While there have been far fewer missions to the outer Solar System than to the inner Solar System, spacecraft destined for the giant planets have conducted a wide range of fundamental investigations, ...returning data that continues to reshape our understanding of these complex systems, sometimes decades after the data were acquired. These data are preserved and accessible from national and international planetary science archives. For all NASA planetary missions and instruments the data are available from the science discipline nodes of the NASA Planetary Data System (PDS). Looking ahead, the PDS will be the primary repository for giant planets data from several upcoming missions and derived datasets, as well as supporting research conducted to aid in the interpretation of the remotely sensed giant planets data already archived in the PDS.
Saturn's Atmosphere at 1–10 Kilometer Resolution Ingersoll, Andrew P.; Ewald, Shawn P.; Sayanagi, Kunio M. ...
Geophysical research letters,
16 August 2018, Letnik:
45, Številka:
15
Journal Article
Recenzirano
Odprti dostop
We present images of Saturn from the final phases of the Cassini mission, including images with 0.5 km per pixel resolution, as high as any Saturn images ever taken. Notable features are puffy clouds ...resembling terrestrial cumulus, shadows indicating cloud height, dome and bowl shaped cloud structures indicating upwelling and downwelling in anticyclones and cyclones respectively, and filaments, which are thread‐like clouds that remain coherent over distances of 20,000 km. From the coherence of the filaments, we give upper bounds on the diffusivity and kinetic energy dissipation. A radiative transfer analysis by Sanz‐Requena et al. (2018) indicates that methane‐band imagery is most useful in determining cloud and haze properties in the 60–250 mbar pressure range. Our methane‐band imagery finds haze in this pressure range covering 64°‐74°planetocentric latitude. Filaments lie within the haze, and cumulus clouds lie below it, but pressure levels are uncertain below the 250 mbar level.
Plain Language Summary
During its final half‐year, the Cassini spacecraft took close‐up images from 3000–4000 km above Saturn's cloud tops. The spatial resolution was as high as any images ever taken of the planet. They revealed isolated puffy clouds like terrestrial cumulus and also more exotic, threadlike clouds ‐ filaments ‐ that would stretch halfway around the Earth if they were on our planet. The filamentary clouds indicate that the level of turbulence in Saturn's atmosphere is very low. The images showed dome‐shaped clouds indicative of upwelling at the centers of anticyclones and bowl‐shaped clouds indicative of downwelling at the centers of cyclones.
Key Points
Close‐up imaging by the Cassini spacecraft reveals long filamentary clouds and puffy cumulus clouds at 0.5 km resolution
A dome‐shaped cloud structure in anticyclones suggests upwelling, and a bowl‐shaped cloud structure in cyclones suggests downwelling
Thread‐like filamentary clouds 20,000 km long suggest a laminar flow with extremely low values of diffusivity and dissipation
Using images from the Cassini spacecraft, we analyzed three ribbon waves in Saturn's 42°N eastward jet at 45°N, 42°N, and 39°N planetocentric latitudes. In this report, we demonstrate that the ...morphology, wavelength, and propagation of the ribbon waves are consistent with barotropic Rossby waves with a smaller baroclinic component. We report on the appearance and disappearance of these waves during Cassini's mission. We suggest that the temporal evolution of these waves are related to the great Saturn storm of 2010–2011.
Plain Language Summary
During their 1980 and 1981 flybys of Saturn, the Voyager spacecraft imaged a dark, sinuous line encircling the planet. This feature, dubbed the ribbon wave after its visual appearance, was embedded in an atmospheric jet stream at 42N latitude. The Cassini spacecraft also discovered waves in the 42N jet during its 2004–2017 Saturn mission. Using images taken by Cassini, we have identified the ribbon waves as Rossby waves, that is, planet‐scale waves that are common in atmospheres, including that of the Earth. Unlike Earth's atmospheric Rossby waves, which are only visible as undulations on weather maps, Saturn's ribbons are visually striking and may be some of the most prominent examples of Rossby waves in the Solar System. The ribbons are composed of a number of wavelengths, each of which is affected differently by the atmosphere and move at different speeds. By measuring the differing speed of these wavelength components, we compared the behavior of the ribbons to theoretical predictions for Rossby waves and estimated basic properties of the atmosphere. Because the ribbons likely extend deep into the atmosphere, they may help shed light on the how the atmosphere behaves at depths that Cassini was not able to observe directly.
Key Points
Cassini observed three wave‐like ribbon features in Saturn's 42N atmospheric jet from 2005 to 2014
The ribbons' morphology, mean wavelengths, and propagation are consistent with Rossby waves
Their propagation places constraints on atmospheric conditions within the jet
•We analyzed Saturn’s North Pole and South Pole as seen by Cassini Orbiter.•Our multispectral analysis reveal the cloud morphology of both of Saturn’s polar vortices.•Our analysis reveals detailed ...structure of the North Polar wind field.•We reveal the presence a bright cloud feature that appears in short wavelengths over the south pole in 2007.•We predict the formation of a bright feature over the north pole before the next equinox.
We present analyses of Saturn’s north pole using high-resolution images captured in late 2012 by the Cassini spacecraft’s Imaging Science Subsystem (ISS) camera. The images reveal the presence of an intense cyclonic vortex centered at the north pole. In the red and green visible continuum wavelengths, the north polar region exhibits a cyclonically spiraling cloud morphology extending from the pole to 85°N planetocentric latitude, with a 4700 km radius. Images captured in the methane bands, which sense upper tropospheric haze, show an approximately circular hole in the haze extending up to 1.5° latitude away from the pole. The spiraling morphology and the “eye”-like hole at the center are reminiscent of a terrestrial tropical cyclone. In the System III reference frame (rotation period of 10h39m22.4s, Seidelmann et al. 2007; Archinal et al. 2011), the eastward wind speed increases to about 140 m s−1 at 89°N planetocentric latitude. The vorticity is (6.5± 1.5)×10−4 s−1 at the pole, and decreases to (1.3± 1.2)×10−4 s−1 at 89°N. In addition, we present an analysis of Saturn’s south polar vortex using images captured in January 2007 to compare its cloud morphology to the north pole. The set of images captured in 2007 includes filters that have not been analyzed before. Images captured in the violet filter (400 nm) also reveal a bright polar cloud. The south polar morphology in 2007 was more smooth and lacked the small clouds apparent around the north pole in 2012. Saturn underwent equinox in August 2009. The 2007 observation captured the pre-equinox south pole, and the 2012 observation captured the post-equinox north pole. Thus, the observed differences between the poles are likely due to seasonal effects. If these differences indeed are caused by seasonal effects, continuing observations of the summer north pole by the Cassini mission should show a formation of a polar cloud that appears bright in short-wavelength filters.
The paper presents velocity fields with ~3‐km spatial resolution of Saturn's north polar vortex (NPV) retrieved using the optical flow method from a sequence of polar‐projected cloud images captured ...by the Imaging Science Subsystem camera on board NASA's Cassini spacecraft. The fields of the velocity magnitude, velocity variation, relative vorticity, divergence, and second invariant are determined to characterize the flow structures of the inner core of the NPV. The mean zonal and mean meridional velocity profiles of the NPV are compared with previous measurements. We also describe the relevant details of application of the optical flow method to planetary cloud‐tracking wind measurements. The mean zonal velocity profile is consistent with the previous measurements using correlation image velocimetry methods. The small but significant meridional velocity corresponds to outwardly spiraling streams observed in the region near the north pole (NP). The concentrated vorticity and second invariant within 1° planetographic latitude of the NP indicate strong rotational motion of the fluid. An analysis is presented to explore a possible physical origin of the observed spiraling node at the NP.
Plain Language Summary
A swirling flow pattern with wind speeds peaking at about 100 m/s was revealed in Saturn's north polar vortex in high‐resolution images captured by the Imaging Science Subsystem camera on board NASA's Cassini spacecraft in November 2012. Using sequences of images that show clouds in the north polar vortex, the motions of these clouds were analyzed to measure the wind speeds in the north polar region. The high‐precision wind measurements presented in the current report are enabled by the optical flow cloud‐tracking method. The time‐averaged wind field shows a well‐defined counterclockwise (cyclonic) vortex at the pole. In particular, the observed flow structures and wind shear near the pole indicate strong rotational motion of the north polar atmosphere with upwelling at the center.
Key Points
The high‐resolution velocity fields of Saturn's north polar vortex (NPV) are extracted from cloud images by using the optical flow method
The vorticity, divergence, and second invariant are obtained to characterize the flow structures of the NPV
The strong rotational motion of the fluid with upwelling is found near the pole
We present three studies of clouds and winds in giant planet atmospheres. The first study focuses on Cassini ISS images of Saturn’s north polar region. We apply a Minnaert-corrected photometric ...analysis to study the cloud colors in 2013 and 2017. Our analysis indicates a general shift in colors from blue to yellow and increases in methane-band reflectivities, both of which are consistent with an increase in the presence of photochemically produced hazes as a response to seasonally increased solar insolation. We also analyze images returned from Cassini's Grand Finale to study Saturn's synoptic scale cloud morphology. The cloud morphology analysis shows there were significant changes on seasonal timescales and changes that occur on the scale of months. In particular, the Hexagon and north polar vortex exhibit the most changes on both timescales. The other two studies focus on the measurement of winds in the atmospheres of Jupiter and Saturn. We present the development of a new cloud-tracking system and its application to New Horizons LORRI images of Jupiter and Cassini ISS images of Saturn. The analysis of New Horizons LORRI images of Jupiter retrieved a global zonal wind profile, filling an important gap in the decades-long record of Jupiter’s winds. The New Horizons wind measurements were compared against wind measurements from Cassini ISS images of Jupiter. Our new measurements hint that there are small changes in Jupiter's wind between the two epochs, especially in the equatorial jets, but the detected changes are comparable to the measurement uncertainties. The analysis of Cassini ISS images of Saturn produced annual global zonal profiles between 2005 and 2016 using filters sensitive to different altitudes. While the winds at the lower altitudes do not exhibit seasonal trends, higher altitude winds show temporal trends in the equatorial region. However, the combination of large uncertainties and the systematic difficulties with tracking clouds in the equatorial region prevent us from drawing a firm conclusion on the existence of such a trend. Additionally, we are unable to resolve the apparent discrepancy in the equatorial winds between the Voyager and Cassini eras.
Centaurs, minor planets with a semi-major axis between the orbits of Jupiter and Neptune (5–30 AU), are thought to be among the most diverse small bodies in the solar system. These important targets ...for future missions may have recently been Kuiper Belt Objects (KBOs), which are thought to be chemically and physically primitive remnants of the early solar system. While the Kuiper Belt spans distances of 30–50 AU, making direct observations difficult, Centaurs' proximity to the Earth and Sun make them more accessible targets for robotic missions. Thus, we outline a mission concept designed to reconnoiter 10199 Chariklo, the largest Centaur and smallest ringed body yet discovered. Named for a legendary Centaur tamer, the conceptual Camilla mission is designed to fit under the cost cap of the National Aeronautics and Space Administration (NASA) New Frontiers program, leveraging a conservative payload to support a foundational scientific investigation to these primitive bodies. Specifically, the single flyby encounter utilizes a combined high-resolution camera/VIS-IR mapping spectrometer, a sub-mm point spectrometer, and a UV mapping spectrometer. In addition, the mission concept utilizes a kinetic impactor, which would provide the first opportunity to sample the composition of potentially primitive subsurface material beyond Saturn, thus providing key insights into solar system origins. Such a flyby of the Chariklo system would provide a linchpin in the understanding of small body composition, evolution, and transport of materials in the solar system.
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•Flyby concept for 10199 Chariklo, the largest Centaur and smallest ring system.•Opportunity to learn about Kuiper Belt Objects much closer to Earth.•Impactor would provide deepest yet subsurface sampling in the outer Solar System.•Mission concept fits well within NASA New Frontiers Program cost cap.•Mission concept may fit within NASA Discovery Program cost cap.
Use of pesticides can have substantial nonlethal impacts on nontarget species, including driving evolutionary change, often with unknown consequences for species, ecosystems, and society. Hyalella ...azteca , a species complex of North American freshwater amphipods, is widely used for toxicity testing of water and sediment and has frequently shown toxicity due to pyrethroid pesticides. We demonstrate that 10 populations, 3 from laboratory cultures and 7 from California water bodies, differed by at least 550-fold in sensitivity to pyrethroids. The populations sorted into four phylogenetic groups consistent with species-level divergence. By sequencing the primary pyrethroid target site, the voltage-gated sodium channel, we show that point mutations and their spread in natural populations were responsible for differences in pyrethroid sensitivity. At least one population had both mutant and WT alleles, suggesting ongoing evolution of resistance. Although nonresistant H. azteca were susceptible to the typical neurotoxic effects of pyrethroids, gene expression analysis suggests the mode of action in resistant H. azteca was not neurotoxicity but was oxidative stress sustained only at considerably higher pyrethroid concentrations. The finding that a nontarget aquatic species has acquired resistance to pesticides used only on terrestrial pests is troubling evidence of the impact of chronic pesticide transport from land-based applications into aquatic systems. Our findings have far-reaching implications for continued uncritical use of H. azteca as a principal species for monitoring and environmental policy decisions.
The precaution adoption process model was used to examine the predictors of 2 behaviors recommended to reduce the risk of developing osteoporosis: calcium consumption and weight-bearing exercise. A ...total of 452 premenopausal women completed a mailed questionnaire assessing stage in the precaution adoption process and 12 knowledge and attitudinal variables. Participants were also given an opportunity to request information about osteoporosis. In all, 11 of the 12 knowledge and attitudinal variables were associated with calcium stage; 8 were associated with exercise stage. Information requests were associated with both calcium and exercise stage. Findings provide substantial support for the precaution adoption process model and suggest that the model can be usefully applied in this area to increase understanding of why many women do not practice behaviors that could reduce their risk of developing osteoporosis.
Proline-glycine-proline (PGP) has been shown to have chemotactic effects on neutrophils via CXCR2 in several lung diseases. PGP is derived from collagen by the combined action of matrix ...metalloproteinase (MMP) 8 and/or MMP9 and prolyl endopeptidase (PE). We investigated the role of PGP in inflammatory bowel disease (IBD).
In intestinal tissue from patients with IBD and mice with dextran sodium sulfate (DSS)-induced colitis, MMP8, MMP9 and PE were evaluated by ELISA, immunoblot and immunohistochemistry. Peripheral blood polymorphonuclear cell (PMN) supernatants were also analysed accordingly and incubated with collagen to assess PGP generation ex vivo. PGP levels were measured by mass spectrometry, and PGP neutralisation was achieved with a PGP antagonist and PGP antibodies.
In the intestine of patients with IBD, MMP8 and MMP9 levels were elevated, while PE was expressed at similar levels to control tissue. PGP levels were increased in intestinal tissue of patients with IBD. Similar results were obtained in intestine from DSS-treated mice. PMN supernatants from patients with IBD were far more capable of generating PGP from collagen ex vivo than healthy controls. Furthermore, PGP neutralisation during DSS-induced colitis led to a significant reduction in neutrophil infiltration in the intestine.
The proteolytic cascade that generates PGP from collagen, as well as the tripeptide itself, is present in the intestine of patients with IBD and mice with DSS-induced colitis. PGP neutralisation in DSS-treated mice showed the importance of PGP-guided neutrophilic infiltration in the intestine and indicates a vicious circle in neutrophilic inflammation in IBD.
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