About

I am a data-driven dynamicist interested in a broad range of problems in exoplanetary science. In particular, I study the formation and evolution, orbital architectures, and interiors/atmospheres of exoplanets. I address these problems using a synergistic approach involving celestial mechanics theory, numerical simulations, and statistical methods.

I am currently a NASA Sagan Fellow at Princeton University. In Fall 2022, I will start as an Assistant Professor at MIT. I obtained my PhD in Astronomy from Yale University in May 2020, and I was an NSF Graduate Research Fellow from 2017-2020. My thesis was titled "Data-Driven Dynamics of Planetary Systems". I spent my first year of graduate school at the University of California Santa Cruz and subsequently transferred to Yale to keep working with my advisor, Professor Greg Laughlin. Before that, I was an undergraduate student and Goldwater Scholar at the University of St. Thomas in St. Paul, Minnesota, where I obtained bachelor's degrees in physics and applied mathematics in 2015.

Hiking next to Lake Michigan in Ludington, MI.

Research

Investigating Exoplanet Orbits and Interiors using Data-Driven Dynamics

Our galaxy contains an abundance of planets that exhibit physical and orbital properties much different from those represented in our own Solar System. Some planets have orbits as small as a few stellar radii and as large as 100 AU; some are as dense as iron while others are puffier than styrofoam; some have highly eccentric and misaligned orbits while others are circular and flat. What generates this diversity? Are there predictable connections between the initial star and protoplanetary disk properties and the final planetary systems we see today?

My research aims to understand the demographics and diversity of extrasolar planetary systems. I use orbital dynamics and theory to study patterns in the observed planetary orbital architectures. This refers to properties like the spacings, eccentricities, inclinations, axial tilts, and planetary size relationships. I specialize in investigating how gravitational interactions like tides, resonances, and spin dynamics sculpt observable exoplanet properties. I have also studied planetary interiors and atmospheres and am interested in the cross-section between orbital dynamics and planetary physical properties. I tend to work closely with data and enjoy following observational mysteries when they arise.

For more information, please see a selection of representative papers below.

Planetary obliquities and tidal orbital dynamics:
  • "Formation of Ultra-Short-Period Planets by Obliquity-Driven Tidal Runaway." (Millholland & Spalding 2020) [ADS]
  • "Obliquity-Driven Sculpting of Exoplanetary Systems." (Millholland & Laughlin 2019) [ADS]
Architectures of short-period systems:
  • "Kepler Multi-Planet Systems Exhibit Unexpected Intra-system Uniformity in Mass and Radius." (Millholland et al. 2017) [ADS]
Resonant planetary systems:
  • "New Constraints on Gliese 876 -- Exemplar of Mean-Motion Resonance." (Millholland et al. 2018) [ADS]
Planetary atmospheres and tidal heating:
  • "Tidally-Induced Radius Inflation of Sub-Neptunes." (Millholland 2019) [ADS]

Publications

First Author Publications

  1. Millholland, S. & Winn, J. "Split Peas in a Pod: Intra-System Uniformity of Super-Earths and Sub-Neptunes." 2021, ApJL, 920, L34 [ADS]
  2. Millholland, S., He, M., Ford, E., et al. "Evidence for a Non-Dichotomous Solution to the Kepler Dichotomy: Mutual Inclinations of Kepler Planetary Systems from Transit Duration Variations." 2021, AJ, 162, 166 [ADS]
  3. Millholland, S. & Spalding, C. "Formation of Ultra-Short-Period Planets by Obliquity-Driven Tidal Runaway." 2020, ApJ, 905, 71 [ADS]
  4. Millholland, S., Petigura, E., & Batygin, K. "Tidal Inflation Reconciles Low-Density Sub-Saturns with Core Accretion." 2020, ApJ, 897, 7 [ADS]
  5. Millholland, S. "Tidally-Induced Radius Inflation of Sub-Neptunes." 2019, ApJ, 886, 72 [ADS]
  6. Millholland, S. & Batygin, K. "Excitation of Planetary Obliquities Through Planet-Disk Interactions." 2019, ApJ, 876, 119 [ADS]
  7. Millholland, S. & Laughlin, G. "Obliquity-Driven Sculpting of Exoplanetary Systems." 2019, Nature Astronomy, 3, 424, arXiv: 1903.01386 [ADS]
  8. Millholland, S. & Laughlin, G. "Obliquity Tides May Drive WASP-12b's Rapid Orbital Decay." 2018, ApJL, 869, L15 [ADS]
  9. Millholland, S., Laughlin, G., Teske, J., et al. "New Constraints on Gliese 876 -- Exemplar of Mean-Motion Resonance." 2018, AJ, 155, 106 [ADS]
  10. Millholland, S., Wang, S., & Laughlin, G. "Kepler Multi-Planet Systems Exhibit Unexpected Intra-system Uniformity in Mass and Radius." 2017, ApJL, 849, L33 AAS Nova [ADS]
  11. Millholland, S. & Laughlin, G. "Supervised Learning Detection of Sixty Non-Transiting Hot Jupiter Candidates." 2017, AJ, 154, 83 [ADS]
  12. Millholland, S. & Laughlin, G. "Constraints on Planet Nine's Orbit and Sky Position within a Framework of Mean-motion Resonances." 2017, AJ, 153, 91 [ADS]
  13. Millholland, S., Wang, S., & Laughlin, G. "On the Detection of Non-Transiting Hot Jupiters in Multiple Planet Systems." 2016, ApJL, 823, L7 [ADS]

Second Author Publications

  1. Weiss, L., Millholland, S., Petigura, E., Adams, F., Batygin, K., Bloch, A., & Mordasini, C. "Architectures of Compact Multi-planet Systems: Diversity and Uniformity." Protostars and Planets VII, submitted
  2. Lillo-Box, J., Millholland, S., & Laughlin, G. "Follow-up of Non-Transiting Planets Detected by Kepler: Confirmation of Three Hot Jupiters and Validation of Three Other Planets." 2021, A&A, 654, 9 [ADS]
  3. Spalding, C. & Millholland, S. "Stellar Oblateness versus Distant Giants in Exciting Kepler Planet Mutual Inclinations." 2020, AJ, 160, 105 [ADS]
  4. Adams, A. D., Millholland, S., & Laughlin, G. "Signatures of Obliquity in Thermal Phase Curves of Hot Jupiters." 2019, AJ, 158, 3 [ADS]

Other Co-Author Publications

  1. Azari, A., Biersteker, J., Dewey, R., Doran, G., et al. including Millholland, S. [16 total] "Integrating Machine Learning for Planetary Science: Perspectives for the Next Decade." 2021, BAAS, 53, 128 (white paper) [ADS]
  2. Davis, A., Wang, S., Jones, M., Eastman, J., Günther, M., Stassun, K., et al. including Millholland, S. [51 total] "TOI 564 b and TOI 905 b: Grazing and Fully Transiting Hot Jupiters Discovered by TESS." 2020, AJ, 160, 229 [ADS]
  3. Bryan, M., Chiang, E., Bowler, B. P., Morley, C. V, Millholland, S., Blunt, S., Ashok, K. B., Nielsen, E., Ngo, H., Mawet, D., Knutson, H. A. "First Measurement of an Extrasolar Planetary-Mass Companion Obliquity." 2020, AJ, 159, 181 [ADS]
  4. Wang, S., Jones, M., Shporer, A., Fulton, B. J., Paredes, L. A., Trifonov, T., Kossakowski, D., Eastman, J., Redfield, S., Günther, M. N., Kreidberg, L., Huang, C. X., Millholland, S., et al. [60 total]  "HD 202772Ab: A Transiting Hot Jupiter Around a Bright, Mildly Evolved Star in a Visual Binary Discovered by TESS." 2019, AJ, 157, 51 [ADS]
  5. Becker, J. C., Khain, T., Hamilton, S. J., Adams, F. C., Gerdes, D. W., Zullo, L., Franson, K., Millholland, S., et al. [66 total] "Discovery and Dynamical Analysis of an Extreme Trans-Neptunian Object with a High Orbital Inclination." 2018, AJ, 156, 81 [ADS]
  6. Janvier, M., Savcheva, A., Pariat, E., Tassev, S., Millholland, S., Bommier, V., McCauley, P., McKillop, S., Dougan, F. "Evolution of Flare Ribbons, Electric Currents and Quasi-separatrix Layers During an X-class Flare." 2016, A&A, 591, A141 [ADS]

Contact

Peyton Hall, Princeton University.
Photo credit: Chang-Goo Kim
ADDRESS
Department of Astrophysical Sciences
Princeton University
4 Ivy Lane
Princeton, NJ 08544

EMAIL
sarah.millholland[at]princeton.edu

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