Excitation of Jovian normal modes by an impact source

Abstract

We estimated the amplitudes of Jovian normal modes excited by a near-surface impact. The planet is modeled as a self-gravitating fluid sphere, and the impact source is approximated by a single force or a point pressure source. The effects of rotation are not included. An impact of a comet with a radius of 3 km and momentum Mν=6.8×10^(23) g-cm/s is modeled as a point source 100 km below the Jovian surface, assumed to be at 1 bar. The peak-to-peak amplitudes of displacement and velocity of disturbance with a period of 700 s are approximately 2.1 m and 1.9 cm/s, respectively, at a distance of 90° from the impact. An amplification of a factor of about 25 occurs near the antipode. This estimate is not sensitive to the assumptions on the density distribution above the surface. The amplitude in the higher altitude can be significantly higher. At shorter periods (100 to 200 s), the amplitudes depend on the source depth. For an impact with Mν=10^(23) g-cm/s, and for a source depth of about 20 to 50 km, the amplitude and the particle velocity at a distance of 90° are of the order of 100 m, and 3 m/s, respectively. The pressure change at a depth of 20 to 50 km is of the order of 20 dyne/cm², or about 2×10^(−6) of the ambient pressure at a depth of 40 km.

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