Photochemical growing of complex organics in planetary atmospheres

UV induced syntheses of organic compounds from the main atmospheric constituents can be a very important source of organics in a given planetary environment provided the atmosphere is in a reduced state. The evolution of a CO₂ rich medium only produces very low yields of formaldehyde and related oxygenated compounds. Considering a CO rich atmosphere, the photochemical yield of O-organics formation is much higher, when the synthesis of N-organics remains difficult. The most favourable atmosphere as far as photochemical organic synthesis is concerned is a CH₄ rich milieu.. The photochemical evolution of such a CH₄ atmosphere under UV irradiation leads to a chain of various organics, the complexity of which increases together with the number of pathways involved in their formation. Their complexity also closely correlates with their UV photoabsorption spectrum: the more complex they are, the more shifted is their UV spectrum toward the visible range. Direct photodissociation of methane requires UV photon of wavelengths shorter than about 145 nm. It mainly produces ethane which absorbs UV at wavelengths shorter than about 160 nm, and acetylene, that presents an absorption spectrum extending up to 200 nm. This shift still continuously increases with further increase in number of C atoms. Unsaturated hydrocarbons with 4 and more C atoms have UV absorption characteristics including noticeable band structures in the 250–300 nm range. This trend has very important implication in the photochemical behaviour of a CH₄-rich planetary atmosphere, as it induces many catalytic processes. The occurrence of such processes is closely related to vertical atmospheric and energy deposition profiles. Titan provides a very good example of such a UV-directed organic atmospheric chemistry.     

Cosac, The Cometary Sampling and Composition Experiment on Philae

Comets are thought to preserve the most pristine material currently present in the solar system, as they are formed by agglomeration of dust particles in the solar nebula, far from the Sun, and their interiors have remained cold. By approaching the Sun, volatile components and dust particles are released forming the cometary coma. During the phase of Heavy Bombardment, 3.8--4 billion years ago, cometary matter was delivered to the Early Earth. Precise knowledge on the physico-chemical composition of comets is crucial to understand the formation of the Solar System, the evolution of Earth and particularly the starting conditions for the origin of life on Earth. Here, we report on the COSAC instrument, part of the ESA cometary mission Rosetta, which is designed to characterize, identify, and quantify volatile cometary compounds, including larger organic molecules, by in situ measurements of surface and subsurface cometary samples. The technical concept of a multi-column enantio-selective gas chromatograph (GC) coupled to a linear reflectron time-of-flight mass-spectrometer instrument is presented together with its realisation under the scientific guidance of the Max-Planck-Institute for Solar System Research in Katlenburg-Lindau, Germany. The instrument's technical data are given; first measurements making use of standard samples are presented. The cometary science community is looking forward to receive fascinating data from COSAC cometary in situ measurements in 2014.     

Production of nitrogen oxides by lightning and coronae discharges in simulated early Earth, Venus and Mars environments.

We present measurements for the production of nitrogen oxides (NO and N2O) in CO2-N2 mixtures that simulate different stages of the evolution of the atmospheres of the Earth, Venus and Mars. The nitrogen fixation rates by two different types of electrical discharges, namely lightning and coronae, were studied over a wide range in CO2 and N2 mixing ratios. Nitric oxide (NO) is formed with a maximum energy yield estimated to be ~1.3 x 10(16) molecule J-1 at 80% CO2 and ~1.3 x 10(14) molecule J-1 at 50% CO2 for lightning and coronae discharges, respectively. Nitrous oxide (N2O) is only formed by coronae discharge with a maximum energy yield estimated to be ~1.2 x 10(13) molecule J-1 at 50% CO2. The pronounced difference in NO production in lightning and coronae discharges and the lack of formation of N2O in lightning indicate that the physics and chemistry involved in nitrogen fixation differs substantially in these two forms of electric energy.