A Neptune-Mass Planet Orbiting the Nearby M Dwarf GJ 436

By P. Butler, S. Vogt, G. Marcy, Debra A. Fischer, Jason T. Wright, G. Henry, Gregory Laughlin, Jack J. Lissauer. 2004

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We report precise Doppler measurements of GJ 436 (M2.5 V) obtained at Keck Observatory. The velocities reveal a planetary companion with orbital period of 2.644 days, eccentricity of 0.12 (consistent with zero), and velocity semiamplitude of K = 18.1 m s-1. The minimum mass (M sin i) for the planet is 0.067MJup = 1.2MNep = 21MEarth, making it the lowest mass exoplanet yet found around a main-sequence star and the first candidate in the Neptune-mass domain. GJ 436 (mass = 0.41 M☉) is only the second M dwarf found to harbor a planet, joining the two-planet system around GJ 876. The low mass of the planet raises questions about its constitution, with possible compositions of primarily H and He gas, ice/rock, or rock-dominated. The implied semimajor axis is a = 0.028 AU = 14 stellar radii, raising issues of planet formation, migration, and tidal coupling with the star. GJ 436 is more than 3 Gyr old, based on both kinematic and chromospheric diagnostics. The star exhibits no photometric variability on the 2.644 day Doppler period to a limiting amplitude of 0.0004 mag, supporting the planetary interpretation of the Doppler periodicity. Photometric transits of the planet across the star are ruled out for gas giant compositions and are also unlikely for solid compositions. As the third closest known planetary system, GJ 436 warrants follow-up observations by high-resolution optical and infrared imaging and by the Space Interferometry Mission.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/acf041a41d5e20773c41865c177a947a7d7fa74f

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The HARPS search for southern extra-solar planets - XXXI. The M-dwarf sample (2011, background): “E P] 2 3 N ov 2 X. Bonfils et al.: The HARPS M-dwarf sample sun-like stars (Bonfils et al. 2006; Butler et al. 2004; Endl et al. 2006; Johnson et al. 2007; Cumming et al. 2008).”
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PLANETS AROUND LOW-MASS STARS (PALMS). IV. THE OUTER ARCHITECTURE OF M DWARF PLANETARY SYSTEMS (2014, background): “This well-established trend between planet occurrence rate and stellar host mass (Butler et al. 2004; Endl et al. 2006; Butler et al. 2006; Johnson et al. 2007; Lovis & Mayor 2007; Cumming et al. 2008; Bowler et al. 2010; Bonfils et al. 2013; Gaidos et al. 2013) lends support to the core accretion…”
A FRAMEWORK FOR QUANTIFYING THE DEGENERACIES OF EXOPLANET INTERIOR COMPOSITIONS (2009, background): “A good example of why quantitative methods to constrain planetary interior compositions are needed is GJ 436b (Butler et al. 2004; Gillon et al. 2007b), a Neptune-mass (Mp = 23.17 ± 0.79M⊕,; Torres et al. (2008)), Neptune-size (Rp = 4.22 +0.09 −0.10R⊕; Torres et al. (2008)) planet in a 2.6-day…”
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The Occurrence and Architecture of Exoplanetary Systems (2014, background): “One secure result is that they have fewer giant planets with P <∼ 1 yr than FGK dwarfs (Butler et al. 2004, Endl et al. 2006, Johnson et al. 2007, Bonfils et al. 2013).”
A New Window into Escaping Exoplanet Atmospheres: 10830 Å Line of Helium (2017, background): “We choose these parameters so that they match the properties of two well-studied exoplanets known to have escaping atmospheres: GJ 436b (Butler et al. 2004), a Neptune-sized planet orbiting an M-type star, and HD 209458b (Henry et al. 2000; Charbonneau et al. 2000), a hot Jupiter around a Sun-like…”
LYα TRANSIT SPECTROSCOPY AND THE NEUTRAL HYDROGEN TAIL OF THE HOT NEPTUNE GJ 436b (2014, methodology): “While many studies utilize IR (700 nm − 3 µm) (e.g. Deming et al. 2007) and optical (400 − 700 nm) (e.g. Butler et al. 2004) wavelengths, UV (1000− 4000 Å) observations provide a unique opportunity to characterize exoplanet exospheres.”
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Toward a Deterministic Model of Planetary Formation. III. Mass Distribution of Short-Period Planets around Stars of Various Masses (2005, background): “But, the much lower mass Mp of GJ436b implies that gas accretion onto it may have been greatly suppressed prior to, during, and after its migration.”
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MULTIWAVELENGTH CONSTRAINTS ON THE DAY–NIGHT CIRCULATION PATTERNS OF HD 189733b (2008, background): “…that information on the atmospheric dynamics of these planets will be applicable to smaller, core-dominated planets such as HD 149026b and GJ 436b (Butler et al. 2004; Sato et al. 2005; Fortney et al. 2006a; Gillon et al. 2007; Deming et al. 2007; Torres et al. 2007; Adams et al. 2008; Winn et…”
AN EFFICIENT AUTOMATED VALIDATION PROCEDURE FOR EXOPLANET TRANSIT CANDIDATES (2012, background): “…face of their host stars were all initially discovered by Doppler surveys, which detected minute radial velocity (RV) variations of stars indicative of the gravitational tug of orbiting planets (Charbonneau et al. 2000; Henry et al. 2000; Butler et al. 2004; Bouchy et al. 2005; Sato et al. 2005).”
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