Study of the Martian cold oxygen corona from the O I 130.4 nm by IUVS/MAVEN

Abstract

First observations of the O I 130.4 nm resonant line performed by the Imaging Ultraviolet Spectrograph (IUVS) aboard the Mars Atmosphere and Volatile EvolutioN mission (MAVEN) are presented in this paper. This emission line is observed during the different orbit phases of MAVEN. The atomic oxygen density and the temperature at 200 km are retrieved from an automatic pipeline using a radiative transfer model for resonant scattering lines for a selection of coronal profiles. These selected profiles are representative of the coronal scans done during the first months of the mission (from November 2014 to January 2015). The derived oxygen density and the temperature near the exobase are in the predicted range by the current thermospheric models of Mars for moderate solar activity, and some diurnal variations are observed. However, the absolute calibration of the instrument significantly limits the accuracy of density and temperature results.

On the evening time exosphere of Mars: Result from MENCA aboard Mars Orbiter Mission

“…Chaufray et al [2015] reported an exospheric temperature between 250 and 329 K, which is also in good agreement with our observations. It may be noted that the temperature is less sensitive to absolute calibration compared to number density.…”

“…The simulations further show that the oxygen exosphere is thermal below 600 km in all seasons. Using Imaging Ultraviolet Spectrograph (IUVS)/MAVEN data, Chaufray et al [2015] derived an oxygen density between 2.1 × 10 7 and 7 × 10 7 cm −3 at 200 km, near ∼19.5 LST, on 3 December 2014. Comparison of the recent MAVEN NGIMS observations with Viking data showed that in the thermosphere neutral scale heights are 50% greater and the exobase is 1 to 2 scale heights higher in the NGIMS observations [Withers et al, 2015].…”

MAVEN IUVS observation of the hot oxygen corona at Mars

“…The initial data reveal an unambiguous transition from the thermal to nonthermal oxygen population with high altitude resolution and signal to noise. Details on the lower altitude thermal oxygen component observed by IUVS may be found in Chaufray et al [2015]. By coadding data from December 2014 to January 2015, an extended coronal brightness profile exceeding the altitude of 1 Mars radius is obtained.…”

The Structure of Titan’s N2 and CH4 Coronae

“…Unfortunately, validating such a speculation is not possible with the INMS data since the CH 4 abundances cannot be retrieved reliably at such high altitudes (see Section 2). For comparison, we note that such a transition in atomic O corona does occur on Mars at around 400km above the exobase (e.g., Chaufray et al 2015;Deighan et al 2015).…”

“…On Mars, the atomic H and O coronae were observed by the UV spectrometer on board Mariner 6, 7, and 9 (Anderson 1974), the Spectroscopy for Investigation of Characteristics of the Atmosphere of Mars (SPICAM) on board Mars Express (MEx) (Chaufray et al 2008), the Alice far-UV imaging spectrograph on board Rosetta (Feldman et al 2011), and the Imaging Ultraviolet Spectrograph (IUVS) on board Mars Atmosphere and Volatile Evolution (MAVEN) Chaufray et al 2015;Deighan et al 2015). It has been suggested that both coronae are composed of a thermal population and a suprathermal population, although the existence of a hot atomic H population was questioned by Rosetta Alice observations (Feldman et al 2011).…”