Whether in the farthest reaches of our solar system, her lab on the Hilltop or her New York Times bestselling book, Professor Sarah Johnson seeks out signs of life — and connection.
Planetary scientist Sarah Johnson has always looked to the stars and wondered what could be up there. Her father, an amateur astronomer and roadside geologist, instilled a love of space and science in Johnson at a young age. She remembers peering into the heavens through binoculars and stopping alongside the highway to look at fossils and unique rock formations.
Now, as a leading figure in the scientific community that studies Mars, Johnson seeks answers to those same questions that she started asking as a young girl. Her quest for answers has taken her to some of the most remote and inhospitable environments on Earth — the McMurdo Dry Valleys in Antarctica, the Atacama Desert in Chile and the salt lakes of Western Australia — and involved closely collaborating with scientists at NASA to design, launch and run spacecraft.
“I feel like planetary scientists have the best job on Earth,” said Johnson. “We get to ask deep questions about the nature of existence, and then send probes made by human hands out into the vastness of space to uncover the answers.”
Johnson conducting research in the salt lakes of Western Australia.
Johnson, who holds dual appointments in the Department of Biology and the School of Foreign Service’s Science, Technology and International Affairs Program, leads a lab at Georgetown that combines techniques from molecular biology and organic geochemistry.
“We spend most of our time trying to understand the presence and preservation of biosignatures within planetary environments — that is, we devise new ways to hunt for signs of life, past and present,” explained Johnson.
Sometimes, that work includes excursions to harsh environments around the globe where life persists against all odds. In deserts and desiccated lakes, Johnson and her team look for subtle signs that life has been there. The biosignatures that the lab researches often reflect interactions between an organism and its environment. Disequilibrium in an environment, such as conspicuous chemical complexity or unexpected accumulations of certain elements, can serve as evidence for the existence of life.
“Fieldwork is one of the best parts of my job,” admits Johnson. “I get to go to the ends of the Earth to find places that bear relevant similarities to other planets and moons—places where we can test our approaches.”
Johnson’s team not only travels to the farthest reaches of the globe, but works with NASA’s Goddard Space Flight Center to analyze samples collected by Mars rovers.
“Sometimes working at the lab bench is just like you’d imagine: we analyze molecules and sequence DNA, and there are centrifuges whirring in the background. Other times the work is a little more sci-fi, like when we don white bunny suits to work with samples that can easily become contaminated,” said Johnson. “We also get to analyze data from current spacecraft, and we all put our heads together to devise new techniques for future missions. It’s a lot of fun, especially when we get a result we didn’t expect.”
Johnson builds upon the legacy of planetary scientists who came before, including Francis J. Heyden, S.J., the eponym of Georgetown’s on-campus observatory.
Some of the most exciting work being done in Johnson’s lab is trying to find new ways to detect life.
“Most strategies for detecting life rely upon finding features known to be associated with life ‘as we know it,’ such as particular classes of molecules, but life may be vastly different on other planets and moons, particularly as we expand our efforts to think about life detection on places like the moons of Jupiter and Saturn — Europa, Enceladus and Titan,” said Johnson. “These places are otherworldly in every sense of the word. Titan, for example, has thick clouds, pale hills and lakes — but it’s a gasoline world. Those lakes are filled with liquid ethane and liquid methane instead of liquid water. What might the chemistry of life look like there? Without presupposing any particular molecular framework, we hope that the new agnostic approaches to life detection we are developing will one day be used from Mars to the far reaches of the solar system.”
Sarah Johnson’s award-winning book, The Sirens of Mars.
For Johnson, the story of science is reflected in a long line of mentors and mentees.
“As I started down my academic journey, I was also incredibly fortunate to have mentors who saw something more in me than I saw in myself, and who took the time and made the effort to provide me with opportunities to grow,” Johnson said.
Like many researchers, Johnson remembers pivotal instructors in her undergraduate career that not only inspired her to pursue her passions but showed her what kinds of career paths were possible.
“I never would have become a planetary scientist, or discovered all the planetary scientists before me, without Ray Arvidson,” said Johnson. “I met him the first day of my freshman year in college and he opened my eyes to Mars science — he taught my classes, gave me a space in his lab and took me to do research all over the country.”
Arvidson, a professor at Washington University in St. Louis, famously served as deputy director of NASA’s Mars Exploration Rover (MER) mission.
“Even though he was helping to run these tremendously complex missions, he always made undergraduate education a priority, both inside and outside of the classroom,” remembered Johnson. “After thirty years of teaching, he’s had an extraordinary influence on the field, and now Mars conferences are completely filled with his former students — what a legacy!”
In her own classrooms and lab, Johnson mentors undergraduates interested in science and gives many the unique opportunity to conduct groundbreaking research in collaboration with some of the brightest minds thinking about outer space. Last year, Johnson Lab alumnae Olivia Gadson (C’23) and Chloe Fishman (C’20) were awarded fellowships through the National Science Foundation’s Graduate Research Fellowship Program, one of the most prestigious fellowship opportunities for graduate students pursuing STEM research.
“Now that I’m in a position to mentor others, I find it incredibly helpful to have had these relationships, since reflecting on them makes it so clear to me that nobody walks their path in life alone,” said Johnson.
“We get to ask deep questions about the nature of existence, and then send probes made by human hands out into the vastness of space to uncover the answers.”
In addition to producing a wealth of research within the scientific community, Johnson has recently branched out into publishing for a wider audience. Her 2020 book, The Sirens of Mars, was a smash hit, receiving wide critical acclaim and being named one of the top books of the year by The New York Times.
Equal parts personal memoir and scientific history, Johnson tells the story of the Red Planet, both its own geological past and humanity’s relationship with it, from a spot in the night sky to a planet populated by spacecraft and robots.
“The Sirens of Mars began as a collection of thoughts that would never find expression in the pages of scientific journals — things I scribbled down as my mind wandered away from a collection of data, and moments I read about, the stories of my colleagues and predecessors that I found inspiring, unlikely or poignant,” said Johnson. “My hope was to reach people who love science but also people who don’t always engage with these topics, to share some of the compelling things about reaching into the night and our fundamentally human drive to explore.”
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