A super-Earth and two sub-Neptunes transiting the nearby and quiet M dwarf TOI-270


One of the primary goals of exoplanetary science is to detect small, temperate planets passing (transiting) in front of bright and quiet host stars. This enables the characterization of planetary sizes, orbits, bulk compositions, atmospheres and formation histories. These studies are facilitated by small and cool M dwarf host stars. Here we report the Transiting Exoplanet Survey Satellite (TESS)1 discovery of three small planets transiting one of the nearest and brightest M dwarf hosts observed to date, TOI-270 (TIC 259377017, with K-magnitude 8.3, and 22.5 parsecs away from Earth). The M3V-type star is transited by the super-Earth-sized planet TOI-270 b (\({1.247}_{ - 0.083}^{ + 0.089}\) R) and the sub-Neptune-sized planets TOI-270 c (2.42 ± 0.13 R) and TOI-270 d (2.13 ± 0.12 R). The planets orbit close to a mean-motion resonant chain, with periods (3.36 days, 5.66 days and 11.38 days, respectively) near ratios of small integers (5:3 and 2:1). TOI-270 is a prime target for future studies because (1) its near-resonance allows the detection of transit timing variations, enabling precise mass measurements and dynamical studies; (2) its brightness enables independent radial-velocity mass measurements; (3) the outer planets are ideal for atmospheric characterization via transmission spectroscopy; and (4) the quietness of the star enables future searches for habitable zone planets. Altogether, very few systems with small, temperate exoplanets are as suitable for such complementary and detailed characterization as TOI-270.

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Fig. 1: The discovery data and orbits of the super-Earth and two sub-Neptunes transiting TOI-270.
Fig. 2: TOI-270 in the context of known exoplanets.
Fig. 3: Expected and apparent TTVs of the TOI-270 system.

Data availability

The TESS data analysed during the current study are available in the Mikulski Archive for Space Telescopes (MAST; http://archive.stsci.edu). The VLT NAOS-CONICA data analysed during the current study are available in the European Southern Observatory archive (http://archive.eso.org). All other datasets analysed and/or generated during the current study are available from M.N.G. on reasonable request.

Code availability

The following code used during the current study is publicly available (access information given in the respective references): python88, numpy89, scipy90, matplotlib91, tqdm (https://doi.org/10.5281/zenodo.1468033), seaborn (https://seaborn.pydata.org/index.html), allesfitter75, ellc76, aflare77, dynesty78, corner92, TESS Transit Finder, a customized version of the Tapir software package93, AstroImageJ94, ttvfast7 and REBOUND95. Any customized scripts built on these codes are available from M.N.G. on reasonable request.

Change history

  • 15 August 2019

    An amendment to this paper has been published and can be accessed via a link at the top of the paper.


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We thank B. J. Fulton and E. Petigura for providing their data to recreate the radius gap histogram in Fig. 2. Funding for the TESS mission is provided by NASA’s Science Mission directorate. We acknowledge the use of public TESS Alert data from pipelines at the TESS Science Office and at the TESS Science Processing Operations Center. This research has made use of the Exoplanet Follow-up Observation Program website, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. This paper includes data collected by the TESS mission, which are publicly available from the Mikulski Archive for Space Telescopes (MAST). Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center for the production of the SPOC data products. TRAPPIST is funded by the Belgian Fund for Scientific Research (Fond National de la Recherche Scientifique, FNRS) under the grant FRFC 2.5.594.09.F, with the participation of the Swiss National Science Fundation (SNF). The research leading to these results has received funding from the ARC grant for Concerted Research Actions, financed by the Wallonia-Brussels Federation. This work uses observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere under ESO programme 102.C-0503(A). This work makes use of results from the European Space Agency (ESA) space mission Gaia. Gaia data are being processed by the Gaia Data Processing and Analysis Consortium (DPAC). Funding for the DPAC is provided by national institutions, in particular the institutions participating in the Gaia MultiLateral Agreement (MLA). This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This research has made use of NASA’s Astrophysics Data System Bibliographic Services. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. M.N.G., C.X.H. and J.B. acknowledge support from MIT’s Kavli Institute as Torres postdoctoral fellows. D.D. acknowledges support for this work provided by NASA through Hubble Fellowship grant HST-HF2-51372.001-A, awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy for NASA, under contract NAS5-26555. T.D. acknowledges support from MIT’s Kavli Institute as a Kavli postdoctoral fellow. Work by B.T.M. was performed under contract with the Jet Propulsion Laboratory (JPL) funded by NASA through the Sagan Fellowship Program executed by the NASA Exoplanet Science Institute. J.G.W. is supported by a grant from the John Templeton Foundation. The opinions expressed in this publication are those of the authors and do not necessarily reflect the views of the John Templeton Foundation. S.W. thanks the Heising-Simons Foundation for their generous support. M.G. and E.J. are FNRS Senior Research Associates. K.H. acknowledges support from STFC grant ST/R000824/1. B.R.-A. acknowledges funding support from Conicyt Pai/Concurso Nacional Inserción En La Academia, Convocatoria 2015 79150050 and Fondecyt through grant 11181295. J.C.S. acknowledges funding support from Spanish public funds for research under projects ESP2017-87676-2-2 and RYC-2012-09913 (Ramón y Cajal programme) of the Spanish Ministry of Science and Education. J.A.D. is a 51 Pegasi b Postdoctoral Fellow.

Author information

M.N.G. led the project and performed and interpreted the global analyses. F.J.P., K.A.C., J.D.A., K.B., K.I.C., T.G., M.G., K.H., G.I., E.J., J.F.K., F.M., G.M., E.P., H.M.R., R.S., J.C.S., T.-G.T., A.S. and I.A.W. carried out the TFOP SG1 photometric follow-up. A.D.F., B.T.M., L.G.B., J.B., J.L.B., M.I. and S.N.Q. carried out the TFOP SG2 spectroscopic follow-up. E.M., D.R.C., I.C., S.B.H., R.A.M. and J.S. performed the TFOP SG3 direct imaging follow-up. F.J.P. worked on the dynamic stability and tides simulations. J.A.D. worked on the stellar parameters (along with A.D.F. and B.T.M.), TTV simulations and Australia National University spectral analysis. D.D. and T.D. performed the global light curve analysis and TTV analysis and D.D. additionally produced the atmospheric characterization prospects. S.R.K. worked on the dynamic stability simulations and habitability prospects. A.D.F. and B.T.M. worked on the FIRE spectra analysis, and C.H., T.D.M. and A.B. worked on the TESS light curve analysis, false positive analysis and stellar parameter analysis, respectively. J.J.L. looked at the orbital dynamics, resonances, and TTVs. A.V. did the archival image analysis and TESS light curve analysis. S.W. contributed to the global light curve analysis. J.G.W. performed the overluminous binary analysis and Hertzsprung−Russell diagram analysis. G.R.R., R.K.V., D.W.L., S.S., J.N.W. and J.M.J. are TESS architects. N.B., N.G., S.L. and B.R.-A. are members of the TESS Science office. D.A.C., G.F., E.B.T. and J.D.T. are members of the TESS Science Processing Operations Center, while M.F. is a member of the TESS Payload Operations Center.

Correspondence to Maximilian N. Günther.

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Günther, M.N., Pozuelos, F.J., Dittmann, J.A. et al. A super-Earth and two sub-Neptunes transiting the nearby and quiet M dwarf TOI-270. Nat Astron 3, 1099–1108 (2019). https://doi.org/10.1038/s41550-019-0845-5

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