There are, she explains, 100 billion stars in our galaxy, most orbited by at least one planet, and over 100 billion galaxies beyond ours. That’s about 1022 stars in the universe. The likelihood that only Earth was able to produce life “I think is pretty low,” Shields says.
“I’m looking for planetary environments that could be conducive to life beyond Earth,” she says. “And my team does that largely using climate models. These are the same kinds of models that can predict climate and weather on Earth.”
Shields plugs information gathered by observational astronomers into such models, along with different potential combinations of other, unknown variables—like the type of light a planet receives from its host star, the composition of its atmosphere and surface, and certain orbital information. “There’s only so much that you can really tell about a planet from the telescope information that you get,” she explains. “We can explore that parameter space with climate models and say: Okay, if it has this surface composition, this is what the temperature would be like on this planet. If it has this atmospheric composition, this type of orbit, this is what the climate would be like, and this is how habitable it would be across its surface.”
Since the early 1990s, astronomers have discovered 6,000 exoplanets. Shields says those in Earth’s size range—in which she’s most interested—number in the hundreds. A smaller subset of those are orbiting in what’s called the “habitable zone” of their star, creating warm enough conditions to maintain water in liquid form—the key to life. So far, as many as 100 or so planets that fall into that category have been identified, but the James Webb Space Telescope, launched in 2021, could find even more potentially habitable planets by detecting “biosignatures” suggesting a biological presence, such as particular gases in their atmospheres or glints that might be reflections of water on the planetary surface.
Being able to detect more of these sorts of signals, Shields says, is the next “big mission” in astronomy.
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Today, in her academic work, her mind hurtles to the farthest reaches of the universe. But in her precious hours outside of academia, she has learned to be still. When her work schedule started to overwhelm her, Shields’s health began to suffer. Then she discovered the practice of yoga nidra—an ancient form of meditation in which practitioners are guided into a deeply restful “yogic sleep.” Shields read the book Do Less: A Revolutionary Approach to Time and Energy Management for Ambitious Women, which claims that 20 or 30 minutes of yoga nidra “feels like three hours of sleep in your body,” she says. “And as the mother of a young child, I was like: Okay, sign me up!”
Last year she trained with Karen Brody, author of Daring to Rest: Reclaim Your Power with Yoga Nidra Rest Meditation, and became a certified facilitator. “It’s been important to me to share it broadly and to really try to do my part to introduce the culture of academia, in particular, to this notion of resting as a daily practice,” she says. Now she’s at work on a book about her attempt to moderate—to resist the temptation to take on too much. She has learned to decline invitations and put firm boundaries between her work and personal life.
Shields has realized that her seemingly disparate interests in astronomy and acting don’t have to be mutually exclusive. Combining them makes her a more effective educator.
On a weekday in August, an ayurvedic soup simmers on her kitchen stove. A music stand occupies the corner of a room where she sometimes picks up her violin and plays fiddle tunes. (Her parents, both professional musicians, derived her name from a chant of vowel sounds they made up.) She mentions the poem “swim | women of color”by Nayyirah Waheed and recites it in a soft, rich voice. Part of it goes: “This structure counts on your inability to say no. mean no. they take no from our first breath. go back and return it to your mouth. your heart. your light.”