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A rocky composition for an Earth-sized exoplanet

Howard, Andrew W. and Sanchis-Ojeda, Roberto and Marcy, Geoffrey W. and Johnson, John Asher and Winn, Joshua N. and Isaacson, Howard and Fischer, Debra A. and Fulton, Benjamin J. and Sinukoff, Evan and Fortney, Jonathan J. (2013) A rocky composition for an Earth-sized exoplanet. Nature, 503 (7476). pp. 381-384. ISSN 0028-0836.

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Planets with sizes between that of Earth (with radius R⊕) and Neptune (about 4 R⊕) are now known to be common around Sun-like stars. Most such planets have been discovered through the transit technique, by which the planet’s size can be determined from the fraction of starlight blocked by the planet as it passes in front of its star. Measuring the planet’s mass—and hence its density, which is a clue to its composition—is more difficult. Planets of size 2–4 R⊕ have proved to have a wide range of densities, implying a diversity of compositions, but these measurements did not extend to planets as small as Earth. Here we report Doppler spectroscopic measurements of the mass of the Earth-sized planet Kepler-78b, which orbits its host star every 8.5 hours (ref. 6). Given a radius of 1.20 ± 0.09 R⊕ and a mass of 1.69 ± 0.41 M⊕, the planet’s mean density of 5.3 ± 1.8 g cm^(−3) is similar to Earth’s, suggesting a composition of rock and iron.

Item Type:Article
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URLURL TypeDescription ReadCube access Paper
Howard, Andrew W.0000-0001-8638-0320
Sanchis-Ojeda, Roberto0000-0002-6193-972X
Marcy, Geoffrey W.0000-0002-2909-0113
Johnson, John Asher0000-0001-9808-7172
Winn, Joshua N.0000-0002-4265-047X
Isaacson, Howard0000-0002-0531-1073
Fischer, Debra A.0000-0003-2221-0861
Fulton, Benjamin J.0000-0003-3504-5316
Sinukoff, Evan0000-0002-5658-0601
Fortney, Jonathan J.0000-0002-9843-4354
Additional Information:© 2013 Macmillan Publishers Limited. Received 25 September 2013; Accepted 11 October 2013; Published online 30 October 2013. This Letter and another were submitted simultaneously and are the result of coordinated, independent radial-velocity observations and analyses of Kepler-78. We thank the HARPS-N team for their collegiality. We also thank E. Chiang, I. Crossfield, R. Kolbl, E. Petigura, and D. Huber for discussions, S. Howard for support, C. Dressing for a convenient packaging of stellar models, and A. Hatzes for a thorough review. This work was based on observations at the W. M. Keck Observatory granted by the University of Hawaii, the University of California, and the California Institute of Technology. We thank the observers who contributed to the measurements reported here and acknowledge the efforts of the Keck Observatory staff. We thank those of Hawaiian ancestry on whose sacred mountain of Mauna Kea we are guests. Kepler was competitively selected as the tenth Discovery mission with funding provided by NASA’s Science Mission Directorate. J.N.W. and R.S.-O. acknowledge support from the Kepler Participating Scientist programme. A.W.H. acknowledges funding from NASA grant NNX12AJ23G. Author Contributions: This measurement was conceived and planned by A.W.H., G.W.M., J.A.J., J.N.W. and R.S.-O. HIRES observations were conducted by A.W.H., G.W.M., H.I, B.J.F. and E.S. The HIRES spectra were reduced and Doppler-analysed by A.W.H., G.W.M., H.I. and J.A.J. Data modelling was done primarily by A.W.H. and R.S.-O. A.W.H. was the primary author of the manuscript, with important contributions from J.N.W., R.S.-O. and J.J.F. Figures were generated by A.W.H., R.S.-O, B.J.F. and E.S. All authors discussed the results, commented on the manuscript and contributed to the interpretation. The authors declare no competing financial interests.
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Issue or Number:7476
Record Number:CaltechAUTHORS:20170621-152543226
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:78433
Deposited By: Tony Diaz
Deposited On:21 Jun 2017 22:33
Last Modified:09 Mar 2020 13:19

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