Why do we find ourselves around a yellow star instead of a red star?

Why do we find ourselves around a yellow star instead of a red star?

Authors:

Haqq-Misra et al

Abstract:
M-dwarf stars are more abundant than G-dwarf stars, so our position as observers on a planet orbiting a G-dwarf raises questions about the suitability of other stellar types for supporting life. If we consider ourselves as typical, in the anthropic sense that our environment is probably a typical one for conscious observers, then we are led to the conclusion that planets orbiting in the habitable zone of G-dwarf stars should be the best place for conscious life to develop. But such a conclusion neglects the possibility that K-dwarfs or M-dwarfs could provide more numerous sites for life to develop, both now and in the future. In this paper we analyze this problem through Bayesian inference to demonstrate that our occurrence around a G-dwarf might be a slight statistical anomaly, but only the sort of chance event that we expect to occur regularly. Even if M-dwarfs provide more numerous habitable planets today and in the future, we still expect mid G- to early K-dwarfs stars to be the most likely place for observers like ourselves. This suggests that observers with similar cognitive capabilities as us are most likely to be found at the present time and place, rather than in the future or around much smaller stars.

HD 3167: Two SuperEarths Found Around a G Dwarf

Two Small Planets Transiting HD 3167

Authors:

Vanderburg et al

Abstract:

We report the discovery of two super-Earth-sized planets transiting the bright (V = 8.94, K = 7.07) nearby late G-dwarf HD 3167, using data collected by the K2 mission. The inner planet, HD 3167 b, has a radius of 1.6 R_e and an ultra-short orbital period of only 0.96 days. The outer planet, HD 3167 c, has a radius of 2.9 R_e and orbits its host star every 29.85 days. At a distance of just 45.8 +/- 2.2 pc, HD 3167 is one of the closest and brightest stars hosting multiple transiting planets, making HD 3167 b and c well suited for follow-up observations. The star is chromospherically inactive and slowly rotating, ideal for radial velocity observations to measure the planets' masses. The outer planet is large enough that it likely has a thick gaseous envelope which could be studied via transmission spectroscopy. Planets transiting bright, nearby stars like HD 3167 are valuable objects to study leading up to the launch of the James Webb Space Telescope.

WASP-113b and WASP-114b: Two inflated hot-Jupiters with contrasting densities

Discovery of WASP-113b and WASP-114b, two inflated hot-Jupiters with contrasting densities

Authors:

Barros et al

Abstract:

We present the discovery and characterisation of the exoplanets WASP-113b and WASP-114b by the WASP survey, {\it SOPHIE} and {\it CORALIE}.

The planetary nature of the systems was established by performing follow-up photometric and spectroscopic observations. The follow-up data were combined with the WASP-photometry and analysed with an MCMC code to obtain system parameters.

The host stars WASP-113 and WASP-114 are very similar. They are both early G-type stars with an effective temperature of ∼5900K, [Fe/H]∼0.12 and Teff ∼4.1dex. However, WASP-113 is older than WASP-114. Although the planetary companions have similar radii, WASP-114b is almost 4 times heavier than WASP-113b. WASP-113b has a mass of 0.48 MJup and an orbital period of ∼4.5days; WASP-114b has a mass of 1.77 MJup and an orbital period of ∼1.5days. Both planets have inflated radii, in particular WASP-113 with a radius anomaly of ℜ=0.35. The high scale height of WASP-113b (∼950 km ) makes it a good target for follow-up atmospheric observations.

EPIC210957318b & EPIC212110888b: An independent discovery of two hot Jupiters

An independent discovery of two hot Jupiters from the K2 mission

Authors:

Brahm et al

Abstract:

We report the discovery of two hot Jupiters using photometry from Campaigns 4 and 5 of the two-wheeled Kepler (K2) mission. EPIC210957318b has a mass of 0.65±0.14MJ, a radius of 1.070±0.018RJ and transits its G dwarf (Teff=5675±50 K), slightly metal rich ([Fe/H]=+0.06±0.04 dex) host star in a 4.1 days circular orbit. EPIC212110888b has a mass of 1.63±0.12MJ, a radius of 1.38±0.014RJ and has an orbital period of 3.0 days in which it orbits a late F dwarf (Teff=6149±55 K) solar metallicity star. Both planets were validated probabilistically and confirmed via precision radial velocity (RV) measurements. They have physical and orbital properties similar to the ones of the already uncovered population of hot Jupiters and are well-suited candidates for further orbital and atmospheric characterization via detailed follow-up observations.

The Search for Extraterrestrial Intelligence in Earth's Solar Transit Zone

The Search for Extraterrestrial Intelligence in Earth's Solar Transit Zone

Authors:

Heller et al

Abstract:

Over the past few years, astronomers have detected thousands of planets and planet candidates by observing their periodic transits in front of their host stars. A related transit method, called transit spectroscopy, might soon allow studies of the chemical imprints of life in extrasolar planetary atmospheres. We here address the reciprocal question, namely, from where is Earth detectable by extrasolar observers using similar methods. Thus, we explore the Earth's transit zone (ETZ), the projection of a band around the Earth's ecliptic onto the celestial plane, where observers can detect Earth transits across the Sun. The ETZ is between 0.520∘ and 0.537∘ wide due to the non-circular Earth orbit. The restricted ETZ (rETZ), where the Earth transits the Sun less than 0.5 solar radii from its center, is about 0.262∘ wide. We compile a target list of 45 K and 37 G dwarf stars inside the rETZ and within 1 kiloparsec (about 3260 lightyears). We construct an analytic galactic disk model and find that about 105 K and G dwarf stars should reside within the rETZ. The ongoing GAIA space mission can potentially discover all G dwarfs among them (several 104) within the next five years. Many more potentially habitable planets orbit dim, unknown M stars in the ETZ and other stars that traversed the ETZ thousands of years ago. If any of these planets host intelligent observers, they could have identified Earth as a habitable or even as a living world long ago and we could be receiving their broadcasts today. The K2 mission, the Allen Telescope Array, and the upcoming Square Kilometer Array might detect such deliberate extraterrestrial messages.

The Kepler Dichotomy in Planetary Disks

The Kepler Dichotomy in Planetary Disks: Linking Kepler Observables to Simulations of Late-Stage Planet Formation

Authors:

Moriarity et al

Abstract:

NASA's Kepler Mission uncovered a wealth of planetary systems, many with planets on short-period orbits. These short-period systems reside around 50% of Sun-like stars and are similarly prevalent around M dwarfs. Their formation and subsequent evolution is the subject of active debate. In this paper, we simulate late-stage, in-situ planet formation across a grid of planetesimal disks with varying surface density profiles and total mass. We compare simulation results with observable characteristics of the Kepler sample. We identify mixture models with different primordial planetesimal disk properties that self-consistently recover the multiplicity, period ratio and duration ratio distributions of the Kepler planets. We draw three main conclusions: (1) We favor a "frozen-in" narrative for systems of short period planets, in which they are stable over long timescales, as opposed to metastable. (2) The "Kepler dichotomy", an observed phenomenon of the Kepler sample wherein the architectures of planetary systems appear to either vary significantly or have multiple modes, can naturally be explained by formation within planetesimal disks with varying surface density profiles. Finally, (3) we quantify the nature of the "Kepler dichotomy" for both GK stars and M dwarfs, and find that it varies with stellar type. While the mode of planet formation that accounts for highly multiplistic systems occurs in 24+/-7% of planetary systems orbiting GK stars, it occurs in 63+/-16% of planetary systems orbiting M dwarfs.

HD 32963b: a Jupiter Analog in a 6 1/2 Year Orbit round a Sun-like Star

The Lick-Carnegie Exoplanet Survey: HD32963 -- A New Jupiter Analog Orbiting a Sun-like Star

Authors:

Rowan et al

Abstract:

We present a set of 109 new, high-precision Keck/HIRES radial velocity (RV) observations for the solar-type star HD 32963. Our dataset reveals a candidate planetary signal with a period of 6.49 ± 0.07 years and a corresponding minimum mass of 0.7 ± 0.03 Jupiter masses. Given Jupiter's crucial role in shaping the evolution of the early Solar System, we emphasize the importance of long-term radial velocity surveys. Finally, using our complete set of Keck radial velocities and correcting for the relative detectability of synthetic planetary candidates orbiting each of the 1,122 stars in our sample, we estimate the frequency of Jupiter analogs across our survey at approximately 3%.

HATS-15b & HATS-16b: Two hot Jupiters Transiting old G dwarf stars

HATS-15 b and HATS-16 b: Two massive planets transiting old G dwarf stars

Authors:

Ciceri et al

Abstract:

We report the discovery of HATS-15 b and HATS-16 b, two massive transiting extrasolar planets orbiting evolved (∼10 Gyr) main-sequence stars. The planet HATS-15 b, which is hosted by a G9V star (V=14.8 mag), is a hot Jupiter with mass of 2.17±0.15MJ and radius of 1.105±0.0.040RJ, and completes its orbit in nearly 1.7 days. HATS-16 b is a very massive hot Jupiter with mass of 3.27±0.19MJ and radius of 1.30±0.15RJ; it orbits around its G3 V parent star (V=13.8 mag) in ∼2.7 days. HATS-16 is slightly active and shows a periodic photometric modulation, implying a rotational period of 12 days which is unexpectedly short given its isochronal age. This fast rotation might be the result of the tidal interaction between the star and its planet.

Evidence for Reflected Light from Gas Giant HD 20872b, the Most Eccentric Exoplanet Known

Evidence for Reflected Light from the Most Eccentric Exoplanet Known

Authors:

Kane et al

Abstract:

Planets in highly eccentric orbits form a class of objects not seen within our Solar System. The most extreme case known amongst these objects is the planet orbiting HD 20782, with an orbital period of 597 days and an eccentricity of 0.96. Here we present new data and analysis for this system as part of the Transit Ephemeris Refinement and Monitoring Survey (TERMS). We obtained CHIRON spectra to perform an independent estimation of the fundamental stellar parameters. New radial velocities from AAT and PARAS observations during periastron passage greatly improve the our knowledge of the eccentric nature of the orbit. The combined analysis of our Keplerian orbital and Hipparcos astrometry show that the inclination of the planetary orbit is greater than 1.25 degrees, ruling out stellar masses for the companion. Our long-term robotic photometry show that the star is extremely stable over long timescales. Photometric monitoring of the star during predicted transit and periastron times using MOST rule out a transit of the planet and reveal evidence of phase variations during periastron. These possible photometric phase variations are likely caused by reflected light from the planet's atmosphere and the dramatic change in star--planet separation surrounding the periastron passage.

HD 175607b: a Hot Neptune in a 29 Day Orbit Around Very Metal Poor G Dwarf

The HARPS search for southern extra-solar planets. XXXIX. HD175607 b, the most metal-poor G dwarf with an orbiting sub-Neptune

Authors:

Mortier et al

Abstract:

Context.

The presence of a small-mass planet (Mp less than 0.1\,MJup) seems, to date, not to depend on metallicity, however, theoretical simulations have shown that stars with subsolar metallicities may be favoured for harbouring smaller planets. A large, dedicated survey of metal-poor stars with the HARPS spectrograph has thus been carried out to search for Neptunes and super-Earths.

Aims.

In this paper, we present the analysis of \object{HD175607}, an old G6 star with metallicity [Fe/H] = -0.62. We gathered 119 radial velocity measurements in 110 nights over a time span of more than nine years.

Methods.

The radial velocities were analysed using Lomb-Scargle periodograms, a genetic algorithm, a Markov chain Monte Carlo analysis, and a Gaussian processes analysis. The spectra were also used to derive stellar properties. Several activity indicators were analysed to study the effect of stellar activity on the radial velocities.

Results.

We find evidence for the presence of a small Neptune-mass planet (Mpsini=8.98±1.10\,M⊕) orbiting this star with an orbital period P=29.01±0.02\, days in a slightly eccentric orbit (e=0.11±0.08). The period of this Neptune is close to the estimated rotational period of the star. However, from a detailed analysis of the radial velocities together with the stellar activity, we conclude that the best explanation of the signal is indeed the presence of a planetary companion rather than stellar related. An additional longer period signal (P∼1400\,d) is present in the data, for which more measurements are needed to constrain its nature and its properties.

Conclusions.

HD 175607 is the most metal-poor FGK dwarf with a detected low-mass planet amongst the currently known planet hosts. This discovery may thus have important consequences for planet formation and evolution theories.

HATS-14b: a hot Jupiter in an Oblique Orbit Around a G Dwarf

A high obliquity orbit for the hot-Jupiter HATS-14b transiting a 5400K star

Authors:

Zhou et al

Abstract:

We report a spin-orbit misalignment for the hot-Jupiter HATS-14b, measuring a projected orbital obliquity of |lambda|= 76 -5/+4 deg. HATS-14b orbits a high metallicity, 5400 K G dwarf in a relatively short period orbit of 2.8 days. This obliquity was measured via the Rossiter-McLaughlin effect, obtained with observations from Keck-HIRES. The velocities were extracted using a novel technique, optimised for low signal-to-noise spectra, achieving a high precision of 4 m/s point-to-point scatter. However, we caution that our uncertainties may be underestimated. Due to the low rotational velocity of the star, the detection significance is dependent on the vsini prior that is imposed in our modelling. Based on trends observed in the sample of hot Jupiters with obliquity measurements, it has been suggested that these planets modify the spin axes of their host stars, with an efficiency that depends on the stellar type and orbital period of the system. In this framework, short-period planets around stars with surface convective envelopes, like HATS-14b, are expected to have orbits that are aligned with the spin axes of their host stars. HATS-14b, however, is a significant outlier from this trend, challenging the effectiveness of the tidal realignment mechanism.

How Common are Nemesis Class Gas Giants and Brown Dwarfs Around G Dwarf Stars?

The VLT/NaCo large program to probe the occurrence of exoplanets and brown dwarfs at wide orbits. III. The frequency of brown dwarfs and giant planets as companions to solar-type stars

Authors:

Reggiani et al

Abstract:

In recent years there have been many attempts to characterize the occurrence of stellar, BD and planetary-mass companions to solar-type stars, with the aim of constraining formation mechanisms. From RV observations a dearth of companions with masses between 10-40 MJup has been noticed at close separations, suggesting the possibility of a distinct formation mechanism for objects above and below this range. We present a model for the substellar companion mass function (CMF). It consists of the superposition of the planet and BD companion mass distributions, assuming that we can extrapolate the RV measured companion mass function for planets to larger separations and the stellar companion mass-ratio distribution over all separations into the BD mass regime. By using both the results of the VLT/NaCo large program and the complementary archive datasets that probe the occurrence of planets and BDs on wide orbits around solar-type stars, we place some constraints on the planet and BD distributions. We developed a MC simulation tool to predict the outcome of a given survey, depending on the shape of the orbital parameter distributions. Comparing the predictions with the results of the observations, we calculate how likely different models are and which can be ruled out. Current observations are consistent with the proposed model for the CMF, as long as a sufficiently small outer truncation radius is introduced for the planet separation distribution. The results of the direct imaging surveys searching for substellar companions around Sun-like stars are consistent with a combined substellar mass spectrum of planets and BDs. This mass distribution has a minimum between 10 and 50 MJup, in agreement with RV measurements. The dearth of objects in this mass range would naturally arise from the shape of the mass distribution, without the introduction of any distinct formation mechanism for BDs.

Prevalence of Earth-size Planets Orbiting Sun-like Stars

Prevalence of Earth-size Planets Orbiting Sun-like Stars

Author:

Petigura

Abstract:

In this thesis, I explore two topics in exoplanet science. The first is the prevalence of Earth-size planets in the Milky Way Galaxy. To determine the occurrence of planets having different sizes, orbital periods, and other properties, I conducted a survey of extrasolar planets using data collected by NASA's Kepler Space Telescope. This project involved writing new algorithms to analyze Kepler data, finding planets, and conducting follow-up work using ground-based telescopes. I found that most stars have at least one planet at or within Earth's orbit and that 26% of Sun-like stars have an Earth-size planet with an orbital period of 100 days or less.

The second topic is the connection between the properties of planets and their host stars. The precise characterization of exoplanet hosts helps to bring planet properties like mass, size, and equilibrium temperature into sharper focus and probes the physical processes that form planets. I studied the abundance of carbon and oxygen in over 1000 nearby stars using optical spectra taken by the California Planet Search. I found a large range in the relative abundance of carbon and oxygen in this sample, including a handful of carbon-rich stars. I also developed a new technique called SpecMatch for extracting fundamental stellar parameters from optical spectra. SpecMatch is particularly applicable to the relatively faint planet-hosting stars discovered by Kepler.

M Dwarfs Have Less Massive Protoplanetary Disks, but More Mass in Their Exoplanets

An Increase in the Mass of Planetary Systems around Lower-Mass Stars

Authors:

Mulders et al

Abstract:

Trends in the planet population with host star mass provide an avenue to constrain planet formation theories. We derive the planet radius distribution function for Kepler stars of different spectral types, sampling a range in host star masses. We find that M dwarf stars have 3.5 times more small planets (1.0-2.8 R_Earth) than main-sequence FGK stars, but two times fewer Neptune-sized and larger planets (>2.8 R_Earth). We find no systematic trend in the planet size distribution between spectral types F, G, and K to explain the increasing occurrence rates. Taking into account the mass-radius relationship and heavy-element mass of observed exoplanets, and assuming those are independent of spectral type, we derive the inventory of the heavy-element mass locked up in exoplanets at short orbits. The overall higher planet occurrence rates around M stars are not consistent with the redistribution of the same mass into more, smaller planets. At the orbital periods and planet radii where Kepler observations are complete for all spectral types, the average heavy-element mass locked up in exoplanets increases roughly inversely with stellar mass from 4 M_Earth in F stars to 5 M_Earth in G and K stars to 7 M_Earth in M stars. This trend stands in stark contrast with observed protoplanetary disk masses that decrease towards lower mass stars, and provides a challenge for current planet formation models. Neither models of in situ formation nor migration of fully-formed planets are consistent with these results. Instead, these results are indicative of large-scale inward migration of planetary building blocks --- either through type-I migration or radial drift of dust grains --- that is more efficient for lower mass stars, but does not result in significantly larger or smaller planets.

HAT-P-55b: A Hot Jupiter Transiting a Sun-like Star

HAT-P-55b: A Hot Jupiter Transiting a Sun-like Star

Authors:

Juncher et al

Abstract:

We report the discovery of a new transiting extrasolar planet, HAT-P-55b. The planet orbits a V = 13.207 +/- 0.039 sun-like star with a mass of 1.013 +/- 0.037 solar masses, a radius of 1.011 +/- 0.036 solar radii and a metallicity of -0.03 +/- 0.08. The planet itself is a typical hot Jupiter with a period of 3.5852467 +/- 0.0000064 days, a mass of 0.582 +/- 0.056 Jupiter masses and a radius of 1.182 +/- 0.055 Jupiter radii. This discovery adds to the increasing sample of transiting planets with measured bulk densities, which is needed to put constraints on models of planetary structure and formation theories.

How Common are Terrestrial Exoplanets Around Kepler's G & K Dwarf Stars?

Terrestrial Planet Occurrence Rates for the Kepler GK Dwarf Sample

Authors:

Burke et al

Abstract:

We measure planet occurrence rates using the planet candidates discovered by the Q1-Q16 Kepler pipeline search. This study examines planet occurrence rates for the Kepler GK dwarf target sample for planet radii, 0.75 less than Rp less than 2.5 Rearth, and orbital periods, 50 less than Porb less than 300 days, with an emphasis on a thorough exploration and identification of the most important sources of systematic uncertainties. Integrating over this parameter space, we measure an occurrence rate of F=0.77 planets per star, with an allowed range of 0.3 less than F less than 1.9. The allowed range takes into account both statistical and systematic uncertainties, and values of F beyond the allowed range are significantly in disagreement with our analysis. We generally find higher planet occurrence rates and a steeper increase in planet occurrence rates towards small planets than previous studies of the Kepler GK dwarf sample. Through extrapolation, we find that the one year orbital period terrestrial planet occurrence rate, zeta_1=0.1, with an allowed range of 0.01 less than zeta_1 less than 2, where zeta_1 is defined as the number of planets per star within 20% of the Rp and Porb of Earth. For G dwarf hosts, the zeta_1 parameter space is a subset of the larger eta_earth parameter space, thus zeta_1 places a lower limit on eta_earth for G dwarf hosts. From our analysis, we identify the leading sources of systematics impacting Kepler occurrence rate determinations as: reliability of the planet candidate sample, planet radii, pipeline completeness, and stellar parameters.

KELT-8b: a Highly Inflated hot Jupiter

KELT-8b: A highly inflated transiting hot Jupiter and a new technique for extracting high-precision radial velocities from noisy spectra

Authors:

Fulton et al

Abstract:

We announce the discovery of a highly inflated transiting hot Jupiter discovered by the KELT-North survey. A global analysis including constraints from isochrones indicates that the V = 10.8 host star (HD 343246) is a mildly evolved, G dwarf with Teff=5754+54−55 K, logg=4.078+0.049−0.054, [Fe/H]=0.272±0.038, an inferred mass M∗=1.211+0.078−0.066 M⊙, and radius R∗=1.67+0.14−0.12 R⊙. The planetary companion has mass MP=0.867+0.065−0.061 MJ, radius RP=1.86+0.18−0.16 RJ, surface gravity loggP=2.793+0.072−0.075, and density ρP=0.167+0.047−0.038 g cm−3. The planet is on a roughly circular orbit with semimajor axis a=0.04571+0.00096−0.00084 AU and eccentricity e=0.035+0.050−0.025. The best-fit linear ephemeris is T0=2456883.4803±0.0007 BJDTDB and P=3.24406±0.00016 days. This planet is one of the most inflated of all known transiting exoplanets, making it one of the few members of a class of extremely low density, highly-irradiated gas giants. The low stellar logg and large implied radius are supported by stellar density constraints from follow-up light curves, plus an evolutionary and space motion analysis. We also develop a new technique to extract high precision radial velocities from noisy spectra that reduces the observing time needed to confirm transiting planet candidates. This planet boasts deep transits of a bright star, a large inferred atmospheric scale height, and a high equilibrium temperature of Teq=1675+61−55 K, assuming zero albedo and perfect heat redistribution, making it one of the best targets for future atmospheric characterization studies.

KOI-614b, KOI-206b, and KOI-680b: A Warm Jupiter and two Highly Inflated Gas Giants

SOPHIE velocimetry of Kepler transit candidates. XV. KOI-614b, KOI-206b, and KOI-680b: a massive warm Jupiter orbiting a G0 metallic dwarf and two highly inflated planets with a distant companion around evolved F-type stars

Authors:

Almenara et al

Abstract:

We report the validation and characterization of three new transiting exoplanets using SOPHIE radial velocities: KOI-614b, KOI-206b, and KOI-680b. KOI-614b has a mass of 2.86±0.35 MJup and a radius of 1.13+0.26−0.18 RJup, and it orbits a G0, metallic ([Fe/H]=0.35±0.15) dwarf in 12.9 days. Its mass and radius are familiar and compatible with standard planetary evolution models, so it is one of the few known transiting planets in this mass range to have an orbital period over ten days. With an equilibrium temperature of Teq=1000±45 K, this places KOI-614b at the transition between what is usually referred to as "hot" and "warm" Jupiters. KOI-206b has a mass of 2.82±0.52 MJup and a radius of 1.45±0.16 RJup, and it orbits a slightly evolved F7-type star in a 5.3-day orbit. It is a massive inflated hot Jupiter that is particularly challenging for planetary models because it requires unusually large amounts of additional dissipated energy in the planet. On the other hand, KOI-680b has a much lower mass of 0.84±0.15 MJup and requires less extra-dissipation to explain its uncommonly large radius of 1.99±0.18 RJup. It is one of the biggest transiting planets characterized so far, and it orbits a subgiant F9-star well on its way to the red giant stage, with an orbital period of 8.6 days. With host stars of masses of 1.46±0.17 M⊙ and 1.54±0.09 M⊙, respectively, KOI-206b, and KOI-680b are interesting objects for theories of formation and survival of short-period planets around stars more massive than the Sun. For those two targets, we also find signs of a possible distant additional companion in the system.

Kepler-444: an 11 Billion+ Year Old System With Five sub Earth Class Exoplanets

An ancient extrasolar system with five sub-Earth-size planets

Authors:

Campante et al

Abstract:

The chemical composition of stars hosting small exoplanets (with radii less than four Earth radii) appears to be more diverse than that of gas-giant hosts, which tend to be metal-rich. This implies that small, including Earth-size, planets may have readily formed at earlier epochs in the Universe's history when metals were more scarce. We report Kepler spacecraft observations of Kepler-444, a metal-poor Sun-like star from the old population of the Galactic thick disk and the host to a compact system of five transiting planets with sizes between those of Mercury and Venus. We validate this system as a true five-planet system orbiting the target star and provide a detailed characterization of its planetary and orbital parameters based on an analysis of the transit photometry. Kepler-444 is the densest star with detected solar-like oscillations. We use asteroseismology to directly measure a precise age of 11.2+/-1.0 Gyr for the host star, indicating that Kepler-444 formed when the Universe was less than 20% of its current age and making it the oldest known system of terrestrial-size planets. We thus show that Earth-size planets have formed throughout most of the Universe's 13.8-billion-year history, leaving open the possibility for the existence of ancient life in the Galaxy. The age of Kepler-444 not only suggests that thick-disk stars were among the hosts to the first Galactic planets, but may also help to pinpoint the beginning of the era of planet formation.

Little Piece of the Fermi Puzzle? Solar Analog Stars With Exoplanets Formed in Inner Galaxy?

Solar analogs with and without planets: TC trends and galactic evolution

Authors:

Adibekyan et al

Abstract:

We explore a sample of 148 solar-like stars to search for a possible correlation between the slopes of the abundance trends versus condensation temperature (known as the Tc slope) both with stellar parameters and Galactic orbital parameters in order to understand the nature of the peculiar chemical signatures of these stars and the possible connection with planet formation. We find that the Tc slope correlates at a significant level with the stellar age and the stellar surface gravity. We also find tentative evidence that the Tc slope correlates with the mean galactocentric distance of the stars (Rmean), suggesting that stars that originated in the inner Galaxy have fewer refractory elements relative to the volatile ones. We found that the chemical peculiarities (small refractory-to-volatile ratio) of planet-hosting stars is probably a reflection of their older age and their inner Galaxy origin. We conclude that the stellar age and probably Galactic birth place are key to establish the abundances of some specific elements.