Sarah C. Millholland

About

I am an Assistant Professor of Physics at the Massachusetts Institute of Technology in the Kavli Institute for Astrophysics and Space Research. As a data-driven dynamicist, I am 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.

Biographical sketch

Before starting at MIT in July 2022, I was a NASA Sagan Fellow at Princeton University from July 2020-June 2022. 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.

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.

• "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]

• "Edge-of-the-Multis: Evidence for a Transition in the Outer Architectures of Compact Multi-Planet Systems." (Millholland et al. 2022) [ADS]
• "Kepler Multi-Planet Systems Exhibit Unexpected Intra-system Uniformity in Mass and Radius." (Millholland et al. 2017) [ADS]

• "New Constraints on Gliese 876 -- Exemplar of Mean-Motion Resonance." (Millholland et al. 2018) [ADS]

• "Tidally-Induced Radius Inflation of Sub-Neptunes." (Millholland 2019) [ADS]

Publications

(underline=student supervised by S.C.M.)

First Author Publications

1. Millholland, S. & Winn, J. "A New Era in Exoplanetary Dynamics: Discoveries and Prospects with JWST." 2024, PNAS, in review
2. Millholland, S., MacLeod, M., & Xiao, F. "Empirical Constraints on Tidal Dissipation in Exoplanet Host Stars." 2024, ApJ, in review
3. Millholland, S., Lara, T., & Toomlaid, J. "Spin Dynamics of Planets in Resonant Chains." 2024, ApJ, 961, 203 [ADS]
4. Millholland, S., He, M., & Zink, J. "Edge-of-the-Multis: Evidence for a Transition in the Outer Architectures of Compact Multi-Planet Systems." 2022, AJ, 164, 72 [ADS]
5. Millholland, S. & Winn, J. "Split Peas in a Pod: Intra-System Uniformity of Super-Earths and Sub-Neptunes." 2021, ApJL, 920, L34 [ADS]
6. 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]
7. Millholland, S. & Spalding, C. "Formation of Ultra-Short-Period Planets by Obliquity-Driven Tidal Runaway." 2020, ApJ, 905, 71 [ADS]
8. Millholland, S., Petigura, E., & Batygin, K. "Tidal Inflation Reconciles Low-Density Sub-Saturns with Core Accretion." 2020, ApJ, 897, 7 [ADS]
9. Millholland, S. "Tidally-Induced Radius Inflation of Sub-Neptunes." 2019, ApJ, 886, 72 [ADS]
10. Millholland, S. & Batygin, K. "Excitation of Planetary Obliquities Through Planet-Disk Interactions." 2019, ApJ, 876, 119 [ADS]
11. Millholland, S. & Laughlin, G. "Obliquity-Driven Sculpting of Exoplanetary Systems." 2019, Nature Astronomy, 3, 424, arXiv: 1903.01386 [ADS]
12. Millholland, S. & Laughlin, G. "Obliquity Tides May Drive WASP-12b's Rapid Orbital Decay." 2018, ApJL, 869, L15 [ADS]
13. Millholland, S., Laughlin, G., Teske, J., et al. "New Constraints on Gliese 876 -- Exemplar of Mean-Motion Resonance." 2018, AJ, 155, 106 [ADS]
14. 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]
15. Millholland, S. & Laughlin, G. "Supervised Learning Detection of Sixty Non-Transiting Hot Jupiter Candidates." 2017, AJ, 154, 83 [ADS]
16. 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]
17. 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. Suar, S. & Millholland, S. "Planetary Obliquity Excitation Through Pre-Main Sequence Stellar Evolution." 2024, AAS Journals, in review
2. Liveoak, D. & Millholland, S. "Formation of Close-in Neptunes Around Low-Mass Stars Through Breaking Resonant Chains." 2024, ApJ, 974, 207 [ADS]
3. Louden, E. & Millholland, S. "Polar Neptunes are Stable to Tides." 2024, ApJ, 974, 304 [ADS]
4. Gupta, A., Millholland, S., Im, H., et al. "A Hot Jupiter Progenitor on a Super-Eccentric, Retrograde Orbit." 2024, Nature, 632, 50 [ADS]
5. Sobski, N. & Millholland, S. "Can Cold Jupiters Sculpt the Edge-of-the-Multis?" 2023, ApJ, 954, 137 [ADS]
6. Jensen, D. & Millholland, S. "Inferred Properties of Planets in Mean-Motion Resonances are Biased by Measurement Noise." 2022, AJ, 164, 144 [ADS]
7. Weiss, L., Millholland, S., Petigura, E., Adams, F., Batygin, K., Bloch, A., & Mordasini, C. "Architectures of Compact Multi-planet Systems: Diversity and Uniformity." 2022, Protostars and Planets VII book chapter, arXiv: 2203.10076 [ADS]
8. 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]
9. Spalding, C. & Millholland, S. "Stellar Oblateness versus Distant Giants in Exciting Kepler Planet Mutual Inclinations." 2020, AJ, 160, 105 [ADS]
10. 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. Lockley, I., Armstrong, D., Fernandez Fernandez, J., Millholland, S., et al. "The TOI-1117 Multi-planetary System: 3 sub-Neptunes, 1 in both the Neptunian Desert and Radius Valley." 2024, MNRAS, in review
2. Kunimoto, M., Zifan, L., Millholland, S., et al. "Two Earth-size Planets and an Earth-size Candidate Transiting the Nearby Star HD 101581." 2024, AJ, in press
3. Lu, T., An, Q., Li, G., Millholland, S., Brandt, G. M., Brandt, T. D. "Planet-Planet Scattering and ZLK Migration: The Dynamical History of HAT-P-11." 2024, ApJ, in review [ADS]
4. Dai, F., Goldberg, M., Batygin, K., et al. including Millholland, S. [14 total] "The Prevalence of Resonance Among Young, Close-in Planets." 2024, AJ, 168, 239 [ADS]
5. Burt, J., Hooton, M., Mamajek, E., Barragan, O, Millholland, S., et al. [15 total] "TOI-1685 b is a Hot Rocky Super-Earth: Updates to the Stellar and Planet Parameters of a Popular JWST Cycle 2 Target." 2024, ApJL, 971, L12 [ADS]
6. Leleu, A., Delisle, J., Burn, R., Izidoro, A., Udry, S., Dumusque, X., Lovis, C., Millholland, S., et al. [15 total] "Resonant Sub-Neptunes are Puffier." 2024, A&A, 687, L1 [ADS]
7. Burdge, K., El-Badry, K., Kara, E., Canizares, C., Chakrabarty, D., Frebel, A., Millholland, S., Rappaport, S., Simcoe, R., Vanderburg, A. "The black hole low mass X-ray binary V404 Cygni is part of a wide hierarchical triple, and formed without a kick." 2024, Nature, in review [ADS]
8. Fairnington, T., Nabbie, E., Huang, C., Zhou, G., Foo, O., Millholland, S., et al. "TOI-5126: A hot super-Neptune and warm Neptune pair discovered by TESS and CHEOPS." 2024, MNRAS, 527, 8768 [ADS]
9. Louden, E., Laughlin, G., & Millholland, S. "Evidence for Two Dissipation Regimes Among the Short-Period Exoplanets." 2023, ApJL, 958, L21 [ADS]
10. Murgas, F., Castro-González, A., Pallé, Pozuelos, F., Millholland, S., Foo, O., et al. "Two super-Earths at the edge of the habitable zone of the nearby M dwarf TOI-2095." 2023, A&A, 677, A182 [ADS]
11. Lu, T., Rein, H., Tamayo, D., Hadden, S., Mardling, R., Millholland, S., & Laughlin, G. "Self-Consistent Spin, Tidal and Dynamical Equations of Motion in the REBOUNDx Framework." 2023, ApJ, 948, 41 [ADS]
12. Bozhilov, V., Antonova, D., Hobson, M., Brahm, R., Jordan, A., et al. including Millholland, S. "A 2:1 Mean-Motion Resonance Super-Jovian Pair Revealed by TESS, FEROS, and HARPS." 2023, ApJL, 946, L36 [ADS]
13. Zhao, L., Kunovac, V., Brewer, J., Llama, J., Millholland, S., et al. [11 total] "Measured Spin-Orbit Alignment of Ultra-Short Period Super-Earth 55 Cancri e." 2023, Nature Astronomy, 7, 198 [ADS]
14. Stefansson, G., Mahadevan, S., Petrovich, C., Winn, J., Kanodia, S., Millholland, S., et al. [37 total] "The Warm Neptune GJ 3470b has a Polar Orbit." 2022, ApJL, 931, 15 [ADS]
15. 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]
16. 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]
17. 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]
18. 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]
19. 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]
20. 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

ADDRESS
MIT Kavli Institute for Astrophysics and Space Research
Massachusetts Institute of Technology
77 Massachusetts Avenue, Building 37, Room 611
Cambridge, Massachusetts 02139

EMAIL
sarah.millholland[at]mit.edu

Contact

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