Spring 2014

By Eddie Schwieterman
Graduate Student, Astronomy

In the spring of last year, I was privileged to conduct my Astrobiology research rotation at the University of Edinburgh and the UK Centre for Astrobiology in Scotland. I worked with Dr. Charles Cockell, who is an eminent astrobiologist and director of the Centre. I’m an astronomer, and the research rotations are designed to give astrobiology graduate students experience outside their primary discipline. The project Dr. Cockell and I designed combined our varied expertise and mutual interest in the topic of remotely detectable biosignatures.

A biosignature is a tell-tale sign that life is present, or that it has modified its environment in some way. The manner in which photosynthetic organisms absorb and reflect light from the Sun is one indication that life is present on the Earth. Many researchers have cited the so-called “red edge” effect, which is a sharp contrast between the efficient absorption of visible light and reflection of most near-infrared light by vegetation, as a potential biosignature that can be searched for in the spectra of alien planets.

We often think of photosynthesizers (and specifically oxygenic photosynthesizers like vegetation and algae) as being the most detectable form of life, because we presume they will be the most abundant. However, pigmentation has evolved for many purposes, including adaptation to extreme environments, and there are examples of macroscopic environments where other kinds of pigments (such as carotenoids) dominate, like hypersaline lakes and ponds.

These bodies are inhabited by pigmented salt-loving Archaea and can be brilliant and varied colors (The Great Salt Lake, the San Francisco salt ponds, and Lake Hillier in Australia are spectacular examples). Dr. Cockell and I decided to investigate the spectral and color diversity of a cross-section of organisms with different pigments and metabolisms during my three-month rotation.

Before my arrival in Edinburgh, we selected the microbes we wanted to culture and study. After I arrived, I learned several techniques and methods in microbiology, including the preparation of culture media, incubation and culturing of microorganisms in liquid and plated cultures, sterilization of lab equipment, anaerobic techniques, use of an anaerobic chamber, and reflectance and transmission spectroscopy of samples.

We measured the reflectance spectra of colonies of almost a dozen different species of microorganisms, all of which were non-photosynthetic or anoxygenic photosynthesizers. Additionally, I folded in my experience working with radiative transfer models to simulate the synthetic spectrum of an Earth-like planet with a surface dominated by a non-photosynthetic pigment (such as the case of hypersaline ponds in limited locales on Earth).

Our final study, which includes my advisor Dr. Victoria Meadows as a co-author, explores the nature, diversity and detectability of non-photosynthetic pigments as potential biosignatures, and has been submitted to Astrobiology.

In addition to being professionally valuable, I found this experience incredibly beneficial on a personal level, in part because I never had the opportunity to study abroad as an undergraduate. I appreciated the chance to see the United Kingdom, interact with astrobiologists from the international community, and work on such an interesting and compelling interdisciplinary project!

About the author: Eddie Schwieterman is a fourth-year Dual-Title Astronomy and Astrobiology PhD student at the University of Washington and a member of the NASA Astrobiology Institute's Virtual Planetary Laboratory, which is headquartered at the University of Washington.

Photos (from top to bottom):

(1) Eddie Schwieterman working with an anaerobic (oxygen-free) chamber to prepare culture media for microorganisms that do not require oxygen.

(2) The salt ponds of San Francisco bay are one example of an environment on Earth where non-photosynthetic organisms dominate the spectral reflectance.

(3) Cultures of anaerobic phototrophs. From left to right: Rhodopseudomonas palustris, Chlorobium tepidum, and Rhodobacter sphaeroides.

(4) Colonies of cultured pigmented microorganisms.

(5) Eddie Schwieterman standing on Calton Hill in Edinburgh, Scotland.

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