What do Earth’s oceans share with an icy moon orbiting Saturn? For Hannah Zanowski, both might be crucial in addressing a key question: What makes a planet habitable? Zanowski combines her passion for oceanography and astronomy to explore this question by modeling earth and exoplanet oceans and climate.
Zanowski, an assistant professor of atmospheric and oceanic sciences (AOS), studies polar oceanography, using climate models to examine the future of our planet’s oceans.
“My research focuses on polar oceanography and the physics of how our own planet’s ocean works,” Zanowski says. “But truthfully, my first love is astronomy and astrophysics, and to some degree, I should probably have my PhD in astrophysics.”
As an undergraduate student at the University of Arizona, Zanowski majored in physics and mathematics before stumbling upon oceanography. But her interest in astronomy never truly left her.
“I’ve always wondered what it might be like to study oceans on other moons in the solar system, for example, the purported oceans on Enceladus and Europa,” Zanowski explains.
This pair of icy moons are believed to have oceans beneath their frozen surface. “With the huge boom in exoplanet discoveries that we’ve had in the past couple of decades, we have a lot of potential ocean worlds out there, both within and outside of our solar system,” Zanowski says.
Zanowski became involved in exoplanet oceanography a few years ago, when she was placed on a hiring committee for what was then a cluster hire to bring in faculty to research the origins of life, both on our planet and in other parts of the universe. It was here that she first began connecting with researchers in astronomy, chemistry, geoscience, and many other departments.
That collaboration was one of the earliest building blocks of the Wisconsin Center for Origins Research (WiCOR), a center that involves nine different academic departments across campus and the College of Letters & Science (AOS, astronomy, botany, chemistry, integrative biology, physics, geoscience, statistics and bacteriology). WiCOR was created to examine two important questions: How do habitable planets form? How does life emerge on habitable planets?
Zanowski’s research focuses specifically on planetary oceanography — including the relationships between oceans, land and the atmosphere — by modeling early Earth and exoplanet conditions to understand what ultimately makes a planet habitable after it forms.
“There’s a lot of stuff we understand about our planet that people don’t necessarily need to rediscover on other planets,” Zanowski says. “We already have a deep understanding of how the different components of the Earth system interact and the coupling between that and life on our planet. If you want to understand how life could start on other planets, you have to first understand how it started here. It’s the best framework we have.”
The key for a planet to be habitable? Water.
But ocean water, as we understand it, isn’t universal. Oceans on exoplanets can vary wildly in chemical composition, making them potentially vastly different than the oceans we are familiar with on Earth. Some have greater salinity, viscosity and acidity. Some will move differently because of how the planet rotates, how deep they are, or how the winds blow.
To understand the processes that make a planet habitable, Zanowski works with her WiCOR colleagues to model early Earth and exoplanet climates, while also pulling in research from the other WiCOR research themes. In this sense, the rest of the WiCOR team serves as a bridge that spans astronomy, chemistry, geoscience, and other scientific disciplines to elucidate the origins of life.
One of the things Zanowski is studying and modeling is Hycean planets — planets with hydrogen-dominated atmospheres and vast oceans. Due to their unusual chemical makeup, these planets can reveal how these oceans potentially regulate climate, cycle nutrients and support life under conditions different than Earth.
Keeping that distinction front of mind is critical, says Zanowski.
“Earth system models were built to model the Earth specifically, so there are certain assumptions baked into the code that may not be appropriate for a different exoplanet — and you might not even realize you’re making them.”
Zanowski’s research through WiCOR is likely to prove pivotal in understanding the ocean’s role in climatic and atmospheric processes on exoplanets.
“From a climate perspective, what is their role? Do they matter that much for climate on different exoplanets?” Zanowski asks. “How much does the salinity of the ocean matter? How is nutrient cycling affected by the coupling between the deep and surface oceans? How does the ocean behave on ice-covered vs. ice-free worlds?”
These are some of the questions she hopes to explore as her colleagues in astronomy collect more information about exoplanets. But one thing remains constant for her: We need to continue to research and understand Earth’s oceans first.
“I see many avenues for growth in our research, and exoplanet research in general. There are a lot of things we could explore,” Zanowski says. “I am interested in where that’s going to take me, and I’m happy to follow where it leads.”