2013 Annual Science Report
NASA Goddard Space Flight Center Reporting | SEP 2012 – AUG 2013
Remote Sensing of Organic Volatiles on Mars and Modeling of Cometary Atmospheres
Using our newly developed analytical routines, Villanueva reported the most comprehensive search for trace species on Mars (Villanueva et al. 2013b, Icarus) and described in detail the chemical taxonomy of comets C/2001 Q4 and C/2002 T7 (de Val-Borro et al. 2013). He expanded our already comprehensive high-resolution spectroscopic database to include billions of spectral lines of ammonia (NH3, Villanueva et al. 2013a), hydrogen cyanide (HCN, Villanueva et al. 2013a, Lippi et al. 2013), hydrogen isocyanide (HNC, Villanueva et al. 2013a), cyanoacetylene (HC3N, Villanueva et al. 2013a), monodeuterated methane (CH3D, Gibb et al. 2013), and methanol (CH3OH, DiSanti et al. 2013). For each species, he developed improved or new fluorescence models using the new spectral models. These permit unprecedented improvement in models of absorption spectra in planetary atmospheres (Earth, Mars), and in computing fluorescence cascades for emission spectra of cometary gases pumped by solar radiation. Villanueva utilized these new models in analyzing spectra of comets that enabled record observations of CO in comet 29P/Schwassmann-Wachmann-1 (see report by Paganini), revealed the unusual organic composition of comet 2P/Encke (see report by Mumma), developed new fluorescence models for the ν2 band of methanol and for the ν3 band of CH3D in comets (see reports by DiSanti and by Bonev), and discovered two modes of water release in comet 103P/Hartley-2 (see report by Bonev).
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.
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.
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).
PROJECT MEMBERS:Geronimo Villanueva
RELATED OBJECTIVES:Objective 1.1
Formation and evolution of habitable planets.
Sources of prebiotic materials and catalysts
Origins and evolution of functional biomolecules
Earth's early biosphere.
Biosignatures to be sought in Solar System materials