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

Abstract

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.

Ring Seismology of the Ice Giants Uranus and Neptune

“…Because the oscillation frequencies depend on the planet's density profile, measurements of these frequencies can probe the planet's internal structure. Efforts to detect oscillations with visible photometry, which were apparently successful for Jupiter (Gaulme et al 2011), have not yet been successful for the ice giants (Gaulme 2017;Rowe et al 2017). Friedson (2020) found that for reasonable amplitudes detection of pressure or temperature variations due to ice giant normal modes is not as promising as the prospect of detecting their gravitational influence on an orbiting spacecraft.…”

Ring Seismology of the Ice Giants Uranus and Neptune

“…Because the oscillation frequencies depend on the planet's density profile, measurements of these frequencies can probe the planet's internal structure. Efforts to detect oscillations with visible photometry, which were apparently successful for Jupiter (Gaulme et al 2011), have not yet been successful for the ice giants (Rowe et al 2017;Gaulme 2017). Friedson (2020) found that for reasonable amplitudes, detection of pressure or temperature variations due to ice giant normal modes is not as promising as the prospect of detecting their gravitational influence on an orbiting spacecraft.…”