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ABSTRACT Recent analyses1,2,3,4 of data from the NASA Kepler spacecraft5 have established that planets with radii within 25 per cent of the Earth’s () are commonplace throughout the Galaxy,

orbiting at least 16.5 per cent of Sun-like stars1. Because these studies were sensitive to the sizes of the planets but not their masses, the question remains whether these Earth-sized

planets are indeed similar to the Earth in bulk composition. The smallest planets for which masses have been accurately determined6,7 are Kepler-10b (1.42) and Kepler-36b (1.49), which are

both significantly larger than the Earth. Recently, the planet Kepler-78b was discovered8 and found to have a radius of only 1.16. Here we report that the mass of this planet is 1.86 Earth

masses. The resulting mean density of the planet is 5.57 g cm−3, which is similar to that of the Earth and implies a composition of iron and rock. Access through your institution Buy or

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A SUPER-MASSIVE NEPTUNE-SIZED PLANET Article 30 August 2023 A WIDE-ORBIT GIANT PLANET IN THE HIGH-MASS B CENTAURI BINARY SYSTEM Article 08 December 2021 NEAR-CIRCULAR ORBITS FOR PLANETS

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_V_ = 12, F8 star. _Astrophys J._ 726, L19–L23 (2011) Article  ADS  Google Scholar  Download references ACKNOWLEDGEMENTS This Letter was submitted simultaneously with the paper by Howard _et

al._17. Both papers are the result of a coordinated effort to carry out independent radial-velocity observations and studies of Kepler-78. Our team greatly appreciates the spirit of this

collaboration, and we sincerely thank A. Howard and his team for the collegial work. We wish to thank the technical personnel of the Geneva Observatory, the Astronomical Technology Centre,

the Smithsonian Astrophysical Observatory and the Telescopio Nazionale Galileo for their enthusiasm and competence, which made the HARPS-N project possible. The HARPS-N project was funded by

the Prodex Program of the Swiss Space Office, the Harvard University Origins of Life Initiative, the Scottish Universities Physics Alliance, the University of Geneva, the Smithsonian

Astrophysical Observatory, the Italian National Astrophysical Institute, the University of St Andrews, Queen’s University Belfast and the University of Edinburgh. P.F. acknowledges support

from the European Research Council/European Community through the European Union Seventh Framework Programme, Starting Grant agreement number 239953, and from the Fundação para a Ciência e a

Tecnologia through grants PTDC/CTE-AST/098528/2008 and PTDC/CTE-AST/098604/2008. The research leading to these results received funding from the European Union Seventh Framework Programme

(FP7/2007-2013) under grant agreement number 313014 (ETAEARTH). AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * Observatoire Astronomique de l’Université de Genève, 51 chemin des Maillettes,

1290 Versoix, Switzerland, Francesco Pepe, Stéphane Udry, Christophe Lovis, Michel Mayor, Fatemeh Motalebi, Didier Queloz & Damien Ségransan * Scottish Universities Physics Alliance,

School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, Fife KY16 9SS, UK, Andrew Collier Cameron, Raphaëlle D. Haywood & Keith Horne * Harvard-Smithsonian

Center for Astrophysics, 60 Garden Street, Cambridge, 02138, Massachusetts, USA David W. Latham, Lars A. Buchhave, David Charbonneau, Courtney D. Dressing, Xavier Dumusque, Sara Gettel, 

Mercedes Lopez-Morales, David Phillips, Dimitar Sasselov & Andrew Szentgyorgyi * INAF - Fundación Galileo Galilei, Rambla José Ana Fernandez Pérez 7, 38712 Breña Baja, Spain, Emilio

Molinari, Rosario Cosentino, Aldo F. M. Fiorenzano & Avet Harutyunyan * INAF - IASF Milano, via Bassini 15, 20133 Milano, Italy, Emilio Molinari * INAF - Osservatorio Astrofisico di

Torino, via Osservatorio 20, 10025 Pino Torinese, Italy, Aldo S. Bonomo & Alessandro Sozzetti * Centre for Star and Planet Formation, Natural History Museum of Denmark, University of

Copenhagen, DK-1350 Copenhagen, Denmark, Lars A. Buchhave * INAF - Osservatorio Astrofisico di Catania, via Santa Sofia 78, 95125 Catania, Italy, Rosario Cosentino * Centro de Astrofísica,

Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal, Pedro Figueira * Dipartimento di Fisica e Astronomia “Galileo Galilei”, Universita’ di Padova, Vicolo dell’Osservatorio 3,

35122 Padova, Italy, Luca Malavolta & Giampaolo Piotto * INAF - Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy, Luca Malavolta, Valerio Nascimbeni 

& Giampaolo Piotto * INAF - Osservatorio Astronomico di Palermo, Piazza del Parlamento 1, 90124 Palermo, Italy, Giusi Micela * Department of Physics, University of Warwick, Gibbet Hill

Road, Coventry CV4 7AL, UK, Don Pollacco * Cavendish Laboratory, J. J. Thomson Avenue, Cambridge CB3 0HE, UK, Didier Queloz * Scottish Universities Physics Alliance, Institute for Astronomy,

Royal Observatory, University of Edinburgh, Blackford Hill, Edinburgh EH93HJ, UK, Ken Rice * Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast,

Belfast BT7 1NN, UK, Christopher A. Watson Authors * Francesco Pepe View author publications You can also search for this author inPubMed Google Scholar * Andrew Collier Cameron View author

publications You can also search for this author inPubMed Google Scholar * David W. Latham View author publications You can also search for this author inPubMed Google Scholar * Emilio

Molinari View author publications You can also search for this author inPubMed Google Scholar * Stéphane Udry View author publications You can also search for this author inPubMed Google

Scholar * Aldo S. Bonomo View author publications You can also search for this author inPubMed Google Scholar * Lars A. Buchhave View author publications You can also search for this author

inPubMed Google Scholar * David Charbonneau View author publications You can also search for this author inPubMed Google Scholar * Rosario Cosentino View author publications You can also

search for this author inPubMed Google Scholar * Courtney D. Dressing View author publications You can also search for this author inPubMed Google Scholar * Xavier Dumusque View author

publications You can also search for this author inPubMed Google Scholar * Pedro Figueira View author publications You can also search for this author inPubMed Google Scholar * Aldo F. M.

Fiorenzano View author publications You can also search for this author inPubMed Google Scholar * Sara Gettel View author publications You can also search for this author inPubMed Google

Scholar * Avet Harutyunyan View author publications You can also search for this author inPubMed Google Scholar * Raphaëlle D. Haywood View author publications You can also search for this

author inPubMed Google Scholar * Keith Horne View author publications You can also search for this author inPubMed Google Scholar * Mercedes Lopez-Morales View author publications You can

also search for this author inPubMed Google Scholar * Christophe Lovis View author publications You can also search for this author inPubMed Google Scholar * Luca Malavolta View author

publications You can also search for this author inPubMed Google Scholar * Michel Mayor View author publications You can also search for this author inPubMed Google Scholar * Giusi Micela

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inPubMed Google Scholar CONTRIBUTIONS The underlying observation programme was conceived and organized by F.P., A.C.C., D.W.L., C.L., D. Ségransan, S.U. and E.M. Observations with HARPS-N

were carried out by A.C.C., A.S.B., D.C., R.C., C.D.D., X.D., P.F., A.F.M.F., S.G., A.H., R.D.H., M.L.-M., V.N., D. Pollacco, D.Q., K.R., A. Sozzetti, A. Szentgyorgyi and C.A.W. The

data-reduction pipeline was adapted and updated by C.L., who also implemented the correction for charge-transfer-efficiency errors and the automatic computation of the activity indicator

log(_R_′HK). M.L.-M. and S.G. independently computed the _S_-index and log(_R_′HK) values. A.C.C., D. Ségransan, A.S.B. and X.D. analysed the data using the offset-correction method. A.C.C.

and D. Ségransan re-analysed the data for the determination of the stellar rotational period based on the Kepler light curve. P.F. investigated for possible correlations between the radial

velocities and the line bisector. L.A.B. conducted the stellar parameter classification analysis for the re-determination of the stellar parameters based on HARPS-N spectra. An independent

determination of the stellar parameters was conducted by L.M. by analysis of the cross-correlation function. D. Ségransan compared many different models to fit the observed data and selected

the most appropriate by using the Bayesian information criterion. D. Ségransan performed a detailed MCMC analysis for the determination of the planetary parameters, with contributions also

from A.S.B. and A. Sozzetti. F.P. was the primary author of the manuscript, with important contributions by D.C., D. Ségransan, D. Sasselov, C.A.W., K.R. and C.L. All authors are members of

the HARPS-N Science Team and have contributed to the interpretation of the data and the results. CORRESPONDING AUTHOR Correspondence to Francesco Pepe. ETHICS DECLARATIONS COMPETING

INTERESTS The authors declare no competing financial interests. EXTENDED DATA FIGURES AND TABLES EXTENDED DATA FIGURE 1 GENERALIZED LOMB–SCARGLE PERIODOGRAM OF SEVERAL PARAMETERS MEASURED BY

HARPS-N. The panels show, from top to bottom, the periodogram of the radial velocities (RV) of Kepler-78, the line bisector (CCF-BIS), the activity indicator (log(_R_′HK)) and the

full-width at half maximum (CCF-FWHM) of Kepler-78. The dotted and dashed horizontal lines represent the 10% and 1% false-alarm probabilities, respectively. The vertical lines show the

stellar rotational period (solid) and its two first harmonics (dashed). All the indicators show excess energy at periods of around 6 d and above, indicating that the peak observed in the

radial-velocity data at a period of about 10 d is most likely to have a stellar origin. The additional power in the line bisector periodogram at periods longer than 1 d is most probably

induced by stellar spots. EXTENDED DATA FIGURE 2 KEPLER LIGHT CURVE OF KEPLER-78D. The data have been de-trended using the PDC-MAP algorithm. Different colours represent different quarters

of observation. EXTENDED DATA FIGURE 3 SPECTRAL ANALYSIS OF THE KEPLER LIGHT CURVE. Left panel, ACF of the Kepler light curve showing correlation peaks every 12.6 d and a decay on an

e-folding timescale of ∼50 d. Right panel, the power spectral distribution of the Kepler light curve. Peaks are well identified at the stellar rotational period of 12.6 d and its two first

harmonics. At shorter periods, the signal and several harmonics of the transiting planet Kepler-78b can be identified. EXTENDED DATA FIGURE 4 PERIODOGRAM OF THE RADIAL-VELOCITY RESIDUALS

AFTER SUBTRACTION OF THE 4.2-D AND 10.0-D STELLAR COMPONENTS. The dotted and dashed horizontal lines represent the 10% and 1% false-alarm probabilities, respectively. The signature of

Kepler-78b (and its aliases) can now clearly be identified with a false-alarm probability significantly lower than 1%. EXTENDED DATA FIGURE 5 PROBABILITY DENSITY FUNCTIONS DERIVED FROM THE

MCMC ANALYSIS. Probability density function of the planetary mass (left) and probability density function of the planetary density (right). SUPPLEMENTARY INFORMATION SUPPLEMENTARY DATA This

file contains HARPS-N Data for Kepler-78b. From left to right are given: Julian Date, Radial Velocity RV, the estimated error _σ_RV on the radial velocity, the Full-Width Half Maximum (FWHM)

and the line-bisector (BIS) of the Cross-Correlation Function (CCF), the CaII activity indicator log(R’HK) and its error _σ_log(R′HK. (TXT 6 kb) POWERPOINT SLIDES POWERPOINT SLIDE FOR FIG.

1 POWERPOINT SLIDE FOR FIG. 2 POWERPOINT SLIDE FOR FIG. 3 RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Pepe, F., Cameron, A., Latham, D. _et al._ An

Earth-sized planet with an Earth-like density. _Nature_ 503, 377–380 (2013). https://doi.org/10.1038/nature12768 Download citation * Received: 25 September 2013 * Accepted: 14 October 2013 *

Published: 30 October 2013 * Issue Date: 21 November 2013 * DOI: https://doi.org/10.1038/nature12768 SHARE THIS ARTICLE Anyone you share the following link with will be able to read this

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