Three Red Suns in the Sky: A Transiting, Terrestrial Planet in a Triple M-dwarf System at 6.9 pc

We present the discovery from Transiting Exoplanet Survey Satellite (TESS) data of LTT 1445Ab. At a distance of 6.9 pc, it is the second nearest transiting exoplanet system found to date, and the closest one known for which the primary is an M dwarf. The host stellar system consists of three mid-to-late M dwarfs in a hierarchical configuration, which are blended in one TESS pixel. We use MEarth data and results from the Science Processing Operations Center data validation report to determine that the planet transits the primary star in the system. The planet has a radius of , an orbital period of days, and an equilibrium temperature of K. With radial velocities from the High Accuracy Radial Velocity Planet Searcher, we place a 3σ upper mass limit of 8.4 on the planet. LTT 1445Ab provides one of the best opportunities to date for the spectroscopic study of the atmosphere of a terrestrial world. We also present a detailed characterization of the host stellar system. We use high-resolution spectroscopy and imaging to rule out the presence of any other close stellar or brown dwarf companions. Nineteen years of photometric monitoring of A and BC indicate a moderate amount of variability, in agreement with that observed in the TESS light-curve data. We derive a preliminary astrometric orbit for the BC pair that reveals an edge-on and eccentric configuration. The presence of a transiting planet in this system hints that the entire system may be co-planar, implying that the system may have formed from the early fragmentation of an individual protostellar core.

[1]  S. Schmidt,et al.  The Ultracool SpeXtroscopic Survey. I. Volume-limited Spectroscopic Sample and Luminosity Function of M7−L5 Ultracool Dwarfs , 2019, The Astrophysical Journal.

[2]  A. D. Feinstein,et al.  Characterizing K2 Candidate Planetary Systems Orbiting Low-mass Stars. IV. Updated Properties for 86 Cool Dwarfs Observed during Campaigns 1–17 , 2019, The Astrophysical journal.

[3]  A. Szentgyorgyi,et al.  Optimizing Ground-based Observations of O2 in Earth Analogs , 2019, The Astronomical Journal.

[4]  J. Haislip,et al.  EvryFlare. I. Long-term Evryscope Monitoring of Flares from the Cool Stars across Half the Southern Sky , 2019, The Astrophysical Journal.

[5]  Kenneth J. Slatten,et al.  The Solar Neighborhood. XLV. The Stellar Multiplicity Rate of M Dwarfs Within 25 pc , 2019, The Astronomical Journal.

[6]  David P. Fleming,et al.  STARRY: Analytic computation of occultation light curves , 2018 .

[7]  Sara Seager,et al.  TESS Discovery of an Ultra-short-period Planet around the Nearby M Dwarf LHS 3844 , 2018, The Astrophysical Journal.

[8]  Joseph E. Rodriguez,et al.  A Second Terrestrial Planet Orbiting the Nearby M Dwarf LHS 1140 , 2018, The Astronomical Journal.

[9]  F. Bouchy,et al.  Radial velocity follow-up of GJ1132 with HARPS , 2018, Astronomy & Astrophysics.

[10]  Steve B. Howell,et al.  Stellar Companions of Exoplanet Host Stars in K2 , 2018, The Astronomical Journal.

[11]  T. A. Lister,et al.  Gaia Data Release 2. Summary of the contents and survey properties , 2018, 1804.09365.

[12]  J. Winters,et al.  The Solar Neighborhood XLIV: RECONS Discoveries within 10 parsecs , 2018, The Astronomical Journal.

[13]  Jie Li,et al.  Kepler Data Validation I—Architecture, Diagnostic Tests, and Data Products for Vetting Transiting Planet Candidates , 2018, 1803.04526.

[14]  Kevin Heng,et al.  The nature of the TRAPPIST-1 exoplanets. , 2018, 1802.01377.

[15]  Daniel Foreman-Mackey,et al.  Scalable Backpropagation for Gaussian Processes using Celerite , 2018, 1801.10156.

[16]  P. Berlind,et al.  LHS 1610A: A Nearby Mid-M Dwarf with a Companion That Is Likely a Brown Dwarf , 2018, 1801.07340.

[17]  Sarah Ballard,et al.  Predicted Number, Multiplicity, and Orbital Dynamics of TESS M-dwarf Exoplanets , 2018, The Astronomical Journal.

[18]  Miguel de Val-Borro,et al.  The Astropy Project: Building an Open-science Project and Status of the v2.0 Core Package , 2018, The Astronomical Journal.

[19]  Philip S. Muirhead,et al.  Supplementary online material for article, "A Catalog of Cool Dwarf Targets for the Transiting Exoplanet Survey Satellite" , 2018 .

[20]  Tyler Robinson,et al.  Observing the Atmospheres of Known Temperate Earth-sized Planets with JWST , 2017, 1708.04239.

[21]  CA,et al.  The Densities of Planets in Multiple Stellar Systems , 2017, 1707.01942.

[22]  Keivan G. Stassun,et al.  The TESS Input Catalog and Candidate Target List , 2017, The Astronomical Journal.

[23]  Joseph E. Rodriguez,et al.  A temperate rocky super-Earth transiting a nearby cool star , 2017, Nature.

[24]  A. Claret.  Limb and gravity-darkening coefficients for the TESS satellite at several metallicities, surface gravities, and microturbulent velocities , 2017 .

[25]  Daniel Foreman-Mackey,et al.  Fast and Scalable Gaussian Process Modeling with Applications to Astronomical Time Series , 2017, 1703.09710.

[26]  D. Ciardi,et al.  Observations of Binary Stars with the Differential Speckle Survey Instrument. VII. Measures from 2010 September to 2012 February at the WIYN Telescope , 2017, 1703.06253.

[27]  S. Udry,et al.  Two massive rocky planets transiting a K-dwarf 6.5 parsecs away , 2017, Nature Astronomy.

[28]  Steve B. Howell,et al.  Assessing the Effect of Stellar Companions from High-resolution Imaging of Kepler Objects of Interest , 2017, 1701.06577.

[29]  P. Cargile,et al.  THE SOLAR NEIGHBORHOOD. XXXVII. THE MASS–LUMINOSITY RELATION FOR MAIN-SEQUENCE M DWARFS , 2016, 1608.04775.

[30]  Peter Tenenbaum,et al.  The TESS science processing operations center , 2016, Astronomical Telescopes + Instrumentation.

[31]  P. Magain,et al.  Temperate Earth-sized planets transiting a nearby ultracool dwarf star , 2016, Nature.

[32]  S. Thompson,et al.  Kepler Archive Manual , 2016 .

[33]  M. Ireland,et al.  THE IMPACT OF STELLAR MULTIPLICITY ON PLANETARY SYSTEMS. I. THE RUINOUS INFLUENCE OF CLOSE BINARY COMPANIONS , 2016, 1604.05744.

[34]  John Salvatier,et al.  Probabilistic programming in Python using PyMC3 , 2016, PeerJ Comput. Sci..

[35]  Xavier Bonfils,et al.  A rocky planet transiting a nearby low-mass star , 2015, Nature.

[36]  Elliott P. Horch,et al.  OBSERVATIONS OF BINARY STARS WITH THE DIFFERENTIAL SPECKLE SURVEY INSTRUMENT. VI. MEASURES DURING 2014 AT THE DISCOVERY CHANNEL TELESCOPE , 2015, 1509.03498.

[37]  Maria Mercedes Lopez-Morales,et al.  The HARPS-N Rocky Planet Search. I. HD 219134 b: A transiting rocky planet in a multi-planet system at 6.5 pc from the Sun , 2015, 1507.08532.

[38]  C. Henze,et al.  DISCOVERY AND VALIDATION OF Kepler-452b: A 1.6 R⨁ SUPER EARTH EXOPLANET IN THE HABITABLE ZONE OF A G2 STAR , 2015, 1507.06723.

[39]  Charles A. Beichman,et al.  UNDERSTANDING THE EFFECTS OF STELLAR MULTIPLICITY ON THE DERIVED PLANET RADII FROM TRANSIT SURVEYS: IMPLICATIONS FOR KEPLER, K2, AND TESS , 2015, 1503.03516.

[40]  John C. Lurie,et al.  THE SOLAR NEIGHBORHOOD. XXXVI. THE LONG-TERM PHOTOMETRIC VARIABILITY OF NEARBY RED DWARFS IN THE VRI OPTICAL BANDS , 2015, 1503.02100.

[41]  A. Rajan,et al.  The M-dwarfs in Multiples (MinMs) survey – I. Stellar multiplicity among low-mass stars within 15 pc , 2015, 1503.00724.

[42]  D. Charbonneau,et al.  THE OCCURRENCE OF POTENTIALLY HABITABLE PLANETS ORBITING M DWARFS ESTIMATED FROM THE FULL KEPLER DATASET AND AN EMPIRICAL MEASUREMENT OF THE DETECTION SENSITIVITY , 2015, 1501.01623.

[43]  K. Braun,et al.  HOW TO CONSTRAIN YOUR M DWARF: MEASURING EFFECTIVE TEMPERATURE, BOLOMETRIC LUMINOSITY, MASS, AND RADIUS , 2015, 1501.01635.

[44]  M. Ireland,et al.  KEPLER-445, KEPLER-446 AND THE OCCURRENCE OF COMPACT MULTIPLES ORBITING MID-M DWARF STARS , 2015, 1501.01305.

[45]  A. Szentgyorgyi,et al.  THE MASS OF Kepler-93b AND THE COMPOSITION OF TERRESTRIAL PLANETS , 2014, 1412.8687.

[46]  D. Queloz,et al.  The HARPS search for southern extra-solar planets - XXXVI. Planetary systems and stellar activity of the M dwarfs GJ 3293, GJ 3341, and GJ 3543 , 2014, 1411.7048.

[47]  Joshua N. Winn,et al.  The Occurrence and Architecture of Exoplanetary Systems , 2014, 1410.4199.

[48]  L. Rogers.  MOST 1.6 EARTH-RADIUS PLANETS ARE NOT ROCKY , 2014, 1407.4457.

[49]  D. Ciardi,et al.  INFLUENCE OF STELLAR MULTIPLICITY ON PLANET FORMATION. II. PLANETS ARE LESS COMMON IN MULTIPLE-STAR SYSTEMS WITH SEPARATIONS SMALLER THAN 1500 AU , 2014, 1407.3344.

[50]  Observatoire de Geneve,et al.  Metallicity of M dwarfs - IV. A high-precision [Fe/H] and Teff technique from high-resolution optical spectra for M dwarfs , 2014, 1406.6127.

[51]  Mark Clampin,et al.  Transiting Exoplanet Survey Satellite , 2014, 1406.0151.

[52]  Shawn Domagal-Goldman,et al.  HABITABLE ZONES AROUND MAIN-SEQUENCE STARS: DEPENDENCE ON PLANETARY MASS , 2014, 1404.5292.

[53]  J. Winters,et al.  THE SOLAR NEIGHBORHOOD. XXXII. THE HYDROGEN BURNING LIMIT, , 2013, 1312.1736.

[54]  Mercedes Lopez-Morales,et al.  FEASIBILITY STUDIES FOR THE DETECTION OF O2 IN AN EARTH-LIKE EXOPLANET , 2013, 1312.1585.

[55]  Thomas Barclay,et al.  INFLUENCE OF STELLAR MULTIPLICITY ON PLANET FORMATION. I. EVIDENCE OF SUPPRESSED PLANET FORMATION DUE TO STELLAR COMPANIONS WITHIN 20 AU AND VALIDATION OF FOUR PLANETS FROM THE KEPLER MULTIPLE PLANET CANDIDATES , 2013, 1309.7097.

[56]  D. Kipping.  Efficient, uninformative sampling of limb darkening coefficients for two-parameter laws , 2013, 1308.0009.

[57]  Prasanth H. Nair,et al.  Astropy: A community Python package for astronomy , 2013, 1307.6212.

[58]  E. Mamajek,et al.  INTRINSIC COLORS, TEMPERATURES, AND BOLOMETRIC CORRECTIONS OF PRE-MAIN-SEQUENCE STARS , 2013, 1307.2657.

[59]  Harvard-Smithsonian CfA,et al.  Stellar Multiplicity , 2013, 1303.3028.

[60]  R. Poole,et al.  FINDING EXTRATERRESTRIAL LIFE USING GROUND-BASED HIGH-DISPERSION SPECTROSCOPY , 2013, 1302.3251.

[61]  R. Deshpande,et al.  HABITABLE ZONES AROUND MAIN-SEQUENCE STARS: NEW ESTIMATES , 2013, 1301.6674.

[62]  Russel J. White,et al.  STELLAR DIAMETERS AND TEMPERATURES. II. MAIN-SEQUENCE K- AND M-STARS , 2012, 1208.2431.

[63]  B. Scott Gaudi,et al.  EXOFAST: A Fast Exoplanetary Fitting Suite in IDL , 2012, 1206.5798.

[64]  J. Krist,et al.  THE SOLAR NEIGHBORHOOD. XXVIII. THE MULTIPLICITY FRACTION OF NEARBY STARS FROM 5 TO 70 AU AND THE BROWN DWARF DESERT AROUND M DWARFS , 2012, 1206.1022.

[65]  Martin C. Stumpe,et al.  Kepler Presearch Data Conditioning II - A Bayesian Approach to Systematic Error Correction , 2012, 1203.1383.

[66]  Hema Chandrasekaran,et al.  Presearch data conditioning in the Kepler Science Operations Center pipeline , 2010, Astronomical Telescopes + Instrumentation.

[67]  M. R. Haas,et al.  OVERVIEW OF THE KEPLER SCIENCE PROCESSING PIPELINE , 2010, 1001.0258.

[68]  Andrei Tokovinin,et al.  SPECKLE INTERFEROMETRY AT THE BLANCO AND SOAR TELESCOPES IN 2008 AND 2009 , 2009, 0911.5718.

[69]  A. Eggenberger,et al.  Detection and Characterization of Planets in Binary and Multiple Systems , 2009, 0910.3332.

[70]  Roberto Baena Gallé,et al.  OBSERVATIONS OF BINARY STARS WITH THE DIFFERENTIAL SPECKLE SURVEY INSTRUMENT. I. INSTRUMENT DESCRIPTION AND FIRST RESULTS , 2009 .

[71]  F. Pepe,et al.  A new list of thorium and argon spectral lines in the visible , 2007, astro-ph/0703412.

[72]  M. Irwin,et al.  The Monitor project: data processing and light curve production , 2006, astro-ph/0612395.

[73]  Philip A. Ianna,et al.  The Solar Neighborhood. XVII. Parallax Results from the CTIOPI 0.9 m Program: 20 New Members of the RECONS 10 Parsec Sample , 2006, astro-ph/0608230.

[74]  F. Adams,et al.  Long-Term Evolution of Close Planets Including the Effects of Secular Interactions , 2006, astro-ph/0606349.

[75]  M. Skrutskie,et al.  The Two Micron All Sky Survey (2MASS) , 2006 .

[76]  Brian D. Mason,et al.  The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog , 2001 .

[77]  Nigel Hambly,et al.  The SuperCOSMOS Sky Survey – II. Image detection, parametrization, classification and photometry , 2001, astro-ph/0108290.

[78]  F. Bouchy,et al.  Fundamental photon noise limit to radial velocity measurements , 2001 .

[79]  M. Holman,et al.  Long-Term Stability of Planets in Binary Systems , 1996, astro-ph/9809315.

[80]  Todd J. Henry,et al.  The mass-luminosity relation for stars of mass 1.0 to 0.08 solar mass , 1993 .

[81]  W. Luyten.  A Catalogue of 7127 Stars in the Northern Hemisphere with Proper Motions Exceeding 0.2 seconds Annually , 1957 .

[82]  David P. Fleming,et al.  ${\mathtt{s}}{\mathtt{t}}{\mathtt{a}}{\mathtt{r}}{\mathtt{r}}{\mathtt{y}}$: Analytic Occultation Light Curves , 2019, The Astronomical Journal.

[83]  S. P. Littlefair,et al.  THE ASTROPY PROJECT: BUILDING AN INCLUSIVE, OPEN-SCIENCE PROJECT AND STATUS OF THE V2.0 CORE PACKAGE , 2018 .

[84]  Martin C. Stumpe,et al.  Multiscale Systematic Error Correction via Wavelet-Based Bandsplitting in Kepler Data , 2014 .

[85]  C. Loore,et al.  The Formation of Stars , 1992 .

[86]  R. Dvorak.  Planetenbahnen in Doppelsternsystemen. , 1982 .

[87]  A. Brun.  A catalogue of 9867 stars in the Southern Hemisphere with proper motions exceeding 0".2 annually , 1957 .

[88]  R. A. Rossiter.  Catalogue of Southern Double Stars , 1955 .