Lunar Based Observations of the Earth as a Planet

The Camera for Lunar Observations of the Variable Earth (CLOVE) is a concept for a moon-based instrument to characterize the remotely detectable physical and biological signatures of Earth over time. The study is being undertaken as part of the NASA Lunar Science Institute’s program “Scientific and Exploration Potential of the Lunar Poles”. The lunar polar surface deployment enables these data to be obtained continuously over long timescales and this unique vantage point makes it possible to track Earth's everchanging photometric, spectral and polarimetric signatures in a manner analogous to future observations of extrasolar terrestrial planets. Empirical data from observations of the Earth from space, from Earthshine and from the field and laboratory will be integrated with state-of-the-art models to help us understand our ability to characterize Earth-like exoplanets, their habitability and evidence for extant life. In the NLSI study we include investigation of circular polarization as a biosignature, try to detect ocean glint from polarization of the Earthshine, and enhance our ability to model the Earth using observations from recent space missions. I. Validation with Spacecraft Observations of the Earth With data from the EPOXI mission (nee Deep Impact), Cowan et al (2009) ApJ, 700, 915 used disk averaged time-resolved photometry of the Earth to understand the extent to which terrestrial features could be extracted. Even with typical cloud cover, both continents and oceans could be identified by proper analysis of the lightcurve. Using long timeseries, wider spectral coverage and simultaneously acquiring ground truth images, CLOVE has the potential to optimize and advance this important technique. The Lunar CRater Observation and Sensing Satellite (LCROSS) made three sets of observations of the Earth en route to the Moon. The data comprise optical/NUV spectroscopy, NIR spectroscopy and both Near IR and Mid IR imaging. Our goal is to utilize these data in conjunction with the tools available through the NASA Astrobiology Institute’s Virtual Planetary laboratory (P.I. Vikki Meadows; see http://vpl.astro.washington.edu) to validate the terrestrial planet models all the way into the thermal IR and to seek identifiable features visible in the optical and NUV spectra. III. Remotely Sensing Life’s Signature A candidate universal biosignature is homochirality, which is likely to be a generic property of all biochemical life. Due to the optical activity of chiral molecules this unique characteristic may provide a suitable remote sensing probe using circular polarization spectroscopy. Photosynthetic microbial organisms are of major importance to astrobiology through the evolutionary advantages accrued by photosynthesis and the easy “observability” of photosynthesis. We have shown that the chiral molecules of photosynthesis produce measureable circular polarization signatures (Sparks et al 2009 PNAS 106, 7816; 2009 JQSRT 110, 1771). Circular polarization spectroscopy could provide a powerful remote sensing technique for generic life searches. Our goal in the current study is to assess the magnitude of any global circular polarization signature that may result from photosynthetic activity and hence its possible utility as a biosignature in the future. Acknowledgements: The Lowell Earthshine observations were obtained by K. Janes at the Perkins telescope, operated by Lowell Observatory and Boston University, using the PRISM instrument, funded by Boston University, NSF and Lowell Observatory, K.A.