Tunable Laser Spectrometers for Planetary Science

Distinguishing planetary formation and evolution pathways and understanding the origins of volatiles on planetary bodies requires determination of relative abundances and isotope ratios in the noble gases, and also of the isotope ratios in C, H, N, O and S at high precisions. Traditional planetary mass spectrometers uniquely provide excellent survey capability including the noble gas relative abundances and their isotope ratios. However, to distinguish planetary evolution models for the outer planets, stable isotope ratios in C and O require precisions of similar to 10 parts per thousand or better, readily achievable with a tunable laser spectrometer (TLS). As demonstrated on the Mars Curiosity rover, and as planned for a now-selected NASA Venus mission, tunable laser spectrometers play a unique role synergistic with the capabilities of planetary mass spectrometers. The TLS technique of recording infrared absorption spectra at ultrahigh resolution (resolving power lambda\8 lambda similar to million) provides unambiguous detection of a wide variety of gases such as H2O, H2O2, H2CO, HOCl, NO, NO2, HNO3, N2O, O-3, CO, CO2, NH3, N2H4, PH3, H2S, SO2, OCS, HCl, HF, O-2, HCN, and CH4, C2H2, C2H4, C2H6 at parts-per-billion levels. Through line-depth or line-area ratio comparisons of adjacent spectral lines, planetary TLS instruments can achieve isotope ratio measurements in C, H, N, O, and S molecules at precisions of similar to 1-2 parts per thousand, including for the triple isotope components of O and S. Expected performance of TLS instruments for Venus, Saturn, Enceladus and Uranus will be described as constrained by actual measurements reported at Mars on the Curiosity rover.

Automated summary

Distinguishing planetary formation and evolution pathways and understanding the origins of volatiles on planetary bodies can be achieved by accurately measuring the relative abundances and isotope ratios in noble gases, as well as the isotope ratios in C, H, N, O and S. Traditional planetary mass spectrometers provide excellent survey capability, while tunable laser spectrometers (TLS) can achieve high precision measurements of isotope ratios in C and O to distinguish planetary evolution models. TLS instruments are capable of detecting a wide variety of gases at parts-per-billion levels and can achieve isotope ratio measurements at precisions of similar to 1-2 parts per thousand for C, H, N, O and S molecules.