On probing the outer planets with the Raman effect

Abstract

The feasibility of using the H2 rotational Raman spectrum to investigate the physical structure of outer planet atmospheres is examined. By selecting distinct wave bands spaced throughout the visible spectrum for observation a wide range in physical depth can be probed. On the basis of a semi‐infinite homogeneous pure H2 atmospheric model, computations of the strengths of the S(0) and S(1) lines have been made for a wide range of physical conditions. For each characteristic wavelength the ratio of the S(0)/S(1) line strengths is independent of the presence of aerosol particles. It provides a useful estimate of Boltzmann temperature. In contrast, the absolute strengths of the S(0) and S(1) lines are extremely sensitive to haze. Extremely small quantities of aerosol particles can be detected even at high altitudes. Initial applications of the Raman probe technique to Jupiter and Uranus are reported. For Jupiter a weak aerosol haze appears to exist at an H2 column density of ⪝17 km amagat. For Uranus, aerosol particles appear to be present at an H2 column density of ⪝104 km amagat. In addition, a significant temperature inversion may be present in the same region of the atmosphere.