First detection of the 63μm atomic oxygen line in the thermosphere of Mars with GREAT/SOFIA

Abstract

Context. The Stratospheric Observatory for Infrared Astronomy (SOFIA) with its 2.5 m telescope provides new science opportunities for spectroscopic observations of planetary atmospheres in the far-infrared wavelength range. Aims. This paper presents first results from the 14 May, 2014 observing campaign of the Martian atmosphere at 4.7 THz using the German REceiver for Astronomy at Terahertz frequencies (GREAT) instrument. Methods. The atomic oxygen 63 µm transition, OI, was detected in absorption against the Mars continuum, with a high signal-to-noise ratio (∼35). A beam-averaged atomic oxygen from a global circulation model was used as input to the radiative transfer simulations of the observed line area and to obtain a new estimate on the column density using a grid-search method. Results. Minimizing differences between the calculated and observed line intensities in the least-square sense yields an atomic oxygen column density of (1.1 ± 0.2) × 10 17 cm −2 . This value is about twice as low as predicted by a modern photochemical model of Mars. The radiative transfer simulations indicate that the line forms in the upper atmospheric region over a rather extended altitude region of 70-120 km. Conclusions. For the first time, a far-infrared transition of the atomic oxygen line was detected in the atmosphere of Mars. The absorption depth provides an estimate on the column density, and this measurement provides additional means to constrain the photochemical models in global circulation models and airglow studies. The lack of other means for monitoring the atomic oxygen in the Martian upper atmosphere makes future observations with the SOFIA observatory highly desirable.

Comparison of the Martian thermospheric density and temperature from IUVS/MAVEN data and general circulation modeling

“…The other was derived from Mars Climate Database (MCD) [ González‐Galindo et al , ], represents larger concentrations of oxygen, and results in stronger cooling by CO 2 . Recent globally averaged measurements [ Rezac et al , ; Mahaffy et al , ] hint that oxygen density profiles lie somewhere between the Nair and MCD models. We denote these scenarios in our discussions as N94 and MCD, correspondingly.…”

THz limb sounder (TLS) for lower thermospheric wind, oxygen density, and temperature

“…The 63.184 μm emission has been observed from balloons [Naylor et al, 1985;Lin et al, 1987;Mlynczak et al, 2004], rocket [Feldman and McNutt, 1969;Offermann and Grossmann, 1978], and space shuttles [Grossmann et al, 2000]. New airborne instruments for astronomy, such as Far Infrared Field-Imaging Line Spectrometer [Klein et al, 2010] and German REceiver for Astronomy at Terahertz frequencies (GREAT) [Rezac et al, 2015], have also observed the terrestrial OI emissions in surveying astronomical objects.…”

High Resolution Terahertz Spectroscopy with Quantum Cascade Lasers

“…10 Since the first flight, many discoveries have been enabled with this LO, for example, the first detection of the OI line in the atmosphere of Mars. 100 In Fig. 12, seven OI spectra of W49 N, a star-forming region about 36 200 light years away from Earth, are shown.…”