Memoirs of a Giant Planet

Yanqin Wu, Yoram Lithwick

Research output: Contribution to journalArticle

Abstract

Saturn is ringing weakly. Exquisite data from the Cassini mission reveal the presence of f-mode oscillations as they excite density waves in Saturn's rings. These oscillations have displacement amplitudes of order 1 m on Saturn's surface. We propose that they result from large impacts in the past. Experiencing little dissipation inside Saturn on account of its weak luminosity, f-modes may live virtually forever, but the very ring waves that reveal their existence also remove energy from them, in 104 to 107 yr for the observed f-modes (spherical degree 2-10). We find that the largest impacts that arrive during these times excite the modes to their current levels, with the exception of the few lowest-degree modes. To explain the latter, either a fortuitously large impact in the recent past or a new source of stochastic excitation is needed. We extend this scenario to Jupiter, which has no substantial rings. With an exceedingly long memory of past bombardments, Jovian f-modes and p-modes can acquire much higher amplitudes, possibly explaining past reports of radial velocity detections, and are potentially detectable by the Juno spacecraft.

Original languageEnglish (US)
Article number142
JournalAstrophysical Journal
Volume881
Issue number2
DOIs
StatePublished - Aug 20 2019

Fingerprint

Saturn
planets
planet
oscillation
ringing
Jupiter
dissipation
Cassini mission
spacecraft
Saturn rings
oscillations
rings
Jupiter (planet)
radial velocity
bombardment
energy
luminosity
excitation

Keywords

  • asteroseismology
  • hydrodynamics
  • instabilities
  • planetary systems
  • turbulence
  • waves

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Wu, Yanqin ; Lithwick, Yoram. / Memoirs of a Giant Planet. In: Astrophysical Journal. 2019 ; Vol. 881, No. 2.
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Memoirs of a Giant Planet. / Wu, Yanqin; Lithwick, Yoram.

In: Astrophysical Journal, Vol. 881, No. 2, 142, 20.08.2019.

Research output: Contribution to journalArticle

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N2 - Saturn is ringing weakly. Exquisite data from the Cassini mission reveal the presence of f-mode oscillations as they excite density waves in Saturn's rings. These oscillations have displacement amplitudes of order 1 m on Saturn's surface. We propose that they result from large impacts in the past. Experiencing little dissipation inside Saturn on account of its weak luminosity, f-modes may live virtually forever, but the very ring waves that reveal their existence also remove energy from them, in 104 to 107 yr for the observed f-modes (spherical degree 2-10). We find that the largest impacts that arrive during these times excite the modes to their current levels, with the exception of the few lowest-degree modes. To explain the latter, either a fortuitously large impact in the recent past or a new source of stochastic excitation is needed. We extend this scenario to Jupiter, which has no substantial rings. With an exceedingly long memory of past bombardments, Jovian f-modes and p-modes can acquire much higher amplitudes, possibly explaining past reports of radial velocity detections, and are potentially detectable by the Juno spacecraft.

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