A stringent upper limit to SO2 in the Martian atmosphere

Surfur-bearing molecules have been found at the surface of Mars by the Viking lander, the Spirit and Opportunity rovers, and the OMEGA infrared spectrometer aboard Mars Express. However, no gaseous sulfur-bearing species have ever been detected in the Martian atmosphere. We search for SO2 signatures in the thermal spectrum of Mars at 7.4 μm using the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infrared Telescope Facility (IRTF). Data were obtained on Oct. 12, 2009 (Ls = 353 ◦ ), in the 1350–1360 cm −1 range, with a spatial resolution of 1 arcsec (after convolution over three pixels along the N-S axis and two steps along the E-W axis) and a resolving power of 80 000. To improve the signal-to-noise ratio (S/N), we co-added the Martian spectrum around the positions of nine selected SO2 transitions with a high S/N and no telluric contamination. From a mean spectrum, averaged over 35 pixels in the region of maximum continuum, we infer a 2σ upper limit of 0.3 ppb to the SO2 mixing ratio, assuming that our instrumental errors are combined according to Gaussian statistics. Our upper limit is three times lower than the upper limit derived by Krasnopolsky (2005, Icarus, 178, 487), who used the same technique on previous TEXES data. In addition, we derive an upper limit of 2 ppb at each spatial pixel of the region observed by TEXES, which covers the longitude ranges 50 E–170 E for latitudes above 30 N, 100 E–170 E for latitudes between 0 and 30 N, and 110 E–170 E for latitudes between 15 S and 0. The non-detection of localized SO2 sources in the observed area is consistent with a homogeneous distribution being expected around equinox for noncondensible species with a lifetime longer than the global mixing time. In view of the typically large SO2/CH4 ratio observed in terrestrial volcanoes, and assuming a comparable volcanic composition for Mars and the Earth, our result reaffirms that a volcanic origin is unlikely for any methane in the Martian atmosphere.

[1]  T. Encrenaz,et al.  Water vapor map of Mars near summer solstice using ground-based infrared spectroscopy , 2010 .

[2]  Andreas Seifahrt,et al.  Status of the Echelon-cross-Echelle Spectrograph for SOFIA , 2010, Astronomical Telescopes + Instrumentation.

[3]  H. Maezawa,et al.  Search of SO2 in the Martian atmosphere by ground-based submillimeter observation , 2009 .

[4]  Franck Lefèvre,et al.  Observed variations of methane on Mars unexplained by known atmospheric chemistry and physics , 2009, Nature.

[5]  Michael D. Smith,et al.  Strong Release of Methane on Mars in Northern Summer 2003 , 2009, Science.

[6]  T. Encrenaz,et al.  Simultaneous mapping of H2O and H2O2 on Mars from infrared high-resolution imaging spectroscopy , 2008 .

[7]  Franz Schreier,et al.  The GEISA spectroscopic database: Current and future archive for Earth and planetary atmosphere studies , 2008 .

[8]  Jeffrey R. Johnson,et al.  Mineralogic constraints on sulfur‐rich soils from Pancam spectra at Gusev crater, Mars , 2007 .

[9]  Franck Lefèvre,et al.  Infrared imaging spectroscopy of Mars : H2O mapping and determination of CO2 isotopic ratios , 2005 .

[10]  V. Krasnopolsky.  A sensitive search for SO2 in the martian atmosphere: Implications for seepage and origin of methane , 2005 .

[11]  Jean-Pierre Bibring,et al.  Sulfates in the North Polar Region of Mars Detected by OMEGA/Mars Express , 2005, Science.

[12]  A. Basilevsky,et al.  Recent and episodic volcanic and glacial activity on Mars revealed by the High Resolution Stereo Camera , 2004, Nature.

[13]  R. Rieder,et al.  Chemistry of Rocks and Soils at Meridiani Planum from the Alpha Particle X-ray Spectrometer , 2004, Science.

[14]  M. D. Smith,et al.  Mineralogy at Meridiani Planum from the Mini-TES Experiment on the Opportunity Rover , 2004, Science.

[15]  Jeffrey R. Johnson,et al.  In Situ Evidence for an Ancient Aqueous Environment at Meridiani Planum, Mars , 2004, Science.

[16]  Marco Giuranna,et al.  Detection of Methane in the Atmosphere of Mars , 2004, Science.

[17]  T. Encrenaz,et al.  Hydrogen peroxide on Mars: evidence for spatial and seasonal variations , 2004 .

[18]  Thérèse Encrenaz,et al.  Chemical markers of possible hot spots on Mars , 2003 .

[19]  D. Jaffe,et al.  TEXES: A Sensitive High‐Resolution Grating Spectrograph for the Mid‐Infrared , 2001, astro-ph/0110521.

[20]  Stephen R. Lewis,et al.  Improved general circulation models of the Martian atmosphere from the surface to above 80 km , 1999 .

[21]  Carol R. Stoker,et al.  Thermal emission spectra of Mars (5.4–10.5 μm): Evidence for sulfates, carbonates, and hydrates , 1989 .

[22]  Klaus Keil,et al.  Geochemical and mineralogical interpretation of the Viking inorganic chemical results , 1977 .