P32B-01 INVITED
Water, Water Everywhere... and Oxidants too!
The current predominant scientific strategy to find evidence for the existence of extraterrestrial life has been to "follow the water". Life on Earth requires the availability of water, so it makes sense that this is a good place to start when trying to evidence of extant or extinct signatures of life beyond our planet. However, life on Earth also requires redox gradients. Respiration and photosynthesis are two such examples of redox chemistry that is essential for life. Planetary surfaces and atmospheres are naturally oxidized by photolytic and radiolytic processes. Even on early Earth and Titan, the natural oxidation of primordial ammonia presumably created the present nitrogen atmospheres, respectively as real and potential abodes for life. In the cases of Mars, Europa and Enceladus, three bodies of intense astrobiological interest, the natural oxidation processes driven by space environment interactions can produce significant quantities of oxidants, which could potentially be utilized to sustain life. We propose, that in addition to the "follow the water" strategy, the scientific community should start to "follow the oxidants", as a potentially important avenue of research and exploration. We address models for oxidant formation in planetary surface irradiation environments, as simulated by laboratory investigations, and apply results to past, recent and ongoing planetary observations of Mars and icy bodies of potential astrobiological interest in the outer solar system.
P32B-02 INVITED
Oxidants on Small Icy Bodies and Snowball Earth
Oxidants such as O2, O3, H2O2 and SO4 are known to be on the surface of icy bodies in the outer solar system and they may be an important source of energy for the subterranean biosphere. During Proterozoic time, Earth experienced "Snowball Earth" events, associated with the nearly complete shutdown of the hydrological cycle. During such long and severe glacial intervals, a weak hydrological cycle coupled with photochemical reactions involving water vapor would give rise to the sustained production of hydrogen peroxide. The photochemical production of hydrogen peroxide has been proposed previously as the primary mechanism for oxidizing the surface of Mars. During a Snowball, hydrogen peroxide could be stored in the ice; it would then be released directly into the ocean and the atmosphere upon melting and could mediate global oxidation events in the aftermath of the Snowball, such as that found in the geological record. There are implications for the evolution of oxygen-mediating and utilizing enzymes and thereby paved the way for the eventual appearance of oxygenic photosynthesis.
P32B-03 INVITED
Electrical Processes on Mars: New Sources and Sinks for Atmospheric Chemistry?
In nature, nearly all processes involving the lofting and transport of dust lead to significant electrification through the phenomenon of triboelectricity, in which macroscopic charge separation occurs due to particle contact and friction. Thus active disturbances in the Martian atmosphere such as dust devils and storms are leading candidate mechanisms that could maintain substantial surface electric fields, in analogy with terrestrial thunderstorms. Given the importance of terrestrial lightning in chemical processes such as Nitrogen fixation, a natural question then becomes whether or not the likely presence of electrified dust on Mars has any impact on atmospheric chemistry. While the existence of electric discharges on Mars has yet to be verified, we have shown that the mere presence of a pre-discharge electric field will energize free electrons in Mars` atmosphere, which subsequently dissociate carbon dioxide and water at rates that rapidly increase with electric field strength. One important consequence of these reactions is the possibility for oxidants to be produced in large quantities. In addition, both the energized electrons and the molecules they dissociate can act as a sink for trace species such as Methane. We discuss the theoretical framework for our approach, in which the Martian atmosphere is treated as a weakly-ionized, highly collisional plasma. We will also discuss how the more general problem of chemistry associated with discharges may be approached on Mars, and compare these mechanisms with terrestrial electrochemical processes, where the generation of new products may be dominated more by thermal timescales and "freezing-out" effects.
P32B-04 INVITED
The formation and fate of oxidants on icy satellite surfaces
It is well known that the bombardment of ice covered surfaces in the outer solar system leads to chemical transformations and alteration of molecular compositions. Among the major radiolysis products remaining trapped within the ice are highly reactive, oxygen rich molecules and radicals. Studies of pure ices have revealed much information about production and survival of oxidants, but real systems are full of impurities and the ability of these oxidizers to react and alter other embedded impurities gives rise to significant indirect channels for radiation-induced chemistry. Observational and experimental evidence indicates that the presence of CO2 is correlated with carbonaceous surfaces rather than strictly the presence of carbon bearing molecules. Graphitic substrate interactions with ice overlayers impede oxidant formation by scavenging of reactively scattered O, O+, OH and other fast, hot fragments. These interfacial reactions consume graphitic and carbonaceous particles and produce formic acid, formaldehyde, CO and CO2. This talk will focus on the role of ice: grain interfacial reactions in determining the potential oxidant inventory.