Kronoseismology: Using Density Waves in Saturn's C Ring to Probe the Planet's Interior

Hedman, M. M.; Nicholson, P. D.

doi:10.1088/0004-6256/146/1/12

Cited by 112 publications

(138 citation statements)

References 21 publications

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“…Re-analyzing the original six waves with this larger data set yielded essentially the same results as our previous analysis (compare the relevant entries in Table 5 with Table 4 The first wave we will consider here is the one designated W83.63 in Colwell et al (2009) (it is also called h in Rosen et al (1991) and wave 18 in Baillié et al (2011)). An example profile of this wave is shown in Figure 3, where it is compared with two nearby waves examined by Hedman & Nicholson (2013). Note this wave is found in a low opticaldepth region between three waves (W82.00, W82.06 and W82.21) that Hedman & Nicholson (2013) identified as m = −3 and another wave (W84.64) that appears to have m = −2 (see Figure 1).…”

Section: Selecting Features To Examinementioning

confidence: 93%

“…For the sake of completeness, we will provide a summary of our analysis methods, and refer the reader to Hedman & Nicholson (2013) for more details on these techniques.…”

Section: Methodsmentioning

confidence: 99%

“…Next, we compute the wavelet power and weighted average wavelet phase φ + φ r for each profile as a function of radius in a specified spatial wavelength band. In Hedman & Nicholson (2013) the wavelength range used was from 0.1 km to 5 km, but here we will use different ranges for different waves. Next, we compute δφ between two cuts as the weighted average difference of the two phase profiles, using the average power in the two profiles as the weighting function.…”

Section: Methodsmentioning

confidence: 99%

“…The analysis performed by Hedman & Nicholson (2013) focused on six density waves which had the strongest opacity variations and the longest wavelengths. These waves were the easiest ones to study and measure, and indeed we obtained extremely precise and robust estimates of these patterns' rotation rates around the planet.…”

Section: Introductionmentioning

confidence: 99%

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More Kronoseismology with Saturn's rings

Hedman

Nicholson

2014

Monthly Notices of the Royal Astronomical Society

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In a previous paper (Hedman and Nicholson 2013), 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 • /day and 834 • /day. 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/year over the last thirty years, implying that the relevant planetary oscillation frequency has been steadily increasing.

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Section: Selecting Features To Examinementioning

confidence: 93%

“…For the sake of completeness, we will provide a summary of our analysis methods, and refer the reader to Hedman & Nicholson (2013) for more details on these techniques.…”

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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More Kronoseismology with Saturn's rings

Hedman

Nicholson

2014

Monthly Notices of the Royal Astronomical Society

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“…The basic idea is that wave features in Saturn's C rings could be created by resonant interactions with fundamental (f ) oscillation modes (i.e., radial order n = 0), since these modes perturb the internal density profile and, therefore, the external gravity field. Twenty years later, observations of stellar occultations of stars by the rings made with Cassini showed that density-wave structures detected in the C-ring were compatible with resonances due to Saturn f -modes [30][31][32]. These observations are the indirect evidence of these wave forcings [32].…”

Section: Seismology and Giant Planetsmentioning

confidence: 93%

Seismology of Giant Planets: General Overview and Results from theKeplerK2 Observations of Neptune

Gaulme

2017

EPJ Web Conf.

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Abstract. For this invited contribution, I was asked to give an overview about the application of helio and asteroseismic techniques to study the interior of giant planets, and to specifically present the recent observations of Neptune by Kepler K2. Seismology applied to giant planets could drastically change our understanding of their deep interiors, as it has happened with the Earth, the Sun, and many main-sequence and evolved stars. The study of giant planets' composition is important for understanding both the mechanisms enabling their formation and the origins of planetary systems, in particular our own. Unfortunately, its determination is complicated by the fact that their interior is thought not to be homogeneous, so that spectroscopic determinations of atmospheric abundances are probably not representative of the planet as a whole. Instead, the determination of their composition and structure must rely on indirect measurements and interior models. Giant planets are mostly fluid and convective, which makes their seismology much closer to that of solar-like stars than that of terrestrial planets. Hence, helioseismology techniques naturally transfer to giant planets. In addition, two alternative methods can be used: photometry of the solar light reflected by planetary atmospheres, and ring seismology in the specific case of Saturn. The current decade has been promising thanks to the detection of Jupiter's acoustic oscillations with the ground-based imaging-spectrometer SYMPA and indirect detection of Saturn's f -modes in its rings by the NASA Cassini orbiter. This has motivated new projects of ground-based and space-borne instruments that are under development. The K2 observations represented the first opportunity to search for planetary oscillations with visible photometry. Despite the excellent quality of K2 data, the noise level of the power spectrum of the light curve was not low enough to detect Neptune's oscillations. The main results from the K2 observations are the clear detection of the well-known differential rotation of Neptune, measured for the first time through the rotational modulation of its photometry, and the detection of the Sun's oscillations, for the first time in an indirect way in intensity measurements.

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