A 1.9 Earth radius rocky planet and the discovery of a non-transiting planet in the Kepler-20 system

Abstract

Kepler-20 is a solar-type star (V = 12.5) hosting a compact system of five transiting planets, all packed within the orbital distance of Mercury in our own Solar System. A transition from rocky to gaseous planets with a planetary transition radius of ~1.6 REarth has recently been proposed by several publications in the literature (Rogers 2015;Weiss & Marcy 2014). Kepler-20b (Rp ~ 1.9 REarth) has a size beyond this transition radius, however previous mass measurements were not sufficiently precise to allow definite conclusions to be drawn regarding its composition. We present new mass measurements of three of the planets in the Kepler-20 system facilitated by 104 radial velocity measurements from the HARPS-N spectrograph and 30 archival Keck/HIRES observations, as well as an updated photometric analysis of the Kepler data and an asteroseismic analysis of the host star (MStar = 0.948+-0.051 Msun and Rstar = 0.964+-0.018 Rsun). Kepler-20b is a 1.868+0.066-0.034 REarth planet in a 3.7 day period with a mass of 9.70+1.41-1.44 MEarth resulting in a mean density of 8.2+1.5-1.3 g/cc indicating a rocky composition with an iron to silicate ratio consistent with that of the Earth. This makes Kepler-20b the most massive planet with a rocky composition found to date. Furthermore, we report the discovery of an additional non-transiting planet with a minimum mass of 19.96+3.08-3.61 MEarth and an orbital period of ~34 days in the gap between Kepler-20f (P ~ 11 days) and Kepler-20d (P ~ 78 days).

arXiv comment33 pages, 8 figures. Accepted for publication in AJ

References in corpus (45)

• Analytic Lightcurves for Planetary Transit Searches
• The generalised Lomb-Scargle periodogram. A new formalism for the floating-mean and Keplerian periodograms
• Planet Occurrence within 0.25 AU of Solar-type Stars from Kepler
• batman: BAsic Transit Model cAlculatioN in Python
• Planetary Candidates Observed by Kepler, III: Analysis of the First 16 Months of Data
• Characteristics of planetary candidates observed by Kepler, II: Analysis of the first four months of data
• On the Unique Solution of Planet and Star Parameters from an Extrasolar Planet Transit Light Curve
• Prevalence of Earth-size planets orbiting Sun-like stars
• The CoRoT satellite in flight : description and performance
• Most 1.6 Earth-Radius Planets are not Rocky
• The Occurrence Rate of Small Planets around Small Stars
• The Mass-Radius Relation for 65 Exoplanets Smaller than 4 Earth Radii
• The CORALIE survey for southern extra-solar planets VII. Two short-period Saturnian companions to HD108147 and HD168746
• The Second-Generation Guide Star Catalog: Description and Properties
• Asteroseismology of Solar-Type and Red-Giant Stars
• Improved parameters for extrasolar transiting planets
• The Role of Core Mass in Controlling Evaporation: the Kepler Radius Distribution and the Kepler-36 Density Dichotomy
• Improving the Efficiency of Markov Chain Monte Carlo for Analyzing the Orbits of Extrasolar Planets
• How Thermal Evolution and Mass Loss Sculpt Populations of Super-Earths and Sub-Neptunes: Application to the Kepler-11 System and Beyond
• Terrestrial Planet Occurrence Rates for the Kepler GK Dwarf Sample
• Three regimes of extrasolar planets inferred from host star metallicities
• Improving Stellar and Planetary Parameters of Transiting Planet Systems: The Case of TrES-2
• Parametrizing the exoplanet eccentricity distribution with the Beta distribution
• A Framework for Characterizing the Atmospheres of Low-Mass Low-Density Transiting Planets
• Breeding Super-Earths and Birthing Super-Puffs in Transitional Disks
• A Detailed Model Grid for Solid Planets from 0.1 through 100 Earth Masses
• Stellar Rotation Periods of the Kepler Objects of Interest: A Dearth of Close-in Planets around Fast Rotators
• The Mass of Kepler-93b and The Composition of Terrestrial Planets
• An Earth-sized planet with an Earth-like density
• Two Earth-sized planets orbiting Kepler-20
• The Sun as a planet-host star: Proxies from SDO images for HARPS radial-velocity variations
• The Kepler-10 planetary system revisited by HARPS-N: A hot rocky world and a solid Neptune-mass planet
• The Formation of Super-Earths and Mini-Neptunes with Giant Impacts
• Minimum Radii of Super-Earths: Constraints from Giant Impacts
• BGLS: A Bayesian formalism for the generalised Lomb-Scargle periodogram
• Kepler-20: A Sun-like Star with Three Sub-Neptune Exoplanets and Two Earth-size Candidates
• Correlations between compositions and orbits established by the giant impact era of planet formation
• Characterizing Distant Worlds with Asterodensity Profiling
• Bayesian priors for the eccentricity of transiting planets
• Kepler-93b: A Terrestrial World Measured to within 120 km, and a Test Case for a New Spitzer Observing Mode
• Asteroseismology of the Transiting Exoplanet Host HD 17156 with HST FGS
• The Kepler-454 System: A Small, Not-rocky Inner Planet, a Jovian World, and a Distant Companion
• Rossiter-McLaughlin Observations of 55 Cnc e
• Characterization of the Kepler-101 planetary system with HARPS-N. A hot super-Neptune with an Earth-sized low-mass companion
• AME - Asteroseismology Made Easy. Estimating stellar properties by use of scaled models

Cited by in corpus (53)

• ESPRESSO@VLT -- On-sky performance and first results
• Compositional imprints in density-distance-time: a rocky composition for close-in low-mass exoplanets from the location of the valley of evaporation
• Revisited Mass-Radius relations for exoplanets below 120 Earth masses
• An Excess of Jupiter Analogs in Super-Earth Systems
• The Super Earth-Cold Jupiter Relations
• Born Dry in the Photo-Evaporation Desert: Kepler's Ultra-Short-Period Planets Formed Water-Poor
• Planetary system around the nearby M dwarf GJ 357 including a transiting, hot, Earth-sized planet optimal for atmospheric characterization
• Cold Jupiters and improved masses in 38 Kepler and K2 small planet systems from 3661 HARPS-N radial velocities. No excess of cold Jupiters in small planet systems
• Predicting the long-term stability of compact multiplanet systems
• Kepler-21b: A rocky planet around a V = 8.25 magnitude star
• Stacked Bayesian general Lomb-Scargle periodogram: Identifying stellar activity signals
• Chemical Fingerprints of Formation in Rocky Super-Earths' Data
• Rocky super-Earths or waterworlds: the interplay of planet migration, pebble accretion and disc evolution
• Influence of sub- and super-solar metallicities on the compositions of solid planetary building blocks
• Testing exoplanet evaporation with multi-transiting systems
• Precise Masses in the WASP-47 System
• Effects of Unseen Additional Planetary Perturbers on Compact Extrasolar Planetary Systems
• How Deep Is the Ocean? Exploring the phase structure of water-rich sub-Neptunes
• The Kepler-19 system: a thick-envelope super-Earth with two Neptune-mass companions characterized using Radial Velocities and Transit Timing Variations
• The Kepler Giant Planet Search. I: A Decade of Kepler Planet-host Radial Velocities from W. M. Keck Observatory
• TOI-431/HIP 26013: a super-Earth and a sub-Neptune transiting a bright, early K dwarf, with a third RV planet
• A framework for the architecture of exoplanetary systems. I. Four classes of planetary system architecture
• Exoplanet Imitators: A test of stellar activity behavior in radial velocity signals
• Validation of 13 Hot and Potentially Terrestrial TESS Planets
• Dependence of Biological Activity on the Surface Water Fraction of Planets
• The first super-Earth Detection from the High Cadence and High Radial Velocity Precision Dharma Planet Survey
• Stellar & Planetary Parameters for K2's Late Type Dwarf Systems from C1 to C5
• Hidden Worlds: Dynamical Architecture Predictions of Undetected Planets in Multi-planet Systems and Applications to TESS Systems
• A Search for Additional Bodies in the GJ 1132 Planetary System from 21 Ground-based Transits and a 100 Hour Spitzer Campaign
• An accurate mass determination for Kepler-1655b, a moderately-irradiated world with a significant volatile envelope
• K2-265 b: A Transiting Rocky Super-Earth
• A Simple Analytical Model for Rocky Planet Interiors
• Visual Analysis and Demographics of Kepler Transit Timing Variations
• TESS Observations of Kepler systems with Transit Timing Variations
• Updated Catalog of Kepler Planet Candidates: Focus on Accuracy and Orbital Periods
• TOI-1075 b: A Dense, Massive, Ultra-Short Period Hot Super-Earth Straddling the Radius Gap
• The origins of nearly coplanar, non-resonant systems of close-in super-Earths
• Stellar abundance of binary stars: their role in determining the formation location of super-Earths and ice giants
• K2-138 g: Spitzer Spots a Sixth Planet for the Citizen Science System
• Multi-Mask Least-Squares Deconvolution: Extracting RVs using tailored masks
• A collage of small planets from the Lick Carnegie Exoplanet Survey : Exploring the super-Earth and sub-Neptune mass regime
• On the Degree of Dynamical Packing in the Kepler Multi-planet Systems
• Transit Duration Variations in Multi-Planet Systems
• Kepler-80 Revisited: Assessing the Participation of a Newly Discovered Planet in the Resonant Chain
• Assessing the Interior Structure of Terrestrial Exoplanets with Implications for Habitability
• Implications of an improved water equation of state for water-rich planets
• SOPHIE velocimetry of Kepler transit candidates. XIX. The transiting temperate giant planet KOI-3680b
• Spaceflight from Super-Earths is difficult
• Orbital obliquity sampling in the Kepler-20 system using the 3D animation software Blender
• Biases from Missing a Small Planet in High Multiplicity Systems
• The Occurrence-weighted Median Planets Discovered by Transit Surveys Orbiting Solar-type Stars and Their Implications for Planet Formation and Evolution
• Constraining stellar rotation and planetary atmospheric evolution of a dozen systems hosting sub-Neptunes and super-Earths
• Do the planets in the HD 34445 system really exist?