detecting ch4 and other trace species on mars with a soir instrument - f montmessin et al 2007
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8/3/2019 Detecting CH4 and Other Trace Species on Mars With a Soir Instrument - F Montmessin Et Al 2007
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European Space Agency
European Mars Science and Exploration Conference: Mars Express & ExoMars
ESTEC, Noordwijk, The Netherlands, 12 - 16 November, 2007
DETECTING CH4 AND OTHER TRACE SPECIES ON MARS WITH A SOIR INSTRUMENT. F.
Montmessin1, A.C. Vandaele
2, E. Neefs
2, J.-L. Bertaux
1, and F. Daerden
2,
1Service d'Aéronomie, réduit de
Verrières, 91371 Verrières le Buisson, France,2Belgian Institute for Space Aeronomy, 3 av Circulaire, 1180
Brussels, Belgium. [email protected]
SOIR (Solar Occultation InfraRed spectrometer)is currently part of the SPICAV/SOIR instrument
[1] on board the Venus Express orbiter. SOIR, an
Echelle spectrometer using an acousto-optic tunable
filter (AOTF) for the order selection, is probing the
atmosphere by the technique of solar occultation,
operating between 2.2 and 4.3 μm, with a resolution
of 0.15 cm-1
. This spectral range is suitable for the
detection of several key components of planetary
atmospheres, in particular that of CH4, using the 3
vibrational band located near 3.3 μm.
Detection of CH4 in the Mars atmosphere has
already been reported [2] using the PFS instrument
on board Mars Express and from ground-based
telescope observations [3]. However, due to the
resolution of PFS instrument (1.4 cm-1
), the P- and
R- branches could not be resolved and the detection
relied on the observation of a sharp feature
attributed to the Q-branch of the band. However,
recent measurements [4,5] have revealed the
presence of 16
C12
O18
C lines in the vicinity of the 3
CH4 band, around 2982 cm-1
, which might impair
the CH4 detection.
With its high resolution capability and its high
signal-to-noise ratio (since observing the sun
directly), the SOIR instrument could resolve
methane individual lines in the 3 vibrational bandregion and provide a very robust CH4 detection. In
addition, it could detect methane isotopomers (such
as13
CH4) and other methane photochemical by-
products (C2H6, H2CO…), thereby providing
important clues on the photochemical cycle of
hydrocarbons on Mars.
We will present simulations of spectra such as
would be recorded by a SOIR instrument probing
the Mars atmosphere, allowing the determination of
lower limits for the detection of trace constituents.
A sensitivity study has also been performed
regarding some of instrumental characteristics of theSOIR instrument (band pass of the AOT filter, order
separation of the Echelle spectrometer).
References: [1] Bertaux, J.-L., et al. (2007), PSS (in
press). [2] Formisano, V. et al. (2004), Science 306 , 1758-
1761. [3] Krasnopolsky et al. (2004), Icarus 172, 537-547
[3] Villanueva, G. et al., Icarus (submitted). [4] Vandaele,
A.C. et al. (2007), 39th
DPS annual Meeting, Abs. #45.03;
Bertaux, J.-L. et al., Icarus (submitted)