DETECTION OF OCEAN GLINT AND OZONE ABSORPTION USING LCROSS EARTH OBSERVATIONS

The Lunar CRater Observation and Sensing Satellite (LCROSS) observed the distant Earth on three occasions in 2009. These data span a range of phase angles, including a rare crescent phase view. For each epoch, the satellite acquired near-infrared and mid-infrared full-disk images, and partial-disk spectra at 0.26-0.65 μm (λ/Δλ ∼ 500) and 1.17-2.48 μm (λ/Δλ ∼ 50). Spectra show strong absorption features due to water vapor and ozone, which is a biosignature gas. We perform a significant recalibration of the UV-visible spectra and provide the first comparison of high-resolution visible Earth spectra to the NASA Astrobiology Institute's Virtual Planetary Laboratory three-dimensional spectral Earth model. We find good agreement with the observations, reproducing the absolute brightness and dynamic range at all wavelengths for all observation epochs, thus validating the model to within the ∼10% data calibration uncertainty. Data-model comparisons reveal a strong ocean glint signature in the crescent phase data set, which is well matched by our model predictions throughout the observed wavelength range. This provides the first observational test of a technique that could be used to determine exoplanet habitability from disk-integrated observations at visible and near-infrared wavelengths, where the glint signal is strongest. We examine the detection of themore » ozone 255 nm Hartley and 400-700 nm Chappuis bands. While the Hartley band is the strongest ozone feature in Earth's spectrum, false positives for its detection could exist. Finally, we discuss the implications of these findings for future exoplanet characterization missions.« less

[1]  Wesley A. Traub,et al.  TERRESTRIAL, HABITABLE-ZONE EXOPLANET FREQUENCY FROM KEPLER , 2011, 1109.4682.

[2]  E. Pall'e,et al.  PHOTOMETRIC VARIABILITY OF THE DISK-INTEGRATED THERMAL EMISSION OF THE EARTH , 2012, 1205.5010.

[3]  E. Pallé,et al.  RECONSTRUCTING THE PHOTOMETRIC LIGHT CURVES OF EARTH AS A PLANET ALONG ITS HISTORY , 2011, 1110.1340.

[4]  Nicolas B. Cowan,et al.  DETERMINING REFLECTANCE SPECTRA OF SURFACES AND CLOUDS ON EXOPLANETS , 2013, 1302.0006.

[5]  E. Gaidos,et al.  Detecting the glint of starlight on the oceans of distant planets , 2008, 0801.1852.

[6]  S. N. Tiwari,et al.  Bidirectional Reflectance Functions for Application to Earth Radiation Budget Studies , 1997 .

[7]  John C. Geary,et al.  The Kepler mission: a wide-field-of-view photometer designed to determine the frequency of Earth-size planets around solar-like stars , 2003, SPIE Astronomical Telescopes + Instrumentation.

[8]  Dorian S. Abbot,et al.  THERMAL PHASES OF EARTH-LIKE PLANETS: ESTIMATING THERMAL INERTIA FROM ECCENTRICITY, OBLIQUITY, AND DIURNAL FORCING , 2012, 1205.5034.

[9]  Philip R. Goode,et al.  Earthshine and the Earth's albedo: 1. Earthshine observations and measurements of the lunar phase function for accurate measurements of the Earth's Bond albedo , 2003 .

[10]  Pierre H. Flamant,et al.  OBSERVATIONS OF HORIZONTALLY ORIENTED ICE CRYSTALS IN CIRRUS CLOUDS WITH POLDER-1/ADEOS-1 , 1999 .

[11]  Patrick G. J. Irwin,et al.  Optimal estimation retrievals of the atmospheric structure and composition of HD 189733b from secondary eclipse spectroscopy , 2011, 1110.2934.

[12]  R. Kopparapu,et al.  A REVISED ESTIMATE OF THE OCCURRENCE RATE OF TERRESTRIAL PLANETS IN THE HABITABLE ZONES AROUND KEPLER M-DWARFS , 2013, 1303.2649.

[13]  William Marshall,et al.  Detection of Water in the LCROSS Ejecta Plume , 2010, Science.

[14]  Dorian S. Abbot,et al.  A FALSE POSITIVE FOR OCEAN GLINT ON EXOPLANETS: THE LATITUDE–ALBEDO EFFECT , 2012, 1205.1058.

[15]  William J. Borucki,et al.  The Kepler Mission: A wide-field transit search for terrestrial planets , 2005 .

[16]  Webster Cash,et al.  CONSTRUCTION OF AN EARTH MODEL: ANALYSIS OF EXOPLANET LIGHT CURVES AND MAPPING THE NEXT EARTH WITH THE NEW WORLDS OBSERVER , 2009 .

[17]  S. Seager,et al.  ALIEN MAPS OF AN OCEAN-BEARING WORLD , 2009, 0905.3742.

[18]  J. Pearl,et al.  Initial data from the Mars Global Surveyor thermal emission spectrometer experiment: Observations of the Earth , 1997 .

[19]  L. Arnold,et al.  A test for the search for life on extrasolar planets - Looking for the terrestrial vegetation signature in the Earthshine spectrum , 2002, astro-ph/0206314.

[20]  P. R. Goode,et al.  Vegetation Signature in the Observed Globally Integrated Spectrum of Earth Considering Simultaneous Cloud Data: Applications for Extrasolar Planets , 2006, astro-ph/0604420.

[21]  Bonnie J. Buratti,et al.  A wavelength-dependent visible and infrared spectrophotometric function for the Moon based on ROLO data , 2011 .

[22]  D. Crisp,et al.  Ground‐based near‐infrared observations of the Venus nightside: The thermal structure and water abundance near the surface , 1996 .

[23]  F. Fressin,et al.  CHARACTERISTICS OF PLANETARY CANDIDATES OBSERVED BY KEPLER. II. ANALYSIS OF THE FIRST FOUR MONTHS OF DATA , 2011, 1102.0541.

[24]  Wesley A. Traub,et al.  Spectrum of a Habitable World: Earthshine in the Near-Infrared , 2006 .

[25]  T. Trautmann,et al.  Characterization of potentially habitable planets: Retrieval of atmospheric and planetary properties from emission spectra , 2013, 1301.0217.

[26]  F. Fressin,et al.  CHARACTERISTICS OF KEPLER PLANETARY CANDIDATES BASED ON THE FIRST DATA SET , 2010, 1006.2799.

[27]  Inseok Song,et al.  MID-INFRARED PROPERTIES OF DISK AVERAGED OBSERVATIONS OF EARTH WITH AIRS , 2008, 0810.2957.

[28]  J. Kasting,et al.  Oxidant abundances in rainwater and the evolution of atmospheric oxygen. , 1985, Journal of geophysical research.

[29]  W. R. Thompson,et al.  A search for life on Earth from the Galileo spacecraft , 1993, Nature.

[30]  Edwin L. Turner,et al.  VARIABILITY OF WATER AND OXYGEN ABSORPTION BANDS IN THE DISK-INTEGRATED SPECTRA OF EARTH , 2013 .

[31]  N. J. Woolf,et al.  The Spectrum of Earthshine: A Pale Blue Dot Observed from the Ground , 2002 .

[32]  D. Charbonneau,et al.  THE OCCURRENCE RATE OF SMALL PLANETS AROUND SMALL STARS , 2013, 1302.1647.

[33]  E. Pall'e,et al.  ON THE EFFECTS OF THE EVOLUTION OF MICROBIAL MATS AND LAND PLANTS ON THE EARTH AS A PLANET. PHOTOMETRIC AND SPECTROSCOPIC LIGHT CURVES OF PALEO-EARTHS , 2013, 1302.4232.

[34]  K. Gorski,et al.  HEALPix: A Framework for High-Resolution Discretization and Fast Analysis of Data Distributed on the Sphere , 2004, astro-ph/0409513.

[35]  Drake Deming,et al.  Rotational Variability of Earth's Polar Regions: Implications for Detecting Snowball Planets , 2011 .

[36]  Remi Soummer,et al.  NEW COMPLETENESS METHODS FOR ESTIMATING EXOPLANET DISCOVERIES BY DIRECT DETECTION , 2010 .

[37]  Philip R. Goode,et al.  Earthshine and the Earth's albedo: 2. Observations and simulations over 3 years , 2003 .

[38]  The University of Tokyo,et al.  MAPPING CLOUDS AND TERRAIN OF EARTH-LIKE PLANETS FROM PHOTOMETRIC VARIABILITY: DEMONSTRATION WITH PLANETS IN FACE-ON ORBITS , 2011, 1106.0136.

[39]  W. A. Traub,et al.  Spectral Evolution of an Earth-like Planet , 2006 .

[40]  Tyler D. Robinson,et al.  DETECTING OCEANS ON EXTRASOLAR PLANETS USING THE GLINT EFFECT , 2010, 1008.3864.

[41]  Darren M. Williams,et al.  LIGHT SCATTERING FROM EXOPLANET OCEANS AND ATMOSPHERES , 2010 .

[42]  D. M. Stam,et al.  Spectropolarimetric signatures of Earth-like extrasolar planets , 2007, 0707.3905.

[43]  Richard G. Lyon,et al.  Detecting biomarkers in exoplanetary atmospheres with a Terrestrial Planet Finder , 2008, Astronomical Telescopes + Instrumentation.

[44]  Satoru Fukuda,et al.  COLORS OF A SECOND EARTH. II. EFFECTS OF CLOUDS ON PHOTOMETRIC CHARACTERIZATION OF EARTH-LIKE EXOPLANETS , 2011, 1102.3625.

[45]  Las Cumbres Observatory Global Telescope Network,et al.  PLANETARY CANDIDATES OBSERVED BY KEPLER. III. ANALYSIS OF THE FIRST 16 MONTHS OF DATA , 2012, 1202.5852.

[46]  Howard Isaacson,et al.  Kepler Planet-Detection Mission: Introduction and First Results , 2010, Science.

[47]  S. Seager,et al.  A TEMPERATURE AND ABUNDANCE RETRIEVAL METHOD FOR EXOPLANET ATMOSPHERES , 2009, 0910.1347.

[48]  Enric Palle,et al.  Biosignatures as revealed by spectropolarimetry of Earthshine , 2012, Nature.

[49]  M. R. Line,et al.  INFORMATION CONTENT OF EXOPLANETARY TRANSIT SPECTRA: AN INITIAL LOOK , 2011, 1111.2612.

[50]  Timothy J. Kane,et al.  SEARCHING FOR WATER EARTHS IN THE NEAR-INFRARED , 2011 .

[51]  S. Seager,et al.  Characterization of extrasolar terrestrial planets from diurnal photometric variability , 2001, Nature.

[52]  S. Fukuda,et al.  COLORS OF A SECOND EARTH: ESTIMATING THE FRACTIONAL AREAS OF OCEAN, LAND, AND VEGETATION OF EARTH-LIKE EXOPLANETS , 2009, 0911.5621.