1
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Wong MH, Rowe-Gurney N, Markham S, Sayanagi KM. Multiple Probe Measurements at Uranus Motivated by Spatial Variability. SPACE SCIENCE REVIEWS 2024; 220:15. [PMID: 38343766 PMCID: PMC10858001 DOI: 10.1007/s11214-024-01050-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/26/2023] [Accepted: 01/18/2024] [Indexed: 02/22/2024]
Abstract
A major motivation for multiple atmospheric probe measurements at Uranus is the understanding of dynamic processes that create and maintain spatial variation in thermal structure, composition, and horizontal winds. But origin questions-regarding the planet's formation and evolution, and conditions in the protoplanetary disk-are also major science drivers for multiprobe exploration. Spatial variation in thermal structure reveals how the atmosphere transports heat from the interior, and measuring compositional variability in the atmosphere is key to ultimately gaining an understanding of the bulk abundances of several heavy elements. We review the current knowledge of spatial variability in Uranus' atmosphere, and we outline how multiple probe exploration would advance our understanding of this variability. The other giant planets are discussed, both to connect multiprobe exploration of those atmospheres to open questions at Uranus, and to demonstrate how multiprobe exploration of Uranus itself is motivated by lessons learned about the spatial variation at Jupiter, Saturn, and Neptune. We outline the measurements of highest value from miniature secondary probes (which would complement more detailed investigation by a larger flagship probe), and present the path toward overcoming current challenges and uncertainties in areas including mission design, cost, trajectory, instrument maturity, power, and timeline.
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Affiliation(s)
- Michael H. Wong
- Center for Integrative Planetary Science, University of California, Berkeley, CA 94720-3411 USA
- Carl Sagan Center for Science, SETI Institute, Mountain View, CA 94043-5232 USA
| | - Naomi Rowe-Gurney
- NASA Goddard Space Flight Center, Greenbelt, MD 20771 USA
- University of Maryland, College Park, MD 20742 USA
- The Center for Research and Exploration in Space Science & Technology (CRESST II), Greenbelt, MD 20771 USA
- The Royal Astronomical Society, Piccadilly, London, W1J 0BD UK
| | - Stephen Markham
- Observatoire de la Côte d’Azur, 06300 Nice, France
- Department of Astronomy, New Mexico State University, Las Cruces, NM 88003 USA
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2
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Soderlund KM, Rovira-Navarro M, Le Bars M, Schmidt BE, Gerkema T. The Physical Oceanography of Ice-Covered Moons. ANNUAL REVIEW OF MARINE SCIENCE 2024; 16:25-53. [PMID: 37669566 DOI: 10.1146/annurev-marine-040323-101355] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/07/2023]
Abstract
In the outer solar system, a growing number of giant planet satellites are now known to be abodes for global oceans hidden below an outer layer of ice. These planetary oceans are a natural laboratory for studying physical oceanographic processes in settings that challenge traditional assumptions made for Earth's oceans. While some driving mechanisms are common to both systems, such as buoyancy-driven flows and tides, others, such as libration, precession, and electromagnetic pumping, are likely more significant for moons in orbit around a host planet. Here, we review these mechanisms and how they may operate across the solar system, including their implications for ice-ocean interactions. Future studies should continue to advance our understanding of each of these processes as well as how they may act together in concert. This interplay also has strong implications for habitability as well as testing oceanic hypotheses with future missions.
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Affiliation(s)
- Krista M Soderlund
- Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, Texas, USA;
| | - Marc Rovira-Navarro
- Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA;
| | - Michael Le Bars
- CNRS, Aix Marseille Univ, Centrale Marseille, IRPHE, Marseille, France;
| | - Britney E Schmidt
- Departments of Astronomy and of Earth and Atmospheric Sciences, Cornell University, Ithaca, New York, USA;
| | - Theo Gerkema
- Department of Estuarine and Delta Systems, NIOZ Royal Netherlands Institute for Sea Research, Yerseke, The Netherlands;
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3
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Castillo‐Rogez J, Weiss B, Beddingfield C, Biersteker J, Cartwright R, Goode A, Melwani Daswani M, Neveu M. Compositions and Interior Structures of the Large Moons of Uranus and Implications for Future Spacecraft Observations. JOURNAL OF GEOPHYSICAL RESEARCH. PLANETS 2023; 128:e2022JE007432. [PMID: 37034459 PMCID: PMC10078161 DOI: 10.1029/2022je007432] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/14/2022] [Revised: 11/29/2022] [Accepted: 12/02/2022] [Indexed: 06/19/2023]
Abstract
The five large moons of Uranus are important targets for future spacecraft missions. To motivate and inform the exploration of these moons, we model their internal evolution, present-day physical structures, and geochemical and geophysical signatures that may be measured by spacecraft. We predict that if the moons preserved liquid until present, it is likely in the form of residual oceans less than 30 km thick in Ariel, Umbriel, and less than 50 km in Titania, and Oberon. The preservation of liquid strongly depends on material properties and, potentially, on dynamical circumstances that are presently unknown. Miranda is unlikely to host liquid at present unless it experienced tidal heating a few tens of million years ago. We find that since the thin residual layers may be hypersaline, their induced magnetic fields could be detectable by future spacecraft-based magnetometers. However, if the ocean is maintained primarily by ammonia, and thus well below the water freezing point, then its electrical conductivity may be too small to be detectable by spacecraft. Lastly, our calculated tidal Love number (k 2) and dissipation factor (Q) are consistent with the Q/k 2 values previously inferred from dynamical evolution models. In particular, we find that the low Q/k 2 estimated for Titania supports the hypothesis that Titania currently holds an ocean.
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Affiliation(s)
| | - Benjamin Weiss
- Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadenaCAUSA
- Department of Earth, Atmospheric and Planetary SciencesMassachusetts Institute of Technology (MIT)CambridgeMAUSA
| | - Chloe Beddingfield
- SETI InstituteMountain ViewCAUSA
- NASA Ames Research CenterMountain ViewCAUSA
| | - John Biersteker
- Department of Earth, Atmospheric and Planetary SciencesMassachusetts Institute of Technology (MIT)CambridgeMAUSA
| | | | - Allison Goode
- Department of Earth, Atmospheric and Planetary SciencesMassachusetts Institute of Technology (MIT)CambridgeMAUSA
| | | | - Marc Neveu
- University of MarylandCollege ParkMDUSA
- NASA Goddard Space Flight CenterGreenbeltMDUSA
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4
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Giant Planet Atmospheres: Dynamics and Variability from UV to Near-IR Hubble and Adaptive Optics Imaging. REMOTE SENSING 2022. [DOI: 10.3390/rs14061518] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/10/2022]
Abstract
Each of the giant planets, Jupiter, Saturn, Uranus, and Neptune, has been observed by at least one robotic spacecraft mission. However, these missions are infrequent; Uranus and Neptune have only had a single flyby by Voyager 2. The Hubble Space Telescope, particularly the Wide Field Camera 3 (WFC3) and Advanced Camera for Surveys (ACS) instruments, and large ground-based telescopes with adaptive optics systems have enabled high-spatial-resolution imaging at a higher cadence, and over a longer time, than can be achieved with targeted missions to these worlds. These facilities offer a powerful combination of high spatial resolution, often <0.05”, and broad wavelength coverage, from the ultraviolet through the near infrared, resulting in compelling studies of the clouds, winds, and atmospheric vertical structure. This coverage allows comparisons of atmospheric properties between the planets, as well as in different regions across each planet. Temporal variations in winds, cloud structure, and color over timescales of days to years have been measured for all four planets. With several decades of data already obtained, we can now begin to investigate seasonal influences on dynamics and aerosol properties, despite orbital periods ranging from 12 to 165 years. Future facilities will enable even greater spatial resolution and, combined with our existing long record of data, will continue to advance our understanding of atmospheric evolution on the giant planets.
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5
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Cochrane CJ, Vance SD, Nordheim TA, Styczinski MJ, Masters A, Regoli LH. In Search of Subsurface Oceans Within the Uranian Moons. JOURNAL OF GEOPHYSICAL RESEARCH. PLANETS 2021; 126:e2021JE006956. [PMID: 35859709 PMCID: PMC9285391 DOI: 10.1029/2021je006956] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2021] [Revised: 11/03/2021] [Accepted: 11/11/2021] [Indexed: 05/04/2023]
Abstract
The Galileo mission to Jupiter discovered magnetic signatures associated with hidden subsurface oceans at the moons Europa and Callisto using the phenomenon of magnetic induction. These induced magnetic fields originate from electrically conductive layers within the moons and are driven by Jupiter's strong time-varying magnetic field. The ice giants and their moons are also ideal laboratories for magnetic induction studies. Both Uranus and Neptune have a strongly tilted magnetic axis with respect to their spin axis, creating a dynamic and strongly variable magnetic field environment at the orbits of their major moons. Although Voyager 2 visited the ice giants in the 1980s, it did not pass close enough to any of the moons to detect magnetic induction signatures. However, Voyager 2 revealed that some of these moons exhibit surface features that hint at recent geologically activity, possibly associated with subsurface oceans. Future missions to the ice giants may therefore be capable of discovering subsurface oceans, thereby adding to the family of known "ocean worlds" in our Solar System. Here, we assess magnetic induction as a technique for investigating subsurface oceans within the major moons of Uranus. Furthermore, we establish the ability to distinguish induction responses created by different interior characteristics that tie into the induction response: ocean thickness, conductivity and depth, and ionospheric conductance. The results reported here demonstrate the possibility of single-pass ocean detection and constrained characterization within the moons of Miranda, Ariel, and Umbriel, and provide guidance for magnetometer selection and trajectory design for future missions to Uranus.
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Affiliation(s)
- C. J. Cochrane
- Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadenaCAUSA
| | - S. D. Vance
- Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadenaCAUSA
| | - T. A. Nordheim
- Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadenaCAUSA
| | | | | | - L. H. Regoli
- Applied Physics LaboratoryJohn Hopkins UniversityBaltimoreMDUSA
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6
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Cochrane CJ, Vance SD, Nordheim TA, Styczinski MJ, Masters A, Regoli LH. In Search of Subsurface Oceans Within the Uranian Moons. JOURNAL OF GEOPHYSICAL RESEARCH. PLANETS 2021. [PMID: 35859709 DOI: 10.1029/2020je006418] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
The Galileo mission to Jupiter discovered magnetic signatures associated with hidden subsurface oceans at the moons Europa and Callisto using the phenomenon of magnetic induction. These induced magnetic fields originate from electrically conductive layers within the moons and are driven by Jupiter's strong time-varying magnetic field. The ice giants and their moons are also ideal laboratories for magnetic induction studies. Both Uranus and Neptune have a strongly tilted magnetic axis with respect to their spin axis, creating a dynamic and strongly variable magnetic field environment at the orbits of their major moons. Although Voyager 2 visited the ice giants in the 1980s, it did not pass close enough to any of the moons to detect magnetic induction signatures. However, Voyager 2 revealed that some of these moons exhibit surface features that hint at recent geologically activity, possibly associated with subsurface oceans. Future missions to the ice giants may therefore be capable of discovering subsurface oceans, thereby adding to the family of known "ocean worlds" in our Solar System. Here, we assess magnetic induction as a technique for investigating subsurface oceans within the major moons of Uranus. Furthermore, we establish the ability to distinguish induction responses created by different interior characteristics that tie into the induction response: ocean thickness, conductivity and depth, and ionospheric conductance. The results reported here demonstrate the possibility of single-pass ocean detection and constrained characterization within the moons of Miranda, Ariel, and Umbriel, and provide guidance for magnetometer selection and trajectory design for future missions to Uranus.
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Affiliation(s)
- C J Cochrane
- Jet Propulsion Laboratory California Institute of Technology Pasadena CA USA
| | - S D Vance
- Jet Propulsion Laboratory California Institute of Technology Pasadena CA USA
| | - T A Nordheim
- Jet Propulsion Laboratory California Institute of Technology Pasadena CA USA
| | | | | | - L H Regoli
- Applied Physics Laboratory John Hopkins University Baltimore MD USA
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7
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Showalter MR. The rings and small moons of Uranus and Neptune. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2020; 378:20190482. [PMID: 33161854 PMCID: PMC7658785 DOI: 10.1098/rsta.2019.0482] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 08/21/2020] [Indexed: 06/11/2023]
Abstract
All four giant planets are encircled by distinctive systems of rings and small, inner satellites. These all reside within or near their central planet's Roche limit, the rough boundary within which bodies held together by self-gravity will be disrupted by tidal forces. However, the similarities of the four ring-moon systems end here; in most other regards, they are remarkably diverse. We study these systems for three key reasons: (1) for the information they reveal about the properties, history and ongoing evolution of the planetary systems of which they are a part; (2) as dynamical analogues for other astrophysical systems such as protoplanetary disks; and (3) for the wealth of fascinating properties and origin scenarios that make them worthy of study in their own right. The inner Uranus system is characterized by 10 narrow rings, some quite dense, as well as a variety of more tenuous structures. These are accompanied by 13 known moons all orbiting interior to Miranda. Nine of these, Bianca through Perdita, comprise the most densely packed set of moons in the solar system, with orbits so close that their interactions appear to drive chaos over time scales approximately 106 years. Neptune has five named rings, all optically thin, interleaved with seven inner moons. The most notable feature is a set of arcs embedded within the Adams ring; two of these arcs have been stable for time scales of decades. This article is part of a discussion meeting issue 'Future exploration of ice giant systems'.
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Schenk PM, Moore JM. Topography and geology of Uranian mid-sized icy satellites in comparison with Saturnian and Plutonian satellites. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2020; 378:20200102. [PMID: 33161858 DOI: 10.1098/rsta.2020.0102] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 08/03/2020] [Indexed: 05/20/2023]
Abstract
Newly processed global imaging and topographic mapping of Uranus's five major satellites reveal differences and similarities to mid-sized satellites at Saturn and Pluto. Three modes of internal heat redistribution are recognized. The broad similarity of Miranda's three oval resurfacing zones to those mapped on Enceladus and (subtly) on Dione are likely due to antipodal diapiric upwelling. Conversely, break-up and foundering of crustal blocks accompanied by extensive (cryo)volcanism is the dominant mode on both Charon and Ariel. Titania's fault network finds parallels on Rhea, Dione, Tethys and possibly Oberon. Differences in the geologic style of resurfacing in the satellite systems (e.g. plains on Charon, Dione, Tethys and perhaps Titania versus ridges on Miranda and Ariel) may be driven by differences in ice composition. Surface processes such as volatile transport may also be indicated by bright and dark materials on Oberon, Umbriel and Charon. The more complete and higher quality observations of the Saturnian and Plutonian mid-sized icy satellites by Cassini and New Horizons reveal a wealth of features and phenomena that cannot be perceived in the more limited Voyager coverage of the Uranian satellites, harbingers of many discoveries awaiting us on a return to Uranus. This article is part of a discussion meeting issue 'Future exploration of ice giant systems'.
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Affiliation(s)
- Paul M Schenk
- Lunar and Planteray Institute/USRA, Houston, TX, USA
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9
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Hueso R, Guillot T, Sánchez-Lavega A. Convective storms and atmospheric vertical structure in Uranus and Neptune. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2020; 378:20190476. [PMID: 33161859 PMCID: PMC7658788 DOI: 10.1098/rsta.2019.0476] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 08/27/2020] [Indexed: 05/20/2023]
Abstract
The ice giants Uranus and Neptune have hydrogen-based atmospheres with several constituents that condense in their cold upper atmospheres. A small number of bright cloud systems observed in both planets are good candidates for moist convective storms, but their observed properties (size, temporal scales and cycles of activity) differ from moist convective storms in the gas giants. These clouds and storms are possibly due to methane condensation and observations also suggest deeper clouds of hydrogen sulfide (H2S) at depths of a few bars. Even deeper, thermochemical models predict clouds of ammonia hydrosulfide (NH4SH) and water at pressures of tens to hundreds of bars, forming extended deep weather layers. Because of hydrogen's low molecular weight and the high abundance of volatiles, their condensation imposes a strongly stabilizing vertical gradient of molecular weight larger than the equivalent one in Jupiter and Saturn. The resulting inhibition of vertical motions should lead to a moist convective regime that differs significantly from the one occurring on nitrogen-based atmospheres like those of Earth or Titan. As a consequence, the thermal structure of the deep atmospheres of Uranus and Neptune is not well understood. Similar processes might occur at the deep water cloud of Jupiter in Saturn, but the ice giants offer the possibility to study these physical aspects in the upper methane cloud layer. A combination of orbital and in situ data will be required to understand convection and its role in atmospheric dynamics in the ice giants, and by extension, in hydrogen atmospheres including Jupiter, Saturn and giant exoplanets. This article is part of a discussion meeting issue 'Future exploration of ice giant systems'.
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Affiliation(s)
- R. Hueso
- Física Aplicada I, Escuela de Ingeniería de Bilbao, UPV/EHU, 48013 Bilbao, Spain
| | - T. Guillot
- Université Côte d’Azur, Laboratoire Lagrange, OCA, CNRS UMR 7293, Nice, France
| | - A. Sánchez-Lavega
- Física Aplicada I, Escuela de Ingeniería de Bilbao, UPV/EHU, 48013 Bilbao, Spain
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10
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Fletcher LN, Simon AA, Hofstadter MD, Arridge CS, Cohen IJ, Masters A, Mandt K, Coustenis A. Ice giant system exploration in the 2020s: an introduction. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2020; 378:20190473. [PMID: 33161857 PMCID: PMC7658778 DOI: 10.1098/rsta.2019.0473] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 08/26/2020] [Indexed: 05/04/2023]
Abstract
The international planetary science community met in London in January 2020, united in the goal of realizing the first dedicated robotic mission to the distant ice giants, Uranus and Neptune, as the only major class of solar system planet yet to be comprehensively explored. Ice-giant-sized worlds appear to be a common outcome of the planet formation process, and pose unique and extreme tests to our understanding of exotic water-rich planetary interiors, dynamic and frigid atmospheres, complex magnetospheric configurations, geologically-rich icy satellites (both natural and captured), and delicate planetary rings. This article introduces a special issue on ice giant system exploration at the start of the 2020s. We review the scientific potential and existing mission design concepts for an ambitious international partnership for exploring Uranus and/or Neptune in the coming decades. This article is part of a discussion meeting issue 'Future exploration of ice giant systems'.
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Affiliation(s)
- L. N. Fletcher
- School of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
| | - A. A. Simon
- NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
| | - M. D. Hofstadter
- Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
| | - C. S. Arridge
- Department of Physics, Lancaster University, Bailrigg, Lancaster LA1 4YB, UK
| | - Ian J. Cohen
- The Johns Hopkins University Applied Physics Laboratory, 11000 Johns Hopkins Road, Laurel, MD 20723, USA
| | - A. Masters
- The Blackett Laboratory, Imperial College London, Prince Consort Road, London SW7 2AZ, UK
| | - K. Mandt
- The Johns Hopkins University Applied Physics Laboratory, 11000 Johns Hopkins Road, Laurel, MD 20723, USA
| | - A. Coustenis
- LESIA – Paris Observatory, CNRS, Paris Science Letters Research University, Univ. Paris-Diderot, Meudon, France
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11
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Evidence for Ammonia-bearing Species on the Uranian Satellite Ariel Supports Recent Geologic Activity. ACTA ACUST UNITED AC 2020. [DOI: 10.3847/2041-8213/aba27f] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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12
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Fletcher LN, de Pater I, Orton GS, Hofstadter MD, Irwin PGJ, Roman MT, Toledo D. Ice Giant Circulation Patterns: Implications for Atmospheric Probes. SPACE SCIENCE REVIEWS 2020. [PMID: 32165773 DOI: 10.1007/s11214-019-0619-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
Atmospheric circulation patterns derived from multi-spectral remote sensing can serve as a guide for choosing a suitable entry location for a future in situ probe mission to the Ice Giants. Since the Voyager-2 flybys in the 1980s, three decades of observations from ground- and space-based observatories have generated a picture of Ice Giant circulation that is complex, perplexing, and altogether unlike that seen on the Gas Giants. This review seeks to reconcile the various competing circulation patterns from an observational perspective, accounting for spatially-resolved measurements of: zonal albedo contrasts and banded appearances; cloud-tracked zonal winds; temperature and para-H2 measurements above the condensate clouds; and equator-to-pole contrasts in condensable volatiles (methane, ammonia, and hydrogen sulphide) in the deeper troposphere. These observations identify three distinct latitude domains: an equatorial domain of deep upwelling and upper-tropospheric subsidence, potentially bounded by peaks in the retrograde zonal jet and analogous to Jovian cyclonic belts; a mid-latitude transitional domain of upper-tropospheric upwelling, vigorous cloud activity, analogous to Jovian anticyclonic zones; and a polar domain of strong subsidence, volatile depletion, and small-scale (and potentially seasonally-variable) convective activity. Taken together, the multi-wavelength observations suggest a tiered structure of stacked circulation cells (at least two in the troposphere and one in the stratosphere), potentially separated in the vertical by (i) strong molecular weight gradients associated with cloud condensation, and by (ii) transitions from a thermally-direct circulation regime at depth to a wave- and radiative-driven circulation regime at high altitude. The inferred circulation can be tested in the coming decade by 3D numerical simulations of the atmosphere, and by observations from future world-class facilities. The carrier spacecraft for any probe entry mission must ultimately carry a suite of remote-sensing instruments capable of fully constraining the atmospheric motions at the probe descent location.
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Affiliation(s)
- Leigh N Fletcher
- 1School of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH UK
| | - Imke de Pater
- 3Department of Astronomy, University of California, 501 Campbell Hall, Berkeley, CA 94720 USA
| | - Glenn S Orton
- 2Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 USA
| | - Mark D Hofstadter
- 2Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 USA
| | - Patrick G J Irwin
- 4Atmospheric, Oceanic and Planetary Physics, University of Oxford, Parks Road, Oxford, OX1 3PU UK
| | - Michael T Roman
- 1School of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH UK
| | - Daniel Toledo
- 4Atmospheric, Oceanic and Planetary Physics, University of Oxford, Parks Road, Oxford, OX1 3PU UK
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13
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Fletcher LN, de Pater I, Orton GS, Hofstadter MD, Irwin PGJ, Roman MT, Toledo D. Ice Giant Circulation Patterns: Implications for Atmospheric Probes. SPACE SCIENCE REVIEWS 2020; 216:21. [PMID: 32165773 PMCID: PMC7040070 DOI: 10.1007/s11214-020-00646-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/05/2019] [Accepted: 02/15/2020] [Indexed: 05/04/2023]
Abstract
Atmospheric circulation patterns derived from multi-spectral remote sensing can serve as a guide for choosing a suitable entry location for a future in situ probe mission to the Ice Giants. Since the Voyager-2 flybys in the 1980s, three decades of observations from ground- and space-based observatories have generated a picture of Ice Giant circulation that is complex, perplexing, and altogether unlike that seen on the Gas Giants. This review seeks to reconcile the various competing circulation patterns from an observational perspective, accounting for spatially-resolved measurements of: zonal albedo contrasts and banded appearances; cloud-tracked zonal winds; temperature and para-H2 measurements above the condensate clouds; and equator-to-pole contrasts in condensable volatiles (methane, ammonia, and hydrogen sulphide) in the deeper troposphere. These observations identify three distinct latitude domains: an equatorial domain of deep upwelling and upper-tropospheric subsidence, potentially bounded by peaks in the retrograde zonal jet and analogous to Jovian cyclonic belts; a mid-latitude transitional domain of upper-tropospheric upwelling, vigorous cloud activity, analogous to Jovian anticyclonic zones; and a polar domain of strong subsidence, volatile depletion, and small-scale (and potentially seasonally-variable) convective activity. Taken together, the multi-wavelength observations suggest a tiered structure of stacked circulation cells (at least two in the troposphere and one in the stratosphere), potentially separated in the vertical by (i) strong molecular weight gradients associated with cloud condensation, and by (ii) transitions from a thermally-direct circulation regime at depth to a wave- and radiative-driven circulation regime at high altitude. The inferred circulation can be tested in the coming decade by 3D numerical simulations of the atmosphere, and by observations from future world-class facilities. The carrier spacecraft for any probe entry mission must ultimately carry a suite of remote-sensing instruments capable of fully constraining the atmospheric motions at the probe descent location.
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Affiliation(s)
- Leigh N. Fletcher
- School of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH UK
| | - Imke de Pater
- Department of Astronomy, University of California, 501 Campbell Hall, Berkeley, CA 94720 USA
| | - Glenn S. Orton
- Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109 USA
| | | | - Patrick G. J. Irwin
- Atmospheric, Oceanic and Planetary Physics, University of Oxford, Parks Road, Oxford, OX1 3PU UK
| | - Michael T. Roman
- School of Physics and Astronomy, University of Leicester, University Road, Leicester, LE1 7RH UK
| | - Daniel Toledo
- Atmospheric, Oceanic and Planetary Physics, University of Oxford, Parks Road, Oxford, OX1 3PU UK
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14
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Maynard-Casely HE. ‘Peaks in space’ – crystallography in planetary science: past impacts and future opportunities. CRYSTALLOGR REV 2016. [DOI: 10.1080/0889311x.2016.1242127] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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15
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Jacobson RA. THE ORBITS OF THE URANIAN SATELLITES AND RINGS, THE GRAVITY FIELD OF THE URANIAN SYSTEM, AND THE ORIENTATION OF THE POLE OF URANUS. ACTA ACUST UNITED AC 2014. [DOI: 10.1088/0004-6256/148/5/76] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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16
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Schenk PM. Ganymede and Callisto: Complex crater formation and planetary crusts. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/91je00932] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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17
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Hillier J, Squyres SW. Thermal stress tectonics on the satellites of Saturn and Uranus. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/91je01401] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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18
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Schenk PM. Crater formation and modification on the icy satellites of Uranus and Saturn: Depth/diameter and central peak occurrence. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/jb094ib04p03813] [Citation(s) in RCA: 80] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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19
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Anderson JD, Campbell JK, Jacobson RA, Sweetnam DN, Taylor AH, Prentice AJR, Tyler GL. Radio science with Voyager 2 at Uranus: Results on masses and densities of the planet and five principal satellites. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/ja092ia13p14877] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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20
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Pollack JB, Rages K, Pope SK, Tomasko MG, Romani PN, Atreya SK. Nature of the stratospheric haze on Uranus: Evidence for condensed hydrocarbons. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/ja092ia13p15037] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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21
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Hudson MK, Clarke JT, Warren JA. Ionospheric dynamo theory for production of far ultraviolet emissions on Uranus. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/ja094ia06p06517] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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22
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Veverka J, Thomas P, Helfenstein P, Brown RH, Johnson TV. Satellites of Uranus: Disk‐integrated photometry from Voyager imaging observations. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/ja092ia13p14895] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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23
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Herbert F. The Uranian corona as a charge exchange cascade of plasma sheet protons. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/92ja02735] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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24
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Lindal GF, Lyons JR, Sweetnam DN, Eshleman VR, Hinson DP, Tyler GL. The atmosphere of Uranus: Results of radio occultation measurements with Voyager 2. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/ja092ia13p14987] [Citation(s) in RCA: 252] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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25
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Gurnett DA, Kurth WS, Scarf FL, Burns JA, Cuzzi JN, Grün E. Micron‐sized particle impacts detected near Uranus by the Voyager 2 Plasma Wave Instrument. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/ja092ia13p14959] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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26
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27
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Thomas PC, Veverka J, Helfenstein P, Brown RH, Johnson TV. Titania's opposition effect: Analysis of Voyager observations. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/ja092ia13p14911] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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28
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Herbert F, Sandel BR, Yelle RV, Holberg JB, Broadfoot AL, Shemansky DE, Atreya SK, Romani PN. The upper atmosphere of Uranus: EUV occultations observed by Voyager 2. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/ja092ia13p15093] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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30
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Ockert ME, Cuzzi JN, Porco CC, Johnson TV. Uranian ring photometry: Results from Voyager 2. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/ja092ia13p14969] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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31
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Lanzerotti LJ, Brown WL, Maclennan CG, Cheng AF, Krimigis SM, Johnson RE. Effects of charged particles on the surfaces of the satellites of Uranus. ACTA ACUST UNITED AC 2012. [DOI: 10.1029/ja092ia13p14949] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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32
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Hartmann WK. Planetary cratering 1. The question of multiple impactor populations: Lunar evidence. ACTA ACUST UNITED AC 2012. [DOI: 10.1111/j.1945-5100.1995.tb01152.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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33
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Abstract
Careful reprocessing of the Voyager images reveals that the Uranìan lambda ring has marked longitudinal variations in brightness comparable in magnitude to those in Saturn's F ring and Neptune's Adams ring. The ring's variations show a dominant five-cycle (72-degree) periodicity, although additional structure down to scales of about 0.5 degree is also present. The ring's shape is defined by a small overall eccentricity plus a six-cycle (60-degree) sinusoidal variation of radial amplitude around 4 kilometers. Both of these properties can be explained by the resonant perturbations of a moon at a semimajor axis of 56,479 kilometers, but no known moon orbits at this location. Unfortunately, the mass required suggests that such a body should have been imaged by Voyager.
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34
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Tyler GL, Sweetnam DN, Anderson JD, Campbell JK, Eshleman VR, Hinson DP, Levy GS, Lindal GF, Marouf EA, Simpson RA. Voyager 2 radio science observations of the uranian system: atmosphere, rings, and satellites. Science 2010; 233:79-84. [PMID: 17812893 DOI: 10.1126/science.233.4759.79] [Citation(s) in RCA: 106] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Voyager 2 radio occultation measurements of the Uranian atmosphere were obtained between 2 and 7 degrees south latitude. Initial atmospheric temperature profiles extend from pressures of 10 to 900 millibars over a height range of about 100 kilometers. Comparison of radio and infrared results yields mole fractions near the tropopause of 0.85 and 0.15 +/- 0.05 for molecular hydrogen and helium, respectively, if no other components are present; for this composition the tropopause is at about 52 kelvins and 110 millibars. Distinctive features in the signal intensity measurements for pressures above 900 millibars strongly favor model atmospheres that include a cloud deck of methane ice. Modeling of the intensity measurements for the cloud region and below indicates that the cloud base is near 1,300 millibars and 81 kelvins and yields an initial methane mole fraction of about 0.02 for the deep atmosphere. Scintillations in signal intensity indicate small-scale stucture throughout the stratosphere and upper troposphere. As judged from data obtained during occultation ingress, the ionosphere consists of a multilayer structure that includes two distinct layers at 2,000 and 3,500 kilometers above the 100-millibar level and an extended topside that may reach altitudes of 10,000 kilometers or more. Occultation measurements of the nine previously known rings at wavelengths of 3.6 and 13 centimeters show characteristic values of optical depth between about 0.8 and 8; the maxim value occurs in the outer region of the in ring, near its periapsis. Forward-scattered signals from this ring have properties that differ from those of any of Saturn's rings, and they are inconsistent with a discrete scattering object or local (three-dimensional) assemblies of orbiting objects. These signals suggest a new kdnd of planetary ring feature characterized by highly ordered cylindrical substructures of radial scale on the order of meters and azimuthal scale of kilometers or more. From radio data alone the mass of the Uranian system is GM(sys) = 5,794,547- 60 cubic kilometers per square second; from a combination of radio and optical navigation data the mass of Uranus alone is GM(u) = 5,793,939+/- 60 cubic kilometers per square second. From all available Voyager data, induding imaging radii, the mean uncompressed density of the five major satellites is 1.40+/- 0.07 grams per cubic centimeter; this value is consistent with a solar mix of material and apparently rules out a cometary origin of the satellites.
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35
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Broadfoot AL, Herbert F, Holberg JB, Hunten DM, Kumar S, Sandel BR, Shemansky DE, Smith GR, Yelle RV, Strobel DF, Moos HW, Donahue TM, Atreya SK, Bertaux JL, Blamont JE, McConnell JC, Dessler AJ, Linick S, Springer R. Ultraviolet spectrometer observations of uranus. Science 2010; 233:74-9. [PMID: 17812892 DOI: 10.1126/science.233.4759.74] [Citation(s) in RCA: 174] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Data from solar and stellar occultations of Uranus indicate a temperature of about 750 kelvins in the upper levels of the atmosphere (composed mostly of atomic and molecular hydrogen) and define the distributions of methane and acetylene in the lower levels. The ultraviolet spectrum of the sunlit hemisphere is dominated by emissions from atomic and molecular hydrogen, which are kmown as electroglow emissions. The energy source for these emissions is unknown, but the spectrum implies excitation by low-energy electrons (modeled with a 3-electron-volt Maxwellian energy distribution). The major energy sink for the electrons is dissociation of molecular hydrogen, producing hydrogen atoms at a rate of 10(29) per second. Approximately half the atoms have energies higher than the escape energy. The high temperature of the atmosphere, the small size of Uranus, and the number density of hydrogen atoms in the thermosphere imply an extensive thermal hydrogen corona that reduces the orbital lifetime of ring particles and biases the size distribution toward larger particles. This corona is augmented by the nonthermal hydrogen atoms associated with the electroglow. An aurora near the magnetic pole in the dark hemisphere arises from excitation of molecular hydrogen at the level where its vertical column abundance is about 10(20) per square centimeter with input power comparable to that of the sunlit electroglow (approximately 2x10(11) watts). An initial estimate of the acetylene volume mixing ratio, as judged from measurements of the far ultraviolet albedo, is about 2 x 10(-7) at a vertical column abundance of molecular hydrogen of 10(23) per square centimeter (pressure, approximately 0.3 millibar). Carbon emissions from the Uranian atmosphere were also detected.
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36
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Abstract
Despite major differences in the solar and internal energy inputs, the atmospheres of the four Jovian planets all exhibit latitudinal banding and high-speed jet streams. Neptune and Saturn are the windiest planets, Jupiter is the most active, and Uranus is a tipped-over version of the others. Large oval storm systems exhibit complicated time-dependent behavior that can be simulated in numerical models and laboratory experiments. The largest storm system, the Great Red Spot of Jupiter, has survived for more than 300 years in a chaotic shear zone where smaller structures appear and dissipate every few days. Future space missions will add to our understanding of small-scale processes, chemical composition, and vertical structure. Theoretical hypotheses about the interiors provide input for fluid dynamical models that reproduce many observed features of the winds, temperatures, and cloud patterns. In one set of models the winds are confined to the thin layer where clouds form. In other models, the winds extend deep into the planetary fluid interiors. Hypotheses will be tested further as observations and theories become more exact and detailed comparisons are made.
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37
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Affiliation(s)
- Floyd Herbert
- Lunar and Planetary Laboratory; University of Arizona; Tucson Arizona USA
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38
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Abstract
The rings of Uranus are oriented edge-on to Earth in 2007 for the first time since their 1977 discovery. This event provides a rare opportunity to observe their dark (unlit) side, where dense rings darken to near invisibility, but faint rings become much brighter. We present a ground-based infrared image of the unlit side of the rings that shows that the system has changed dramatically since previous views. A broad cloud of faint material permeates the system but is not correlated with the well-known narrow rings or with the embedded dust belts imaged by the Voyager spacecraft. Although some differences can be explained by the unusual viewing angle, we conclude that the dust distribution within the system has changed substantially since the 1986 Voyager encounter and that it occurs on much larger scales than has been seen in other planetary systems.
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Affiliation(s)
- Imke de Pater
- Astronomy Department, 601 Campbell Hall, University of California, Berkeley, CA 94720, USA.
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39
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Abstract
Deep exposures of Uranus taken with the Hubble Space Telescope reveal two small moons and two faint rings. All of them orbit outside of Uranus's previously known (main) ring system but are interior to the large, classical moons. The outer new moon, U XXVI Mab, orbits at roughly twice the radius of the main rings and shares its orbit with a dust ring. The second moon, U XXVII Cupid, orbits just interior to the satellite Belinda. A second ring falls between the orbits of Portia and Rosalind, in a region with no known source bodies. Collectively, these constitute a densely packed, rapidly varying, and possibly unstable dynamical system.
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Affiliation(s)
- Mark R Showalter
- SETI Institute, 515 North Whisman Road, Mountain View, CA 94043, USA.
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40
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Fagents SA. Considerations for effusive cryovolcanism on Europa: The post-Galileo perspective. ACTA ACUST UNITED AC 2003. [DOI: 10.1029/2003je002128] [Citation(s) in RCA: 116] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Sarah A. Fagents
- Hawaii Institute of Geophysics and Planetology, School of Ocean and Earth Sciences and Technology; University of Hawaii at Manoa; Honolulu Hawaii USA
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41
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Burns JA, Hamilton DP, Showalter MR. Dusty Rings and Circumplanetary Dust: Observations and Simple Physics. ASTRONOMY AND ASTROPHYSICS LIBRARY 2001. [DOI: 10.1007/978-3-642-56428-4_13] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
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42
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Colwell JE, Esposito LW, Bundy D. Fragmentation rates of small satellites in the outer solar system. ACTA ACUST UNITED AC 2000. [DOI: 10.1029/1999je001209] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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43
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Abstract
Near-infrared images of Uranus taken with the Hubble Space Telescope in July and October 1997 revealed discrete clouds with contrasts exceeding 10 times the highest contrast observed before with other techniques. At visible wavelengths, these 10 clouds had lower contrasts than clouds seen by Voyager 2 in 1986. Uranus' rotational rates for southern latitudes were identical in 1986 and 1997. Clouds in northern latitudes rotate slightly more slowly than clouds in opposite southern latitudes.
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Affiliation(s)
- E Karkoschka
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721-0092, USA.
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44
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45
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46
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Pappalardo RT, Reynolds SJ, Greeley R. Extensional tilt blocks on Miranda: Evidence for an upwelling origin of Arden Corona. ACTA ACUST UNITED AC 1997. [DOI: 10.1029/97je00802] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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47
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Wilson L, Head JW, Pappalardo RT. Eruption of lava flows on Europa: Theory and application to Thrace Macula. ACTA ACUST UNITED AC 1997. [DOI: 10.1029/97je00412] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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48
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Strazzulla G. Ion irradiation: its relevance to the evolution of complex organics in the outer solar system. ADVANCES IN SPACE RESEARCH : THE OFFICIAL JOURNAL OF THE COMMITTEE ON SPACE RESEARCH (COSPAR) 1997; 19:1077-1084. [PMID: 11541336 DOI: 10.1016/s0273-1177(97)00356-6] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Ion irradiation of carbon containing ices produces several effects among which the formation of complex molecules and even refractory organic materials whose spectral color and molecular complexity both depend on the amount of deposited energy. Here results from laboratory experiments are summarized. Their relevance for the formation and evolution of simple molecules and complex organic materials on planetary bodies in the external Solar System is outlined.
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Affiliation(s)
- G Strazzulla
- Osservatorio Astrofisico, Citta Universitaria, Catania, Italy
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49
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Fridman AM, Khoruzhii OV, Gor'kavyi NN. Drift mechanism caused by a nonlinear wave and the Cassini Division and Uranian rings formation. CHAOS (WOODBURY, N.Y.) 1996; 6:334-347. [PMID: 12780262 DOI: 10.1063/1.166193] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
The mechanism leading to the observed coexistence of gaps and narrow ringlets in the planetary rings is found. It is based upon the quasi-stationary radial drift of the matter under action of two forces in the disk plane: the Coriolis force and the Reynolds stresses. To an accuracy of the factor of 2 the first force coincides with the Lorentz force, therefore the radial drift in rings is similar to the gradient drift of plasma in the magnetic field. The second force is produced by the wave generated by the nearby satellite in the resonance position. In inertial systems, the second force alone causes a matter flow in its direction, called acoustic streaming. Since the radial drift is caused by nonlinear time-averaged force of high-frequency harmonic interactions in the wave, it exists in the wave propagation zone: from the birth place of the wave-the resonance position, up to the reflection point of the wave, where its group velocity vanishes. Our estimations show that the size of the density wave propagation zone corresponding to the density wave which had been formerly generated the 2:1 orbital resonance with Mimas is consistent with the width of the Cassini Division. In our case the nature of the radial drift is such that first of all it clears out the farthest from the resonance position; later, the closer areas also get affected by the drift. The zone closest to the resonance position itself is the last to be involved in the process. The matter carried away by the drift is partially accumulated near the resonance position forming a narrow dense ringlet. (c) 1996 American Institute of Physics.
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Affiliation(s)
- A. M. Fridman
- Institute of Astronomy RAS, Pyatnitskaya Str. 48, Moscow 109017, RussiaCrimean Astrophysical Observatory, Simeiz, Ukraine
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50
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Abstract
The Galileo probe performed the first in situ measurements of the atmosphere of Jupiter on 7 December 1995. The probe returned data until it reached a depth corresponding to an atmospheric pressure of approximately 24 bars. This report presents a brief overview of the origins and purpose of the mission. Science objectives, entry parameters and mission events, and results are described. The remaining reports address in more detail the individual experiments summarized here.
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Affiliation(s)
- R E Young
- NASA Ames Research Center, Moffett Field, CA 94035, USA
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