“I love to push the theories out of their comfort zone. I want to see the theoreticians scratching their heads, not knowing what’s going on. Some of my results directly challenged the current models, and I love that—I see this as an opportunity to get better models and refine our theoretical understanding.”

Juan Ignacio Espinoza-Retamal, PH.D.

Picture our home solar system: a neat stack of planets orbiting the Sun like grooves on a record, all spinning in the same flat plane. Now imagine the opposite—planets moving in wildly tilted orbits, misaligned with their stars and with one another. These seemingly chaotic architectures are more common than once expected. Dr. Juan Ignacio Espinoza-Retamal wants to understand why and what that means for the history of planetary systems, including our own. 

His own origin story unfolded in a small city in Chile, far from traditional scientific hubs. Dr. Espinoza-Retamal had always been enthralled by the vastness of the universe and the planets in our solar system, but he knew little about exoplanets. A visit to the Cerro Tololo Inter-American Observatory and a chance conversation during his final undergraduate year changed everything. Today, he studies the geometries of planetary systems, tracing these physical clues back to the formation and evolution of solar systems. 

For decades, astronomers have studied the geometries and origins of primarily Hot Jupiters, the massive gas giants easy to detect with existing instruments. Dr. Espinoza-Retamal is eager to push beyond these limits by measuring the tilts of smaller exoplanets similar to Neptune. He also wants to understand their connection to Cold Jupiters—giant planets orbiting far from their host stars, like the Jupiter of our home solar system. This will be possible thanks to the Gaia space mission and its astrometry technique, which detects planets through their gravitational tugs and is uniquely sensitive to orbital orientations. The latest Gaia data release is exactly what Dr. Espinoza-Retamal needs to tell a more complete story about planetary systems. 

From his personal path to the frontiers of exoplanet research, Dr. Espinoza-Retamal knows that science—and the scientific field—is stronger when we challenge biases based on limited evidence and perspectives. Through talks and mentoring, he encourages enthusiastic young researchers from backgrounds underrepresented in planetary science, particularly those from Latin America.  

As a 51 Pegasi b Fellow, Dr. Espinoza-Retamal will employ two complementary methods. First, using the world’s best Doppler instruments, which measure frequency shifts in starlight, he will gauge stellar obliquities—how aligned a planet’s orbit is with its host star’s equator. Second, using Gaia astrometric data, he will search for planets and measure mutual inclinations—how aligned planets are within the same system. Together, these measurements will help reveal the dynamical pathways that produce the stunning diversity of planetary systems spinning across the universe. 

Dr. Espinoza-Retamal received his Ph.D. in astrophysics from Pontificia Universidad Católica de Chile in Summer 2025.