Observed Properties of Extrasolar Planets Howard, Andrew W.
Science (American Association for the Advancement of Science),
05/2013, Volume:
340, Issue:
6132
Journal Article
Peer reviewed
Open access
Observational surveys for extrasolar planets probe the diverse outcomes of planet formation and evolution. These surveys measure the frequency of planets with different masses, sizes, orbital ...characteristics, and host star properties. Small planets between the sizes of Earth and Neptune substantially outnumber Jupiter-sized planets. The survey measurements support the core accretion model, in which planets form by the accumulation of solids and then gas in protoplanetary disks. The diversity of exoplanetary characteristics demonstrates that most of the gross features of the solar system are one outcome in a continuum of possibilities. The most common class of planetary system detectable today consists of one or more planets approximately one to three times Earth's size orbiting within a fraction of the Earth-Sun distance.
We present the first results from our Keck program investigating the orbital architectures of planet-hosting multiple star systems. We combine our Keck/NIRC2 adaptive optics astrometry with ...multi-epoch Keck/HIRES RVs of all three stars to determine a precise orbit for the BC pair around A, given their empirically constrained masses. We measure minimal astrometric motion, but our RVs reveal significant orbital velocity and acceleration. We validate that the system is dynamically stable in its present configuration via n-body simulations. We find that the A-BC orbit and planetary orbits are likely aligned (98%) given that they both have edge-on orbits and misalignment induces precession of the planets out of transit. We conclude that the stars were likely on their current orbits during the epoch of planet formation, truncating the protoplanetary disk at ~2 AU.
Determining whether Earth-like planets are common or rare looms as a touchstone in the question of life in the universe. We searched for Earth-size planets that cross in front of their host stars by ...examining the brightness measurements of 42,000 stars from National Aeronautics and Space Administration's Kepler mission. We found 603 planets, including 10 that are Earth size (1—2 R⊕) and receive comparable levels of stellar energy to that of Earth (0.25 — 4 F⊕). We account for Kepler's imperfect detectability of such planets by injecting synthetic planet—caused dimmings into the Kepler brightness measurements and recording the fraction detected. We find that 11 ± 4% of Sun-like stars harbor an Earth-size planet receiving between one and four times the stellar intensity as Earth. We also find that the occurrence of Earth-size planets is constant with increasing orbital period (P), within equal intervals of logP up to ∼200 d. Extrapolating, one finds $5.7^{+1.7}_{-2.2}\%$ of Sun-like stars harbor an Earth-size planet with orbital periods of 200—400 d.
Abstract
We have established precise planet radii, semimajor axes, incident stellar fluxes, and stellar masses for 909 planets in 355 multi-planet systems discovered by
Kepler
. In this sample, we ...find that planets within a single multi-planet system have correlated sizes: each planet is more likely to be the size of its neighbor than a size drawn at random from the distribution of observed planet sizes. In systems with three or more planets, the planets tend to have a regular spacing: the orbital period ratios of adjacent pairs of planets are correlated. Furthermore, the orbital period ratios are smaller in systems with smaller planets, suggesting that the patterns in planet sizes and spacing are linked through formation and/or subsequent orbital dynamics. Yet, we find that essentially no planets have orbital period ratios smaller than 1.2, regardless of planet size. Using empirical mass–radius relationships, we estimate the mutual Hill separations of planet pairs. We find that 93% of the planet pairs are at least 10 mutual Hill radii apart, and that a spacing of ∼20 mutual Hill radii is most common. We also find that when comparing planet sizes, the outer planet is larger in 65% ± 0.4% of cases, and the typical ratio of the outer to inner planet size is positively correlated with the temperature difference between the planets. This could be the result of photo-evaporation.
Since 2014, NASA's K2 mission has observed large portions of the ecliptic plane in search of transiting planets and has detected hundreds of planet candidates. With observations planned until at ...least early 2018, K2 will continue to identify more planet candidates. We present here 275 planet candidates observed during Campaigns 0-10 of the K2 mission that are orbiting stars brighter than 13 mag (in Kepler band) and for which we have obtained high-resolution spectra (R = 44,000). These candidates are analyzed using the vespa package in order to calculate their false-positive probabilities (FPP). We find that 149 candidates are validated with an FPP lower than 0.1%, 39 of which were previously only candidates and 56 of which were previously undetected. The processes of data reduction, candidate identification, and statistical validation are described, and the demographics of the candidates and newly validated planets are explored. We show tentative evidence of a gap in the planet radius distribution of our candidate sample. Comparing our sample to the Kepler candidate sample investigated by Fulton et al., we conclude that more planets are required to quantitatively confirm the gap with K2 candidates or validated planets. This work, in addition to increasing the population of validated K2 planets by nearly 50% and providing new targets for follow-up observations, will also serve as a framework for validating candidates from upcoming K2 campaigns and the Transiting Exoplanet Survey Satellite, expected to launch in 2018.
Abstract
The size of a planet is an observable property directly connected to the physics of its formation and evolution. We used precise radius measurements from the California-
Kepler
Survey to ...study the size distribution of 2025
Kepler
planets in fine detail. We detect a factor of ≥2 deficit in the occurrence rate distribution at 1.5–2.0
. This gap splits the population of close-in (
P
< 100 days) small planets into two size regimes:
and
, with few planets in between. Planets in these two regimes have nearly the same intrinsic frequency based on occurrence measurements that account for planet detection efficiencies. The paucity of planets between 1.5 and 2.0
supports the emerging picture that close-in planets smaller than Neptune are composed of rocky cores measuring 1.5
or smaller with varying amounts of low-density gas that determine their total sizes.
Probing the connection between a star's metallicity and the presence and properties of any associated planets offers an observational link between conditions during the epoch of planet formation and ...mature planetary systems. We explore this connection by analyzing the metallicities of Kepler target stars and the subset of stars found to host transiting planets. After correcting for survey incompleteness, we measure planet occurrence: the number of planets per 100 stars with a given metallicity M. Planet occurrence correlates with metallicity for some, but not all, planet sizes and orbital periods. For warm super-Earths having P = 10-100 days and = 1.0-1.7 , planet occurrence is nearly constant over metallicities spanning −0.4 to +0.4 dex. We find 20 warm super-Earths per 100 stars, regardless of metallicity. In contrast, the occurrence of warm sub-Neptunes ( = 1.7-4.0 ) doubles over that same metallicity interval, from 20 to 40 planets per 100 stars. We model the distribution of planets as , where β characterizes the strength of any metallicity correlation. This correlation steepens with decreasing orbital period and increasing planet size. For warm super-Earths β = , while for hot Jupiters β = . High metallicities in protoplanetary disks may increase the mass of the largest rocky cores or the speed at which they are assembled, enhancing the production of planets larger than 1.7 . The association between high metallicity and short-period planets may reflect disk density profiles that facilitate the inward migration of solids or higher rates of planet-planet scattering.
We identify a sub-Neptune exoplanet (Rp = 2.5 0.2 ) transiting a solar twin in the Ruprecht 147 star cluster (3 Gyr, 300 pc, Fe/H = +0.1 dex). The ∼81 day light curve for EPIC 219800881 (V = 12.71) ...from K2 Campaign 7 shows six transits with a period of 13.84 days, a depth of ∼0.06%, and a duration of ∼4 hr. Based on our analysis of high-resolution MIKE spectra, broadband optical and NIR photometry, the cluster parallax and interstellar reddening, and isochrone models from PARSEC, Dartmouth, and MIST, we estimate the following properties for the host star: M = 1.01 0.03 , R = 0.95 0.03 , and = 5695 50 K. This star appears to be single based on our modeling of the photometry, the low radial velocity (RV) variability measured over nearly 10 yr, and Keck/NIRC2 adaptive optics imaging and aperture-masking interferometry. Applying a probabilistic mass-radius relation, we estimate that the mass of this planet is Mp = 7 + 5 - 3 , which would cause an RV semi-amplitude of K = 2 1 that may be measurable with existing precise RV facilities. After statistically validating this planet with BLENDER, we now designate it K2-231b, making it the second substellar object to be discovered in Ruprecht 147 and the first planet; it joins the small but growing ranks of 22 other planets and three candidates found in open clusters.
Abstract
We present a high-precision radial velocity (RV) survey of 719 FGKM stars, which host 164 known exoplanets and 14 newly discovered or revised exoplanets and substellar companions. This ...catalog updated the orbital parameters of known exoplanets and long-period candidates, some of which have decades-longer observational baselines than they did upon initial detection. The newly discovered exoplanets range from warm sub-Neptunes and super-Earths to cold gas giants. We present the catalog sample selection criteria, as well as over 100,000 RV measurements, which come from the Keck-HIRES, APF-Levy, and Lick-Hamilton spectrographs. We introduce the new RV search pipeline
RVSearch
(
https://california-planet-search.github.io/rvsearch/
) that we used to generate our planet catalog, and we make it available to the public as an open-source Python package. This paper is the first study in a planned series that will measure exoplanet occurrence rates and compare exoplanet populations, including studies of giant planet occurrence beyond the water ice line, and eccentricity distributions to explore giant planet formation pathways. We have made public all radial velocities and associated data that we use in this catalog.
Abstract
We used high-precision radial velocity measurements of FGKM stars to determine the occurrence of giant planets as a function of orbital separation spanning 0.03–30 au. Giant planets are more ...prevalent at orbital distances of 1–10 au compared to orbits interior or exterior of this range. The increase in planet occurrence at ∼1 au by a factor of ∼4 is highly statistically significant. A fall-off in giant planet occurrence at larger orbital distances is favored over models with flat or increasing occurrence. We measure
14.1
−
1.8
+
2.0
giant planets per 100 stars with semimajor axes of 2–8 au and
8.9
−
2.4
+
3.0
giant planets per 100 stars in the range 8–32 au, a decrease in occurrence with increasing orbital separation that is significant at the ∼2
σ
level. We find that the occurrence rate of sub-Jovian planets (0.1–1 Jupiter masses) is also enhanced for 1–10 au orbits. This suggests that lower-mass planets may share the formation or migration mechanisms that drive the increased prevalence near the water–ice line for their Jovian counterparts. Our measurements of cold gas giant occurrence are consistent with the latest results from direct imaging surveys and gravitational lensing surveys despite different stellar samples. We corroborate previous findings that giant planet occurrence increases with stellar mass and metallicity.
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