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2008 Annual Science Report

University of Hawaii, Manoa Reporting  |  JUL 2007 – JUN 2008

The Effect of Lunar-Like Satellites on the Orbital Infrared Lightcurves of Earth-Analog Planets

Project Summary

We have performed calculations that consider what an Earth-like planet with a large Moon would look like orbiting a distant star. Such observations may one day be possible with space based observatories such as NASA’s Terrestrial Planet Finder (TPF) mission.

4 Institutions
3 Teams
0 Publications
0 Field Sites
Field Sites

Project Progress

We investigate the influence of lunar-like satellites on the infrared orbital light curves of Earth-analog extra-solar planets. Such light curves will be obtained by NASA’s Terrestrial Planet Finder (TPF) and ESA’s Darwin missions as a consequence of repeat observations to confirm the companion status of a putative planet and to determine its orbit. We use an energy balance model to calculate disk-averaged infrared (bolometric) fluxes from planet-satellite systems over a full orbital period (one year). The satellites are assumed to lack an atmosphere, have a low thermal inertia like that of the Moon and span a range of plausible radii. The planets are assumed to have thermal and orbital properties that mimic those of the Earth while their obliquities and orbital longitudes of inferior conjunction remain free parameters. Even if the gross thermal properties of the planet can be independently constrained (e.g. via spectroscopy or visible-wavelength detection of specular glint from a surface ocean) only the largest ( ? Mars-size) lunar-like satellites can be detected by light curve data from a TPF-like instrument (i.e. one that achieves a photometric signal-to-noise of 10-20 at infrared wavelengths). Non-detection of a lunar-like satellite can obfuscate the interpretation of a given system’s infrared light curve so that it may resemble a single planet with high obliquity, different orbital longitude of vernal equinox relative to inferior conjunction and in some cases drastically different thermal characteristics. If the thermal properties of the planet are not independently established then the presence of a lunar-like satellite cannot be inferred from infrared data, thus demonstrating that photometric light curves alone can only be used for preliminary study and that the addition of spectroscopic data will be necessary to properly characterize extra-solar Earth-like planets.

    Eric Gaidos Eric Gaidos
    Project Investigator
    Nick Moskovitz
    Doctoral Student

    Objective 1.2
    Indirect and direct astronomical observations of extrasolar habitable planets