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Published April 19, 2017 | Submitted + Supplemental Material
Journal Article Open

A temperate rocky super-Earth transiting a nearby cool star


M dwarf stars, which have masses less than 60 per cent that of the Sun, make up 75 per cent of the population of the stars in the Galaxy. The atmospheres of orbiting Earth-sized planets are observationally accessible via transmission spectroscopy when the planets pass in front of these stars. Statistical results suggest that the nearest transiting Earth-sized planet in the liquid-water, habitable zone of an M dwarf star is probably around 10.5 parsecs away. A temperate planet has been discovered orbiting Proxima Centauri, the closest M dwarf, but it probably does not transit and its true mass is unknown. Seven Earth-sized planets transit the very low-mass star TRAPPIST-1, which is 12 parsecs away, but their masses and, particularly, their densities are poorly constrained. Here we report observations of LHS 1140b, a planet with a radius of 1.4 Earth radii transiting a small, cool star (LHS 1140) 12 parsecs away. We measure the mass of the planet to be 6.6 times that of Earth, consistent with a rocky bulk composition. LHS 1140b receives an insolation of 0.46 times that of Earth, placing it within the liquid-water, habitable zone. With 90 per cent confidence, we place an upper limit on the orbital eccentricity of 0.29. The circular orbit is unlikely to be the result of tides and therefore was probably present at formation. Given its large surface gravity and cool insolation, the planet may have retained its atmosphere despite the greater luminosity (compared to the present-day) of its host star in its youth. Because LHS 1140 is nearby, telescopes currently under construction might be able to search for specific atmospheric gases in the future.

Additional Information

© 2017 Macmillan Publishers Limited, part of Springer Nature. Received 22 December 2016; Accepted 09 March 2017; Published online 19 April 2017. We thank the staff at the Cerro Tololo Inter-American Observatory for assistance in the construction and operation of MEarth-South. The MEarth team acknowledges funding from the David and Lucille Packard Fellowship for Science and Engineering (awarded to D.C.). This material is based on work supported by the National Science Foundation under grants AST-0807690, AST-1109468, AST-1004488 (Alan T. Waterman Award) and AST-1616624. This publication was made possible through the support of a grant from the John Templeton Foundation and NASA XRP Program #NNX15AC90G. The opinions expressed in this publication are those of the authors and do not necessarily reflect the views of the John Templeton Foundation. HARPS observations were made with European Southern Observatory (ESO) telescopes under observing programs 191.C-0873 and 198.C-0838. This work was performed in part under contract with the Jet Propulsion Laboratory (JPL) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. E.R.N. is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-1602597. N.C.S. acknowledges support from Fundação para a Ciência e a Tecnologia (FCT) through national funds and by FEDER through COMPETE2020 by grants UID/FIS/04434/2013&POCI-01-0145-FEDER-007672 and PTDC/FIS-AST/1526/2014&POCI-01-0145-FEDER-016886. N.C.S. was also supported by FCT through Investigador FCT contract reference IF/00169/2012/CP0150/CT0002. X.B., X.D. and T.F. acknowledge the support of the INSU/PNP (Programme national de planétologie) and INSU/PNPS (Programme national de physique stellaire). X.B., J.-M.A. and A.W. acknowledge funding from the European Research Council under ERC Grant Agreement no. 337591-ExTrA. We thank A. Vanderburg for backseat MCMCing. This publication makes use of data products from the Two Micron All Sky Survey (2MASS), which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by NASA and the National Science Foundation. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the JPL/California Institute of Technology, funded by NASA. This research has made extensive use of the NASA Astrophysics Data System (ADS), and the SIMBAD database, operated at CDS, Strasbourg, France. Code availability: The EMCEE code is available as a Python install and is publicly available on GitHub (https://github.com/dfm/emcee). JKTEBOP and the modifications performed to it are also publicly available on GitHub (https://github.com/mdwarfgeek/eb). These codes were used to produce the light curve and radial-velocity models used in the analysis of our data. The code used to determine the planetary orbit and mass, with Gaussian process regression to account for the magnetic activity variations of the host star, is not yet publically available, but we are currently working to make it so. Data availability: All data used in this work are provided as Supplementary Data, and are available on the MEarth project webpage (https://www.cfa.harvard.edu/MEarth/Welcome.html) and via the online repository FigShare (https://figshare.com/s/9e2b29d4f7a8043ca071 for MEarth and PEST photometry; https://figshare.com/s/49625e95aabf9e1f2ae6 for HARPS radial-velocity data). The authors declare no competing financial interests. Nature thanks A. Hatzes and the other anonymous reviewer(s) for their contribution to the peer review of this work.

Attached Files

Submitted - 1704.05556.pdf

Supplemental Material - nature22055-s1.txt

Supplemental Material - nature22055-s2.txt

Supplemental Material - nature22055-sf1.jpg

Supplemental Material - nature22055-sf2.jpg

Supplemental Material - nature22055-sf3.jpg

Supplemental Material - nature22055-sf4.jpg

Supplemental Material - nature22055-sf5.jpg

Supplemental Material - nature22055-sf6.jpg

Supplemental Material - nature22055-sf7.jpg

Supplemental Material - nature22055-sf8.jpg


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August 19, 2023
October 25, 2023