Introduction

Please credit S. Seager if using this figure in presentations.

Over 400 planets are known to orbit nearby, sun-like stars. These planets are called “exoplanets”. Professor Seager’s favorite exoplanet diagram is the mass-period diagram shown to the left. This diagram (updated monthly) shows that exoplanets have all masses and semi-major axes possible, showcasing the random nature of planet formation and migration. The different planet detection techniques are shown in the diagram. Parts of the diagram with no planets are where technology can not yet reach exoplanets.

 

 


Exoplanet Atmospheres

EclipseThe goal in studying exoplanet atmospheres is to understand the atmospheric composition and temperature. We want to be able to recognize planet atmospheres like Earth’s: with water vapor, oxygen, ozone, and carbon dioxide. These strong absorbers would make the major contributions to the spectrum we could observe from afar. While the detection of true Earth twins is some time off, we are busy trying to understand hot Jupiter and hot Neptune atmospheres observed by primary and secondary eclipses for transiting exoplanets. Professor Seager’s group’s research focuses on computer models of exoplanet atmospheres and interpretation of data from space telescopes.

Selection of Prof. Seager’s most significant papers on exoplanet atmospheres

The first paper on hot Jupiter atmospheres
Seager, S., & Sasselov, D. D. 1998, “Extrasolar Giant Planets Under Strong Stellar Irradiation”, ApJ, 502, L157-161.View PDF

The first description of exoplanet transmission spectra, that led to the first detection of an exoplanet atmosphere
Seager, S., & Sasselov, D. D. 2000, “Theoretical Transmission Spectra During an Extrasolar Giant Planet Transit”, ApJ, 537, 916-921. View PDF

Co-authored one of the first two independent detections of photons from an exoplanet atmosphere
Deming, D., Seager, S., Richardson, L. J., & Harrington, J. 2005, “Detection of Infrared Radiation from an Extrasolar Planet”, Nature, 434, 740-743. View PDF

General description of super Earth atmospheres, lead by Prof. Seager’s student Eliza Miller-Ricci
Miller-Ricci, E., Seager, S., & Sasselov, D. 2009 “The Atmospheric Signatures of Super-Earths: How to Distinguish Between Hydrogen-Rich and Hydrogen-Poor Atmospheres”, ApJ, 690, 1056-1067. View PDF

Exoplanet Interior Composition

mass radius

The goal in studying exoplanet interiors is to learn what individual exoplanets are made of, and even what their internal structure might be. Professor Seager’s work has focused on the mass-radius relationships for exoplanets of a wide range of compositions and masses. Prof. Seager and colleagues. Exoplanet researchers have realized that there are fatal limitations to uncovering the interior composition of an exoplanet because only the mass and radius can be measured—no other information about the interior. This deadlock can be slightly aided in the future when enough exoplanets are found to do statistics, or possibly when molecules can be detected in super-Earth atmospheres in the future.

To download a MATLAB code to compute your own ternary diagrams for a super Earth of a given mass and radius: View Page

Selection of Prof. Seager’s most significant papers on exoplanet interiors.

Explanation of why the mass-radius relationships for planets of any composition are similar
Seager, S., Kuchner, M., Hier-Majumder, C. A., & Militzer, 2007, “Mass- View PDF

Carbon planet prediction
Kuchner, M. & Seager, S., Extrasolar Carbon Planets, submitted to Astrobiology View PDF

Exoplanet Biosignatures and Earth Twin Planets

bio signaturesBiosignatures are signs of life in an exoplanet atmosphere or on an exoplanet surface. Earth’s biosignatures are oxygen (produced only in large quantities by plants and photosynthetic bacteria) and ozone (photochemically produced in the atmosphere from oxygen). Nitrous oxide is an atmospheric gas also produced by life, but is difficult to detect. Methane is produced both biologically and from mid-ocean ridge volcanism. Water vapor is considered a sign of habitability, because all life on Earth needs liquid water; atmospheric water vapor is indicative of liquid water oceans for terrestrial-like planets.

Earth twins refer to planets just like Earth, orbiting sun-like stars with liquid water oceans, continents, and thin atmospheres.

Co-authored the first paper describing how to use an Earth-twin’s reflected light curve to determine the rotation rate and possibly infer the presence of weather and continents Ford, E. B., Seager, S., & Turner, E. L. 2001, “Characterization of Extrasolar Terrestrial Planets from Diurnal Photometric Variability”, Nature, 412, 885-887. Read More...

Updated at
Palle, E., Ford, E. B., Seager, S., Montanes-Rodriguez, P., & Vazquez, M. 2008, “Identifying the Rotation Rate and the Presence of Dynamic Weather on Extrasolar Earth-like Planets from Photometric Observations”, ApJ, 676, 1319-1329. View PDF

A very useful paper summarizing Earth’s biosignatures (in which Prof. Seager played only a minor role)
Des Marais, D. J., Harwit, M., Jucks, K., Kasting, J. F., Lunine, J. I., Lin, D., Seager, S., Schneider, J., Traub, W., & Woolf, N. 2002, “Remote Sensing of Planetary Properties and Biosignatures on Extrasolar Terrestrial Planets”, Astrobiology, 2, 153-181. View PDF

Seager’s main work on exoplanet biosignatures is in progress.

Exoplanet Other

Professor Seager has worked on a variety of other topics in exoplanets.

One of her favorite papers is about how to extract information from a transit light curve, by recognizing that there are five equations and five unknowns for a circular orbit
Seager, S., & Mallen-Ornelas, G. 2003, “On the Unique Solution of Planet and Star Parameters from an Extrasolar Planet Transit Light Curve”, ApJ, 585, 1038-1055.View PDF

She also published the first paper on constraining exoplanet rotation rates from oblateness measurements during transit
Seager, S., & Hui, L. 2002,“Constraining the Rotation Rate of Transiting Extrasolar Planets by an Oblateness Measurement”, ApJ, 574, 1004-1010.View PDF

The first paper on reflected light and polarization signatures
Seager, S., Whitney, B. A., & Sasselov, D. D. 2000, “Light Curves and Polarization of the Close-in Extrasolar Giant Planets”, ApJ, 540, 504-520.View PDF

And co-authored the first and to date only paper in exoplanet atmospheric refraction
Hui, L., & Seager, S. 2002, “Atmospheric Lensing and Oblateness Effect During an Extrasolar Planetary Transit”, ApJ, 572, 540-555.View PDF

Exoplanet Space Telescopes

keplerProf Seager and her group are involved with using data from two exoplanet space telescopes: Kepler and EPOXI. In the past, they also helped interpret hot Jupiter upper limits to reflected light from MOST. Prof. Seager is a participating scientist member of the Kepler Science Team. Prof Seager is leading a concept study on ExoplanetSat, a nanosatellite concept study to find transiting Earth-size planets around the nearest, brightest sun-like stars in the sky.

Recombination in the Early Universe

Professor Seager’s career started with recombination in the early Universe. This  research field has seen a resurgence with the upcoming launch of ESA’s Planck Space Telescope. Prof. Seager is no longer actively working in this field of research.  Prof. Seager’s major contribution to recombination in the early Universe is in the form of two papers:

A summary paper
Seager, S., Sasselov, D. D., & Scott, D. 1999, “A New Calculation of the Recombination Epoch”, 1999, ApJ, 523, L1-5.View PDF
and the full description
Seager, S., Sasselov, D. D., & Scott, D. 2000, “How Exactly Did the Universe Become Neutral?”, ApJS, 128, 407-430.View PDF