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Project Progress

The most comprehensive search for trace species in the atmosphere of Mars

Our recent work on Mars (Villanueva et al. 2013b) became one of the most-read planetary papers of 2013, as recently ranked by Elsevier among all its journals/papers. In this extensive paper, we present a comprehensive search for trace species on Mars, targeting multiple volatile organic gases (CH₄, CH₃OH, H₂CO, C₂H₆, C₂H₂, C₂H₄), hydroperoxyl (HO₂), several nitrogen compounds (N₂O, NH₃, HCN), and two chlorinated species (HCl, CH₃Cl) based on rovibrational spectra in the 2.8-3.7 μm spectral region. The data were acquired over a period of 4 years (2006-2010) using powerful infrared high-resolution spectrometers (CRIRES, NIRSPEC, CSHELL) at high-altitude observatories (VLT, Keck-2, NASA-IRTF), and they span a broad range of seasons, Doppler shifts and spatial coverage (latitude-longitude) on Mars. In this paper, we present results from a selection of high-quality spectra obtained on four separate dates, representing a fraction of our search space. For most of these species we derived the most stringent upper limits ever obtained, and because the targeted gases have substantially different resident lifetimes in the Martian atmosphere (from hours to centuries), our measurements not only test for current release but also provide stringent limits on the average levels of release. In particular, we sampled the same regions where plumes of methane were recently reported (e.g., Syrtis Major and Valles Marineris), allowing us to test for seasonal and temporal variability.

Advanced fluorescence models for simple molecules and validation from cometary spectra

In this reporting period, we completed the development of full cascade fluorescence models for NH₃, HCN and HNC, and a new model for the ν1 rovibrational band of HC₃N (Villanueva et al. 2013a). The models are based on abinitio spectral databases containing millions of spectral lines and also include extremely precise spectral information contained in several high-resolution spectral databases. Using these new models we derive detailed cascade maps for these species, and obtain realistic fluorescence efficiencies applicable to high-resolution infrared spectra. The new models permit accurate synthesis of line-by-line spectra for a wide range of rotational temperatures. We validated the models by comparing simulated emissions of these nitrogen species with measured spectra of comet C/2007 W1 (Boattini) acquired with high-resolution infrared spectrometers at high altitude sites. The new models accurately describe the complex emission spectrum, thereby providing distinct rotational temperatures and production rates at greatly improved accuracy compared with results derived from earlier fluorescence models. In addition, we made use of the completeness and scope of the new databases to investigate possible HCN ↔ HNC radiative isomerization mechanisms, obtaining estimates of conversion efficiencies under typical cometary conditions.

Building an extensive taxonomy for comets based on their volatile compositions:
Using our newly developed and complete molecular databases for H₂O, CH₃OH, C₂H₆, NH₃, HCN, HC₃N, CO, etc., we obtained record observations of CO in comet 29P (Paganini et al. 2013), revealed the unusual organic composition of comet 2P (Radeva et al. 2013), discovered two modes of water release in comet 103P (Bonev et al. 2013), and described in detail the chemical taxonomy of comets C/2001 Q4 and C/2002 T7 (de Val-Borro et al. 2013).