2011 Annual Science Report
VPL at University of Washington Reporting | SEP 2010 – AUG 2011
Astronomical Observations of Planetary Atmospheres and Exoplanets
This task encompasses remote-sensing observations of Solar System and extrasolar planets made by the VPL team. These observations, while providing scientific exploration in its own right, also allow us to test our planetary models and help advance techniques to retrieve information from the astronomical data that we obtain. This can include improving our understanding of the accuracy of inputs into our models, such as spectral databases. This year we made and/or analyzed observations of Mars, Venus and Earth taken by ground-based and spaceborne observatories, to better understand how well we can determine planetary properties like surface temperature and atmospheric composition, when a terrestrial planet is observed only as a distant point of light.
In this task we acquire and use observations of planets in our Solar System and extrasolar planets to understand the detectability of planetary characteristics in these data.
This year, in Crow et al. (2011), we explored the extent to which Earth’s blue color and lack of strong methane absorption at visible wavelengths makes it a unique body within the Solar System, and we proposed that these two traits may work as a simple filter for searching for Earth-like planets with a telescope such as the Terrestrial Planet Finder. This paper synthesized modeling results and a large number of observations of Solar System bodies, including EPOXI observations of Earth, the Moon, and Mars.
In Cowan et al. (2011), we compared EPOXI observations of Earth’s polar regions to a simple model of the visible-light appearance of the Snowball Earth, uncovering distinct differences between the two, which indicates that it is possible to distinguish between a snowball planet and a pole-on view of an Earth-like planet. We also find that even in the pole-on view, the visible lightcurve is dominated by mid-latitudes, which in the case of the Earth show strong variations due to oceans and continents. The VPL Earth model was used in this paper to validate a retrieval technique, which was employed in Cowan et al. (2009) to map the longitudinal distribution of Earth’s continents and oceans from time-resolved, disk-integrated photometric observations of Earth. In other work, we are analyzing near-infrared EPOXI spectra of the Earth and Mars to determine the likely error in temperature retrieval for disk-integrated Mars and Earth data at these wavelengths.
We have also acquired near-infrared observations of Venus with the Apache Point Observatory 3.5m telescope, and the Anglo Australian 3.9m telescope. We are currently exploring the detectability of planetary characteristics for photochemical haze enshrouded planets in the disk-average for the Apache Point dataset. Using the AAT dataset we investigated the distribution of carbon monoxide in the lower atmosphere of Venus using observation of the 2.3um band. The spatial distribution of CO mapped appears to show a strong Hadley-cell (Cotton et al., 2011).
In work lead by Australian collaborator Dr. Jeremy Bailey, we published a detailed model on the VSTAR radiative transfer modeling code (Bailey and Kedziora-Chudzer, 2011) for analysis of data from a wide range of objects including Solar System plants, exoplanets, brown dwarfs and cools stars. We also adapted VSTAR to model polarized radiative transfer using two different polarized radiative transfer algorithms (discrete ordinate and adding doubling) and tested the results by comparison with polarized radiative transfer benchmarks. We studied the near-infrared spectra of Titan and the solar system giant planets making use of new methane spectral line data based largely on laboratory measurements from the Grenoble group (Bailey et al., 2011). The Titan model enabled the measurement of Titan’s D/H ratio and led to the discovery of new CH3D bands in its spectrum in the 2μm region. Dr. Bailey continued to participate as a team member in the Anglo-Australian Planet Search program.
PROJECT INVESTIGATORS:Victoria Meadows
Project InvestigatorJeremy Bailey
PROJECT MEMBERS:David Crisp
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