Frequency dependence of tidal Q

Richard Greenberg

Research output: Contribution to journalArticlepeer-review

2 Scopus citations


For studies of tidal evolution, values of the key parameter Q, and its frequency dependence, are often derived from estimates of internal energy dissipation when a satellite, planet, or star is physically distorted. Such estimates come from geophysical or astrophysical modeling, from seismic data, from ad hoc assumptions, or from constraints based on current spins and orbits. In a standard procedure, Q values are used to determine the lag in the response to each Fourier component of the tidal potential. The separate components are then co-added. The basis for this procedure is the analogy of the damped, driven, harmonic oscillator. However, this lag-and-add procedure would not be justifiable even for such a simple system, except for a very specific dependence of Q on frequency. There is no reason to expect the lag-and-add procedure to be relevant for a complex system, because the relationship between dissipation rates and tidal lags is unknown. This widely applied type of model is a reasonable approximation only if the decomposed tidal potential involves a narrow range of frequencies, and thus may only be appropriate for analyses to low order in orbital eccentricity and inclination.

Original languageEnglish (US)
Pages (from-to)L42-L45
JournalAstrophysical Journal Letters
Issue number1
StatePublished - Jun 10 2009


  • Celestial mechanics
  • Planetary systems
  • Planets and satellites: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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