I study planets orbiting other stars

I use telescopes on the ground and in space to search for planets, probe their atmospheres, measure their masses, and constrain their bulk compositions. I am curious about how planets form and evolve with time, the frequency of planetary systems in the Galaxy, and the prospects for detecting life on planets outside of our Solar System. I am currently serving on the "Exoplanets, Astrobiology, and the Solar System" panel for the Astro2020 Decadal Survey.

How common are planetary systems?

My research group is interested in the prevalence of planetary systems orbiting other stars and how the properties of those planets depend on the characteristics of the host star. We tend to concentrate on stars known as "M Dwarfs." These stars, also dubbed "Red Dwarfs," are significantly smaller than the Sun and are the most common type of star in the galaxy. Exploring the properties of planetary systems orbiting M dwarfs allows us to estimate the overall frequency of planetary systems and test models of planet formation.

Related Publications: Dressing et al. 2017; Dressing & Charbonneau 2015

Which planets are rocky?

Our solar system features two main types of planets. Mercury, Venus, Earth, and Mars are all terrestrial (rocky) planets while the outer planets (Jupiter, Saturn, Uranus, and Neptune) are dominated by gas and ice. By using the radial velocity ("Doppler Wobble") technique to measure the masses of planets orbiting other stars and the transit technique to measure planet radii, my group is determining the bulk densities of planets and constraining their bulk compositions. We aim to determine which planets could have rocky surfaces like the Earth.

Related Publications: Mayo et al. 2019; Dressing et al. 2018, 2015

Which planets are habitable?

One of the driving questions in exoplanet research is the question of whether planetary systems orbiting other stars might support life. My group is investigating the impact of stellar activity and high-energy stellar radiation on planetary systems in order to determine which planets might be suitable places for life.

Science Lead: Ellie Schwab Abrahams

Selected Recent Publications

The blurbs below are summaries of recent work by my group. For a complete list of publications, please see my CV.

  • An 11 Earth-mass, Long-Period Sub-Neptune Orbiting a Sun-like Star

    Mayo et al. (2019, accepted to AJ, arXiv:1908.08585)

    Lead author graduate student Andrew Mayo used archival radial velocities (RVs) from Keck/HIRES and new RVs from TNG/HARPS-N to determine the mass of Kepler-538b, a 2.2 Earth-radius planet with an orbital period of 81 days. Kepler-538b is the smallest planet with an orbital period longer than 50 days and an RV mass measurement. Andy was able to push RV mass measurement to longer orbital periods by employing a Gaussian process to model both the radial velocities and the full-width half-maximum of the cross-correlation function.

  • Characterizing K2 Candidate Planetary Systems IV: Updated Properties for 86 Cool Dwarfs Observed During Campaigns 1-17

    Dressing et al. (2019, AJ)

    Using distances derived from Gaia DR2 and medium-resolution near-infrared spectra obtained with IRTF/SpeX and Palomar/TSPEC, we determined the spectral types, temperatures, masses, radii, and metallicities of possible cool dwarfs suspected to host transiting planets. Compared to the radii reported in the Ecliptic Plane Input Catalog, our revised stellar radii are 40% larger, indicating that the radii of associated planet candidates are also likely to be underestimated.

  • Characterizing K2 Candidate Planetary Systems III: A High-Mass and a Low Envelope Fraction for the Warm Neptune K2-55b

    Dressing et al. (2018, AJ)

    By obtaining radial velocities with Keck/HIRES, we measured the mass of the Neptune-sized planet K2-55b and discovered that it can be modeled as a rocky planet capped by a modest H/He envelope (12% of the planet mass). The absence of a substantial volatile envelope despite the high mass of K2-55b poses a challenge to current theories of gas giant formation. We theorized that K2-55b may have escaped runaway accretion by migration, late formation, or inefficient core accretion, or that K2-55b was stripped of its envelope by a late giant impact.

  • Characterizing K2 Candidate Planetary Systems II: Planetary Systems Observed During Campaigns 1-7

    Dressing et al. (2017, AJ)

    Having previously used near-infrared spectroscopy to improve the characterization of 76 low-mass stars around which K2 had detected 79 candidate transiting planets, we combined our improved stellar characterizations with new fits to the K2 photometry to revise planet properties. We calculated the false positive probabilities that the transit-like signals are actually caused by non- planetary astrophysical phenomena and rejected five new transit-like events and three previously reported events as false positives. We also statistically validated 17 planets (7 of which were previously unpublished), confirmed the earlier validation of 22 planets, and announced 17 newly discovered planet candidates.