Saturn’s ring spokes typically appear over an 8-year duration centered on equinox. Hubble Space Telescope observations in 2021 indicate the beginning of a new spoke season as Saturn approaches ...equinox in 2025. The spokes show increased contrast and longevity in 2022, persisting for up to eleven hours. The spokes are visible from UV to near-IR and are slightly bluer (i.e., less red) than the rings, but we find no significant wavelength dependence in the spectral contrast, which approximates their optical depth). Spoke rotation rates are between 606 and 626 minutes, consistent with either Keplerian rotation or possibly the variable rotation rate of Saturn’s kilometric radiation (SKR). Spoke activity is expected to increase over the next several years.
Abstract
Some of the small inner moons of Uranus have very closely-spaced orbits. Multiple numerical studies have found that the moons Cressida and Desdemona, within the Portia subgroup, are likely ...to collide in less than 100 Myr. The subsequent discovery of three new moons (Cupid, Perdita, and Mab) made the system even more crowded. In particular, it has been suggested that the Belinda group (Cupid, Belinda, and Perdita) will become unstable in as little as 10
5
yr. Here we revisit the issue of the stability of the inner moons of Uranus using updated orbital elements and considering tidal dissipation. We find that the Belinda group can be stable on 10
8
yr timescales due to an orbital resonance between Belinda and Perdita. We find that tidal evolution cannot form the Belinda–Perdita resonance, but convergent migration could contribute to the long-term instability of the Portia group. We propose that Belinda captured Perdita into the resonance during the last episode of disruption and reaccretion among the inner moons, possibly hundreds of Myr ago.
Spiral waves propagating in Saturn's rings have wavelengths that vary with radial position within the disc. The best-quality observations of these waves have the form of radial profiles centred on a ...particular azimuth. In that context, the wavelength of a given spiral wave is seen to change substantially with position along the one-dimensional profile. In this paper, we review the use of Morlet wavelet analysis to understand these waves. When signal to noise is high and the cause of the wave is well understood, wavelet analysis has been used to solve for wave parameters that are diagnostic of local disc properties. Waves that are not readily perceptible in the spatial domain signal can be clearly identified. Furthermore, filtering in wavelet space, followed by the reverse wavelet transform, has been used to isolate the part of the signal that is of interest. When the cause of the wave is not known, comparing the phases of the complex-valued wavelet transforms from many profiles has been used to determine wave parameters that cannot be determined from any single profile. When signal to noise is low, co-adding wavelet transforms while manipulating the phase has been used to boost a wave's signal above detection limits.
This article is part of the theme issue 'Redundancy rules: the continuous wavelet transform comes of age'.
The rings of Saturn are delicate, enigmatic, beautiful, and useful. NASA's Cassini spacecraft has been studying them (and the rest of the Saturn system) over the course of a spectacularly successful ...13-year mission, but its concluding year has been the most spectacular of all--practically a whole new mission. In December 2016, Cassini commenced weekly plunges through the ring plane just off the outer edge of the main rings (activity termed the "Ring-Grazing Orbits"), and transitioned in April 2017 to weekly plunges between the rings and the planet's cloud-tops (the "Grand Finale" orbits). The mission concluded in September 2017 with a final descent into the planet's atmosphere, to preclude possible terrestrial contamination of Saturn's moons. Tiscareno details NASA's Cassini spacecraft successful 13-year mission in studying Saturn and its system.
We carried out extensive numerical orbit integrations to probe the long-term chaotic dynamics of the two strongest mean-motion resonances of Neptune in the Kuiper Belt, the 3:2 (Plutinos) and 2:1 ...(Twotinos). Our primary results include a computation of the relative volumes of phase space characterized by large- and small-resonance libration amplitudes, and maps of resonance stability measured by mean chaotic diffusion rate. We find that Neptune's 2:1 resonance has weaker overall long-term stability than the 3:2-only ~15% of Twotinos are projected to survive for 4 Gyr, compared to ~27% of Plutinos, based on an extrapolation from our 1-Gyr integrations. We find that Pluto has only a modest effect, causing a ~4% decrease in the Plutino population that survives to 4 Gyr. Given current observational estimates, and assuming an initial distribution of particles proportional to the local phase-space volume in the resonance, we conclude that the primordial populations of Plutinos and Twotinos formerly made up more than half the population of the classical and resonant Kuiper Belt. We also conclude that Twotinos were originally nearly as numerous as Plutinos; this is consistent with predictions from early models of smooth giant planet migration and resonance sweeping of the Kuiper Belt and provides a useful constraint for more detailed models.
Hydrogen peroxide at the poles of Ganymede Trumbo, Samantha K; Brown, Michael E; Bockelée-Morvan, Dominique ...
Science advances,
07/2023, Letnik:
9, Številka:
29
Journal Article
Recenzirano
Odprti dostop
Ganymede is the only satellite in the solar system known to have an intrinsic magnetic field. Interactions between this field and the Jovian magnetosphere are expected to funnel most of the ...associated impinging charged particles, which radiolytically alter surface chemistry across the Jupiter system, to Ganymede's polar regions. Using observations obtained with JWST as part of the Early Release Science program exploring the Jupiter system, we report the discovery of hydrogen peroxide, a radiolysis product of water ice, specifically constrained to the high latitudes. This detection directly implies radiolytic modification of the polar caps by precipitation of Jovian charged particles along partially open field lines within Ganymede's magnetosphere. Stark contrasts between the spatial distribution of this polar hydrogen peroxide, those of Ganymede's other radiolytic oxidants, and that of hydrogen peroxide on neighboring Europa have important implications for understanding water-ice radiolysis throughout the solar system.
Aims. Generally, the oblateness of a planet or moon is what causes rings to settle into its equatorial plane. However, the recent suggestion that a ring system might exist (or have existed) about ...Rhea, a moon whose shape includes a strong prolate component pointed toward Saturn, raises the question of whether rings around a triaxial primary can be stable. We study the role of prolateness in the behavior of rings around Rhea and extend our results to similar problems such as possible rings around exoplanets. Methods. Using a Hamiltonian approach, we point out that the dynamical behavior of ring particles is governed by three different time scales: the orbital period of the particles, the rotation period of the primary, and the precession period of the particles’ orbital plane. In the case of Rhea, two of these are well separated from the third, allowing us to average the Hamiltonian twice. To study the case of slow rotation of the primary, we also carry out numerical simulations of a thin disk of particles undergoing secular effects and damping. Results. In the case of Rhea, the averaging reduces the Hamiltonian to an oblate potential, under which rings would be stable only in the equatorial plane. This is not the case for Iapetus; rather, it is the lack of a prolate component to its shape that allows Iapetus to host rings. Plausible exoplanets should mostly be in the same regime as Rhea, though other outcomes are possible. The numerical simulations indicate that, even when the double averaging is irrelevant, rings settle in the equatorial plane on an approximately constant time scale.
We propose a mechanism for the observed non-keplerian motion (Tiscareno et al., 2010a) of “propeller” moons embedded in Saturn's rings. Our mechanism, in which radial variations in surface density – ...external to, and unaffected by, the embedded moon – result in an equilibrium semimajor axis for the moon due to “Type I” angular momentum exchange (Crida et al., 2010), provides a good fit to the observations. Future observations should distinguish between our model and others recently proposed.
► We propose a mechanism for the observed non-keplerian motion of “propeller” moons. ► “Type I” angular momentum exchange can lead to an equilibrium semimajor axis for the moon. ► Our mechanism provides a good fit to the observations. ► Future observations should distinguish between our model and others recently proposed.
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.
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