Cassini imaging of Jupiter's atmosphere, satellites, and rings.
Southwest Research Institute1, California Institute of Technology2, University of Arizona3, Goddard Institute for Space Studies4, Cornell University5, Queen Mary University of London6, University of Paris7, Free University of Berlin8, German Aerospace Center9, University of California, Los Angeles10
07 Mar 2003-Science (American Association for the Advancement of Science)-Vol. 299, Iss: 5612, pp 1541-1547
TL;DR: Findings on Jupiter's zonal winds, convective storms, low-latitude upper troposphere, polar stratosphere, and northern aurora are reported, including previously unseen emissions arising from Io and Europa in eclipse, and a giant volcanic plume over Io's north pole are described.
Abstract: The Cassini Imaging Science Subsystem acquired about 26,000 images of the Jupiter system as the spacecraft encountered the giant planet en route to Saturn. We report findings on Jupiter's zonal winds, convective storms, low-latitude upper troposphere, polar stratosphere, and northern aurora. We also describe previously unseen emissions arising from Io and Europa in eclipse, a giant volcanic plume over Io's north pole, disk-resolved images of the satellite Himalia, circumstantial evidence for a causal relation between the satellites Metis and Adrastea and the main jovian ring, and information on the nature of the ring particles.
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TL;DR: A forward modelling approach has been used to relate observations at cloud level to models of shallow or deep jet structure as mentioned in this paper. But the model cannot reproduce all of the observed phenomena, including the stability of Jupiter's zonal jets and the evolution of vortices.
Abstract: The Galileo and Cassini spacecrafts have greatly enhanced the observational record of Jupiter's tropospheric dynamics, particularly through returning high spatial resolution, multi-spectral and global imaging data with episodic coverage over periods of months to years. These data, along with those from Earth-based telescopes, have revealed the stability of Jupiter's zonal jets, captured the evolution of vortices and equatorial waves, and mapped the distributions of lightning and moist convection. Because no observations of Jupiter's interior exist, a forward modelling approach has been used to relate observations at cloud level to models of shallow or deep jet structure, shallow or deep jet forcing and energy transfer between turbulence, vortices and jets. A range of observed phenomena can be reproduced in shallow models, though the Galileo probe winds and jet stability arguments hint at the presence of deep jets. Many deep models, however, fail to reproduce Jupiter-like non-zonal features (e.g. vortices). Jupiter's dynamics likely include both deep and shallow processes, requiring an integrated approach to future modelling—an important goal for the post-Galileo and Cassini era.
389 citations
TL;DR: The Cassini Imaging Science Subsystem (ISS) is the highest-resolution two-dimensional imaging device on the Cassini Orbiter and has been designed for investigations of the bodies and phenomena found within the Saturnian planetary system.
Abstract: The Cassini Imaging Science Subsystem (ISS) is the highest-resolution two-dimensional imaging device on the Cassini Orbiter and has been designed for investigations of the bodies and phenomena found within the Saturnian planetary system. It consists of two framing cameras: a narrow angle, reflecting telescope with a 2-m focal length and a square field of view (FOV) 0.35∘ across, and a wide-angle refractor with a 0.2-m focal length and a FOV 3.5∘ across. At the heart of each camera is a charged coupled device (CCD) detector consisting of a 1024 square array of pixels, each 12 μ on a side. The data system allows many options for data collection, including choices for on-chip summing, rapid imaging and data compression. Each camera is outfitted with a large number of spectral filters which, taken together, span the electromagnetic spectrum from 200 to 1100 nm. These were chosen to address a multitude of Saturn-system scientific objectives: sounding the three-dimensional cloud structure and meteorology of the Saturn and Titan atmospheres, capturing lightning on both bodies, imaging the surfaces of Saturn’s many icy satellites, determining the structure of its enormous ring system, searching for previously undiscovered Saturnian moons (within and exterior to the rings), peering through the hazy Titan atmosphere to its yet-unexplored surface, and in general searching for temporal variability throughout the system on a variety of time scales. The ISS is also the optical navigation instrument for the Cassini mission. We describe here the capabilities and characteristics of the Cassini ISS, determined from both ground calibration data and in-flight data taken during cruise, and the Saturn-system investigations that will be conducted with it. At the time of writing, Cassini is approaching Saturn and the images returned to Earth thus far are both breathtaking and promising.
379 citations
Cites background or methods from "Cassini imaging of Jupiter's atmosp..."
...These provide the best visibility of stratospheric aerosols and potential UV auroral phenomena (as observed at Jupiter; Porco et al. 2003), and may aid discrimination of satellite and ring surface materials of special interest such as carbonaceous materials (Wagner et al., 1987)....
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...In contrast, ISS can image the aurora in visible light on the night side of the planet, and with much higher spatial resolution, than HST; it did so at Jupiter (Porco et al., 2003)....
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...Multi-spectral, spatial mosiacs are acquired at several time steps, following a particular feature from day side to night side as was done by Galileo and Cassini at Jupiter (Little et al., 1999; Gierasch et al., 2000; Porco et al., 2003)....
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...…will allow us to extend our knowledge of the jet structure on Saturn farther poleward than was possible with Voyager, just as we did on Jupiter (Porco et al., 2003), though observations of the north pole will not take place until after the nominal 4-year mission when that pole is finally…...
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...Cassini observations of the jovian ring taken alone (Porco et al., 2003) and in combination with other spacecraft and Earth-based observations of the ring (Throop et al., 2004) have indicated that irregularly shaped, small (µm-sized) particles are more likely than spherical Mie scattering…...
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TL;DR: This work presents a numerical model of three-dimensional rotating convection in a relatively thin spherical shell that generates both types of jets and implies that Jupiter's latitudinal transition in jet width corresponds to a separation between the bottom-bounded flow structures in higher latitudes and the deep equatorial flows.
Abstract: The bands of Jupiter represent a global system of powerful winds. Broad eastward equatorial jets are flanked by smaller-scale, higher-latitude jets flowing in alternating directions. Jupiter's large thermal emission suggests that the winds are powered from within, but the zonal flow depth is limited by increasing density and electrical conductivity in the molecular hydrogen-helium atmosphere towards the centre of the planet. Two types of planetary flow models have been explored: shallow-layer models reproduce multiple high-latitude jets, but not the equatorial flow system, and deep convection models only reproduce an eastward equatorial jet with two flanking neighbours. Here we present a numerical model of three-dimensional rotating convection in a relatively thin spherical shell that generates both types of jets. The simulated flow is turbulent and quasi-two-dimensional and, as observed for the jovian jets, simulated jet widths follow Rhines' scaling theory. Our findings imply that Jupiter's latitudinal transition in jet width corresponds to a separation between the bottom-bounded flow structures in higher latitudes and the deep equatorial flows.
269 citations
Book•
10 May 2017TL;DR: In this article, the authors present a survey of the current understanding of the atmospheric evolution and climate on Earth, on other rocky planets within our Solar System, and on planets far beyond.
Abstract: As the search for Earth-like exoplanets gathers pace, in order to understand them, we need comprehensive theories for how planetary atmospheres form and evolve. Written by two well-known planetary scientists, this text explains the physical and chemical principles of atmospheric evolution and planetary atmospheres, in the context of how atmospheric composition and climate determine a planet's habitability. The authors survey our current understanding of the atmospheric evolution and climate on Earth, on other rocky planets within our Solar System, and on planets far beyond. Incorporating a rigorous mathematical treatment, they cover the concepts and equations governing a range of topics, including atmospheric chemistry, thermodynamics, radiative transfer, and atmospheric dynamics, and provide an integrated view of planetary atmospheres and their evolution. This interdisciplinary text is an invaluable one-stop resource for graduate-level students and researchers working across the fields of atmospheric science, geochemistry, planetary science, astrobiology, and astronomy.
256 citations
TL;DR: Jupiter: The Planet, Satellites and Magnetosphere (JPLM) as discussed by the authors is an encyclopedic volume that summarizes current knowledge of the Jovian system.
Abstract: In June 2001, with the Galileo mission ending and the Cassini mission having encountered Jupiter on its way to Saturn, a conference (titled “Jupiter: The Planet, Satellites and Magnetosphere,” sponsored by NASA, the Jet Propulsion Laboratory, Ball Aerospace, Southwest Research Institute, and the University of Colorado) was held on 25–30 June 2001, in Boulder, Colorado, to provide a framework for generating a comprehensive volume that would summarize current knowledge of the Jovian system. Three years later, this encyclopedic volume, Jupiter: The Planet, Satellites and Magnetosphere, was published, presenting an impressive detailed guide for understanding this complex system.
247 citations
References
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TL;DR: A detailed description of modern ¹-matrix FORTRAN codes which incorporate all recent developments, are publicly available on the World Wide Web, and are, apparently, the most efficient and powerful tool for accurately computing light scattering by randomly oriented rotationally symmetric particles is provided.
Abstract: We describe in detail a software implementation of a current version of the ¹-matrix method for computing light scattering by polydisperse, randomly oriented, rotationally symmetric particles. The FORTRAN ¹-matrix codes are publicly available on the World Wide We ba thttp://www.giss.nasa.gov/&crmim .W egiv eal lnecessar yformulas ,describ einpu tand output parameters, discuss numerical aspects of ¹-matrix computations, demonstrate the capabilities and limitations of the codes, and discuss the performance of the codes in comparison with other available numerical approaches. Published by Elsevier Science Ltd. 1. I NTRODUCTION The ¹-matrix method is a powerful exact technique for computing light scattering by nonspherical particles based on numerically solving Maxwell's equations. Although the method is, potentially, applicable to any particle shape, most practical implementations of the technique pertain to bodies of revolution. The method was initially developed by Waterman and has been significantly improved as described in Refs. 2—6. Specifically, Refs. 4 and 6 extend the method to much larger size parameters and aspect ratios, Ref. 2 presents an efficient analytical procedure for computing the scattering properties of randomly oriented particles, Ref. 3 describes an automatic convergence procedure convenient in massive computer calculations for particle polydispersions, and Ref. 5 presents benchmark ¹-matrix computations for particles with non-smooth surfaces (finite circular cylinders). A general review of the ¹-matrix method can be found in Ref. 7. In this paper we provide a detailed description of modern ¹-matrix FORTRAN codes which incorporate all recent developments, are publicly available on the World Wide Web, and are, apparently, the most efficient and powerful tool for accurately computing light scattering by randomly oriented rotationally symmetric particles. For the first time, we collect in one place all necessary formulas, discuss numerical aspects for ¹-matrix computations, describe the input and output parameters, and demonstrate the capabilities and limitations of the codes. The paper is intended to serve as a detailed user guide to a versatile tool suitable for a wide range of practical applications. We specifically target the users who are interested in practical applications of the ¹-matrix method rather than in details of its mathematical formulation.
815 citations
University of Arizona1, United States Geological Survey2, Jet Propulsion Laboratory3, California Institute of Technology4, University College London5, RAND Corporation6, Smithsonian Astrophysical Observatory7, State University of New York System8, Cornell University9, New Mexico State University10, University of Hawaii11, NASA Headquarters12, University of Wisconsin-Madison13
TL;DR: The cameras aboard Voyager 1 have provided a closeup view of the Jupiter system, revealing heretofore unknown characteristics and phenomena associated with the planet's atmosphere and the surfaces of its five major satellites.
Abstract: The cameras aboard Voyager 1 have provided a closeup view of the Jupiter system, revealing heretofore unknown characteristics and phenomena associated with the planet's atmosphere and the surfaces of its five major satellites. On Jupiter itself, atmospheric motions-the interaction of cloud systems-display complex vorticity. On its dark side, lightning and auroras are observed. A ring was discovered surrounding Jupiter. The satellite surfaces display dramatic differences including extensive active volcanism on Io, complex tectonism on Ganymede and possibly Europa, and flattened remnants of enormous impact features on Callisto.
699 citations
TL;DR: In this article, reflectivity data from Doppler radars are used to construct vertical profiles of radar reflectivity (VPRR) of convective cells in mesoscale convective systems (MCSs) in three different environmental regimes.
Abstract: Reflectivity data from Doppler radars are used to construct vertical profiles of radar reflectivity (VPRR) of convective cells in mesoscale convective systems (MCSs) in three different environmental regimes. The National Center for Atmospheric Research CP-3 and CP-4 radars are used to calculate median VPRR for MCSs in the Oklahoma-Kansas Preliminary Regional Experiment for STORM-Central in 1985. The National Oceanic and Atmospheric Administration-Tropical Ocean Global Atmosphere radar in Darwin, Australia, is used to calculate VPRR for MCSs observed both in oceanic, monsoon regimes and in continental, break period regimes during the wet seasons of 1987/88 and 1988/89. The midlatitude and tropical continental VPRRs both exhibit maximum reflectivity somewhat above the surface and have a gradual decrease in reflectivity with height above the freezing level. In sharp contrast, the tropical oceanic profile has a maximum reflectivity at the lowest level and a very rapid decrease in reflectivity with height beginning just above the freezing level. The tropical oceanic profile in the Darwin area is almost the same shape as that for two other tropical oceanic regimes, leading to the conclustion that it is characteristic. The absolute values of reflectivity in the 0 to 20 C range are compared with values in the literature thought to represent a threshold for rapid storm electrification leading to lightning, about 40 dBZ at -10 C. The large negative vertical gradient of reflectivity in this temperature range for oceanic storms is hypothesized to be a direct result of the characteristically weaker vertical velocities observed in MCSs over tropical oceans. It is proposed, as a necessary condition for rapid electrification, that a convective cell must have its updraft speed exceed some threshold value. Based upon field program data, a tentative estimate for the magnitude of this threshold is 6-7 m/s for mean speed and 10-12 m/s for peak speed.
496 citations
TL;DR: In this paper, a spherical harmonic model of the magnetic field of Jupiter was derived from in situ magnetic field measurements and remote observations of the position of the foot of the Io flux tube in Jupiter's ionosphere.
Abstract: Spherical harmonic models of the planetary magnetic field of Jupiter are obtained from in situ magnetic field measurements and remote observations of the position of the foot of the Io flux tube in Jupiter's ionosphere. The Io flux tube (IFT) footprint locates the ionospheric footprint of field lines traced from Io's orbital radial distance in the equator plane (5.9 Jovian radii). The IFT footprint is a valuable constraint on magnetic field models, providing “ground truth” information in a region close to the planet and thus far not sampled by spacecraft. The magnetic field is represented using a spherical harmonic expansion of degree and order 4 for the planetary (“internal”) field and an explicit model of the magnetodisc for the field (“external”) due to distributed currents. Models fitting Voyager 1 and Pioneer 11 magnetometer observations and the IFT footprint are obtained by partial solution of the underdetermined inverse problem using generalized inverse techniques. Dipole, quadrupole, octupole, and a subset of higher-degree and higher-order spherical harmonic coefficients are determined and compared with earlier models.
426 citations
TL;DR: In this article, a simple empirical model of the field and flow in the middle magnetosphere is used to estimate the field-aligned currents flowing into and out of the equatorial current sheet associated with the breakdown of corotation.
390 citations