On the detectability of Jovian oscillations with infrared heterodyne measurements

Abstract

The possibility of detecting global oscillations of Jupiter by measuring the Doppler shift of far infrared emission lines formed in the lower stratosphere of the planet was investigated. The pure rotational quadrupole lines S(0) and S(1) of molecular hydrogen, located near 28 and 17 μm, present attractive characteristics for this research. Their observations require the use of infrared heterodyne techniques, with a resolving power around 10 6. We have calculated the expected line profiles due to these transitions on Jupiter and used them to evaluate the feasibility of the method. Measurements of the S(0) and S(1) lines over a period of a few nights would permit the detection of modes with periods of 5 to 20 min and Doppler shifts corresponding to velocities as low as 1 m · sec −1, which is less than the value recently announced by Schmider and Mosser (1990, Seismology of Jupiter. In Progress of Seismology of the Sun and Stars, Proceedings, Oji International Seminar, Hokone, Japan. Springer-Verlag, Berlin) and Schmider et al. (1991, Astron. Astrophys. 248, 281–291) from observations of the Jovian troposphere in the visible range. Possible limitations of the method resulting from instrumental considerations, the fluctuations of the telescope guiding system and from the atmospheric transmission and seeing are discussed. Results from measurements proposed here, along with those from the visible observations, can be used to test existing models for Jovian oscillations and their altitude dependence.