Raea Hicks

Laboratory Studies of Titan and Early Earth Tholins

Titan, Saturn’s largest moon, is the most Earth-like planetary body in the solar system.  It has volcanoes, lakes filled with liquid hydrocarbons, and a thick nitrogen-rich atmosphere.  About 2% of Titan’s atmosphere is methane, which undergoes photodissociation at the alpha-Lyman wavelength (121.6 nm).  Methane fragments recombine into heavier organic molecules such as aliphatic and polycyclic aromatic hydrocarbons.  The larger hydrocarbons condense into aerosols, particles suspended in air.  I use a gas mixing chamber, a UV lamp, and a flow-tube setup (figure below) to create aerosol that have analogous properties to those found on Titan.  Carl Sagan has termed these planetary aerosol analogues “tholins.”

The early Earth atmosphere probably underwent photochemistry similar to the photochemistry currently occurring in Titan’s atmosphere.  Models show that a small amount of methane is able to account for the warming required to warm the Earth above the freezing point of liquid water, thereby solving the Faint Young Sun paradox.  Thus, the atmosphere of Titan serves as an analogue to the one that was present during the rise of life on Earth.

My research in the Tolbert group focuses on laboratory studies of tholins by electron ionization mass spectrometry.  I use the Aerodyne Quadrupole Aerosol Mass Spectrometer (Q-AMS) and High Resolution Time-of-Flight AMS (HR-ToF AMS) to determine the chemical identity of the gases that condense to form tholins.  The AMS focuses aerosol into a particle beam, pumps away the surrounding gases, then vaporizes and ionizes the constituent molecules for time-of-flight and quadrupole mass spectrometery.

Currently, I am investigating the formation mechanism of the early Earth tholins.  My future research will involve studying the changes in molecular composition of Titan tholins induced by differences in temperature and pressure.  I also plan to investigate the changes effected by introducing trace gases into the mixture.  I am particularly excited about upcoming collaborations with early Earth geologists to relate my data to the rock and fossil record.