Life on Other Worlds

Astrobiology, or the study of and search for life in the universe, brings together many different kinds of science. Some astrobiologists study life on Earth-- especially life in extreme environments-- to uncover the limits of where life might exist. Some of their investigations have led to life in such surprising places, it may as well seem alien to humans. (Image Credit: NASA/JPL-Caltech/T. Pyle (SSC))

Astrobiologist Dr. Nathalie A. Cabrol explores high altitude lakes in the Andes as analogs to early Mars. She documents life’s adaptation to extreme environments, the effect of rapid climate change on lake ecosystems and habitats, its geobiological signatures, and relevance to planetary exploration. Dr. Cabrol is the Director of the Carl Sagan Center for Research at the SETI Institute, where she leads the strategic vision for science and exploration. She heads projects in planetary science and astrobiology, develops science exploration strategies for Mars, Titan, and the Outer Solar System icy moons, and designs robotic field experiments. (Image courtesy SETI Institute)

Just recently, a stinky molecule known as phosphine was detected in the atmosphere of our neighboring planet, Venus. You might wonder why anyone would care about a smelly gas on another planet-- but phosphine is an example of a biosignature, a chemical compound that we think might point to the existence of life. Finding phosphine doesn’t necessarily mean that life exists on Venus-- there need to be follow up investigations to be sure-- but it’s definitely an exciting hint that something interesting might be happening there. (Image Credit: ISAS, JAXA, Akatsuki)

Besides studying life on Earth, and looking at neighboring planets and moons, many astrobiologists hope to discover life on planets outside our solar system, orbiting other stars. These planets, known as exoplanets, were first discovered in the mid-1990s, but for over 20 years after, finding them was hardscrabble work. It was especially hard to find planets that might be small and rocky, like Earth, Venus, and Mars are. Since those planets are some of the prime places to look for life in our solar system, astrobiologists hoped to find them around other stars, too. (Image Credit: NASA-JPL/Caltech)

Astronomers look for planets that are similar to Earth, because Earth is still the only planet we know definitely has life on it. But if life on Earth can live in a lot of different environments, how do we figure out where alien life might be? And what does it mean for a planet to be “like Earth”? Astronomers start with looking for planets that are roughly the same size as the terrestrial planets in our solar system that have (or might have had) life: Earth, Venus, and Mars. Ideally, they also want to find planets in what’s called the habitable zone. (Image Credits: NASA Ames/SETI Institute/JPL-Caltech)

Different kinds of stars emit different amounts and energies of light, so the location of the habitable zone changes depending on what kind of star a planet is orbiting. Stars that are smaller than our sun emit only a little bit of light, and their light is mostly red, low-energy light, while stars that are bigger than our sun emit lots of highly energetic, blue light. You can think of the location of the habitable zone like where you’d sit around a campfire to be warm: if you are around a big, blazing bonfire, you’d want to sit farther away to be warm (but not too hot!), and if your fire was small, you’d need to sit closer to the fire to be warm enough. (Image Credit: NASA/Kepler Mission/Dana Berry)

Dr. Aomawa Shields is a Clare Boothe Luce Associate Professor in the Department of Physics & Astronomy at UC Irvine, and an astrobiologist whose research focuses on exploring the possible climates and potential habitability of Earth-sized planets orbiting cool, low-mass stars. Because exoplanets are so far away, it can be challenging to know what their climate might be like-- so Dr. Shields uses computer models, along with observational data from space- and ground-based observatories, to carry out her research. In addition to her award-winning scientific research, Dr. Shields is also the Founder and Director of the organization Rising Stargirls, which encourages girls of all colors and backgrounds to explore and discover the universe using theater, writing, and visual art. She is the proud mother of 3 year old rising stargirl Garland-Rose, who she and husband Steven have deemed the most extraordinary lifeform in their universe. (Image Courtesy of Ryan Lash/TED)

Of course, finding signs of life from biosignatures might tell us life is there, but it doesn’t tell us everything we might want to know. After all, the organism that has arguably had the biggest effect on Earth’s atmosphere-- cyanobacteria-- isn’t the kind of life people often picture when they think of aliens. You owe a lot to cyanobacteria, whether you know it or not: without them, the Earth’s atmosphere wouldn't be full of the oxygen human beings need to breathe. But when most people picture “aliens”, they often think about life that we might be able to communicate with. 

Dr. Jill Tarter has spent the majority of her professional career attempting to answer the old human question “Are we alone?” by searching for evidence of technological civilizations beyond Earth-- you may even be familiar with her work as portrayed by Jodie Foster in the movie Contact! Dr. Tarter is the Emeritus Chair for SETI Research at the SETI Institute in Mountain View, California. She served as Project Scientist for NASA’s SETI program, the High Resolution Microwave Survey and has conducted numerous observational programs at radio observatories worldwide. She is a Fellow of the AAAS, the California Academy of Sciences, and the Explorers Club, she was named one of the Time 100 Most Influential People in the World in 2004, and one of the Time 25 in Space in 2012, received a TED prize in 2009, two public service awards from NASA, multiple awards for communicating science to the public, and has been honored as a woman in technology. Since the termination of funding for NASA’s SETI program in 1993, she has served in a leadership role to design and build the Allen Telescope Array and to secure private funding to continue the exploratory science of SETI. (Image Courtesy of Seth Shostak).