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2009 Annual Science Report

NASA Jet Propulsion Laboratory - Titan Reporting  |  JUL 2008 – AUG 2009

Executive Summary

This summary covers the first six months of the JPL-Titan team, hereinafter the NAI Titan team, activities since the initiation of funding. Some members of this team were funded for only three months of this reporting period.

A series of coupled model simulations and novel laboratory experiments comprise the core research program of the NAI Titan team. The objective of this coordinated research is to understand the extent to which processes that could be active currently in Titan could lead to the formation of significant prebiotic molecular compounds, to be defined hereinafter as being composed of atoms of hydrogen, carbon, nitrogen, and oxygen. These processes might have been important in the early Earth environment and be on the path to the formation of life.

During this initial reporting period, two research themes—“Titan’s geology—places where organic chemistry can operate” and “The complexity of atmospheric organic chemistry“—received most of the available funding. Work on the third theme – “The evolved chemical state of the Titan surface” – started at a very low level.

All of the research in each theme involves the development of new models and laboratory experiments such that the work during this reporting period consisted primarily of model development and acquisition and installation of new laboratory facilities. An overview of what has occurred in each of the themes is presented in what follows.

The model simulations and laboratory experiments planned under Theme 1 – “Titan’s geology—places where organic chemistry can operate” – shall outline possible physical contexts where, in the current Titan environment, prebiotic compounds might likely be formed.

Two sets of conditions in the modern Titan environment may allow sufficient mixing of organic compounds with liquid water over a sufficient time period to allow extensive formation of prebiotic compounds. Model work has started on the simulation of a large impact on the Titan surface that would produce zones of liquid water in the midst of surface deposits of organic material for a finite period of time. Research also is being focused on a simulation of cryovolcanism, a phenomena in which zones of liquid water form in the subsurface and flow onto the surface.

A new laboratory facility has been prepared (Figure 1) to simulate the degree of mixing between liquid hydrocarbons and water ice. The liquid hydrocarbon lakes seen on the Titan surface are sited in a bedrock of water ice. In such a context, there is a prospect for prebiotic compound formation too.

Theme 2 – “The complexity of atmospheric organic chemistry” – will address the questions: to what extent large organic molecules might form in the current Titan atmosphere and what processes and where this formation might occur. The development of a master atmospheric model and laboratory simulations of potential atmospheric chemical and physical processes comprise this research program.

The master model of the Titan atmosphere will explore homogeneous and heterogeneous gas-phase processes and condensed phase chemistry leading to the formation of large organic compounds. The development of several components of this model has started in the reporting period. The results of a simulation of aerosol formation in the lower atmosphere compare well with measurements acquired by the Huygens probe Descent Imager/Spectral Radiometer (DISR) instrument. A model of the physical atmosphere and how it varies with altitude, latitude, and season is being developed to define an atmospheric reference context for modeling gas phase and condensed phase chemical processes.

Initial work on several different laboratory experiments to simulate actual processes in the Titan atmosphere has begun in these first six months. A new laboratory apparatus is being developed to measure the rate of homogeneous nucleation. Formation of these aerosols and subsequent growth through accretion of additional atmospheric constituents sets the stage for condensed phase macromolecular formation. A new laboratory apparatus also is being created (Figure 2) to simulate how long wavelength radiation can initiate photochemical transformations in the condensed phase. Another parallel laboratory investigation is being prepared to form aerosols, photolyze them directly, and measure the resulting large organic molecular products.

Theme 3 – “The evolved chemical state of the Titan surface” – a multi-laboratory experimental investigation into possible prebiotic compound formation on the Titan surface has started with two activities. The experimental apparatus has been developed (Figure 3) for one of these initial studies that will quantify the degree to which organic compounds from the atmosphere can dissolve in liquid methane/ethane. Another laboratory investigation has begun a consideration of catalytic activity due to micrometeorite materials on the Titan surface that could lead to prebiotic molecular formation.

Additional work has pursued the question of whether standard physical and chemical processes that can occur readily in a planetary environment elsewhere in the universe have life as their outcome. As Titan might prove to be a setting for a rich production of prebiotic compounds, it is significant that conditions in which a Titan-like object might exist occur around a large fraction of stars in the galaxy. Thus Titan-like objects should be important targets in a program characterizing extrasolar planets.