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Research Article

Prevalence of Earth-size planets orbiting Sun-like stars

Erik A. Petigura, Andrew W. Howard, and Geoffrey W. Marcy
  1. aAstronomy Department, University of California, Berkeley, CA 94720; and
  2. bInstitute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822

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PNAS first published November 4, 2013; https://doi.org/10.1073/pnas.1319909110
Erik A. Petigura
aAstronomy Department, University of California, Berkeley, CA 94720; and
bInstitute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822
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  • For correspondence: epetigura@berkeley.edu
Andrew W. Howard
bInstitute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822
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Geoffrey W. Marcy
aAstronomy Department, University of California, Berkeley, CA 94720; and
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  1. Contributed by Geoffrey W. Marcy, October 22, 2013 (sent for review October 18, 2013)

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Significance

A major question is whether planets suitable for biochemistry are common or rare in the universe. Small rocky planets with liquid water enjoy key ingredients for biology. We used the National Aeronautics and Space Administration Kepler telescope to survey 42,000 Sun-like stars for periodic dimmings that occur when a planet crosses in front of its host star. We found 603 planets, 10 of which are Earth size and orbit in the habitable zone, where conditions permit surface liquid water. We measured the detectability of these planets by injecting synthetic planet-caused dimmings into Kepler brightness measurements. We find that 22% of Sun-like stars harbor Earth-size planets orbiting in their habitable zones. The nearest such planet may be within 12 light-years.

Abstract

Determining whether Earth-like planets are common or rare looms as a touchstone in the question of life in the universe. We searched for Earth-size planets that cross in front of their host stars by examining the brightness measurements of 42,000 stars from National Aeronautics and Space Administration’s Kepler mission. We found 603 planets, including 10 that are Earth size (Formula) and receive comparable levels of stellar energy to that of Earth (Formula). We account for Kepler’s imperfect detectability of such planets by injecting synthetic planet–caused dimmings into the Kepler brightness measurements and recording the fraction detected. We find that 11 ± 4% of Sun-like stars harbor an Earth-size planet receiving between one and four times the stellar intensity as Earth. We also find that the occurrence of Earth-size planets is constant with increasing orbital period (P), within equal intervals of logP up to ∼200 d. Extrapolating, one finds Formula% of Sun-like stars harbor an Earth-size planet with orbital periods of 200–400 d.

  • extrasolar planets
  • astrobiology

Footnotes

  • ↵1To whom correspondence should be addressed. E-mail: epetigura{at}berkeley.edu.
  • Author contributions: E.A.P., A.W.H., and G.W.M. designed research, performed research, analyzed data, and wrote the paper.

  • The authors declare no conflict of interest.

  • Data deposition: The Kepler photometry is available at the Milkulski Archive for Space Telescopes (archive.stsci.edu). All spectra are available to the public on the Community Follow-up Program website (cfop.ipac.caltech.edu).

  • This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1319909110/-/DCSupplemental.

Freely available online through the PNAS open access option.

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Prevalence of Earth-size planets
Erik A. Petigura, Andrew W. Howard, Geoffrey W. Marcy
Proceedings of the National Academy of Sciences Nov 2013, 201319909; DOI: 10.1073/pnas.1319909110

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Prevalence of Earth-size planets
Erik A. Petigura, Andrew W. Howard, Geoffrey W. Marcy
Proceedings of the National Academy of Sciences Nov 2013, 201319909; DOI: 10.1073/pnas.1319909110
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