I am a 51 Pegasi b postdoctoral fellow at UC Berkeley Department of Astronomy. I harness a wide variety of techniques to detect and characterize gas giant planets outside our solar system to explore how planetary systems form and evolve. Currently I am leading a near-infrared high-resolution spectroscopy survey to directly detect thermal emission of gas giant planets in their infancy. With these spectra I measure how fast these planets spin, a new and promising characteristic that provides a unique window into planet accretion histories and can give us clues as to how these planets formed.

Obliquity of an Extrasolar Planetary-Mass Companion

The obliquity of a planet, the orientation of its spin axis relative to its orbital plane, reflects its formation and evolutionary history. We measured the first obliquity of a planetary-mass companion outside the Solar System. We constrained all three of the system's angular momentum vectors: how the companion spin axis, the stellar spin axis, and the orbital plane are inclined relative to our line of sight. While the stellar obliquity marginally prefers alginment, the companion obliquity favors misalignment. Evaluating possible origin scenarios, we found that while collisions, secular spin-orbit resonances, and Kozai-Lidov oscillations are unlikely, formation by gravitational instability in a gravito-turbulent disk appears promising.

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First Constraints on Planetary Angular Momentum Evolution

Rotation rates provide a unique window into planet accretion histories and can give us clues as to how they formed. By doubling the number of planetary spin measurements I placed the first constraints on the spin distribution and angular momentum evolution in this mass regime. These constraints show that planetary spin is set very early on in a planet's lifetime, possibly through interactions between a planet and its circumplanetary disk.

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An Excess of Jupiter Analogs in Super-Earth Systems

Jupiter and Saturn played a significant role in the formation and evolution of the solar system terrestrial planets. However, the role that exoplanet analogs to Jupiter and Saturn play in the formation and evolution of super-Earths, the most common kind of exoplanet, was unknown due to the limited sensitivity of exoplanet detection methods to gas giants at these wide separations. Harnessing the abundance of public RV data for 65 systms hosting inner super-Earths, I searched for long term RV trends indicating the presence of an outer gas giant companion. I found that super-Earth systems have more Jupiter analogs than you would expect just based on chance, indicating that these outer gas giant planets either actively help super-Earth formation, or are instead signposts of favorable formation conditions.

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Occurrence of Long-Period Gas Giant Planets

Characterizing the statistical properties of long-period gas giant planets presents an exciting avenue to explore how inner solar systems form and evolve. I led a Doppler survey at Keck to search for long-period gas giant companions in 123 known planetary systems. I found that hot gas giants seem to be more likely to have an outer companion than cold gas giants, and that planets in multi-body systems have higher average eccentricities than do single-planet systems. These both indicate that dynamical interactions between planets play an important role in the evolution of these systems.

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Searching for Scatterers

Direct imaging surveys have uncovered an unexpected population of massive gas giants on extremely wide orbits that challenge convential formation models. One proposed formation pathway is that these companions formed closer in to their host stars and were subsequently scattered out to where we see them today by a more massive body in the system. I led a direct imaging survey using NIRC2 at Keck to search for potential scatterers in these systems. I found that there were no additional companions in these systems above our detection limits, and that constraints on eccentricity distributions for two previously confirmed wide-separation companions favored low to moderate eccentricities. Both of these findings disfavor the scattering scenario as a dominant formation pathway for this population.

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CV and Publications

PhD Astrophysics, Caltech, 2018
MS Astrophysics, Caltech, 2014
BA Astrophysics, Harvard University, 2012

Download a pdf version of my CV here.

Contact Information

email: martalbryan AT berkeley DOT edu
office: Campbell Hall 249
mail: Department of Astronomy
501 Campbell Hall
University of California
Berkeley, CA 94720-3411