Joshua Sebree

My research program falls into two categories.  Part of my work aims to explore the new aspects of prebiotic and Titan-like aerosols and their importance both in interpreting data from NASA missions and in understanding how biological molecules may form in abiotic environments.  The other part is exploring the chemistry that gives rise to and sustains life in astrobiological field environments, such as caves.

1. The effect of trace species on bulk aerosols
The majority of Titan aerosol studies start with a premix of several percent methane in nitrogen. This premix is then exposed to an energy source to initialize reactions. The resulting aerosols are then characterized using a variety of methods including infrared (IR) spectroscopy and mass spectrometry (MS). While this “Titan Standard” mixture is a good starting point, from the Cassini mission, it is becoming evident that other atmospheric constituents should be taken into account. Data from the Cassini spacecraft has allowed for the identification of numerous trace (>1%) species in Titan’s atmosphere including acetylene (C2H2), carbon monoxide (CO), hydrogen cyanide (HCN), cyanoacetylene (HC3N) and benzene (C6H6), to name a few. Preliminary results from my current study demonstrates that the photolysis of larger aromatics (naphthalene and quinoline) at ppm levels leads to the formation of large poly-aromatic systems containing eight or more aromatic rings. We have also demonstrated that far-IR (50-600 cm-1) spectra of these new aerosols have features similar to those observed by Cassini that have not been match previously by laboratory-created aerosols. Building upon this work, my research group is focusing on how trace compounds, such as cyanoacetylene and HCN interact with these aromatic seeded aerosols and how they may lead to the incorporation of nitrogen and possible formation of PANHs within the aerosols.

2. Cave Research
Wind Cave national Park represents a unique opportunity to study an accessible, yet isolated, extremophile ecosystem.  The cave is one of the oldest (>300 Myr), longest, and most complex cave systems in the world.  With over 150 miles of mapped passageways, Wind Cave serves as the only natural access to the Madison formation aquifer via a series of lakes in the deepest section of the cave.  These lakes contain an isolated, nutrient-limited biome that may serve as the most accessible natural analog for low-biomass aqueous environments such as the oceans of Enceladus and Europa.  Access to these lakes requires climbing and crawling ~3 km underground through passageways as small as 20 cm, limiting the amount of anthropomorphic contamination from human visitors.  All living organisms require three things to survive: sources of energy, water, and nutrients.  Extremophiles are organisms that have evolved to live in environments that severely lack one or more of these.  Given the limited nutrients available in Wind Cave, microbial life found deep i the cave is expected to make extreme adaptations to survive.  Samples from water in the cave are being tested and cultured.  This will tell us about what life can thrive in the extreme environment of the cave, and is critical in determining what types of organisms can be found in other extreme environments.