More Kronoseismology with Saturn's rings Hedman, M. M; Nicholson, P. D
Monthly Notices of the Royal Astronomical Society,
10/2014, Letnik:
444, Številka:
2
Journal Article
Recenzirano
Odprti dostop
In a previous paper, we developed tools which allowed us to confirm that several of the waves in Saturn's rings were likely generated by resonances with fundamental sectoral normal modes inside ...Saturn itself. Here we use these same tools to examine eight additional waves that are probably generated by structures inside the planet. One of these waves appears to be generated by a resonance with a fundamental sectoral normal mode with azimuthal harmonic number m = 10. If this attribution is correct, then the m = 10 mode must have a larger amplitude than the modes with m = 5–9, since the latter do not appear to generate strong waves. We also identify five waves with pattern speeds between 807° and 834° d−1. Since these pattern speeds are close to the planet's rotation rate, they probably are due to persistent gravitational anomalies within the planet. These waves are all found in regions of enhanced optical depth known as plateaux, but surprisingly the surface mass densities they yield are comparable to the surface mass densities of the background C-ring. Finally, one wave appears to be a one-armed spiral pattern whose rotation rate suggests it is generated by a resonance with a structure inside Saturn, but the nature of this perturbing structure remains unclear. Strangely, the resonant radius for this wave seems to be drifting inwards at an average rate of 0.8 km yr−1 over the last 30 yr, implying that the relevant planetary oscillation frequency has been steadily increasing.
•Data from multiple stellar occultations are used to study waves in Saturn’s B ring.•Different parts of the Janus 2:1 wave appear to have different pattern speeds.•The B-ring’s typical surface mass ...density appears to be between 40 and 140 g/cm2.•The B-ring’s surface mass density is not strongly correlated with optical depth.
Saturn’s B ring is the most opaque ring in our Solar System, but many of its fundamental parameters, including its total mass, are not well constrained. Spiral density waves generated by mean-motion resonances with Saturn’s moons provide some of the best constraints on the rings’ mass density, but detecting and quantifying such waves in the B ring has been challenging because of this ring’s high opacity and abundant fine-scale structure. Using a wavelet-based analyses of 17 occultations of the star γ Crucis observed by the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft, we are able to examine five density waves in the B ring. Two of these waves are generated by the Janus 2:1 and Mimas 5:2 Inner Lindblad Resonances at 96,427 km and 101,311 km from Saturn’s center, respectively. Both of these waves can be detected in individual occultation profiles, but the multi-profile wavelet analysis reveals unexpected variations in the pattern speed of the Janus 2:1 wave that might arise from the periodic changes in Janus’ orbit. The other three wave signatures are associated with the Janus 3:2, Enceladus 3:1 and Pandora 3:2 Inner Lindblad Resonances at 115,959 km, 115,207 km and 108,546 km. These waves are not visible in individual profiles, but structures with the correct pattern speeds can be detected in appropriately phase-corrected average wavelets. Estimates of the ring’s surface mass density derived from these five waves fall between 40 and 140 g/cm2, even though the ring’s optical depth in these regions ranges from ∼1.5 to almost 5. This suggests that the total mass of the B ring is most likely between one-third and two-thirds the mass of Saturn’s moon Mimas.
•The heritability for bipolar disorder was 60% using a novel statistical approach taking into account available time of follow-up, and controlling for sex and year of birth.•The heritability was ...similar to previous family studies performed on the Swedish register data, using traditional twin-modeling methods, indicating that previous methodology have been sufficient.•We detected no influence from common environmental factors in our heritability analysis, due to lack of power. Future studies using transnational twin cohorts to expand the sample-size are needed.•The prevalence for bipolar disorder was higher in females, but genetic factors did not contribute to those sex-differences.
Twin- and family studies have shown variations in the heritability estimates of bipolar disorder (BPD). The current study uses an updated statistical methodology for heritability estimation in BPD by taking available time of follow-up into account while controlling for co-variates. We identified monozygotic and dizygotic same and different sex twins with BPD (n = 804) or unaffected from BPD (n = 91,604) from the Swedish Twin Register and the National Patient Register. We applied structural equational modeling with inversed probability weighting to estimate the heritability, taking into account censoring and truncation of data. Sex-limitation models were constructed to analyze qualitative or quantitative sex-differences in BPD. Heritability for BPD was 60.4% (95% Confidence Interval: 50.3–70.5) after age, sex, left-hand truncation and censoring of the data was taken into account. A larger proportion of females were affected from BPD (females 62.2%; males 37.8%, p < 0.001), but no sex-difference in BPD heritability was found, nor any sex-specific genetic effects. We demonstrated a robust 60% heritability for BPD with no evidence of sex-specific genetic effects on disease liability.
Saturn's C ring contains multiple spiral patterns that appear to be density waves driven by periodic gravitational perturbations. In other parts of Saturn's rings, such waves are generated by ...Lindblad resonances with Saturn's various moons, but most of the wave-like C-ring features are not situated near any strong resonance with any known moon. Using stellar occultation data obtained by the Visual and Infrared Mapping Spectrometer on board the Cassini spacecraft, we investigate the origin of six unidentified C-ring waves located between 80,900 and 87,200 km from Saturn's center. By measuring differences in the waves' phases among the different occultations, we are able to determine both the number of arms in each spiral pattern and the speeds at which these patterns rotate around the planet. We find that all six of these waves have between two and four arms and pattern speeds between 1660degrees day-1 and 1861degrees day-1. These speeds are too large to be attributed to any satellite resonance. Instead, they are comparable to the predicted pattern speeds of waves generated by low-order normal-mode oscillations within the planet. The precise pattern speeds associated with these waves should therefore provide strong constraints on Saturn's internal structure. Furthermore, we identify multiple waves with the same number of arms and very similar pattern speeds, indicating that multiple m = 3 and m = 2 sectoral (l = m) modes may exist within the planet.
High angular resolution images of IRC+10216 are presented in several near-infrared wavelengths spanning more than 8 years. These maps have been reconstructed from interferometric observations ...obtained at both Keck and the VLT, and also from stellar occultations by the rings of Saturn observed with the Cassini spacecraft. The dynamic inner regions of the circumstellar environment are monitored over eight epochs ranging between 2000 January and 2008 July. The system is shown to experience substantial evolution within this period including the fading of many previously reported persistent features, some of which had been identified as the stellar photosphere. These changes are discussed in the context of existing models for the nature of the underlying star and the circumstellar environment. With access to these new images, we are able to report that none of the previously identified bright spots in fact contains the star, which is buried in its own dust and not directly visible in the near-infrared.
Although development of microbiota in childhood has been linked to chronic immune-related conditions, early childhood determinants of microbiota development have not been fully elucidated. We used ...16S rRNA sequencing to analyse faecal and saliva samples from 83 children at four time-points during their first 2 years of life and from their mothers. Our findings confirm that gut microbiota in infants have low diversity and highlight that some properties are shared with the oral microbiota, although inter-individual differences are present. A considerable convergence in gut microbiota composition was noted across the first 2 years of life, towards a more diverse adult-like microbiota. Mode of delivery accounted for some of the inter-individual variation in early childhood, but with a pronounced attenuation over time. Our study extends previous research with further characterization of the major shift in gut microbiota composition during the first 2 years of life.
ABSTRACT The recent discovery of dense rings around the Centaur Chariklo (and possibly Chiron) reveals that complete dense planetary rings are not only found around Saturn and Uranus, but also around ...small bodies orbiting in the vicinity of those giant planets. This report examines whether or not there could be a physical process that would make rings more likely to form or persist in this particular part of the outer solar system. Specifically, the ring material orbiting Saturn and Uranus appears to be much weaker than the material forming the innermost moons of Jupiter and Neptune. Also, the mean surface temperatures of Saturn's, Uranus's, and Chariklo's rings are all close to 70 K. Thus the restricted distribution of dense rings in our solar system may arise because icy materials are particularly weak around that temperature.
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.
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
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.
PDF
