Search

JWST measured the infrared spectra of Saturn's rings and several of its small moons (Epimetheus, Pandora, Telesto and Pallene) as part of Guaranteed Time Observation program 1247. The NIRSpec instrument obtained near-infrared spectra of the small moons between 0.6 and 5.3 microns, which are all dominated by water-ice absorption bands. The shapes of the water-ice bands for these moons suggests that their surfaces contain variable mixes of crystalline and amorphous ice or variable amounts of contaminants and/or sub-micron ice grains. The near-infrared spectrum of Saturn's A ring has exceptionally high signal-to-noise between 2.7 and 5 microns and is dominated by features due to highly crystalline water ice. The ring spectrum also confirms that the rings possess a 2-3% deep absorption at 4.13 microns due to deuterated water-ice previously seen by the Visual and Infrared Mapping Spectrometer onboard the Cassini spacecraft. This spectrum also constrains the fundamental absorption bands of carbon dioxide and carbon monoxide and may contain evidence for a weak aliphatic hydrocarbon band. Meanwhile, the MIRI instrument obtained mid-infrared spectra of the rings between 4.9 and 27.9 microns, where the observed signal is a combination of reflected sunlight and thermal emission. This region shows a strong reflectance peak centered around 9.3 microns that can be attributed to crystalline water ice. Since both the near and mid-infrared spectra are dominated by highly crystalline water ice, they should provide a useful baseline for interpreting the spectra of other objects in the outer solar system with more complex compositions., Comment: Accepted for Publication in JGR Planets

Geological investigations planned for the Europa Clipper mission will examine the formation, evolution, and expression of geomorphic structures found on the surface. Understanding geologic features, their formation, and any recent activity are key inputs in constraining Europa’s potential for habitability. In addition to providing information about the moon’s habitability, the geologic study of Europa is compelling in and of itself. Here we provide a high-level, cross-instrument, and cross-discipline overview of the geologic investigations planned within the Europa Clipper mission. Europa’s fascinating collection of ice-focused geology provides an unparalleled opportunity to investigate the dynamics of icy shells, ice-ocean exchange processes, and global-scale tectonic and tidal stresses. We present an overview of what is currently known about the geology of Europa, from global to local scales, highlighting outstanding issues and open questions, and detailing how the Europa Clipper mission will address them. We describe the mission’s strategy for searching for and characterizing current activity in the form of possible active plumes, thermal anomalies, evidence for surface changes, and extremely fresh surface exposures. The complementary and synergistic nature of the data sets from the various instruments and their integration will be key to significantly advancing our understanding of Europa’s geology.

Enceladus is a prime target in the search for life in our Solar System, having an active plume that is likely to be connected to a large liquid water sub-surface ocean. Using the sensitive near-infrared spectograph instrument on board the James Webb Space Telescope, we searched for organic compounds and characterized the plume’s composition and structure. The observations directly sample the fluorescence emissions of H2O and reveal an extraordinarily extensive plume (up to 10,000 km or 40 Enceladus radii) at cryogenic temperatures (25 K) embedded in a large bath of emission originating from Enceladus’ torus. Intriguingly, the observed outgassing rate (300 kg s−1) is similar to that derived from close-up observations with Cassini 15 years ago, and the torus density is consistent with previous spatially unresolved measurements with Herschel 13 years ago, which indicates that the vigour of gas eruption from Enceladus has been relatively stable over decadal timescales. This level of activity is sufficient to maintain a derived column density of 4.5 × 1017 m−2 for the embedding equatorial torus, and establishes Enceladus as the prime source of water across the Saturnian system. We performed searches for several non-water gases (CO2, CO, CH4, C2H6, CH3OH), but none were identified in the spectra. On the surface of the trailing hemisphere, we observe strong H2O ice features, including its crystalline form, yet we do not recover CO2, CO or NH3 ice signatures from these observations. As we prepare to send new spacecraft into the outer Solar System, these observations demonstrate the unique ability of the James Webb Space Telescope to provide critical support for the exploration of distant icy bodies and cryovolcanic plumes., QC 20231107

Enceladus' plume consists mainly of a mixture of water vapor and solid ice particles that may originate from a subsurface ocean. The physical processes underlying Enceladus' plume particle dynamics are still being debated, and quantifying the particles' size distribution and launch velocities can help constrain these processes. Cassini's Visual and Infrared Mapping Spectrometer (VIMS) observed the Enceladus plume over a wavelength range of 0.9 micron to 5.0 microns for a significant fraction of Enceladus' orbital period on three dates in the summer of 2017. We find that the relative brightness of the plume on these different dates varies with wavelength, implying that the particle size distribution in the plume changes over time. These observations also enable us to study how the particles' launch velocities vary with time and observed wavelength. We find that the typical launch velocity of particles remains between 140 m/s and 148 m/s at wavelengths between 1.2 microns and 3.7 microns. This may not be consistent with prior models where particles are only accelerated by interactions with the vent walls and gas, and could imply that mutual particle collisions close to the vent are more important than previously recognized., Comment: 13 pages, 8 figures, accepted for publication in PSJ

Enceladus is a prime target in the search for life in our solar system, having an active plume likely connected to a large liquid water subsurface ocean. Using the sensitive NIRSpec instrument onboard JWST, we searched for organic compounds and characterized the plume's composition and structure. The observations directly sample the fluorescence emissions of H2O and reveal an extraordinarily extensive plume (up to 10,000 km or 40 Enceladus radii) at cryogenic temperatures (25 K) embedded in a large bath of emission originating from Enceladus' torus. Intriguingly, the observed outgassing rate (300 kg/s) is similar to that derived from close-up observations with Cassini 15 years ago, and the torus density is consistent with previous spatially unresolved measurements with Herschel 13 years ago, suggesting that the vigor of gas eruption from Enceladus has been relatively stable over decadal timescales. This level of activity is sufficient to maintain a derived column density of 4.5x1017 m-2 for the embedding equatorial torus, and establishes Enceladus as the prime source of water across the Saturnian system. We performed searches for several non-water gases (CO2, CO, CH4, C2H6, CH3OH), but none were identified in the spectra. On the surface of the trailing hemisphere, we observe strong H2O ice features, including its crystalline form, yet we do not recover CO2, CO nor NH3 ice signatures from these observations. As we prepare to send new spacecraft into the outer solar system, these observations demonstrate the unique ability of JWST in providing critical support to the exploration of distant icy bodies and cryovolcanic plumes., Comment: Accepted for publication in Nature Astronomy on May 17th 2023

The zeta ring is the innermost component of the Uranian ring system. It is of scientific interest because its morphology changed significantly between the Voyager 2 encounter in 1986 and subsequent Earth-based observations around 2007. It is also of practical interest because some Uranus mission concepts have the spacecraft pass through the inner flank of this ring. Recent re-examinations of the Voyager 2 images have revealed additional information about this ring that provide a more complete picture of the ring's radial brightness profile and phase function. These data reveal that this ring's brightness varies with phase angle in a manner similar to other tenuous rings, consistent with it being composed primarily of sub-millimeter-sized particles. The total cross section of particles within this ring can also be estimated from these data, but translating that number into the actual risk to a spacecraft flying through this region depends on a number of model-dependent parameters. Fortunately, comparisons with Saturn's G and D rings allows the zeta-ring's particle number density to be compared with regions previously encountered by the Voyager and Cassini spacecraft. Finally, these data indicate that the observed changes in the zeta-ring's structure between 1986 and 2007 are primarily due to a substantial increase in the amount of dust at distances between 38,000 km and 40,000 km from Uranus' center., Comment: 28 Pages, 12 Figures, Accepted for publication in PSJ, fixed a few small issues found in the proofs

Saturn's C ring contains multiple structures that appear to be density waves driven by time-variable anomalies in the planet's gravitational field. Semi-empirical extensions of density wave theory enable the observed wave properties to be translated into information about how the pattern speeds and amplitudes of these gravitational anomalies have changed over time. Combining these theoretical tools with wavelet-based analyses of data obtained by the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft reveals a suite of structures in Saturn's gravity field with azimuthal wavenumber 3, rotation rates between 804 degrees/day and 842 degrees/day and local gravitational potential amplitudes between 30 and 150 cm^2/s^2. Some of these anomalies are transient, appearing and disappearing over the course of a few Earth years, while others persist for decades. Most of these persistent patterns appear to have roughly constant pattern speeds, but there is at least one structure in the planet's gravitational field whose rotation rate steadily increased between 1970 and 2010. This gravitational field structure appears to induce two different asymmetries in the planet's gravity field, one with azimuthal wavenumber 3 that rotates at roughly 810 degrees/day and another with azimuthal wavenumber 1 rotating three times faster. The atmospheric processes responsible for generating the latter pattern may involve solar tides., Comment: 60 pages, 29 Figures, accepted for publication in the Planetary Science Journal

Current knowledge of the Uranian system is limited to observations from the flyby of Voyager 2 and limited remote observations. However, Uranus remains a highly compelling scientific target due to the unique properties of many aspects of the planet itself and its system. Future exploration of Uranus must focus on cross-disciplinary science that spans the range of research areas from the planet's interior, atmosphere, and magnetosphere to the its rings and satellites, as well as the interactions between them. Detailed study of Uranus by an orbiter is crucial not only for valuable insights into the formation and evolution of our solar system but also for providing ground truths for the understanding of exoplanets. As such, exploration of Uranus will not only enhance our understanding of the ice giant planets themselves but also extend to planetary dynamics throughout our solar system and beyond. The timeliness of exploring Uranus is great, as the community hopes to return in time to image unseen portions of the satellites and magnetospheric configurations. This urgency motivates evaluation of what science can be achieved with a lower-cost, potentially faster-turnaround mission, such as a New Frontiers–class orbiter mission. This paper outlines the scientific case for and the technological and design considerations that must be addressed by future studies to enable a New Frontiers–class Uranus orbiter with balanced cross-disciplinary science objectives. In particular, studies that trade scientific scope and instrumentation and operational capabilities against simpler and cheaper options must be fundamental to the mission formulation.

Objectives: Our goal was to evaluate whether four-dimensional (4D) flow magnetic resonance imaging (MRI) can predict the growth rate of dilatation of the ascending aorta (AA) in patients with a tricuspid, normally functioning aortic valve. Methods: In this prospective clinical study, aortic 4D flow MRI was performed at the Kuopio University Hospital on 30 patients diagnosed with AA dilatation (maximum diameter >40 mm) between August 2017 and July 2020. The MRI was repeated after a 1-year follow-up, with AA dimensions and 4D flow parameters analysed retrospectively at both time points. The standard error of measurement was used to assess the statistical significance of the growth rate of AA dilatation. Flow displacement (FD) was transformed to a class-scaled parameter using FD ≥5% as a threshold. Results: Statistically significant growth [median 2.1 mm (1.5–2.2 mm); P = 0.03] was detected in 6 male patients (20%); the AA diameter remained unchanged [0.2 mm (−0.3 to 0.9 mm)] in 24 patients (80%). An increased FD at the baseline was associated with significant growth during the 1-year follow-up in the proximal AA. An association was detected between decreased total wall shear stress and significant aortic growth in the inner curve of the sinotubular junction [529 mPa (449–664 mPa) vs 775 mPa (609–944 mPa); P = 0.03] and the anterior side of the proximal aortic arch [356 mPa (305–367 mPa) vs 493 mPa (390–586 mPa); P < 0.001]. Conclusions: FD and decreased wall shear stress seem to be associated with significant growth of AA dilatation at the 1-year follow-up. Thus, 4D flow MRI might be useful in assessing risk for AA diameter growth in patients with a tricuspid aortic valve.

Background: The heart’s position determined as the heart–aorta angle (HAA) has been demonstrated to associate with ascending aortic (AA) dilatation. Visceral adipose tissue (VAT) and aortic elongation may shift the heart to the steeper position. Purpose: To investigate whether VAT and aortic length influence the HAA. Material and methods: We examined 346 consecutive patients (58.4% men; mean age = 67.0 ± 14.1 years) who underwent aortic computed tomography angiography (CTA). HAA was measured as the angle between the long axis of the heart and AA midline. The amount of VAT was measured at the level of middle L4 vertebra from a single axial CT slice. Aortic length was measured by combining four anatomical segments in different CTA images. The amount of VAT and aortic length were determined as mild with values in the lowest quartile and as excessive with values in the other three quartiles. Results: A total of 191 patients (55.2%) had no history of aortic diseases, 134 (38.7%) displayed AA dilatation, 8 (2.3%) had abdominal aortic aneurysm (AAA), and 13 (3.8%) had both AA dilatation and AAA. There was a strong nonlinear regression between smaller HAA and VAT/height, and HAA and aortic length/height. Median HAA was 124.2° (interquartile range 119.0°–130.8°) in patients with a mild amount of VAT versus 120.5° (interquartile range 115.4°–124.7°) in patients with excessive VAT (P < 0.001). Conclusion: An excessive amount of VAT and aortic elongation led to a steeper heart position. These aspects may possess clinical value when evaluating aortic diseases in obese patients.

Current knowledge of the Uranian system is limited to observations from the flyby of Voyager 2 and limited remote observations. However, Uranus remains a highly compelling scientific target due to the unique properties of many aspects of the planet itself and its system. Future exploration of Uranus must focus on cross-disciplinary science that spans the range of research areas from the planet's interior, atmosphere, and magnetosphere to the its rings and satellites, as well as the interactions between them. Detailed study of Uranus by an orbiter is crucial not only for valuable insights into the formation and evolution of our solar system but also for providing ground truths for the understanding of exoplanets. As such, exploration of Uranus will not only enhance our understanding of the ice giant planets themselves but also extend to planetary dynamics throughout our solar system and beyond. The timeliness of exploring Uranus is great, as the community hopes to return in time to image unseen portions of the satellites and magnetospheric configurations. This urgency motivates evaluation of what science can be achieved with a lower-cost, potentially faster-turnaround mission, such as a New Frontiers–class orbiter mission. This paper outlines the scientific case for and the technological and design considerations that must be addressed by future studies to enable a New Frontiers–class Uranus orbiter with balanced cross-disciplinary science objectives. In particular, studies that trade scientific scope and instrumentation and operational capabilities against simpler and cheaper options must be fundamental to the mission formulation.

Saturn's C ring contains multiple structures that appear to be density waves driven by time-variable anomalies in the planet's gravitational field. Semi-empirical extensions of density wave theory enable the observed wave properties to be translated into information about how the pattern speeds and amplitudes of these gravitational anomalies have changed over time. Combining these theoretical tools with wavelet-based analyses of data obtained by the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft reveals a suite of structures in Saturn's gravity field with azimuthal wavenumber 3, rotation rates between 804 degrees/day and 842 degrees/day and local gravitational potential amplitudes between 30 and 150 cm^2/s^2. Some of these anomalies are transient, appearing and disappearing over the course of a few Earth years, while others persist for decades. Most of these persistent patterns appear to have roughly constant pattern speeds, but there is at least one structure in the planet's gravitational field whose rotation rate steadily increased between 1970 and 2010. This gravitational field structure appears to induce two different asymmetries in the planet's gravity field, one with azimuthal wavenumber 3 that rotates at roughly 810 degrees/day and another with azimuthal wavenumber 1 rotating three times faster. The atmospheric processes responsible for generating the latter pattern may involve solar tides., Comment: 60 pages, 29 Figures, accepted for publication in the Planetary Science Journal

Studying lunar dust is vital to the exploration of the Moon and other airless planetary bodies. The Ultraviolet and Visible Spectrometer (UVS) on board the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft conducted a series of Almost Limb activities to look for dust near the dawn terminator region. During these activities the instrument stared at a fixed point in the zodiacal background off the Moon's limb while the spacecraft moved in retrograde orbit from the sunlit to the unlit side of the Moon. The spectra obtained from these activities probe altitudes within a few kilometers of the Moon's surface, a region whose dust populations were not well constrained by previous remote-sensing observations from orbiting spacecraft. Filtering these spectra to remove a varying instrumental signal enables constraints to be placed on potential signals from a dust atmosphere. These filtered spectra are compared with those predicted for dust atmospheres with various exponential scale heights and particle size distributions to yield upper limits on the dust number density for these potential populations. For a differential size distribution proportional to $s^{-3}$ (where $s$ is the particle size) and a scale height of 1 km, we obtain an upper limit on the number density of dust particles at the Moon's surface of 142 $m^{-3}$., Comment: Accepted for publication in JGR: Planets

Saturn's rings act as a system of innumerable test particles that are remarkably sensitive to periodic disturbances in the planet's gravitational field. We identify 15 additional density and bending waves in Saturn's C ring driven by the planet's internal normal mode oscillations. Taking advantage of a highly accurate absolute radius scale for the rings, we are able to detect weak, high-wavenumber (up to m=14) waves with km-scale radial wavelengths. From a systematic scan of the entire C ring, we report the discovery and identification of 11 new Outer Lindblad Resonances (OLRs), two counterpart inner Lindblad resonances (ILRs), and two new Outer Vertical Resonances (OVRs). The close agreement of the observed resonance locations and wave rotation rates with the predictions of models of Saturn's interior suggests that all of the new waves are driven by Saturnian f-mode oscillations. As classified by their spherical harmonic shapes, the modes in question range in azimuthal wavenumber from m=8 to 14, with associated resonance orders l-m ranging from 0 to 8, where l is the overall angular wavenumber of the mode. Our suite of detections for l-m=4 is now complete from m=8 to m=14. Curiously, detections with l-m=2 are less common. These newly-identified non-sectoral waves sample latitudinal as well as radial structure within the planet and may thus provide valuable constraints on Saturn's differential rotation. Allowing for the fact that the two ILR-type waves appear to be due to the same normal modes as two of the OLR-type waves, the 13 additional modes identified here bring to 34 the number of distinct f-modes suitable for constraining interior models., Comment: Accepted for publication in Icarus

Saturn's E ring consists of micron-sized particles launched from Enceladus by that moon's geological activity. A variety of small-scale structures in the E-ring's brightness have been attributed to tendrils of material recently launched from Enceladus. However, one of these features occurs at a location where Enceladus' gravitational perturbations should concentrate background E-ring particles into structures known as satellite wakes. While satellite wakes have been observed previously in ring material drifting past other moons, these E-ring structures would be the first examples of wakes involving particles following horseshoe orbits near Enceladus' orbit. The predicted intensity of these wake signatures are particularly sensitive to the fraction E-ring particles' on orbits with low eccentricities and semi-major axes just outside of Enceladus' orbit, and so detailed analyses of these and other small-scale E-ring features should place strong constraints on the orbital properties and evolution of E-ring particles., Comment: 18 pages, 10 figures, accepted for publication in PSJ, Revised to fix small errors found in proofs

In addition to its suite of narrow dense rings, Uranus is surrounded by an extremely complex system of dusty rings that were most clearly seen by the Voyager spacecraft after it flew past the planet. A new analysis of the highest resolution images of these dusty rings reveals that a number of them are less than 20 km wide. The extreme narrowness of these rings, along with the fact that most of them do not appear to fall close to known satellite resonances, should provide new insights into the forces responsible for sculpting the Uranian ring system., Comment: 17 Pages, 10 Figures, Accepted for publication in the Planetary Science Journal, Revised to reflect corrections made at proof stage

Enceladus is the first planetary object for which direct sampling of a subsurface water reservoir, likely habitable, has been performed. Over a decade of flybys and seven flythroughs of its watery plume, the Cassini spacecraft determined that Enceladus possesses all the ingredients for life. The existence of active eruptions blasting fresh water into space, makes Enceladus the easiest target in the search for life elsewhere in the Solar System. Flying again through the plume with more advanced instruments, landing at the surface near active sources and collecting a sample for return to Earth are the natural next steps for assessing whether life emerges in this active world. Characterizing this habitable world also requires detailed mapping and monitoring of its tidally-induced activity, from the orbit as well as from the surface using complementary platforms. Such ambitious goals may be achieved in the future in the framework of ESA large or medium-class missions in partnership with other international agencies, in the same spirit of the successful Cassini-Huygens mission. For all these reasons, exploring habitable ocean worlds, with Enceladus as a primary target, should be a priority topic of the ESA Voyage 2050 programme.

Background/Aim: Dilatation of the main pulmonary artery (mPA) is a common incidental finding in chest imaging and often leads to consultation. The aim of this study was to determine the prevalence of mPA dilatation in a coronary artery CT angiography (CCTA) population. Patients and Methods: The study investigated 985 consecutive patients scheduled for diagnostic CCTA. The transverse axial diameter of the mPA was measured. The prevalence of mPA dilatation was estimated using different reference values (Framingham Heart Study: 28.9 mm for males and 26.9 mm for females, Bozlar: 29.5 mm for both genders and Karazincir: 32.6 mm for males and 31.9 mm for females). Results: The patient mean age was 53.0±9.7 years (66.5% were women). Body surface area (BSA) correlated moderately with the mPA diameter (r=0.423, p<0.001). The prevalence of mPA dilatation varied from 5.9% (Karazincir) to 33.7% (Framingham Heart Study) in the overall study population. Conclusion: The prevalence of mPA dilatation is high in a CCTA patient population when using a cut-off value from the Framingham Heart Study.

Tiivistelmä. Tutkimuksen aiheena on opettajan käyttämä positiivinen pedagogiikka ensimmäisen vuosiluokan syksyllä. Positiivinen pedagogiikka sisältää ajatuksen välittävästä vuorovaikutuksesta, innostavan ilmapiirin luomisesta, oppilaan autonomian tukemisesta sekä luonteenvahvuuksien ja tunnekasvatuksen huomioimisesta osana opetusta. Sillä tavoitellaan oppilaan kokonaisvaltaista hyvinvointia. Positiivinen pedagogiikka on rantautunut Suomeen 2010-luvun puolivälissä, joten sen tutkiminen käytännön opettajan työssä on ajankohtaista. Tutkimuksen aineisto kerättiin Pohjois-Pohjanmaalaisella alakoululla syksyllä 2020. Aineisto koostui etnografiselle tutkimukselle tyypillisistä aineistonkeruumenetelmistä: havainnoinnista ja haastattelusta. Havainnointi kohdistui kahteen yhteisopettajuutta toteuttavaan ensimmäisen vuosiluokan opettajaan, joille toteutettiin yksilölliset teemahaastattelut. Tutkimuskysymys oli: “Miten positiivinen pedagogiikka näyttäytyy opettajan toiminnassa alakoulun ensimmäisellä vuosiluokalla?” Aineiston analyysissä hyödynnettiin teoriaohjaavaa sisällönanalyysiä. Tutkimustulokset jakautuivat positiivisen pedagogiikan osa-alueisiin teoriatiedon pohjalta, joihin sisältyi positiivisen pedagogiikan toimintaa kuvaavia käsitteitä. Tuloksissa korostui välittävän vuorovaikutuksen, innostavan ilmapiirin ja oppilaan autonomian tukemisen merkitys osana opettajan käyttämää positiivista pedagogiikkaa. Tuloksissa havaittiin monipuolisesti positiivisen pedagogiikan ajattelun mukaisia piirteitä, mutta sille tyypillisten harjoitteiden teettäminen osana opetusta oli hyvin vähäistä. Merkittävä tutkimustulos oli, että oppilaiden luonteenvahvuuksien huomioiminen sekä tunnekasvatuksen harjoittaminen osana opetusta ensimmäisellä vuosiluokalla oli suppeaa. Positiivisen pedagogiikan mukaista ajattelua voidaan pitää välittävän pedagogiikan lähtökohtana. Sen antamia mahdollisuuksia oppilaan hyvinvoinnin kehittäjänä ei voida liikaa korostaa. Positiivisen pedagogiikan harjoittaminen e

Studying lunar dust is vital to the exploration of the Moon and other airless planetary bodies. The Ultraviolet and Visible Spectrometer (UVS) on board the Lunar Atmosphere and Dust Environment Explorer (LADEE) spacecraft conducted a series of Almost Limb activities to look for dust near the dawn terminator region. During these activities the instrument stared at a fixed point in the zodiacal background off the Moon's limb while the spacecraft moved in retrograde orbit from the sunlit to the unlit side of the Moon. The spectra obtained from these activities probe altitudes within a few kilometers of the Moon's surface, a region whose dust populations were not well constrained by previous remote-sensing observations from orbiting spacecraft. Filtering these spectra to remove a varying instrumental signal enables constraints to be placed on potential signals from a dust atmosphere. These filtered spectra are compared with those predicted for dust atmospheres with various exponential scale heights and particle size distributions to yield upper limits on the dust number density for these potential populations. For a differential size distribution proportional to $s^{-3}$ (where $s$ is the particle size) and a scale height of 1 km, we obtain an upper limit on the number density of dust particles at the Moon's surface of 142 $m^{-3}$., Comment: Accepted for publication in JGR: Planets

Saturn's rings act as a system of innumerable test particles that are remarkably sensitive to periodic disturbances in the planet's gravitational field. We identify 15 additional density and bending waves in Saturn's C ring driven by the planet's internal normal mode oscillations. Taking advantage of a highly accurate absolute radius scale for the rings, we are able to detect weak, high-wavenumber (up to m=14) waves with km-scale radial wavelengths. From a systematic scan of the entire C ring, we report the discovery and identification of 11 new Outer Lindblad Resonances (OLRs), two counterpart inner Lindblad resonances (ILRs), and two new Outer Vertical Resonances (OVRs). The close agreement of the observed resonance locations and wave rotation rates with the predictions of models of Saturn's interior suggests that all of the new waves are driven by Saturnian f-mode oscillations. As classified by their spherical harmonic shapes, the modes in question range in azimuthal wavenumber from m=8 to 14, with associated resonance orders l-m ranging from 0 to 8, where l is the overall angular wavenumber of the mode. Our suite of detections for l-m=4 is now complete from m=8 to m=14. Curiously, detections with l-m=2 are less common. These newly-identified non-sectoral waves sample latitudinal as well as radial structure within the planet and may thus provide valuable constraints on Saturn's differential rotation. Allowing for the fact that the two ILR-type waves appear to be due to the same normal modes as two of the OLR-type waves, the 13 additional modes identified here bring to 34 the number of distinct f-modes suitable for constraining interior models., Comment: Accepted for publication in Icarus

In addition to its suite of narrow dense rings, Uranus is surrounded by an extremely complex system of dusty rings that were most clearly seen by the Voyager spacecraft after it flew past the planet. A new analysis of the highest resolution images of these dusty rings reveals that a number of them are less than 20 km wide. The extreme narrowness of these rings, along with the fact that most of them do not appear to fall close to known satellite resonances, should provide new insights into the forces responsible for sculpting the Uranian ring system., Comment: 17 Pages, 10 Figures, Accepted for publication in the Planetary Science Journal, Revised to reflect corrections made at proof stage

Saturn's E ring consists of micron-sized particles launched from Enceladus by that moon's geological activity. A variety of small-scale structures in the E-ring's brightness have been attributed to tendrils of material recently launched from Enceladus. However, one of these features occurs at a location where Enceladus' gravitational perturbations should concentrate background E-ring particles into structures known as satellite wakes. While satellite wakes have been observed previously in ring material drifting past other moons, these E-ring structures would be the first examples of wakes involving particles following horseshoe orbits near Enceladus' orbit. The predicted intensity of these wake signatures are particularly sensitive to the fraction E-ring particles' on orbits with low eccentricities and semi-major axes just outside of Enceladus' orbit, and so detailed analyses of these and other small-scale E-ring features should place strong constraints on the orbital properties and evolution of E-ring particles., Comment: 18 pages, 10 figures, accepted for publication in PSJ, Revised to fix small errors found in proofs

In the absence of direct observations of Europa's particle plumes, deposits left behind during eruptive events would provide the best evidence for recent geological activity, and would serve as indicators of the best places to search for ongoing activity on the icy moon. Here, we model the morphological and spectral signatures of europan plume deposits, utilizing constraints from recent Hubble Space Telescope observations as model inputs. We consider deposits emplaced by plumes that are 1 km to 300 km tall, and find that in the time between the Galileo Mission and the arrival of the Europa Clipper spacecraft, plumes that are < 7 km tall are most likely to emplace deposits that could be detected by spacecraft cameras. Deposits emplaced by larger plumes could be detected by cameras operating at visible wavelengths provided that their average particle size is sufficiently large, their porosity is high, and/or they are salt-rich. Conversely, deposits emplaced by large plumes could be easily detected by near-IR imagers regardless of porosity, or individual particle size or composition. If low-albedo deposits flanking lineated features on Europa are indeed cryoclastic mantlings, they were likely emplaced by plumes that were less than 4 km tall, and deposition could be ongoing today. Comparisons of the sizes and albedos of these deposits between the Galileo and Europa Clipper missions could shed light on the size and frequency of cryovolcanic eruptions on Europa., Comment: 50 pages, 12 Figures, accepted for publication in Icarus

Objectives: The aim of this study was to evaluate whether the orientation of the heart, measured as an angle between the long axis of the heart and ascending aorta midline (heart-aorta-angle, HAA), associates with ascending aortic (AA) dilatation. Furthermore, the association between HAA and wall shear stress (WSS) was studied. Methods: HAA was retrospectively measured in 1000 consecutive coronary artery computed tomographic angiography (CCTA) images in patients with low-to-moderate pretest probability for coronary artery disease (CAD). To evaluate the effects of HAA on AA flow, 4D flow MRI was performed for 28 patients with AA dilatation (> 40 mm) and WSS was analyzed. Results: The mean age of patients undergoing CCTA was 52.9 ± 9.8 years; 66.5% were women. Their median HAA was 128.7° and interquartile range 123.3–134.1°. HAA was significantly smaller in patients with dilated AA (median 126.7° [121.3–130.8°]) compared with the patients with normal AA (median 129.5° [124.3–135.3°], p < 0.001). HAA was smaller in males (p < 0.001) and in patients with diabetes (p = 0.016), hypertension (p = 0.001), CAD (p = 0.003), hypercholesterolemia (p < 0.001), and bicuspid aortic valve (p = 0.025) than without these factors. In a subpopulation without any of these underlying diseases (n = 233), HAA was still significantly smaller in the patients with dilated AA (median 127.9° [124.3–134.3°]) compared with patients with normal AA (median 131.9° [127.6–136.9°], p = 0.013). In 4D flow MRI, a smaller HAA correlated with increased total WSS in the outer curvature of the proximal AA (r = − 0.510, p = 0.006). Conclusions: A smaller HAA associates with AA dilatation and affects the blood flow in the proximal AA.

Objectives: To clarify the prevalence and risk factors of ascending aortic (AA) dilatation according to ESC 2014 guidelines. Methods: This study included 1000 consecutive patients scheduled for diagnostic coronary artery computed tomographic angiography. AA diameter was retrospectively measured in 3 planes: sinus valsalva, sinotubular junction, and tubular part. The threshold for AA dilatation was set to > 40 mm which has been suggested as an upper normal limit for AA diameter in ESC 2014 guidelines on aortic diseases. Aortic size index (ASI) using the ratio between aortic diameter and body surface area (BSA) was applied as a comparative measurement. The threshold for AA dilatation was set to the upper limit of normal distribution exceeding two standard deviations (95%). Risk factors for AA dilatation were collected from medical records. Results: The patients’ mean age was 52.9 ± 9.8 years (66.5% women). The prevalence of AA dilatation was 23.0% in the overall study population (52.5% males) and 15.1% in the subgroup of patients with no coronary artery disease or bicuspid (BAV)/mechanical aortic valve (n = 365). According to the normal-distributed ASI values, the threshold for sinus valsalva was defined as 23.2 mm/m2 and for tubular part 22.2 mm/m2 in the subgroup. Higher BSA was associated with larger AA dimensions (r = 0.407, p < 0.001). Male gender (p < 0.001), BAV (p < 0.001), hypertension (p = 0.009) in males, and smoking (p < 0.001) appeared as risk factors for AA dilatation. Conclusions: The prevalence of AA dilatation is high with current ESC guidelines for normal AA dimension, especially in males. Body size is strongly associated with AA dimensions; it would be more reliable to use BSA-adjusted AA diameters for the definition of AA dilatation.

Tiivistelmä. Tutkielman tavoitteena oli selvittää, voiko oppilaan liikkujaidentiteettiä kehittää positiivisen pedagogiikan avulla alkuopetuksen liikunnan oppiaineessa. Tutkielmassa käsitellään TARGET-mallin elementtien käyttöä positiivisen pedagogiikan tukena myönteisen motivaatioilmaston luomisessa liikunnan oppitunneilla. Tutkimuskysymyksenä oli, miten positiivisen pedagogiikan ja TARGET-mallin elementtien hyödyntämisellä voidaan vaikuttaa yksilön liikkujaidentiteetin kehittymiseen alkuopetuksen liikunnanopetuksessa. Liikunnallisen elämäntavan sisäistäminen on ajankohtainen aihe, koska lasten fyysinen aktiivisuus on vähentynyt. Perusta liikunnalliselle elämäntavalle luodaan varhain lapsena. Alkuopetuksen aikana oppilas kokee ensimmäiset kokemuksensa koululiikunnasta ja suhtautuminen liikuntaa kohtaan määräytyy kokemusmaailman pohjalta. Oppilaan liikkujaidentiteetti alkaa rakentumaan jo ensimmäisten kouluvuosien aikana. Opettajan tekemillä pedagogisilla ratkaisuilla on suuri merkitys oppilaan käsitykseen itsestään liikkujana. Opettaja voi tukea oppilaan liikkujaidentiteetin kehittymistä positiivisen pedagogiikan keinojen avulla. Johtopäätöksenä voidaan todeta, että positiivisen pedagogiikan ja TARGET-mallin elementtien hyödyntämisellä osana alkuopetuksen liikunnanopetusta, voidaan vaikuttaa positiivisesti oppilaan liikkujaidentiteetin kehittymiseen. Tutkielman pohjalta voidaan todeta positiivisen pedagogiikan vaikuttavan positiivisesti niin luokan motivaatioilmaston kehittymiseen kuin yksittäisen oppilaan myönteisten kokemusten saantiin liikunnanopetuksessa.

We now know that the outer solar system is host to at least six diverse planetary ring systems, each of which is a scientifically compelling target with the potential to inform us about the evolution, history and even the internal structure of the body it adorns. These diverse ring systems represent a set of distinct local laboratories for understanding the physics and dynamics of planetary disks, with applications reaching beyond our Solar System. We highlight the current status of planetary rings science and the open questions before the community to promote continued Earth-based and spacecraft-based investigations into planetary rings. As future spacecraft missions are launched and more powerful telescopes come online in the decades to come, we urge NASA for continued support of investigations that advance our understanding of planetary rings, through research and analysis of data from existing facilities, more laboratory work and specific attention to strong rings science goals during future mission selections.

A dusty ringlet designated R/2006 S3, also known as the "Charming Ringlet", is located around 119,940 km from the center of Saturn within the Laplace Gap in the Cassini Division. Prior to 2010, the ringlet had a simple radial profile and a predictable eccentric shape with two components, one forced by solar radiation pressure and the other freely precessing around the planet. However, observations made by the Cassini spacecraft since late 2012 revealed a shelf of material extending inwards from the ringlet that was not present in the earlier observations. Closer inspection of images obtained after 2012 shows that sometime between 2010 and 2012 the freely-precessing component of the ringlet's eccentricity increased by over 50%, and that for at least 3 years after 2012 the ringlet had longitudinal brightness variations that rotated around the planet at a range of rates corresponding to roughly 60 km in orbital semi-major axis. Some event therefore disturbed this ringlet between 2010 and late 2012., Comment: 23 Pages, 11 Figures, accepted for Publication in PSJ, Small corrections made to fix typos identified in proofs

In the absence of direct observations of Europa's particle plumes, deposits left behind during eruptive events would provide the best evidence for recent geological activity, and would serve as indicators of the best places to search for ongoing activity on the icy moon. Here, we model the morphological and spectral signatures of europan plume deposits, utilizing constraints from recent Hubble Space Telescope observations as model inputs. We consider deposits emplaced by plumes that are 1 km to 300 km tall, and find that in the time between the Galileo Mission and the arrival of the Europa Clipper spacecraft, plumes that are < 7 km tall are most likely to emplace deposits that could be detected by spacecraft cameras. Deposits emplaced by larger plumes could be detected by cameras operating at visible wavelengths provided that their average particle size is sufficiently large, their porosity is high, and/or they are salt-rich. Conversely, deposits emplaced by large plumes could be easily detected by near-IR imagers regardless of porosity, or individual particle size or composition. If low-albedo deposits flanking lineated features on Europa are indeed cryoclastic mantlings, they were likely emplaced by plumes that were less than 4 km tall, and deposition could be ongoing today. Comparisons of the sizes and albedos of these deposits between the Galileo and Europa Clipper missions could shed light on the size and frequency of cryovolcanic eruptions on Europa., Comment: 50 pages, 12 Figures, accepted for publication in Icarus

We examine the surface brightnesses of Saturn's smaller satellites using a photometric model that explicitly accounts for their elongated shapes and thus facilitates comparisons among different moons. Analyses of Cassini imaging data with this model reveals that the moons Aegaeon, Methone and Pallene are darker than one would expect given trends previously observed among the nearby mid-sized satellites. On the other hand, the trojan moons Calypso and Helene have substantially brighter surfaces than their co-orbital companions Tethys and Dione. These observations are inconsistent with the moons' surface brightnesses being entirely controlled by the local flux of E-ring particles, and therefore strongly imply that other phenomena are affecting their surface properties. The darkness of Aegaeon, Methone and Pallene is correlated with the fluxes of high-energy protons, implying that high-energy radiation is responsible for darkening these small moons. Meanwhile, Prometheus and Pandora appear to be brightened by their interactions with nearby dusty F ring, implying that enhanced dust fluxes are most likely responsible for Calypso's and Helene's excess brightness. However, there are no obvious structures in the E ring that would preferentially brighten these two moons, so there must either be something subtle in the E-ring particles' orbital properties that leads to asymmetries in the relevant fluxes, or something happened recently to temporarily increase these moons' brightnesses., Comment: 93 pages, 23 figures, 28 tables. Accepted for publication in AJ. Updated to fix some typographical errors identified in the proof stage

We describe the prediction, design, execution and calibration of stellar and solar occultation observations of Saturn's rings by the Visual and Infrared Mapping Spectrometer (VIMS) instrument on the Cassini spacecraft. Particular attention is paid to the technique developed for onboard acquisition of the stellar target and to the geometric and photometric calibration of the data. Examples of both stellar and solar occultation data are presented, highlighting several aspects of the data as well as the different occultation geometries encountered during Cassini's 13 year orbital tour. Complete catalogs of ring stellar and solar occultations observed by Cassini-VIMS are presented, as a guide to the standard data sets which have been delivered to the Planetary Data System's Ring Moon Systems Node., Comment: 90 Pages, 22 Figures, Accepted for Publication in Icarus

Given current uncertainties in the cratering rates and geological histories of icy objects in the outer solar system, it is worth considering how the ages of icy surfaces could be constrained with measurements from future landed missions. A promising approach would be to determine cosmic-ray exposure ages of surface deposits by measuring the amounts of cosmogenic Lithium, Beryllium and Boron at various depths within a few meters of the surface. Preliminary calculations show that ice that has been exposed to cosmic radiation for one billion years should contain these cosmogenic nuclei at concentrations of a few parts per trillion, so any future experiment that might attempt to perform this sort of measurement will need to meet stringent sensitivity requirements., Comment: 7 pages, accepted for publication in Icarus

We identify multiple periodic dusty structures in Saturn's Roche Division, a faint region spanning the $\sim3000$ km between the A and F rings. The locations and extent of these features vary over Cassini's tour of the Saturn system, being visible in 2006 and 2016-2017, but not in 2012-2014. These changes can be correlated with variations in Saturn's magnetospheric periods. In 2006 and 2016-2017, one of the drifting magnetospheric periods would produce a 3:4 resonance within the Roche Division, but in 2012-2014 these resonances would move into the A ring as the magnetospheric periods converged. A simple model of magnetic perturbations indicates that the magnetic field oscillations responsible for these structures have amplitudes of a few nanotesla, comparable to the magnetic field oscillation amplitudes of planetary period oscillations measured by the magnetometer onboard Cassini. However, some previously unnoticed features at higher radii have expected pattern speeds that are much slower than the magnetospheric periodicities. These structures may reflect an unexpectedly long-range propagation of resonant perturbations within dusty rings., Comment: Accepted for publication in Icarus

Density waves in Saturn's rings are usually tightly wrapped spiral patterns generated by resonances with either Saturn's moons or structures inside the planet. However, between the Barnard and Bessel Gaps in the Cassini Division (i.e. between 120,240 and 120,300 km from Saturn's spin axis), there are density variations that appear to form an axisymmetric density wave consisting of concentric zones of varying densities that propagate radially through the rings. Axisymmetric waves cannot be generated directly by a satellite resonance, but instead appear to be excited by interference between a nearby satellite resonance and normal mode oscillations on the inner edge of the Barnard Gap. Similar axisymmetric waves may exist just interior to other resonantly confined edges that exhibit a large number of normal modes, including the Dawes ringlet in the outer C ring and the outermost part of the B ring., Comment: 17 pages, 15 figures. Accepted for publication in MNRAS

The D68 ringlet is the innermost narrow feature in Saturn's rings. Prior to 2014, the brightness of this ringlet did not vary much with longitude, but sometime in 2014 or 2015 a series of bright clumps appeared within D68. These clumps were up to four times brighter than the typical ringlet, occurred within a span of ~ 120 degrees in corotating longitude, and moved at an average rate of 1751.7 degrees/day during the last year of the Cassini mission. The slow evolution and relative motions of these clumps suggest that they are composed of particles with a narrow (sub-kilometer) spread in semi-major axis. The clumps therefore probably consist of fine material released by collisions among larger (up to 20 meters wide) objects orbiting close to D68. The event that triggered the formation of these bright clumps is still unclear, but it could have some connection to the material observed when the Cassini spacecraft passed between the planet and the rings., Comment: 22 Pages, 9 Figures, 3 Supplemental Data Tables, Accepted for Publication in Icarus. Some typographical errors found at proof stage corrected, along with longitude ranges in Table 1

Background: The relationship between blood flow characteristics and ascending aortic (AA) dilatation has not been studied in patients with a tricuspid aortic valve (TAV) without aortic stenosis. Purpose: To evaluate whether 4D flow characteristics determined in MRI are related to AA dilatation by comparing dilated AA and nondilated AA subjects with TAV. Study Type: Prospective. Population: Twenty patients with dilated AA and 20 age‐matched patients with nondilated AA. Field Strength/Sequence: 1.5T/4D flow, 2D flow, and anatomic images. Assessment: Altogether, 16 different 4D flow parameters were assessed in 10 planes in the thoracic aorta. Intra‐ and interobserver reproducibility were analyzed. Statistical Tests: Independent t‐test for normally distributed and the Mann–Whitney test for skewed distributed parameters were used. A paired‐samples t‐test was used to compare 2D and 4D flow parameters. Intraclass correlation coefficient (ICC) was used in intra‐ and interobserver reproducibility analysis. Results: Aortic flow was displaced from the centerline of the aorta in the proximal and tubular planes. Flow displacement (FD) was greatest in the proximal plane of AA and was higher in dilated AA (4.5%, range 3.0–5.8%) than in nondilated AA (2.0%, 1.0–3.0%, P < 0.001). Total wall shear stress (WSS) values were 1.3 ± 0.4 times higher on the displaced side than on the opposite side of the aorta (P < 0.01). The circumferential WSS (WSSC) ratio to total WSS was greater in dilated AA, being 0.48 ± 0.11 vs. 0.32 ± 0.09 in the inner curvature of the proximal AA (P < 0.001) and 0.37 ± 0.11 vs. 0.26 ± 0.07 in the whole aortic ring in the distal AA (P < 0.001). Depending on 4D flow parameters, reproducibility varied from excellent (ICC = 0.923) to very low (ICC = 0.204). Data Conclusion: The present study demonstrates that 4D flow measurements help to visualize the pathological flow patterns related to aortic dilatation. Flow displacement and an increased WSSc

We describe the prediction, design, execution and calibration of stellar and solar occultation observations of Saturn's rings by the Visual and Infrared Mapping Spectrometer (VIMS) instrument on the Cassini spacecraft. Particular attention is paid to the technique developed for onboard acquisition of the stellar target and to the geometric and photometric calibration of the data. Examples of both stellar and solar occultation data are presented, highlighting several aspects of the data as well as the different occultation geometries encountered during Cassini's 13 year orbital tour. Complete catalogs of ring stellar and solar occultations observed by Cassini-VIMS are presented, as a guide to the standard data sets which have been delivered to the Planetary Data System's Ring Moon Systems Node., Comment: 90 Pages, 22 Figures, Accepted for Publication in Icarus

We identify multiple periodic dusty structures in Saturn's Roche Division, a faint region spanning the $\sim3000$ km between the A and F rings. The locations and extent of these features vary over Cassini's tour of the Saturn system, being visible in 2006 and 2016-2017, but not in 2012-2014. These changes can be correlated with variations in Saturn's magnetospheric periods. In 2006 and 2016-2017, one of the drifting magnetospheric periods would produce a 3:4 resonance within the Roche Division, but in 2012-2014 these resonances would move into the A ring as the magnetospheric periods converged. A simple model of magnetic perturbations indicates that the magnetic field oscillations responsible for these structures have amplitudes of a few nanotesla, comparable to the magnetic field oscillation amplitudes of planetary period oscillations measured by the magnetometer onboard Cassini. However, some previously unnoticed features at higher radii have expected pattern speeds that are much slower than the magnetospheric periodicities. These structures may reflect an unexpectedly long-range propagation of resonant perturbations within dusty rings., Comment: Accepted for publication in Icarus

Given current uncertainties in the cratering rates and geological histories of icy objects in the outer solar system, it is worth considering how the ages of icy surfaces could be constrained with measurements from future landed missions. A promising approach would be to determine cosmic-ray exposure ages of surface deposits by measuring the amounts of cosmogenic Lithium, Beryllium and Boron at various depths within a few meters of the surface. Preliminary calculations show that ice that has been exposed to cosmic radiation for one billion years should contain these cosmogenic nuclei at concentrations of a few parts per trillion, so any future experiment that might attempt to perform this sort of measurement will need to meet stringent sensitivity requirements., Comment: 7 pages, accepted for publication in Icarus

Density waves in Saturn's rings are usually tightly wrapped spiral patterns generated by resonances with either Saturn's moons or structures inside the planet. However, between the Barnard and Bessel Gaps in the Cassini Division (i.e. between 120,240 and 120,300 km from Saturn's spin axis), there are density variations that appear to form an axisymmetric density wave consisting of concentric zones of varying densities that propagate radially through the rings. Axisymmetric waves cannot be generated directly by a satellite resonance, but instead appear to be excited by interference between a nearby satellite resonance and normal mode oscillations on the inner edge of the Barnard Gap. Similar axisymmetric waves may exist just interior to other resonantly confined edges that exhibit a large number of normal modes, including the Dawes ringlet in the outer C ring and the outermost part of the B ring., Comment: 17 pages, 15 figures. Accepted for publication in MNRAS

The D68 ringlet is the innermost narrow feature in Saturn's rings. Prior to 2014, the brightness of this ringlet did not vary much with longitude, but sometime in 2014 or 2015 a series of bright clumps appeared within D68. These clumps were up to four times brighter than the typical ringlet, occurred within a span of ~ 120 degrees in corotating longitude, and moved at an average rate of 1751.7 degrees/day during the last year of the Cassini mission. The slow evolution and relative motions of these clumps suggest that they are composed of particles with a narrow (sub-kilometer) spread in semi-major axis. The clumps therefore probably consist of fine material released by collisions among larger (up to 20 meters wide) objects orbiting close to D68. The event that triggered the formation of these bright clumps is still unclear, but it could have some connection to the material observed when the Cassini spacecraft passed between the planet and the rings., Comment: 22 Pages, 9 Figures, 3 Supplemental Data Tables, Accepted for Publication in Icarus. Some typographical errors found at proof stage corrected, along with longitude ranges in Table 1

We examine the surface brightnesses of Saturn's smaller satellites using a photometric model that explicitly accounts for their elongated shapes and thus facilitates comparisons among different moons. Analyses of Cassini imaging data with this model reveals that the moons Aegaeon, Methone and Pallene are darker than one would expect given trends previously observed among the nearby mid-sized satellites. On the other hand, the trojan moons Calypso and Helene have substantially brighter surfaces than their co-orbital companions Tethys and Dione. These observations are inconsistent with the moons' surface brightnesses being entirely controlled by the local flux of E-ring particles, and therefore strongly imply that other phenomena are affecting their surface properties. The darkness of Aegaeon, Methone and Pallene is correlated with the fluxes of high-energy protons, implying that high-energy radiation is responsible for darkening these small moons. Meanwhile, Prometheus and Pandora appear to be brightened by their interactions with nearby dusty F ring, implying that enhanced dust fluxes are most likely responsible for Calypso's and Helene's excess brightness. However, there are no obvious structures in the E ring that would preferentially brighten these two moons, so there must either be something subtle in the E-ring particles' orbital properties that leads to asymmetries in the relevant fluxes, or something happened recently to temporarily increase these moons' brightnesses., Comment: 93 pages, 23 figures, 28 tables. Accepted for publication in AJ. Updated to fix some typographical errors identified in the proof stage

We present new results obtained by the Radio and Plasma Wave Science Langmuir probe on board Cassini during the Grand Finale. The total direct current sampled by the Langmuir probe at negative bias voltage is used to study the effect of the ring shadows on the structure of the Kronian topside ionosphere. The D and C rings and the Cassini Division are confirmed to be optically thin to extreme ultraviolet solar radiation. However, different responses from the opaque A and B rings are observed. The edges of the A ring shadow are shown to match the A ring boundaries, unlike the B ring, which indicates variable responses to the B ring shadow. We show that the variable responses are due to the ionospheric plasma, more precisely to the longer chemical lifetime of H+ compared to H-2(+) and H-3(+), suggesting that the plasma is transported from the sunlit region to the shadowed one in the ionosphere. Plain Language Summary As Saturn's northern hemisphere experienced summer during the Grand Finale, the planet's northern dayside hemisphere and its rings were fully illuminated by the Sun. However, the southern hemisphere was partly obscured because of the shadows cast by the A and B rings. Using the in situ measurements of the Langmuir probe part of the Radio and Plasma Wave Science investigation on board the Cassini spacecraft, we study for the first time the effect of the ring shadows on Saturn's ionosphere. From the ring shadows signatures on the total ion current collected by the Langmuir probe, we show that the A and B rings are optically thicker (to the solar extreme ultraviolet radiation) than the inner C and D rings and the Cassini Division to the solar extreme ultraviolet radiation. Moreover, we reproduce the boundaries of the A ring and the outer edge of the B ring. Furthermore, observed variations with respect to the inner edge of the B ring imply a delayed response of the ionospheric H+ because of its long lifetime and suggest that the ionospheric plasma is transpor

The Pioneer and Voyager spacecraft made close-up measurements of Saturn's ionosphere and upper atmosphere in the 1970s and 1980s that suggested a chemical interaction between the rings and atmosphere. Exploring this interaction provides information on ring composition and the influence on Saturn's atmosphere from infalling material. The Cassini Ion Neutral Mass Spectrometer sampled in situ the region between the D ring and Saturn during the spacecraft's Grand Finale phase. We used these measurements to characterize the atmospheric structure and material influx from the rings. The atmospheric He/H-2 ratio is 10 to 16%. Volatile compounds from the rings (methane; carbon monoxide and/or molecular nitrogen), as well as larger organic-bearing grains, are flowing inward at a rate of 4800 to 45,000 kilograms per second.

Recent studies of stellar occultations observed by the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft have demonstrated that multiple spiral wave structures in Saturn's rings are probably generated by normal-mode oscillations inside the planet. Wavelet-based analyses have been able to unambiguously determine both the number of spiral arms and the rotation rate of many of these patterns. However, there are many more planetary normal modes that should have resonances in the rings, implying that many normal modes do not have sufficiently large amplitudes to generate obvious ring waves. Fortunately, recent advances in wavelet analysis allow weaker wave signals to be uncovered by combining data from multiple occultations. These new analytical tools reveal that a pattern previously identified as a single spiral wave actually consists of two superimposed waves, one with 5 spiral arms rotating at 1593.6 degrees/day and one with 11 spiral arms rotating at 1450.5 degrees/day. Furthermore, a broad search for new waves revealed four previously unknown wave patterns with 6, 7, 8 and 9 spiral arms rotating around the planet at 1538.2 degrees/day, 1492.5 degrees/day, 1454.2 degrees/day and 1421.8 degrees/day, respectively. These six patterns provide precise frequencies for another six fundamental normal modes inside Saturn, yielding what is now a complete sequence of fundamental sectoral normal modes with azimuthal wavenumbers from 2 to 10. These frequencies should place strong constraints on Saturn's interior structure and rotation rate, while the relative amplitudes of these waves should help clarify how the corresponding normal modes are excited inside the planet., Comment: 18 pages, 24 figures, updated to fix some typographical errors identified in proofs

On day 138 of 2010, the plume of dust and gas emerging from Enceladus' South Polar Terrain passed between the Sun and the Cassini spacecraft. This solar occultation enabled Cassini's Ultraviolet Imaging Spectrograph (UVIS) and the Visual and Infrared Mapping Spectrometer (VIMS) to obtain simultaneous measurements of the plume's gas and dust components along the same lines of sight. The UVIS measurements of the plume's gas content are described in Hansen et al. (2011, GRL 38:11202) , while this paper describes the VIMS data and the information they provide about the plume's particle content. Together, the VIMS and UVIS measurements reveal that the plume material above Baghdad and Damascus sulci has a dust-to-gas mass ratio that is roughly an order of magnitude higher than the material above Alexandria and Cairo sulci. Similar trends in the plume's dust-to-gas ratio are also found in data obtained when Cassini flew through the plume in 2009, during which time the Ion and Neutral Mass Spectrometer (INMS), Radio and Plasma Wave Science instrument (RPWS) and Cosmic Dust Analyzer (CDA) instruments made in-situ measurements of the plume's gas and dust densities (Dong et al. 2015 JGR 120:915-937). These and other previously-published systematic differences in the material erupting from different fissures likely reflect variations in subsurface conditions across Encealdus' South Polar Terrain., Comment: 24 pages, 14 figures, submitted for publication in Icarus

Recent studies of stellar occultations observed by the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft have demonstrated that multiple spiral wave structures in Saturn's rings are probably generated by normal-mode oscillations inside the planet. Wavelet-based analyses have been able to unambiguously determine both the number of spiral arms and the rotation rate of many of these patterns. However, there are many more planetary normal modes that should have resonances in the rings, implying that many normal modes do not have sufficiently large amplitudes to generate obvious ring waves. Fortunately, recent advances in wavelet analysis allow weaker wave signals to be uncovered by combining data from multiple occultations. These new analytical tools reveal that a pattern previously identified as a single spiral wave actually consists of two superimposed waves, one with 5 spiral arms rotating at 1593.6 degrees/day and one with 11 spiral arms rotating at 1450.5 degrees/day. Furthermore, a broad search for new waves revealed four previously unknown wave patterns with 6, 7, 8 and 9 spiral arms rotating around the planet at 1538.2 degrees/day, 1492.5 degrees/day, 1454.2 degrees/day and 1421.8 degrees/day, respectively. These six patterns provide precise frequencies for another six fundamental normal modes inside Saturn, yielding what is now a complete sequence of fundamental sectoral normal modes with azimuthal wavenumbers from 2 to 10. These frequencies should place strong constraints on Saturn's interior structure and rotation rate, while the relative amplitudes of these waves should help clarify how the corresponding normal modes are excited inside the planet., Comment: 18 pages, 24 figures, updated to fix some typographical errors identified in proofs

On day 138 of 2010, the plume of dust and gas emerging from Enceladus' South Polar Terrain passed between the Sun and the Cassini spacecraft. This solar occultation enabled Cassini's Ultraviolet Imaging Spectrograph (UVIS) and the Visual and Infrared Mapping Spectrometer (VIMS) to obtain simultaneous measurements of the plume's gas and dust components along the same lines of sight. The UVIS measurements of the plume's gas content are described in Hansen et al. (2011, GRL 38:11202) , while this paper describes the VIMS data and the information they provide about the plume's particle content. Together, the VIMS and UVIS measurements reveal that the plume material above Baghdad and Damascus sulci has a dust-to-gas mass ratio that is roughly an order of magnitude higher than the material above Alexandria and Cairo sulci. Similar trends in the plume's dust-to-gas ratio are also found in data obtained when Cassini flew through the plume in 2009, during which time the Ion and Neutral Mass Spectrometer (INMS), Radio and Plasma Wave Science instrument (RPWS) and Cosmic Dust Analyzer (CDA) instruments made in-situ measurements of the plume's gas and dust densities (Dong et al. 2015 JGR 120:915-937). These and other previously-published systematic differences in the material erupting from different fissures likely reflect variations in subsurface conditions across Encealdus' South Polar Terrain., Comment: 24 pages, 14 figures, submitted for publication in Icarus

The Voyager 2 Radio Science Subsystem occultations of the Uranian alpha and beta rings exhibit quasi-periodic optical depth variations with radial wavelengths that vary with longitude. These patterns may be wakes from small moonlets orbiting exterior to these rings. Based on the observed structures in the rings, we estimate that the moonlets would need to be located about 100 km exterior to the rings' semimajor axes and be 2-7 km in radius. Such moonlets could help keep the rings confined. Due to their small radii and presumed low albedo, the expected brightness of these moonlets is on the order of the noise in Voyager 2 images., Comment: Accepted for publication in AJ. Fixed typos to match published article