Once in a Pale Blue Dot: Simulated Observations of an Extrasolar Earth-Moon System

Details Once in a Pale Blue Dot: Simulated Observations of an Extrasolar Earth-Moon System Once in a Pale Blue Dot: Simulated Observations of an Extrasolar Earth-Moon System

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p24c..02r&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #P24C-02

Biology

[5200] Planetary Sciences: Astrobiology, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [6296] Planetary Sciences: Solar System Objects / Extra-Solar Planets

Scientific paper

The inability of the Moon to efficiently circulate energy from its day side to its night side leads to large surface temperatures on its illuminated hemisphere. As a result, the Moon can contribute a significant amount of flux to spatially unresolved thermal infrared (IR) observations of the Earth-Moon system, especially at wavelengths where Earth's atmosphere is absorbing. We have paired the NASA Astrobiology Institute's Virtual Planetary Laboratory three-dimensional spectral Earth model with a model of the phase dependent IR spectrum of the Moon to investigate the effects of an unresolved companion on observations of Earthlike extrasolar planets. For an extrasolar Earth-Moon system observed at full phase at IR wavelengths, the Moon consistently comprises about 20% of the total signal, approaches 30% of the signal in the 9.6 μm ozone band and the 15 μm carbon dioxide band, makes up as much as 80% of the total signal in the 6.3 μm water band, and more than 90% of the signal in the 4.3 μm carbon dioxide band. These excesses translate to inferred brightness temperatures for Earth that are too large by about 20-40 K, and demonstrate that the presence of an undetected satellite can have a significant impact on the spectroscopic characterization of terrestrial exoplanets. The thermal flux contribution from an airless companion depends strongly on the star-planet-observer angle (i.e., the phase angle), allowing moons to mimic or mask seasonal variations in the host planet's IR spectrum. We show that, by differencing IR observations of an Earth with a companion taken at both gibbous phase and at crescent phase, Moon-sized satellites may be detectable by future exoplanet characterization missions for a wide range of system inclinations.

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