Tunable Laser Spectrometers for Planetary Science

• Published in: Space science reviews 2023-12, Vol.219 (8), p.78, Article 78
• Main Authors: Webster, Christopher R., Hofmann, Amy E., Mahaffy, Paul R., Atreya, Sushil K., House, Christopher H., Simon, Amy A., Garvin, James B.
• Format: Article
• Language: English
• Subjects: Absorption spectra; Abundance; Aerospace Technology and Astronautics; Ammonia; Astrophysics and Astroparticles; Carbon dioxide; Curiosity (Mars rover); Enceladus; Gases; Hydrogen peroxide; Hydrogen sulfide; Infrared absorption; Infrared spectra; Isotope ratios; Laser spectrometers; Lasers; Line spectra; Mars; Mass spectrometers; Mass spectrometry; Nitrogen dioxide; Nitrous oxide; Physics; Physics and Astronomy; Planet formation; Planetary evolution; Planetary mass; Planetology; Rare gases; Ratios; Resolution; Space Exploration and Astronautics; Space missions; Space Sciences (including Extraterrestrial Physics; Spectrometers; Stable isotopes; Sulfur dioxide; Tunable lasers; Venus
• ISSN: 0038-6308; 1572-9672
• DOI: 10.1007/s11214-023-01023-4

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 ∼10‰ 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 λ / δ λ ∼ 5 million) provides unambiguous detection of a wide variety of gases such as H 2 O, H 2 O 2 , H 2 CO, HOCl, NO, NO 2 , HNO 3 , N 2 O, O 3 , CO, CO 2 , NH 3 , N 2 H 4 , PH 3 , H 2 S, SO 2 , OCS, HCl, HF, O 2 , HCN, and CH 4 , C 2 H 2 , C 2 H 4 , C 2 H 6 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 ∼1–2‰, 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.