Docent lecture (docentföreläsning): Physical and chemical processes in Titan's atmosphere
by
Wolf Geppert(SU Fysikum)
→
Europe/Stockholm
FA31
FA31
Description
Saturn’s moon Titan (the second largest satellite in the solar system) is a unique object in many respects, one of them being the presence of a dense atmosphere, which, like the one encountered on our own planet, is dominated by nitrogen (95 %), with hydrocarbons making up the rest of it. The Cassini-Huygens mission, launched by several national and multinational space agencies (e. g. ESA, NASA), has delivered a cornucopia of new, often surprising data on physical parameters and the chemical composition of Titan’s atmosphere.
In this lecture I will present basic physical and chemical properties of Titan’s atmosphere, including the methane cycle, which is similar to the water cycle on Earth. The question how Titan’s atmosphere reached the present composition is still not completely solved: several theories have been formulated in this context and will be discussed in the lecture.
Furthermore, the versatile molecular processes in the upper layers of Titan’s ionosphere triggered by impact of solar UV photons, magnetospheric electrons and cosmic rays will be presented. The different types of ionospheric reactions and their most crucial properties (e. g. temperature dependences) will be discussed.
In the end, these processes can result in generation of more complex nitrogen-containing molecules and polymers like tholines, which are thought to form the orange-coloured haze enveloping Titan. This haze plays a big role in the thermal balance of the regulation of the temperature of the moon. Tholines have also been found to form biomolecule precursors like amino acids and nucleobases upon hydrolysis. Such a production pathway has also been invoked for the formation of these compounds on early Earth (whose atmosphere might have likened the one on Titan). The feasibility of this way of formation of the most basic biomolecules will also be discussed.
Despite the success of Cassini-Huygens, many questions remain. Therefore new missions to Titan, namely “Titan Explorer”(NASA) and TANDEM(ESA)” are planned to go ahead in about 2018. The scientific issues to be addressed by this mission will be shortly presented.
