2013 Annual Science Report
VPL at University of Washington Reporting | SEP 2012 – AUG 2013
Exoplanet Detection and Characterization: Observations
In this task, VPL researchers use astronomical instrumentation to detect and measure the properties of exoplanets. They also study terrestrial planets in our Solar System that can serve as practice targets for exoplanet observational techniques. These observations help us to develop and understand the techniques and measurements required to learn about planetary environments. Although many of these observations are now made on planets that are too large, or too close to their stars to be habitable, once proven, these techniques can then be adapted to help characterize the smaller, cooler planets that may be habitable.
In this task, VPL researchers use astronomical instrumentation to detect and measure the properties of exoplanets. They also study terrestrial planets in our Solar System that can serve as practice targets for exoplanet observational techniques.
Transit spectroscopy of gas giant planets is necessary as a prelude to habitable planet spectroscopy, but gas-giant spectroscopy (e.g., using NICMOS on the Hubble Space Telescope) has been difficult and controversial. This year, Deming, Agol, Wilkins and Dobbs-Dixon used the WFC3 instrument on the Hubble Space Telescope to observe several giant transiting planets with the new spatial scanning mode (Deming et al., 2013). They achieved extremely high precision measurements for transit spectroscopy and provided the first detection of water vapor absorption in several transiting extrasolar gas giants. They are now extending this technique to smaller planets (Wilkins et al., in prep).
Deming and Sheets also used a new technique to characterize the atmospheres of Kepler’s planet candidates, something that is not possible to do by direct observations of the planets themselves. Grouping the planets by their expected physical and orbital characteristics, they calculated average transit and eclipse data for all planets in a given group. This allows extraction of small signals that are not amenable to detection for single planets, and provides a statistical characterization of the atmospheres of small Kepler planets such as super-Earths. They detect light emitted and/or reflected from planets smaller than Saturn at secondary eclipse, and they are also looking for light refracted by the planetary atmospheres at transit. (Sheets et al., in prep).
Agol, with Barnes and Dobbs-Dixon carried out studies of transiting exoplanets with the Kepler, Hubble, and Spitzer Space telescopes. The most notable discovery was the planet Kepler-62f, which is the smallest radius-confirmed planet falling within a star’s habitable zone to date (Borucki et al., 2013). Agol also helped to characterize planets in multi-planet systems with the observational technique of transit-timing variations. Barnes served as the planetary habitability expert for an international team that used the radial velocity technique for planet detection to discover 6-7 planets orbiting the nearby M dwarf star Gl 667C, including at least 3 in the habitable zone (Anglada-Escude et al., 2013). Barnes and Agol, with colleagues, continued VPL efforts to discover Earth-mass planets via transit observations (Becker et al., 2013). This study examined a bright transiting planet to search for signal variations resulting from an unseen companion, however, no additional planets were detected. Agol and Barnes also participated in a searches for transit timing variations in the transits of the known hot Jupiters XO-2b and TrES-3b, but did not detect any (Kundurthy et al., 2013a,b) Additionally, we performed a detailed dynamical study of the 2:1 resonance, demonstrating for the first time that Earth-mass planets can perturb a transiting Jupiter-mass planet strongly enough to produce an observable signal, while still remaining in a dynamically stable configuration. In Lee et al. (2013) and Ma et al. (2013), Agol and Barnes contributed to the detection of brown dwarfs in short-period orbits in the Sloan Digital Sky Survey, which are astrophysically rare objects. Although these brown dwarfs are not habitable, these systems provides clues to their formation and physical properties, which could provide valuable insight into the potential habitability of any planets that may eventually be discovered to orbit brown dwarfs.
We also continued observations of relevant Solar System planets this year. Arney, Meadows and Crisp generated synthetic spectra from the SMART radiative transfer model to analyze observations of Venus. These analyses were used to produce the first simultaneous spatially-resolved maps of H2O, HCl, CO, OCS, and SO2 abundances in the Venusian lower atmosphere. Certain species displayed surprising hemispherical dichotomies. These observations are being used to better understand the atmospheric chemistry and cloud properties and dynamics on this hot terrestrial planet. (Arney et al., in prep).
PROJECT INVESTIGATORS:Victoria Meadows
Project InvestigatorJeremy Bailey
PROJECT MEMBERS:Eric Agol
RELATED OBJECTIVES:Objective 1.2
Indirect and direct astronomical observations of extrasolar habitable planets.
Outer Solar System exploration
Biosignatures to be sought in nearby planetary systems