Sarah Stewart Johnson | The Explorers Club 50

Sarah and Scott Tighe collecting samples from an ancient lakebed in the McMurdo Dry Valleys, wearing Tyvek suits to protect cells preserved for millions of years from contamination Author: Dave Goerlitz

Planetary Scientist

beyond the blue dot

meet sarah

Sarah Stewart Johnson seeks to understand the presence and preservation of biosignatures, or traces of life, within planetary environments on Earth and in space. Her lab at Georgetown University is also involved in active planetary exploration, analyzing data from current spacecraft and devising new techniques for future missions. She has served on the science teams for NASA’s Spirit, Opportunity, and Curiosity Rovers and is a Visiting Scientist with NASA Goddard’s Planetary Environments Lab. She has also written for the New Yorker, New York Times, Los Angeles Times, and Boston Globe, and her recent book, The Sirens of Mars, was selected as one of the New York Times 100 Notable Books of 2020.

Nominated by: Milbry Polk, MED' 95

Class of 2024 Location USA

Follow sarah's work:

Sarah and her graduate student Maggie Weng doing field work in the Atacama Desert, the driest place on Earth other than the poles Author: Elena Zaikova

Answering life’s deepest questions is, to me, the highest purpose of exploration, and my work searching for life in the universe has brought me face to face with many of those questions. Where did we come from? Why is there something and not nothing? How can life adapt to the harshest environments imaginable and still survive? Of all these questions, none is more important to me than knowing if we are alone in the universe.

Scientifically, the discovery of life beyond Earth would revolutionize biology as completely as the discovery of gravity revolutionized physics. It would provide a second data point beyond the carbon-based, DNA-based life we know on Earth, opening up a new world of research possibilities. On a human level, finding a second genesis would give us deep insight into the nature of our own existence, upending long-held philosophical and theological assumptions, provoking thrilling new questions: How many times has life emerged in the universe? How many wondrous forms exist—and how do they compare to us? Is life a predictable consequence of energetic systems, or are we more than that? What could a discovery tell us about the future of our human project?

After decades of investment in space exploration, I believe that making this breakthrough is now, finally, within our reach. I feel incredibly fortunate to be part of this endeavor.

Members of Mars Exploration Rover Science Team, including Sarah, looking at data just returned from Meridiani Planum, Mars Author: John Beck

Sarah making geochemical measurements in Western Australia Author: Bethany Ehlmann

“In the quest to find life beyond our planet, we are not just exploring the cosmos; we are challenging the limits of our imagination and reshaping the very fabric of what it means to be alive in the universe.”

- Sarah Stewart Johnson

Sarah collecting samples from Lake Magic, an acid salt lake in Western Australia with mineralogy similar to Mars Author: John Lavinsky

My favorite project right now involves not trying to detect life as we know it but trying to detect life as we don’t know it. It arose from reflecting on how, time and again, we’ve been bowled over by the strangeness of other worlds. For instance, we know of no planet more similar to Earth than Mars, and yet Mars is indescribably foreign. Mars lacks plate tectonics, a magnetic field, and has a minimal protective atmosphere. An electrostatic dust, the consistency of red flour, coats the surface, lofted by dust devils into the achingly thin air. The terrain is ancient, exposed to radiation, and bewilderingly empty.

As we search for life there, our detection methodologies and expectations too often presume that the life we seek is similar to the life we know from Earth, focusing on familiar signatures of biologic processes, such as certain classes of molecules. However, we can also search for more general and inclusive indications of life without presupposing any specific underlying biochemistry or particular molecular framework.

I’m currently leading a team called the Laboratory for Agnostic Biosignatures, devising ways to detect signs of things like chemical complexity, elemental and isotopic accumulations, chemical disequilibrium, and even energy transfer. I love this project because it forces me to contend with the truly alien, like trying to imagine a color I’ve never seen. I hope the new tools and techniques we’re developing will one day be used to look for life from Mars to the far reaches of our Solar System—including places like the icy moons of Jupiter and Saturn—and eventually, perhaps, even planets around other stars.

Sarah exploring the desert of Al Dhafra on the back of a camel Author: Maria Gutiérrez

Sarah in the lab with Georgetown undergraduate Angela Bai Author: Paul Jones

Sarah in the lab supervising DNA extractions by Georgetown undergraduate Angela Bai Author: Paul Jones

Sarah marveling at the first rover image beyond the rim of Endurance Crater, Mars, projected on the walls of mission control at NASA’s Jet Propulsion Laboratory Author: John Beck

Sarah climbing aboard a helicopter bound for the McMurdo Dry Valleys Author: Dave Goerlitz

Sarah and her graduate student Maggie Weng exploring the Atacama Desert as a Mars analog environment Author: Elena Zaikova

VIEW THE EC50 2024 PRINT PUBLICATION