Unraveling the enigma of life in universe

When he enrolled in Purdue University for his doctoral studies, after graduating from the University of Kansas in 2006 with a bachelor’s degree in chemistry, Dr. Joshua Sebree hoped to study meteorites. There was one problem, though: the faculty member working on meteorites was not accepting any new students.
 
Fortunately, there was another professor who was using physical and organic chemistry methods to study gases in the atmosphere of Saturn’s largest moon, Titan.
 
“I loved organic [chemistry], working with lasers sounded fun, and, of course, Titan being a moon of Saturn, and me being a space nut, it just kind of clicked,” Dr. Sebree recalls.
 
He completed his Ph.D. in physical chemistry in 2011 and joined NASA’s Goddard Space Flight Center near Washington DC as a post-doctoral fellow because he “wanted to stay in the planetary science aspect of things rather than the laser spectroscopy side of things.”
 
Moreover, he preferred to “do aerosols, basically the big particles in the atmosphere, instead of single molecule stuff.” Besides, it was Titan again. “The same planet, just a little different twist on the chemistry,” he explains.
 
At Goddard, Dr. Sebree also worked with a team developing several of the many components included in various Mars rovers and orbiters.
 
He enjoyed his work at NASA but he wanted to move into academia. “I have always loved teaching and working with students,” he says.
 
Dr. Sebree also felt that Washington DC was too busy a place for him to raise a young family in. So, he started looking for a university where he could teach and still devote time to work in the laboratory, rather than being stuck behind a desk and writing grant applications for the rest of his career.
 
“An undergraduate university like UNI was what I was looking for,” he says.
 
The decision to come to UNI was made even easier as he fell in love with the campus and the Cedar Falls community on his first visit to UNI. 
 
He joined UNI in 2013 as an Assistant Professor of Astrochemistry and Astrobiology in the Department of Chemistry and Biochemistry.
 
Asked to describe the goals of his current research, Dr. Sebree explains that he is concerned primarily with understanding the formation of prebiotic molecules in the abiotic environments of our solar system, such as Titan. Abiotic environments are those devoid of life. Prebiotic molecules are the chemical precursors and building blocks of life.
 
He studies the photochemical reactions that occur in Titan’s atmosphere. Given enough energy from sunlight and an appropriate mixture of nitrogen, methane and other organic molecules in the atmosphere, these reactions may lead to the formation of prebiotic molecules like amino acids and nucleobases.
 
Initially suspended in aerosol particles in the atmosphere of Titan, these compounds eventually would settle down on the surface to undergo further reactions, possibly leading to the formation of biological molecules. This would explain one way that interactions between abiotic environments and prebiotic molecules could lead to the development of biological molecules in those environments.
 
To illustrate the concept, Dr. Sebree draws a comparison with conditions found in some modern cities on our own planet.
 
“Today we get the photochemical smog of Beijing and L.A., and that’s a deadly, noxious poison — you don’t want to breathe it in. Back before life really began, similar smogs were on Earth, but, you know, we have life,” he says.
 
“Now on Pluto and Titan, we have those same types of smog, lots of methane with nitrogen and sunlight, and it gives brown and orange materials that rain out on to the surface and give all these pretty colors.”
 
He describes the brown and orange materials, referred to as tholins, as “essentially an organic soup of molecules that may or may not contain molecules important for life as we know it.” He is also working to describe the fates of these compounds after their formation in the atmosphere, where the prebiotic aerosols undergo additional photochemical reactions before eventually collecting on the surface of Titan as tholins.
 
Dr. Sebree hypothesizes that perhaps it is on the extremely cold surface of water ice and rock—dissolved in Titan’s liquid methane and ethane—that these tholin compounds may encounter further contingencies that could potentially allow for extreme forms of life to evolve in an environment much colder and harsher than our own planet.
 
He believes that an understanding of what happens when tholin-like compounds interact with different solvents under various temperatures, say the low temperature on Titan, may help us to better understand where to search for possible chemical precursors of life in the universe.
 
Dr. Sebree recreates in his laboratory’s reaction chamber the conditions found in the abiotic atmosphere of Titan, which allows him to produce compounds similar in composition to the aerosols and tholins observed on Titan.
 
To strengthen the explanatory power of his system, he incorporates into the design of his experiments actual spectral data of the compounds on Titan, as collected by the infrared spectrophotometers and mass spectrometers aboard NASA’s Cassini-Huygens mission. These instruments are capable of measuring the sizes and compositions of the compounds that make up the aerosols and tholins on Titan.
 
He compares the Titan spectral data to the spectral data of the aerosols and tholin-like materials generated in his lab at UNI. This helps him to determine whether or not the compounds created in his lab are consistent in composition with the compounds observed on Titan.
 
His team has already discovered that the far-infrared spectra of new compounds created first in his laboratory match features of tholins observed on Titan by the Cassini spacecraft, but which have previously gone undescribed by other researchers.
 
Last fall, Dr. Sebree along with Dr. Alexa Sedlacek and Dr. Xinhua Shen of the Department of Earth Science launched the UNI BETA Project.
 
The three-part project, supported through a three-year STEM grant awarded by the Iowa Space Grant Consortium, traces the biogeochemical evolution of Earth’s atmosphere.
 
The part that he leads examines the prebiotic chemistry of the hazes on the primordial Earth, dating back to about four billion years ago, and will “attempt to detect photo-chemically produced biomolecules (amino acids, nucleobases) and the conditions necessary to make them.” 
 

Ryan Lockard, Volunteer, UNI STEM