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Title: Characterizing the Purple Earth: Modeling the globally integrated spectral variability of the Archean Earth

Ongoing searches for exoplanetary systems have revealed a wealth of planets with diverse physical properties. Planets even smaller than the Earth have already been detected and the efforts of future missions are aimed at the discovery, and perhaps characterization, of small rocky exoplanets within the habitable zone of their stars. Clearly, what we know about our planet will be our guideline for the characterization of such planets. However, the Earth has been inhabited for at least 3.8 Gyr and its appearance has changed with time. Here, we have studied the Earth during the Archean eon, 3.0 Gyr ago. At that time, one of the more widespread life forms on the planet was purple bacteria. These bacteria are photosynthetic microorganisms and can inhabit both aquatic and terrestrial environments. Here, we use a radiative transfer model to simulate the visible and near-infrared radiation reflected by our planet, taking into account several scenarios regarding the possible distribution of purple bacteria over continents and oceans. We find that purple bacteria have a reflectance spectrum that has a strong reflectivity increase, similar to the red edge of leafy plants, although shifted redward. This feature produces a detectable signal in the disk-averaged spectra of our planet,more » depending on cloud amount and purple bacteria concentration/distribution. We conclude that by using multi-color photometric observations, it is possible to distinguish between an Archean Earth in which purple bacteria inhabit vast extensions of the planet and a present-day Earth with continents covered by deserts, vegetation, or microbial mats.« less
Authors:
; ; ;  [1] ;  [2] ;  [3] ;  [4]
  1. Instituto de Astrofísica de Canarias (IAC), Vía Láctea s/n E-38200, La Laguna (Spain)
  2. NASA Ames Research Center, Exobiology Branch, Mountain View, CA 94035 (United States)
  3. NASA Goddard Institute for Space Studies, New York, NY 10025 (United States)
  4. Department of Microbiology, Faculty of Biology, University of La Laguna, ES-38206 La Laguna (Spain)
Publication Date:
OSTI Identifier:
22348346
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 780; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; BACTERIA; COLOR; CONCENTRATION RATIO; DISTRIBUTION; NEAR INFRARED RADIATION; PLANETS; RADIANT HEAT TRANSFER; REFLECTIVITY; SATELLITE ATMOSPHERES; SATELLITES; SPECTRA; STARS; SURFACES