of Techology; Estados Unidos Fil: Neubauer, Fritz M.. Universitat Zu Köln; Alemania Fil: Motschmann, Uwe. Deutsches Zentrum Fur Luft- Und Raumfahrt; Alemania. Technische Universitat Braunschweig; Alemania Fil: Bertucci, Cesar. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Edberg, Niklas J. T.. Instiutet For Rymdfysik; Suecia Fil: Hospodarsky, George B.. University Of Iowa; Estados Unidos Fil: Kurth, William S.. University Of Iowa; Estados Unidos
- Published
- 2016
16. Cassini observations of ionospheric plasma in Saturn's magnetotail lobes
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Henrik Melin, Sarah V. Badman, Caitriona M. Jackman, Mariana Felici, Daniel B. Reisenfeld, Nick Sergis, Andrew J. Coates, William S. Kurth, D. G. Mitchell, Michele K. Dougherty, and Chris S. Arridge
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Ionosphere/Magnetosphere Interactions ,010504 meteorology & atmospheric sciences ,Magnetosphere ,MAGNETOSPHERIC DYNAMICS ,Astronomy & Astrophysics ,lobe ,ION COMPOSITION ,01 natural sciences ,KILOMETRIC RADIATION ,Solar Wind/Magnetosphere Interactions ,Planetary Sciences: Solar System Objects ,ionospheric outflow ,Saturn ,0103 physical sciences ,Magnetospheric Physics ,Ionosphere ,Enceladus ,010303 astronomy & astrophysics ,Research Articles ,Saturn's hexagon ,0105 earth and related environmental sciences ,Physics ,Science & Technology ,POLAR WIND ,MAGNETIC-FIELD ,Plasma sheet ,Astronomy ,Magnetospheric Configuration and Dynamics ,ATMOSPHERE ,REGIONS ,Solar wind ,Geophysics ,Polar wind ,Space and Planetary Science ,SOLAR-WIND ,Magnetosphere of Saturn ,Physical Sciences ,RADIO-EMISSION ,ENCELADUS ,magnetosphere ,Cassini ,Magnetotail ,Magnetosphere/Ionosphere Interactions ,Research Article - Abstract
Studies of Saturn's magnetosphere with the Cassini mission have established the importance of Enceladus as the dominant mass source for Saturn's magnetosphere. It is well known that the ionosphere is an important mass source at Earth during periods of intense geomagnetic activity, but lesser attention has been dedicated to study the ionospheric mass source at Saturn. In this paper we describe a case study of data from Saturn's magnetotail, when Cassini was located at ≃ 2200 h Saturn local time at 36 R S from Saturn. During several entries into the magnetotail lobe, tailward flowing cold electrons and a cold ion beam were observed directly adjacent to the plasma sheet and extending deeper into the lobe. The electrons and ions appear to be dispersed, dropping to lower energies with time. The composition of both the plasma sheet and lobe ions show very low fluxes (sometimes zero within measurement error) of water group ions. The magnetic field has a swept‐forward configuration which is atypical for this region, and the total magnetic field strength is larger than expected at this distance from the planet. Ultraviolet auroral observations show a dawn brightening, and upstream heliospheric models suggest that the magnetosphere is being compressed by a region of high solar wind ram pressure. We interpret this event as the observation of ionospheric outflow in Saturn's magnetotail. We estimate a number flux between (2.95 ± 0.43) × 109 and (1.43 ± 0.21) × 1010 cm−2 s−1, 1 or about 2 orders of magnitude larger than suggested by steady state MHD models, with a mass source between 1.4 ×102 and 1.1 ×103 kg/s. After considering several configurations for the active atmospheric regions, we consider as most probable the main auroral oval, with associated mass source between 49.7 ±13.4 and 239.8 ±64.8 kg/s for an average auroral oval, and 10 ±4 and 49 ±23 kg/s for the specific auroral oval morphology found during this event. It is not clear how much of this mass is trapped within the magnetosphere and how much is lost to the solar wind., Key Points Tailward observation of ionospheric plasma in the magnetotail lobeEvidence for simultaneous reconnection in the plasma sheetFirst observational estimate at Saturn of mass source rate from the ionosphere to the magnetotail
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- 2016
17. Field-aligned currents in Saturn’s magnetosphere: Observations from the F-ring orbits
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Stanley W. H. Cowley, Michele K. Dougherty, G. Provan, G. J. Hunt, Emma J. Bunce, David J. Southwood, Science and Technology Facilities Council (STFC), and The Royal Society
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Engineering ,NORTHERN ,010504 meteorology & atmospheric sciences ,Saturn (rocket family) ,F-ring orbits ,FLOW ,Magnetosphere ,Library science ,Astronomy & Astrophysics ,01 natural sciences ,PERIODICITIES ,0103 physical sciences ,Boundary data ,0201 Astronomical and Space Sciences ,010303 astronomy & astrophysics ,field-aligned currents ,0105 earth and related environmental sciences ,Science & Technology ,POLAR IONOSPHERE ,business.industry ,CURRENT SYSTEMS ,CASSINI ,Planetary Data System ,MODEL ,Geophysics ,Saturn ,Space and Planetary Science ,PLANETARY PERIOD OSCILLATIONS ,Physical Sciences ,magnetosphere ,0401 Atmospheric Sciences ,Space Science ,business - Abstract
We investigate the azimuthal magnetic field signatures associated with high‐latitude field‐aligned currents observed during Cassini's F‐ring orbits (October 2016–April 2017). The overall ionospheric meridional current profiles in the northern and southern hemispheres, that is, the regions poleward and equatorward of the field‐aligned currents, differ most from the 2008 observations. We discuss these differences in terms of the seasonal change between data sets and local time (LT) differences, as the 2008 data cover the nightside while the F‐ring data cover the post‐dawn and dusk sectors in the northern and southern hemispheres, respectively. The F‐ring field‐aligned currents typically have a similar four current sheet structure to those in 2008. We investigate the properties of the current sheets and show that the field‐aligned currents in a hemisphere are modulated by that hemisphere's “planetary period oscillation” (PPO) systems. We separate the PPO‐independent and PPO‐related currents in both hemispheres using their opposite symmetry. The average PPO‐independent currents peak at ~1.5 MA/rad just equatorward of the open closed field line boundary, similar to the 2008 observations. However, the PPO‐related currents in both hemispheres are reduced by ~50% to ~0.4 MA/rad. This may be evidence of reduced PPO amplitudes, similar to the previously observed weaker equatorial oscillations at similar dayside LTs. We do not detect the PPO current systems' interhemispheric component, likely a result of the weaker PPO‐related currents and their closure within the magnetosphere. We also do not detect previously proposed lower latitude discrete field‐aligned currents that act to “turn off” the PPOs.
- Published
- 2018
18. Physical Processes in the Dusty Plasma of the Enceladus Plume
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Patrick Meier, Victoria Yaroshenko, Uwe Motschmann, and Hermann Lühr
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Dusty plasma ,010504 meteorology & atmospheric sciences ,Plasma ,Geophysics ,Enceladus flybys ,Icy moon ,Magnetometer ,01 natural sciences ,Magnetic field ,law.invention ,Plume ,symbols.namesake ,Orbiter ,law ,0103 physical sciences ,symbols ,Langmuir probe ,Environmental science ,Cassini ,PlanetMag ,Enceladus ,010303 astronomy & astrophysics ,0105 earth and related environmental sciences - Abstract
This chapter presents a short overview of physical processes in a specific plasma region (a so-called plume) found by the Cassini orbiter in the vicinity of the icy moon Enceladus. In particular, we summarize highlights of scientific results which have been performed by German research groups in GFZ German Research Centre for Geosciences, Potsdam and Technical University of Braunschweig as part of the Special Priority Program “PlanetMag” of the Deutsche Forschungsgemeinschaft between 2013 and 2016. The highlights cover mostly those theoretical and numerical studies in which measurements of different Cassini instruments could be compared with theory or where the phenomenon has a diagnostic application. Dust charging, role of dust size distributions, and dust charge fluctuations are discussed. The findings are used for interpretations of the Cassini Plasma Spectrometer data and improve constraints on the dust characteristics. Then the main forces and dust dynamics are discussed in conditions relevant for the near-Enceladus environment. It is also examined how the charged dust can affect the plasma shielding length which is of importance for the reliable Cassini Langmuir probe measurements. Considering the dust grains as heavy negative ion species, the electric conductivity tensor is modified, whose elements are the key quantities for understanding the magnetic field perturbations registered by the Cassini Magnetometer during Enceladus flybys.
- Published
- 2018
19. Distribution and Repeatability of Corneal Astigmatism Measurements (Magnitude and Axis) Evaluated With Color Light Emitting Diode Reflection Topography
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George Asimellis and Anastasios John Kanellopoulos
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Adult ,Male ,astigmatism repeatability ,Aging ,Materials science ,Adolescent ,Light ,Basic Investigation ,genetic structures ,Color ,Astigmatism ,law.invention ,Cornea ,Young Adult ,Optics ,law ,color LED reflection topography ,medicine ,Humans ,Prospective Studies ,Corneal surface ,Aged ,astigmatism shift with aging ,business.industry ,Corneal Topography ,Reproducibility of Results ,Repeatability ,Middle Aged ,medicine.disease ,eye diseases ,Ophthalmology ,Reflection (mathematics) ,axis and magnitude of astigmatism ,Magnitude (astronomy) ,Female ,Cassini ,sense organs ,business ,Corneal astigmatism ,Follow-Up Studies ,Light-emitting diode - Abstract
Purpose: To evaluate and investigate the distribution and repeatability of anterior corneal surface astigmatism measurements (axis and magnitude) using a novel corneal topographer. Methods: Anterior corneal surface astigmatism was investigated in a total of 195 eyes using a novel multicolored spot reflection topographer (Cassini; i-Optics). Two patient groups were studied, a younger-age group A and an older-age group B. Three consecutive acquisitions were obtained from each eye. The repeatability of measurement was assessed using Bland–Altman plot analysis and is reported as the coefficient of repeatability. Results: Group A (average age 34.3 years) had on average with-the-rule astigmatism, whereas the older-age group B (average age 72.3 years) had on average against-the-rule astigmatism. Average astigmatism magnitude measurement repeatability in group A was 0.4 diopters (D) and in group B 0.4 D. Average astigmatism axis measurement repeatability in group A was 5.4 degrees and in group B 5.5 degrees. The axis measurement repeatability improved with increasing magnitude of astigmatism: in the subgroups with astigmatism between 3.0 and 6.0 D, the axis repeatability was 1.4 degrees (group A) and 1.2 degrees (group B), whereas in the subgroups with astigmatism larger than 6.0 D, the repeatability was 1.1 and 0.6 degrees, respectively. Conclusions: This novel corneal topography device seems to offer high precision in reporting corneal astigmatism. This study reaffirms the established trend of a corneal astigmatism shift from an average “with-the-rule” to “against-the-rule” with aging.
- Published
- 2015
20. Influence of local ionization on ionospheric densities in Titan's upper atmosphere
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Roger V. Yelle, Erik Vigren, Véronique Vuitton, Marina Galand, Anne Wellbrock, Andrew J. Coates, Jun Cui, Luc Sagnières, and Panayotis Lavvas
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Solar System ,Extreme ultraviolet lithography ,Astrophysics ,Radiation ,Physics::Geophysics ,Ion ,Astrobiology ,Fusion, plasma och rymdfysik ,symbols.namesake ,Ionization ,Physics::Atomic and Molecular Clusters ,Astrophysics::Solar and Stellar Astrophysics ,Atmosphere of Titan ,Physics ,upper atmosphere ,Fusion, Plasma and Space Physics ,Geophysics ,Space and Planetary Science ,Physics::Space Physics ,ionization processes ,symbols ,Cassini ,Astrophysics::Earth and Planetary Astrophysics ,Ionosphere ,Titan ,Titan (rocket family) - Abstract
Titan has the most chemically complex ionosphere of the solar system. The main sources of ions on the dayside are ionization by EUV solar radiation and on the nightside include ionization by precipitated electrons from Saturn's magnetosphere and transport of ions from the dayside, but many questions remain open. How well do models predict local ionization rates? How strongly do the ionization processes drive the ionospheric densities locally? To address these questions, we have carried out an analysis of ion densities from the Ion and Neutral Mass Spectrometer (INMS) from 16 close flybys of Titan's upper atmosphere. Using a simple chemical model applied to the INMS data set, we have calculated the ion production rates and local ionization frequencies associated with primary ions and . We find that on the dayside the solar energy deposition model overestimates the INMS-derived production rates by a factor of 2. On the nightside, however, the model driven by suprathermal electron intensities from the Cassini Plasma Spectrometer Electron Spectrometer sometimes agrees and other times underestimates the INMS-derived production rates by a factor of up to 2-3. We find that below 1200km, all ion number densities correlate with the local ionization frequency, although the correlation is significantly stronger for short-lived ions than long-lived ions. Furthermore, we find that, for a given N-2 local ionization frequency, has higher densities on the dayside than on the nightside. We explain that this is due to CH4 being more efficiently ionized by solar photons than by magnetospheric electrons for a given amount of N-2 ionization.
- Published
- 2015
21. Detection of a strongly negative surface potential at Saturn's moon Hyperion
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Geraint H. Jones, Krishan K. Khurana, J. S. Leisner, Tom Nordheim, Andrew J. Coates, Norbert Krupp, William S. Kurth, Michele K. Dougherty, J. H. Waite, and Elias Roussos
- Subjects
Electron spectrometer ,Electron ,Saturn ,cps ,Saturn's moons ,Geosciences, Multidisciplinary ,Physics ,Science & Technology ,Spacecraft ,Spectrometer ,Waves in plasmas ,business.industry ,LUNAR-SURFACE ,Astronomy ,Geology ,Plasma ,Research Letters ,Geophysics ,surface charging ,Physical Sciences ,Physics::Space Physics ,E-RING ,Cathode ray ,General Earth and Planetary Sciences ,Cassini ,Astrophysics::Earth and Planetary Astrophysics ,business ,Hyperion - Abstract
On 26 September 2005, Cassini conducted its only close targeted flyby of Saturn's small, irregularly shaped moon Hyperion. Approximately 6 min before the closest approach, the electron spectrometer (ELS), part of the Cassini Plasma Spectrometer (CAPS) detected a field-aligned electron population originating from the direction of the moon's surface. Plasma wave activity detected by the Radio and Plasma Wave instrument suggests electron beam activity. A dropout in energetic electrons was observed by both CAPS-ELS and the Magnetospheric Imaging Instrument Low-Energy Magnetospheric Measurement System, indicating that the moon and the spacecraft were magnetically connected when the field-aligned electron population was observed. We show that this constitutes a remote detection of a strongly negative (~ −200 V) surface potential on Hyperion, consistent with the predicted surface potential in regions near the solar terminator.
- Published
- 2014
22. New Release of the High-Resolution Mimas Atlas derived from Cassini-ISS Images
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Roatsch, Thomas, Kersten, Elke, Matz, Klaus-Dieter, and Porco, Carolyn
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Saturnian system ,Mimas ,Cassini - Published
- 2017
23. NLDSAR - Cassini Non-Local Denoised SAR Dataset
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Antoine Lucas, Antoine Lucas, Charles Deledalle, Oded Aharonson, and Alexander Hayes
- Subjects
Speckle ,Cassini ,Non-local denoising ,Titan ,SAR - Abstract
The Cassini Synthetic Aperture Radar (SAR) has been acquiring images of Titan's surface since October 2004. Radar data suffer from speckle noise hindering interpretation of small-scale features and comparison of reimaged regions for topography derivation and potential detection. By combining a state of the art denoising algorithm with mapping and quantitative measurements we greatly offer previously unattainable insights and introducing the denoising version of the Cassini SAR named NLDSAR. The Cassini Synthetic Aperture Radar (SAR) has been acquiring images of Titan's surface since October 2004. Radar data suffer from speckle noise hindering interpretation of small-scale features and comparison of reimaged regions for topography derivation and potential detection. By combining a state of the art denoising algorithm with mapping and quantitative measurements we greatly offer previously unattainable insights and introducing the denoising version of the Cassini SAR named NLDSAR. Caltech Release [v1] is the very first (*alpha*) release that is now publicaly available with few rules of road described below. The data are corrected with incidence angle with the same emperical correction than the BIDR data set. Note that some swaths are badly navigated as reprojection has been performed since (e.g., Ta-T30,*reproc1*). Consequently, the dataset need to be used *very* wisely, therefore, any intend user of the NLDSAR data, may need to contact: Antoine Lucas (dralucas [~@~] geophysx.edu.eu.org) for further information;At least, you agree to cite the following paper in any communication (paper, conference, press release, outreach etc.): Lucas et al., Insights into Titan's geology and hydrology based on enhanced image processing of Cassini RADAR data Journal of Geophys. Research, doi:10.1002/2013JE004584, 2014. List of papers that have been based on the Caltech Release: - Insights into Titan's geology and hydrology based on enhanced image processing of Cassini RADAR data A. Lucas, O. Aharonson, C-A. Deledalle, A. Hayes, R. Kirk, E. Howington-Kraus and the CRST Journal of Geophys. Research, doi:10.1002/2013JE004584, 2014 - Growth mechanisms and dune orientation on Titan A. Lucas, S. Rodriguez, C. Narteau, B. Charnay, T. Tokano, A. Garcia, M. Thiriet, S. Courrech du Pont, A. Hayes, R. Lorenz, O. Aharonson Geophys. Research Letters, doi:10.1002/2014GL060971, 2014 - Methane storms as a driver of Titan's dune orientation B. Charnay, E. Barth, S. Rafkin, C Narteau, S. Lebonnois, S. Rodriguez, S. Courrech du Pont, A. Lucas Nature Geoscience, doi:10.1038/ngeo2406, 2015 - Compositional and spatial variations in Titan dune and interdune regions from Cassini VIMS and RADAR L. E. Bonnefoy, A. G. Hayes, P. O. Hayne, M. J. Malaska, A. Le Gall, A. Solominodou, A. Lucas Icarus, doi:10.1016/j.icarus.2015.09.014, 2015 - Sand dune patterns on Titan controlled by long-term climate cycles RC Ewing, AG Hayes, A Lucas Nature Geoscience, doi:10.1038/ngeo2323, 2015, {"references":["Lucas et al. (2014), Insights into Titan's geology and hydrology based on enhanced image processing of Cassini RADAR data, doi:10.1002/2013JE004584"]}
- Published
- 2017
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24. Ion densities and magnetic signatures of dust pickup at Enceladus
- Author
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Alexandre Wennmacher, Uwe Motschmann, Joachim Saur, Michele K. Dougherty, Sven Simon, Patrick Meier, Hendrik Kriegel, and Darrell F. Strobel
- Subjects
Physics ,Monte Carlo method ,Dust ,Plasma ,simulation ,Hybrid ,Magnetic field ,Computational physics ,Ion ,Astrobiology ,Plume ,Enceladus ,Geophysics ,Space and Planetary Science ,Ionization ,Cassini ,Pickup ,MAG data ,Astrophysics::Earth and Planetary Astrophysics ,Astrophysics::Galaxy Astrophysics - Abstract
Encedalus' plume of charged dust has been shown to strongly modify the plasma structures. Therefore, we analyze the magnetic signatures of dust to constrain the dust plume. For the first time, the mutual feedback between the nanograins and their plasma environment is investigated. Our model combines plasma simulations by means of the A.I.K.E.F. (Adaptive Ion-Kinetic Electron-Fluid) code with Monte Carlo simulations of the 3-D profiles of the gas and dust plumes. Data from several instruments of Cassini are considered: the neutral plume model is in good agreement with INMS data, whereas theoretical predictions of the peak ion density are compared against CAPS data, and properties of the dust are obtained by comparing our results with MAG data from the recent E14–E19 flybys. Our main results are (1) due to the ion-neutral chemistry, H3O+ is the predominant ion species within the plume; (2) the high nanograin densities observed by CAPS require an increased effective ionization frequency to fulfill quasi-neutrality; (3) the nanograin pickup current makes only a minor contribution to the current systems; i.e., the major contribution of the dust arises from electron absorption; (4) the pickup of nanograins is clearly visible in the magnetic field signatures, even including the distant encounter E15; (5) MAG data indicate a southward extension of the charged dust plume of at least 4 Enceladus radii; (6) the modification of the currents by the nanograins is responsible for the surprising fact that Cassini did not detect a region with a reduced magnetic field strength.
- Published
- 2014
25. Recent improvements of the Saturnian satellites atlases: Mimas, Enceladus, and Dione
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E. Kersten, T. Roatsch, Angelika Hoffmeister, Klaus-Dieter Matz, Marita Wählisch, and Carolyn C. Porco
- Subjects
Icy satellites ,Saturninan system ,Space and Planetary Science ,Astronomy ,Cassini ,Astronomy and Astrophysics ,Imaging science ,Enceladus ,Saturnian ,Geology ,Saturnian system ,Astrobiology - Abstract
The Cassini Imaging Science Subsystem (ISS) acquired many high-resolution images (
- Published
- 2013
26. Imaging observationplanning for Dione, Rhea, Iapetus, and Phoebe in the Cassini primary mission
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Denk, Tilmann, Roatsch, Thomas, and Matz, Klaus-Dieter
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Saturn ,Icy satellites ,Cassini - Published
- 2016
27. Saturnian moon Iapetus - Global albedo enigma and Cassini ISS observations
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Denk, T., Spencer, J.R., Roatsch, Thomas, Schmedemann, Nico, and Galuba, Goetz
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Iapetus ,Cassini - Published
- 2016
28. Cartography of the medium-sized Saturnian satellites based on Cassini-ISS images
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Roatsch, Thomas, Kersten, Elke, Matz, Klaus-Dieter, Scholten, Frank, Wagner, Roland, and Porco, Carolyn
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Saturn ,Icy satellites ,Cassini - Published
- 2016
29. Completed global control network and basemap of Enceladus
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Becker, T.L., Bland, M., Edmundson, K., Soderblom, L.A., Takir, D., Patterson, G.W., Collins, G.C., Pappalardo, R.T., Roatsch, Thomas, and Schenk, P.
- Subjects
Enceladus ,control network ,Cassini - Published
- 2016
30. Stellar Astrophysics With Cassini: Syzygies, Stardust, and the Sizes Of Stars
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Stewart, Paul Nathan
- Subjects
mira ,circumstellar enviornment ,stellar imaging ,Astrophysics::Solar and Stellar Astrophysics ,Cassini ,Astrophysics::Cosmology and Extragalactic Astrophysics ,Astrophysics::Earth and Planetary Astrophysics ,Astrophysics::Galaxy Astrophysics - Abstract
The Cassini spacecraft has been exploring the complex and fascinating Saturnian system for over a decade. This thesis presents Cassini observations employed for the study of evolved stars. Utilising the on-board near-infrared spectrometer, we demonstrate the recovery of flux calibrated stellar spectra. Data were taken from a publicly-accessible archive, and the overwhelming majority were obtained for various spacecraft engineering and calibration purposes; their application to stellar astrophysics being an opportunistic extension to the mission outcomes. An atlas of stellar spectra has been compiled utilising existing observations acquired to monitor the performance of the instrument. Exploiting archival observations of stars as they are occulted by edges within Saturn’s rings, we demonstrate the recovery of stellar spatial information, specifically angular diameters, and compare these to measurements from ground-based interferometry. High-resolution two-dimensional images of stellar environments are reconstructed by tomographically combining these occultation observations from different edges within the planetary rings. An extensive astrophysical study of the evolved star Mira employing all of these techniques over multiple epochs reveals spectrally dependant molecular shells in its extended atmosphere, and allows for the appraisal of state-of-the-art models which aim to describe the atmospheres of such stars. Finally, the carbon star, IRC+10216 is shown to be embedded in a dynamic shroud of thick dusty circumstellar clouds, challenging existing models of the inner structure of the stellar environment.
- Published
- 2016
31. Magnetic reconnection in Saturn's magnetotail: A comprehensive magnetic field survey
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A W, Smith, C M, Jackman, and M F, Thomsen
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Solar Physics, Astrophysics, and Astronomy ,Planetary Magnetospheres ,Planetary Sciences: Solar System Objects ,Saturn ,Magnetospheres ,Physics::Space Physics ,Space Plasma Physics ,Magnetospheric Physics ,Data Analysis: Algorithms and Implementation ,Magnetic Reconnection ,Planetary Sciences: Comets and Small Bodies ,Cassini ,Astrophysics::Earth and Planetary Astrophysics ,Computational Geophysics ,Magnetotail ,Planetary Sciences: Solid Surface Planets ,Planetary Sciences: Fluid Planets ,Research Articles ,Research Article - Abstract
Reconnection within planetary magnetotails is responsible for locally energizing particles and changing the magnetic topology. Its role in terms of global magnetospheric dynamics can involve changing the mass and flux content of the magnetosphere. We have identified reconnection related events in spacecraft magnetometer data recorded during Cassini's exploration of Saturn's magnetotail. The events are identified from deflections in the north‐south component of the magnetic field, significant above a background level. Data were selected to provide full tail coverage, encompassing the dawn and dusk flanks as well as the deepest midnight orbits. Overall 2094 reconnection related events were identified, with an average rate of 5.0 events per day. The majority of events occur in clusters (within 3 h of other events). We examine changes in this rate in terms of local time and latitude coverage, taking seasonal effects into account. The observed reconnection rate peaks postmidnight with more infrequent but steady loss seen on the dusk flank. We estimate the mass loss from the event catalog and find it to be insufficient to balance the input from the moon Enceladus. Several reasons for this discrepancy are discussed. The reconnection X line location appears to be highly variable, though a statistical separation between events tailward and planetward of the X line is observed at a radial distance of between 20 and 30R S downtail. The small sample size at dawn prevents comprehensive statistical comparison with the dusk flank observations in terms of flux closure., Key Points New algorithm developed to find reconnection related events in spacecraft magnetometer dataThe 2094 events identified across the magnetotail at an average rate of 5.0 per dayReconnection X line location appears to be highly variable
- Published
- 2015
32. Structured ionospheric outflow during the Cassini T55–T59 Titan flybys
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Jan-Erik Wahlund, Michiko Morooka, David Andrews, Andrew J. Coates, Cesar Bertucci, Anne Wellbrock, Niklas J. T. Edberg, Stan W. H. Cowley, M. K. Dougherty, and K. Ågren
- Subjects
Physics ,Atmospheric escape ,Ambipolar diffusion ,Ciencias Físicas ,Magnetosphere ,Astronomy and Astrophysics ,Astrophysics ,Geophysics ,Plume ,Astronomía ,symbols.namesake ,Current sheet ,Space and Planetary Science ,symbols ,Cassini ,Outflow ,Ionosphere ,Titan ,Titan (rocket family) ,CIENCIAS NATURALES Y EXACTAS - Abstract
During the final three of the five consecutive and similar Cassini Titan flybys T55–T59 we observe a region characterized by high plasma densities (electron densities of 1–8 cm3 ) in the tail/nightside of Titan. This region is observed progressively farther downtail from pass to pass and is interpreted as a plume of ionospheric plasma escaping Titan, which appears steady in both location and time. The ions in this plasma plume are moving in the direction away from Titan and are a mixture of both light and heavy ions with composition revealing that their origin are in Titan’s ionosphere, while the electrons are more isotropically distributed. Magnetic field measurements indicate the presence of a current sheet at the inner edge of this region. We discuss the mechanisms behind this outflow, and suggest that it could be caused by ambipolar diffusion, magnetic moment pumping or dispersive Alfve´n waves. Fil: Edberg, N. J. T.. Swedish Institute of Space Physics; Suecia Fil: Ågren, K.. Swedish Institute of Space Physics; Suecia Fil: Wahlund, J. E.. Swedish Institute of Space Physics; Suecia Fil: Morooka, M. W.. Swedish Institute of Space Physics; Suecia Fil: Andrews, D. J.. University of Leicester; Reino Unido Fil: Cowley, S. W. H.. University of Leicester; Reino Unido Fil: Wellbrock, A.. University College London; Estados Unidos Fil: Coates, A. J.. University College London; Estados Unidos Fil: Bertucci, Cesar. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Dougherty, M. K.. Imperial College London; Reino Unido
- Published
- 2011
33. High-resolution Dione atlas derived from Cassini-ISS images
- Author
-
E. Kersten, Frank Scholten, G. Neukum, Tilmann Denk, Carolyn C. Porco, Marita Wählisch, Klaus-Dieter Matz, T. Roatsch, Roland Wagner, and Angelika Hoffmeister
- Subjects
Icy Satellites ,Space and Planetary Science ,Atlas (topology) ,Planetary Mapping ,High resolution ,Cassini ,Astronomy and Astrophysics ,Imaging science ,Geology ,Saturnian system ,Remote sensing - Abstract
The Cassini imaging science subsystem (ISS) acquired 449 high-resolution images ( http://ciclops.org/maps ].
- Published
- 2008
34. High-resolution Enceladus atlas derived from Cassini-ISS images
- Author
-
Bernd Giese, Angelika Hoffmeister, Gerhard Neukum, Frank Scholten, Paul Helfenstein, Carolyn C. Porco, Roland Wagner, Marita Wählisch, Thomas Roatsch, Anne Kuhn, and Klaus-Dieter Matz
- Subjects
Icy Satellites ,Enceladus ,Space and Planetary Science ,Atlas (topology) ,High resolution ,Astronomy ,Cassini ,Astronomy and Astrophysics ,Imaging science ,Geology ,Saturnian system ,Remote sensing - Abstract
The Cassini Imaging Science Subsystem (ISS) acquired 377 high-resolution images ( http://ciclops.org/maps ).
- Published
- 2008
35. A new Enceladus base map and global control network in support of geological mapping
- Author
-
Bland, M. T., Becker, T.L., Edmundson, K., Patterson, G.W., Collins, G., Pappalardo, R.T., Kattenhorn, Simon, Roatsch, Thomas, and Schenk, P.
- Subjects
Enceladus ,Cassini ,Saturnian satellites - Published
- 2015
36. Topographic modeling of Phoebe using Cassini images
- Author
-
Bernd Giese, Tilmann Denk, Gerhard Neukum, Thomas Roatsch, and Carolyn C. Porco
- Subjects
Digital image correlation ,Orientation (computer vision) ,Astronomy and Astrophysics ,Radius ,craters ,topographic mapping ,Geodesy ,Phoebe ,Impact crater ,Space and Planetary Science ,digital terrain model ,Saturn ,Cassini ,Imaging science ,Digital elevation model ,Image resolution ,Geology ,Remote sensing - Abstract
High-resolution Cassini stereo images of Saturn's moon Phoebe have been used to derive a regional digital terrain model (DTM) and an orthoimage mosaic of the surface. For DTM-control a network of 130 points measured in 14 images (70–390 m/pixel resolution) was established which was simultaneously used to determine the orientation of the spin-axis. The J2000 spin-axis was found at Dec=78.0°±0.1° and RA=356.6°±0.3°, substantially different from the former Voyager solution. The control points yield a mean figure radius of 107.2 km with RMS residuals of 6.2 km demonstrating the irregular shape of this body. The DTM was computed from densely spaced conjugate image points determined by methods of digital image correlation. It has a horizontal resolution of 1–2 km and vertical accuracies in the range 50–100 m. It is limited in coverage, but higher in resolution than the previously derived global shape model of Phoebe [Porco et al., 2005. Cassini imaging science: initial results on Phoebe and Iapetus. Science 307, 1237–1242] and allows us to study the morphology of the surface in more detail. There is evidence for unconsolidated material from a steep and smooth slope at the rim of a 100 km impact feature. There are several conically shaped craters on Phoebe, which may hint at highly porous and low compaction material on the surface.
- Published
- 2006
37. Mapping of the icy Saturnian satellites: First results from Cassini-ISS
- Author
-
Frank Scholten, Peter C. Thomas, Tilmann Denk, Carolyn C. Porco, Paul Helfenstein, Klaus-Dieter Matz, Marita Wählisch, G. Neukum, T. Roatsch, and Angelika Hoffmeister
- Subjects
Saturn ,Icy satellites ,Space and Planetary Science ,Astronomy ,Cassini ,Astronomy and Astrophysics ,Saturnian ,Enceladus ,Geology ,Astrobiology ,Saturnian system - Abstract
Images of the icy Saturnian satellites Mimas, Enceladus, Tethys, Dione, Rhea, Iapetus, and Phoebe, derived by the Voyager and Cassini cameras are used to produce new local high-resolution image mosaics as well as global mosaics [http://ciclops.org, http://photojournal.jpl.nasa.gov]. These global mosaics are valuable both for scientific interpretation and for the planning of future flybys later in the ongoing Cassini orbital tour. Furthermore, these global mosaics can be extended to standard cartographic products.
- Published
- 2006
38. The Sand Seas of Titan: Cassini RADAR Observations of Longitudinal Dunes
- Author
-
Howard A. Zebker, L. Roth, Ralph D. Lorenz, Bryan Stiles, Charles Elachi, Y. Anderson, Ellen R. Stofan, Roberto Seu, K. Kelleher, Giovanni Picardi, Gian Gabriele Ori, K. L. Mitchell, E. Reffet, Duane O. Muhleman, Jonathan I. Lunine, Jani Radebaugh, Enrico Flamini, G. Boubin, Yonggyu Gim, Lauren Wye, S. D. Wall, G. Francescetti, Robert West, Matthew A. Allison, S. Vetrella, Rosaly M. C. Lopes, G. Hamilton, Philip S. Callahan, Laurence A. Soderblom, R. Boehmer, S. Shaffer, Steven J. Ostro, Randolph L. Kirk, Pierre Encrenaz, Scott Hensley, M. A. Janssen, Flora Paganelli, William L. Johnson, Francesco Posa, Charles A. Wood, R. D., Lorenz, S., Wall, J., Radebaugh, G., Boubin, E., Reffet, M., Janssen, E., Stofan, R., Lope, R., Kirk, C., Elachi, J., Lunine, K., Mitchell, F., Paganelli, L., Soderblom, C., Wood, L., Wye, H., Zebker, Y., Anderson, S., Ostro, M., Allison, R., Boehmer, P., Callahan, P., Encrenaz, G. G., Ori, Franceschetti, Giorgio, Y., Gim, G., Hamilton, S., Hensley, W., Johnson, K., Kelleher, D., Muhleman, G., Picardi, F., Posa, L., Roth, R., Seu, S., Shaffer, B., Stile, Vetrella, Sergio, E., Flamini, R., West, Lunar and Planetary Laboratory [University of Arizona] (LPL), University of Arizona, Jet Propulsion Laboratory, California Institute of Technology (JPL), Proxemy Research, Bowie, US Geological Survey, Flagstaff, Planetary Science Institute, Tucson, AZ 85719, USA and Wheeling Jesuit College, Wheeling, Stanford University, Goddard Institute for Space Studies, National Aeronautics and Space Administration New York, Observatoire de Paris, Université Paris sciences et lettres (PSL), Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique (LERMA), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université de Cergy Pontoise (UCP), Université Paris-Seine-Université Paris-Seine-Centre National de la Recherche Scientifique (CNRS), Instrumentation et télédétection, Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique et Atmosphères = Laboratory for Studies of Radiation and Matter in Astrophysics and Atmospheres (LERMA), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-CY Cergy Paris Université (CY)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-CY Cergy Paris Université (CY), International Research School of Planetary Sciences, Dipartimento di Scienze, Università d'Annunzio, Facoltá di Ingegneria, Geological and Planetary Sciences, California Institute of Technology, Pasadena, Universitá La Sapienza, Istituto Nazionale per la Fisica della Materia (INFM) and Dip. Interateneo di Fisica, and Agenzia Spaziale Italiana (ASI)
- Subjects
Geologic Sediments ,Radar ,Multidisciplinary ,Extraterrestrial Environment ,Titan moon ,Wind ,Hydrocarbons ,Radar observations ,Radar imaging ,Wavelength ,symbols.namesake ,Saturn ,Surface winds ,symbols ,Cassini ,Particle Size ,Spacecraft ,[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph] ,Titan (rocket family) ,Methane ,Geomorphology ,Geology ,Remote sensing - Abstract
The most recent Cassini RADAR images of Titan show widespread regions (up to 1500 kilometers by 200 kilometers) of near-parallel radar-dark linear features that appear to be seas of longitudinal dunes similar to those seen in the Namib desert on Earth. The Ku-band (2.17-centimeter wavelength) images show approximately 100-meter ridges consistent with duneforms and reveal flow interactions with underlying hills. The distribution and orientation of the dunes support a model of fluctuating surface winds of approximately 0.5 meter per second resulting from the combination of an eastward flow with a variable tidal wind. The existence of dunes also requires geological processes that create sand-sized (100- to 300-micrometer) particulates and a lack of persistent equatorial surface liquids to act as sand traps.
- Published
- 2006
39. Release of volatiles from a possible cryovolcano from near-infrared imaging of Titan
- Author
-
S. Lemouelic, P. D. Nicholson, Angioletta Coradini, Katrin Stephan, L. A. Soderblom, C.K. Scholz, Priscilla Cerroni, Yves Langevin, Giancarlo Bellucci, Robert H. Brown, Kevin H. Baines, Dale P. Cruikshank, Vittorio Formisano, Sebastien Rodriguez, Robert M. Nelson, Christophe Sotin, Pierre Drossart, Ralf Jaumann, Thomas B. McCord, Dennis L. Matson, Bruno Sicardy, Fabrizio Capaccioni, Bonnie J. Buratti, Jean-Pierre Bibring, M. Combes, Roger N. Clark, Laboratoire de Planétologie et Géodynamique [UMR 6112] (LPG), Université d'Angers (UA)-Université de Nantes - UFR des Sciences et des Techniques (UN UFR ST), Université de Nantes (UN)-Université de Nantes (UN)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Jet Propulsion Laboratory (JPL), NASA-California Institute of Technology (CALTECH), Astrogeology Science Center [Flagstaff], United States Geological Survey [Reston] (USGS), Istituto di Fisica dello Spazio Interplanetario (IFSI), National Research Council of Italy | Consiglio Nazionale delle Ricerche (CNR), Institut d'astrophysique spatiale (IAS), Université Paris-Sud - Paris 11 (UP11)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National d’Études Spatiales [Paris] (CNES), Laboratoire d'études spatiales et d'instrumentation en astrophysique (LESIA), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Paris Diderot - Paris 7 (UPD7)-Centre National de la Recherche Scientifique (CNRS), NASA Ames Research Center (ARC), Department of Earth and Space Sciences [Seattle], and University of Washington [Seattle]
- Subjects
Solar System ,Extraterrestrial Environment ,010504 meteorology & atmospheric sciences ,[PHYS.ASTR.EP]Physics [physics]/Astrophysics [astro-ph]/Earth and Planetary Astrophysics [astro-ph.EP] ,Infrared Rays ,Infrared ,cryovolcanism ,Saturnian satellites ,near-infrared ,01 natural sciences ,Methane ,Astrobiology ,symbols.namesake ,chemistry.chemical_compound ,0103 physical sciences ,Photography ,VIMS ,Spacecraft ,Atmosphere of Titan ,Moon ,010303 astronomy & astrophysics ,ComputingMilieux_MISCELLANEOUS ,0105 earth and related environmental sciences ,geography ,Multidisciplinary ,Life on Titan ,geography.geographical_feature_category ,Geography ,Atmosphere ,Ice ,Cryovolcano ,Hydrocarbons ,Satellites de Glace ,Saturn ,Volcano ,chemistry ,13. Climate action ,symbols ,Environmental science ,Cassini ,Gases ,Titan ,Titan (rocket family) - Abstract
The surface of Saturn's largest moon, Titan, is coated in a dense methane-rich atmosphere that prevents high-resolution imaging at visible wavelengths. During its first Titan flyby last October, the Cassini spacecraft's visual and infrared mapping spectrometer (VIMS) was able to reveal detailed surface structures, as reported in this issue. Notable features include a circular structure 30 km in diameter, thought to be a cryogenic dome. This may be volcanic, which could explain how the methane in Titan's atmosphere is replenished. Titan is the only satellite in our Solar System with a dense atmosphere. The surface pressure is 1.5 bar (ref. 1) and, similar to the Earth, N2 is the main component of the atmosphere. Methane is the second most important component2, but it is photodissociated on a timescale of 107 years (ref. 3). This short timescale has led to the suggestion that Titan may possess a surface or subsurface reservoir of hydrocarbons4,5 to replenish the atmosphere. Here we report near-infrared images of Titan obtained on 26 October 2004 by the Cassini spacecraft. The images show that a widespread methane ocean does not exist; subtle albedo variations instead suggest topographical variations, as would be expected for a more solid (perhaps icy) surface. We also find a circular structure ∼30 km in diameter that does not resemble any features seen on other icy satellites. We propose that the structure is a dome formed by upwelling icy plumes that release methane into Titan's atmosphere.
- Published
- 2005
40. The Cassini solar Faraday rotation experiment
- Author
-
Christopher T. Russell, John D. Anderson, Luciano Iess, Michael K. Bird, E. A. Jensen, and Sami W. Asmar
- Subjects
cassini ,coronal magnetic field ,faraday rotation ,k-band ,x-band ,Atmospheric Science ,Electron density ,Aerospace Engineering ,Solar radius ,symbols.namesake ,Faraday effect ,Physics ,Solar conjunction ,Astronomy ,Astronomy and Astrophysics ,Solar maximum ,Polarization (waves) ,Magnetic field ,Computational physics ,Geophysics ,Space and Planetary Science ,Physics::Space Physics ,symbols ,General Earth and Planetary Sciences ,Astrophysics::Earth and Planetary Astrophysics ,Ionosphere - Abstract
The Cassini Faraday rotation experiment improves the current understanding of the coronal magnetic field by making the first measurements of the magnetic field within two solar radii of the south pole and by allowing the separation of the changing electron density from the magnetic field during transient crossings of the line of sight. Simultaneous ranging data to Cassini also contributes to the growing body of empirical electron density models by providing electron density data at solar maximum at varying latitudes including over the poles. Faraday rotation data in the solar corona were collected in 2002 and 2003 using the Cassini spacecraft in cruise to Saturn. Although Cassini primarily transmits in right-hand polarization, enough left-hand is produced to enable polarization measurements. We show that during solar conjunction Faraday rotation is measurable with Cassini. In the X- and Ka-bands both datasets currently show an asymmetric diurnal pattern in polarization not associated with the ionosphere. The Ka-band is much more sensitive to pointing accuracy and experienced periods of power drop outs which caused the left-circularly polarized signal to drop into the noise on occasion during the 2003 conjunction. Interpretation of the dataset is deferred to future papers.
- Published
- 2005
41. Radar: The Cassini Titan Radar Mapper
- Author
-
Steven J. Ostro, Randolph L. Kirk, Laurence A. Soderblom, L. Borgarelli, Giovanni Picardi, M. A. Janssen, Duane O. Muhleman, Pierre Encrenaz, Francesco Posa, L.E. Roth, Charles A. Wood, Chris Rapley, Michael Allison, Ralph D. Lorenz, Jonathan I. Lunine, William T. K. Johnson, Charles Elachi, Howard A. Zebker, Eastwood Im, Roberto Seu, S. Vetrella, S. D. Wall, C., Elachi, M. D., Allison, L., Borgarelli, E., Encrenaz, E., Im, M. A., Janssen, W. T. K., Johnson, R. L., Kirk, R. D., Lorenz, J. I., Lunine, D. O., Muhleman, S. J., Ostro, G., Picardi, F., Posa, C. G., Rapley, L. E., Roth, R., Seu, L. A., Soderblom, Vetrella, Sergio, S. D., Wall, C. A., Wood, H. A., Zebker, Jet Propulsion Laboratory, California Institute of Technology (JPL), Goddard Institute for Space Studies, National Aeronautics and Space Administration New York, Alenia Aerospazio, Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique (LERMA), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université de Cergy Pontoise (UCP), Université Paris-Seine-Université Paris-Seine-Centre National de la Recherche Scientifique (CNRS), Instrumentation et télédétection, Laboratoire d'Etude du Rayonnement et de la Matière en Astrophysique et Atmosphères = Laboratory for Studies of Radiation and Matter in Astrophysics and Atmospheres (LERMA), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-CY Cergy Paris Université (CY)-École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS)-CY Cergy Paris Université (CY), US Geological Survey, Flagstaff, Lunar and Planetary Laboratory [University of Arizona] (LPL), University of Arizona, Geological and Planetary Sciences, California Institute of Technology, Pasadena, Universitá La Sapienza, Dipartimento Interateneo di Fisica, Politecnico di Bari, British Antarctic Survey, Natural Environment Research Council, Facoltá di Ingegneria, University of North Dakota, and Stanford University
- Subjects
Radar altimeter ,Titan moon ,Astronomy and Astrophysics ,Scatterometer ,Space-based radar ,law.invention ,Radar engineering details ,Radar astronomy ,Space and Planetary Science ,law ,Radar imaging ,3D radar ,Cassini ,Radar ,[PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph] ,Remote sensing - Abstract
International audience; The Cassini RADAR instrument is a multimode 13.8 GHz multiple-beam sensor that can operate as a synthetic-aperture radar (SAR) imager, altimeter, scatterometer, and radiometer. The principal objective of the RADAR is to map the surface of Titan. This will be done in the imaging, scatterometer, and radiometer modes. The RADAR altimeter data will provide information on relative elevations in selected areas. Surfaces of the Saturn's icy satellites will be explored utilizing the RADAR radiometer and scatterometer modes. Saturn's atmosphere and rings will be probed in the radiometer mode only. The instrument is a joint development by JPL/NASA and ASI. The RADAR design features significant autonomy and data compression capabilities. It is expected that the instrument will detect surfaces with backscatter coefficient as low as -40 dB.
- Published
- 2004
42. Cassini/VIMS observations of the moon
- Author
-
Roger N. Clark, Kevin H. Baines, Jean-Pierre Bibring, P. D. Nicholson, Bruno Sicardy, Dennis L. Matson, Angioletta Coradini, Yves Langevin, Thomas B. McCord, E. Miller, Bonnie J. Buratti, Fabrizio Capaccioni, Pierre Drossart, Vittorio Formisano, Ralf Jaumann, Christophe Sotin, Vito Mennella, Robert H. Brown, Robert M. Nelson, Giancarlo Bellucci, Priscilla Cerroni, and Dale P. Cruikshank
- Subjects
Atmospheric Science ,Spectrometer ,Infrared ,VIMS spectra ,Aerospace Engineering ,Astronomy ,Astronomy and Astrophysics ,Lunar limb ,Spectral line ,Astrobiology ,Geophysics ,Space and Planetary Science ,General Earth and Planetary Sciences ,Cassini ,Moon ,Geology - Abstract
In this paper, we present preliminary scientific results obtained from the analysis of VIMS (Visible and Infrared Mapping Spectrometer) lunar images and spectra. These data were obtained during the Cassini Earth flyby in August 1999. Spectral ratios have been produced in order to derive lunar mineralogical maps. Some spectra observed at the north-east lunar limb, show few unusual absorption features located at 0.357, 0.430 and 0.452 μm, the origin of which is presently unknown.
- Published
- 2002
43. 10 Years of Mapping the Icy Saturnian Satellites
- Author
-
Roatsch, Thomas, Kersten, Elke, Matz, Klaus-Dieter, and Porco, Carolyn
- Subjects
Cartography ,Planetary Mapping ,Cassini ,Saturnian satellites - Published
- 2014
44. Cusp observation at Saturn's high-latitude magnetosphere by the Cassini spacecraft
- Author
-
J M, Jasinski, C S, Arridge, L, Lamy, J S, Leisner, M F, Thomsen, D G, Mitchell, A J, Coates, A, Radioti, G H, Jones, E, Roussos, N, Krupp, D, Grodent, M K, Dougherty, and J H, Waite
- Subjects
Physics::Plasma Physics ,Physics::Space Physics ,Research Letter ,reconnection ,Astrophysics::Solar and Stellar Astrophysics ,cusp ,dispersion ,Cassini ,Astrophysics::Earth and Planetary Astrophysics ,plasma - Abstract
We report on the first analysis of magnetospheric cusp observations at Saturn by multiple in situ instruments onboard the Cassini spacecraft. Using this we infer the process of reconnection was occurring at Saturn's magnetopause. This agrees with remote observations that showed the associated auroral signatures of reconnection. Cassini crossed the northern cusp around noon local time along a poleward trajectory. The spacecraft observed ion energy-latitude dispersions—a characteristic signature of the terrestrial cusp. This ion dispersion is “stepped,” which shows that the reconnection is pulsed. The ion energy-pitch angle dispersions suggest that the field-aligned distance from the cusp to the reconnection site varies between ∼27 and 51 RS. An intensification of lower frequencies of the Saturn kilometric radiation emissions suggests the prior arrival of a solar wind shock front, compressing the magnetosphere and providing more favorable conditions for magnetopause reconnection. Key Points We observe evidence for reconnection in the cusp plasma at Saturn We present evidence that the reconnection process can be pulsed at Saturn Saturn's cusp shows similar characteristics to the terrestrial cusp
- Published
- 2014
45. Evidence for a Polar Ethane Cloud on Titan
- Author
-
Vincent Boudon, Christopher P. McKay, Pascal Rannou, Robert H. Brown, B. J. Buratti, Caitlin A. Griffith, Ralf Jaumann, P. D. Nicholson, Athena Coustenis, Pierre Drossart, Paulo Penteado, Kevin H. Baines, Roger N. Clark, A. Negrao, Service d'aéronomie (SA), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)
- Subjects
North pole ,Extraterrestrial Environment ,010504 meteorology & atmospheric sciences ,Photochemistry ,Infrared ,Atmospheric sciences ,01 natural sciences ,Latitude ,Astrobiology ,Ethane Cloud ,Saturnian System ,Troposphere ,symbols.namesake ,0103 physical sciences ,VIMS ,Spacecraft ,010303 astronomy & astrophysics ,0105 earth and related environmental sciences ,[PHYS.PHYS.PHYS-AO-PH]Physics [physics]/Physics [physics]/Atmospheric and Oceanic Physics [physics.ao-ph] ,Ethane ,Multidisciplinary ,Atmosphere ,Ice ,Cold Temperature ,Saturn ,13. Climate action ,symbols ,Polar ,Cassini ,Gases ,Titan ,Titan (rocket family) ,Methane ,Geology - Abstract
Spectra from Cassini's Visual and Infrared Mapping Spectrometer reveal the presence of a vast tropospheric cloud on Titan at latitudes 51 degrees to 68 degrees north and all longitudes observed (10 degrees to 190 degrees west). The derived characteristics indicate that this cloud is composed of ethane and forms as a result of stratospheric subsidence and the particularly cool conditions near the moon's north pole. Preferential condensation of ethane, perhaps as ice, at Titan's poles during the winters may partially explain the lack of liquid ethane oceans on Titan's surface at middle and lower latitudes.
- Published
- 2006
46. Cartographic Mapping of the Icy Satellites using Cassini ISS images
- Author
-
Kersten, Elke, Roatsch, Thomas, Hoffmeister, Angelika, and Porco, C. C.
- Subjects
Satunian satellites ,Cassini ,Planetray Mapping - Published
- 2013
47. Recent Improvements of the Atlases of the Saturnian Satellites Mimas and Enceladus
- Author
-
Kersten, Elke, Roatsch, Thomas, Hoffmeister, Angelika, Matz, Klaus-Dieter, Preusker, Frank, Wagner, Roland, Helfenstein, Paul, and Porco, Carolyn
- Subjects
Icy satellites ,Cassini - Published
- 2012
48. Jetting Activity and Thermal Emission across the South Polar Terrain of Enceladus: Observations and Comparisons with Shear-Heating Models
- Author
-
Porco, Carolyn, DiNino, Daiana, Nimmo, Francis, Ingersoll, Andrew, Helfenstein, Paul, Roatsch, Thomas, and Mitchell, Colin
- Subjects
Enceladus ,Icy Satellites ,Cassini - Published
- 2012
49. Photometric Observations of Interstellar Hydrogen by HDAC: In-flight Calibration and First Results
- Author
-
Keller, Horst-Uwe, Skorov, Y., Katushkina, O., Izmodenov, V., Reulke, Ralf, and Glassmeier, K.
- Subjects
Lyman ,HDAC ,SPICA ,Cassini - Published
- 2012
50. Dark and Bright Albedo Changes in the Wake of a Titan Rainstorm
- Author
-
Barnes, Jason W., Buratti, B. J., Turtle, E. P., Bow, J., Dalba, P. A., Perry, J., Rodriguez, S., LeMouelic, S., Baines, K. H., Sotin, C., Lorenz, R. D., Malaska, M. J., McCord, T. B., Clark, R. N., Jaumann, R., Hayne, P. O., Nicholson, P. D., Soderblom, J. M., and Soderblom, L. A.
- Subjects
Albedo ,ISS ,VIMS ,Cassini ,Titan - Published
- 2012
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