Letter to the Editor

Curiosity Mars methane measurements are not confused by ozone

¹ NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
e-mail: Chris.R.Webster@jpl.nasa.gov
² NASA Goddard Space Flight Center, Greenbelt, MD, USA
³ University of Michigan, Ann Arbor, MI, USA

Received: 1 July 2020
Accepted: 9 August 2020

Abstract

In the detection of methane in the atmosphere of Mars by the Tunable Laser Spectrometer on the Sample Analysis at Mars (TLS-SAM) on the Curiosity rover, the possibility of confusing ozone lines with those of methane is ruled out by the ultrahigh spectral resolution of the instrument. Even at the low background levels of methane (∼0.5 ppbv) detected by ingesting the atmosphere over a CO₂ scrubber (Linde 13X) that enriches the methane abundance relative to CO₂ by 25 times, the recorded TLS spectra show no presence of, and therefore no interference by, ozone lines. If O₃ lines were to appear in the TLS spectra, they would be readily distinguishable from those of CH₄. The inability of TLS-SAM to detect ozone spectral lines above its noise levels is consistent with a report that O₃ decomposes in the presence of Linde 13X material, so that it would not arrive at the TLS sample cell in a significant quantity. With the exact enrichment factor for ozone undetermined, TLS-SAM is unable to produce meaningful upper limits to the atmospheric ozone abundance.