Deuterated methane observed on Saturn

The detection of CH3D in the 5-micron spectrum of Saturn, as obtained by a Fourier transform spectrometer, is reported. A CH3D abundance of 2.6 plus or minus 0.8 centimeter-amagat has been found along with a temperature of 175 plus or minus 30 K for the mean level of spectroscopic line formation. This suggests that the observed flux is due to thermal radiation from relatively deep levels within the atmosphere. This CH3D abundance indicates a deuterium/hydrogen ratio of approximately 2 x 10 to the -5th power, which is of a magnitude similar to that of Jupiter. This value is considerably lower than the terrestrial and meteoritic value of 15 x 10 to the -5th power. If stellar processing of the deuterium that formed the solar system is minimal, this ratio may be representative of the primordial ratio at the time of the formation of the universe.