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| Titel |
HDO/H2O, CO2 isotopic ratio, and CH4 distributions on Mars observed by SUBARU/IRCS |
| VerfasserIn |
Shohei Aoki, Hiromu Nakagawa, Yasumasa Kasaba, Hideo Sagawa, Marco Giuranna |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250077821
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| Zusammenfassung |
| We report the latitudinal and local time variations of HDO/H2O, CO2 isotopic ratio, and CH4
on Mars from ground-based observations using the Infrared Camera and Spectrograph
(IRCS) installed at the Subaru Telescope.
The distributions of the isotopic ratios enable to visualize the water and carbon
dioxide cycle on Mars. Furthermore, the recent discovery of CH4 on Mars has led to
much discussion on its source and sink. However, they are still less investigated. We
performed observations of these trace gases with SUBARU/IRCS on 30 November 2011
(Ls=37°), 4-5 January 2012 (Ls=52°), and 12 April 2012 (Ls=96°). We used the
cross-dispersed echelle spectroscopy of IRCS with high spectral resolution (R~20,000)
in order to detect narrow Martian lines. Our observations were covered the five
spectral bands, 2.85-2.93 μm, 3.01-3.10 μm, 3.28-3.36 μm, 3.48-3.57 μm, and
3.71-3.81 μm. This allows us to do simultaneous observations of multiple lines of H2O,
HDO, CO2 (628), CO2 (627), CO2 (626), and CH4. Our data sets can be used for
investigating (1) the latitudinal distribution of the trace gases at different seasons
(including local summer), and (2) their local time dependence (and/or longitudinal
distributions). The observation on April is joint one with the Planetary Fourier Spectrometer
onboard Mars Express. Such simultaneous observations of CH4 between ground-based
telescopes and a spacecraft are quite essential for the verification of its controversial
existence.
In order to determinate the amounts of the trace gases, the contributions between terrestrial
and Martian lines should be separated. Although our observations were performed when the
Doppler shift between Mars and Earth was relatively large (> 10km/s), the Martian lines are
still inside of the deep terrestrial lines. For separation, we developed a radiative transfer
model with line-by-line method. The model is taken account into the terrestrial H2O, O3,
CH4 and their isotope lines, the Martian H2O, HDO, CO2 and CH4 lines, solar lines, and the
instrumental line shape function.
Using the model, we derived HDO/H2O distributions. Our preliminary results at Ls=52°
suggest that (1) the latitudinal distribution shows increase around sub-solar latitude (~20°N),
and (2) the local time (or longitudinal) dependence is not clearly appeared. In addition, we
detected the enhancement of HDO amount at high latitudes from the data observed at
Ls=96°. It would be due to sublimation of the north polar cap, and the HDO/H2O ratio will
be discussed. |
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