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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.

Analysis of the metallicities of more than 400 stars hosting 600 candidate extrasolar planets shows that the planets can be categorized by size into three populations — terrestrial-like planets, gas dwarf planets with rocky cores and hydrogen–helium envelopes, and ice or gas giant planets — on the basis of host star metallicity. Three regimes of exoplanet radius arising from host star metallicities Soon after the discovery of the first exoplanets, it was suggested that host star metallicity — the abundance of elements other than hydrogen and helium — has a role in the formation of planetary systems. Here Lars Buchhave et al . report the metallicity and other stellar parameters of more than 400 stars hosting 600 exoplanet candidates and find that the exoplanets can be categorized into three populations defined by statistically distinct metallicity regions and planetary radii. The three are terrestrial-like exoplanets, gas dwarf exoplanets with rocky cores and H/He envelopes, and ice/gas-giant exoplanets. Approximately half of the extrasolar planets (exoplanets) with radii less than four Earth radii are in orbits with short periods 1 . Despite their sheer abundance, the compositions of such planets are largely unknown. The available evidence suggests that they range in composition from small, high-density rocky planets to low-density planets consisting of rocky cores surrounded by thick hydrogen and helium gas envelopes. Here we report the metallicities (that is, the abundances of elements heavier than hydrogen and helium) of more than 400 stars hosting 600 exoplanet candidates, and find that the exoplanets can be categorized into three populations defined by statistically distinct (∼4.5 σ ) metallicity regions. We interpret these regions as reflecting the formation regimes of terrestrial-like planets (radii less than 1.7 Earth radii), gas dwarf planets with rocky cores and hydrogen–helium envelopes (radii between 1.7 and 3.9 Earth radii) and ice or gas giant planets (radii greater than 3.9 Earth radii). These transitions correspond well with those inferred from dynamical mass estimates 2 , 3 , implying that host star metallicity, which is a proxy for the initial solids inventory of the protoplanetary disk, is a key ingredient regulating the structure of planetary systems.

Doppler spectroscopic measurements of the mass of the Earth-sized planet Kepler-78b reveal that its mean density is similar to Earth’s, suggesting a composition of rock and iron. Like Earth — but a lot hotter A few exoplanets of about the size or mass of Earth have been discovered. Now, for the first time, both size and mass have been determined for one of them. Kepler-78b, first described in August this year, is close-in to its host star, which it orbits every 8.5 hours. Two groups have been able to exploit the closeness of planet and star to make Doppler spectroscopic measurements of the mass of Kepler-78b. The teams, led by Andrew Howard and Francesco Pepe, used different telescopes to arrive at mass estimates of 1.69 ± 0.41 and 1.86 +0.38/−0.245 Earth masses, respectively. They calculate the planet's mean density at 5.3 and 5.57 g cm −3 , very similar to Earth's and consistent with an Earth-like composition of rock and iron. Planets with sizes between that of Earth (with radius ) and Neptune (about 4 ) are now known to be common around Sun-like stars 1 , 2 , 3 . Most such planets have been discovered through the transit technique, by which the planet’s size can be determined from the fraction of starlight blocked by the planet as it passes in front of its star. Measuring the planet’s mass—and hence its density, which is a clue to its composition—is more difficult. Planets of size 2–4 have proved to have a wide range of densities, implying a diversity of compositions 4 , 5 , but these measurements did not extend to planets as small as Earth. Here we report Doppler spectroscopic measurements of the mass of the Earth-sized planet Kepler-78b, which orbits its host star every 8.5 hours (ref. 6 ). Given a radius of 1.20 ± 0.09 and a mass of 1.69 ± 0.41 , the planet’s mean density of 5.3 ± 1.8 g cm −3 is similar to Earth’s, suggesting a composition of rock and iron.

We analyze 8 years of precise radial velocity measurements from the Keck Planet Search, characterizing the detection threshold, selection effects, and completeness of the survey. We first carry out a systematic search for planets, by assessing the false-alarm probability associated with Keplerian orbit fits to the data. This allows us to understand the detection threshold for each star in terms of the number and time baseline of the observations, and the underlying “noise” from measurement errors, intrinsic stellar jitter, or additional low-mass planets. We show that all planets with orbital periods P < 2000 days P < 2000     days , velocity amplitudes K > 20 m s-1 K > 20     m   s - 1 , and eccentricities e ≲ 0.6 e ≲ 0.6 have been announced, and we summarize the candidates at lower amplitudes and longer orbital periods. For the remaining stars, we calculate upper limits on the velocity amplitude of a companion. For orbital periods less than the duration of the observations, these are typically10 m s-1 10     m   s - 1 and increase∝ P 2 ∝ P 2 for longer periods. We then use the nondetections to derive completeness corrections at low amplitudes and long orbital periods and discuss the resulting distribution of minimum mass and orbital period. We give the fraction of stars with a planet as a function of minimum mass and orbital period and extrapolate to long-period orbits and low planet masses. A power-law fit for planet masses>0.3 M J > 0.3     M J and periods< 2000 days < 2000     days gives a mass-period distribution dN = CM α P β d ln Md ln P d N = C M α P β d ln M d ln P withα = -0.31 ± 0.2 α = - 0.31 ± 0.2 ,β = 0.26 ± 0.1 β = 0.26 ± 0.1 , and the normalization constant C C such that 10.5% of solar type stars have a planet with mass in the range0.3–10 M J 0.3 – 10     M J and orbital period 2–2000 days. The orbital period distribution shows an increase in the planet fraction by a factor of≈5 ≈ 5 for orbital periods≳300 days ≳ 300     days . Extrapolation gives 17%–20% of stars having gas giant planets within 20 AU. Finally, we constrain the occurrence rate of planets orbiting M dwarfs compared to FGK dwarfs, taking into account differences in detectability.

Nine point sources appeared within half an hour on a region within ∼ 10 arcmin of a red-sensitive photographic plate taken in April 1950 as part of the historic Palomar Sky Survey. All nine sources are absent on both previous and later photographic images, and absent in modern surveys with CCD detectors which go several magnitudes deeper. We present deep CCD images with the 10.4-m Gran Telescopio Canarias, reaching brightness r ∼ 26 mag, that reveal possible optical counterparts, although these counterparts could equally well be just chance projections. The incidence of transients in the investigated photographic plate is far higher than expected from known detection rates of optical counterparts to e.g. flaring dwarf stars, Fast Radio Bursts, Gamma Ray Bursts or microlensing events. One possible explanation is that the plates have been subjected to an unknown type of contamination producing mainly point sources with of varying intensities along with some mechanism of concentration within a radius of ∼ 10 arcmin on the plate. If contamination as an explanation can be fully excluded, another possibility is fast (t < 0.5 s) solar reflections from objects near geosynchronous orbits. An alternative route to confirm the latter scenario is by looking for images from the First Palomar Sky Survey where multiple transients follow a line.

The transits of two Sun-like stars by small planets in an open star cluster are reported; such a stellar environment is unlike that of most planet-hosting field stars, and suggests that the occurrence of planets is unaffected by the stellar environment in open clusters. A global rate of planet formation Until now only four planets — with masses similar to Jupiter — have been found orbiting stars in old open clusters, compared with more than 800 — mostly Neptune-sized — orbiting 'field stars' outside clusters. Most stars and planets form in open clusters that break up within a few hundred million years as stars drift away to become field stars. Older open clusters survive because they were denser in stars when they formed, a stellar environment very different from that of other planet-hosting field stars. This paper, part of the Kepler Cluster Study, describes observations of the transits of two Sun-like stars by planets smaller than Neptune in the 1-billion-year-old open cluster NGC6811. This demonstrates that small planets can form and survive in a dense cluster environment, and implies that the frequency and properties of planets in open clusters are consistent with those of planets around field stars in our Galaxy. Most stars and their planets form in open clusters. Over 95 per cent of such clusters have stellar densities too low (less than a hundred stars per cubic parsec) to withstand internal and external dynamical stresses and fall apart within a few hundred million years 1 . Older open clusters have survived by virtue of being richer and denser in stars (1,000 to 10,000 per cubic parsec) when they formed. Such clusters represent a stellar environment very different from the birthplace of the Sun and other planet-hosting field stars. So far more than 800 planets have been found around Sun-like stars in the field 2 . The field planets are usually the size of Neptune or smaller 3 , 4 , 5 . In contrast, only four planets have been found orbiting stars in open clusters 6 , 7 , 8 , all with masses similar to or greater than that of Jupiter. Here we report observations of the transits of two Sun-like stars by planets smaller than Neptune in the billion-year-old open cluster NGC6811. This demonstrates that small planets can form and survive in a dense cluster environment, and implies that the frequency and properties of planets in open clusters are consistent with those of planets around field stars in the Galaxy.

Sixty commercial honey bee colonies were monitored over the course of one year with the goal of assessing potential correlations between measured colony strength and environmental stressors, including exposures to pesticides and pathogens. We developed a new method for assessing colony health by determining the fractional change in population of the four colonies on each pallet between peak population on 1 June and the last population assessment prior to winter on 1 October. This fractional change in population was evaluated as a function of pesticide load per pallet for each of the 37 pesticide chemicals detected, grouping pallets by beekeeper. The analysis of individual chemicals showed that both imidacloprid and cyprodinil were negatively correlated with colony health, while tau-fluvalinate and dinotefuran (at very low concentrations) were positively correlated, possibly because of effects on Varroa control. Exposure to groups of chemicals was also evaluated. Normalization of each chemical concentration to the maximum observed for that chemical provided an equal weighting for each chemical, even though their relative occurrence in the environment and their effective toxicities might differ. A total of 24 chemical groups whose members share a structural commonality, a functional commonality, or suspected synergistic actions were considered, demonstrating negative correlations between colony health and exposures to neonicotinoids as a group and neonicotinoids in combination with (1) methoxyfenozide (2) organophosphates, and (3) diflubenzuron. Analysis of several groups of fungicides applied to almonds during pollination also showed negative correlations with colony health.

The search for technosignatures from hypothetical galactic civilizations is going through a new phase of intense activity. For the first time, a significant fraction of the vast search space is expected to be sampled in the foreseeable future, potentially bringing informative data about the abundance of detectable extraterrestrial civilizations or the lack thereof. Starting from the current state of ignorance about the galactic population of nonnatural electromagnetic signals, we formulate a Bayesian statistical model to infer the mean number of radio signals crossing Earth, assuming either nondetection or the detection of signals in future surveys of the Galaxy. Under fairly noninformative priors, we find that not detecting signals within about 1 kly from Earth, while suggesting the lack of galactic emitters or at best the scarcity thereof, is nonetheless still consistent with a probability exceeding 10% that typically over ∼ 100 signals could be crossing Earth, with radiated power analogous to that of the Arecibo radar, but coming from farther in the Milky Way. The existence in the Galaxy of potentially detectable Arecibo-like emitters can be reasonably ruled out only if all-sky surveys detect no such signals up to a radius of about 40 kly, an endeavor requiring detector sensitivities thousands times higher than those of current telescopes. Conversely, finding even one Arecibo-like signal within ∼ 1000 light years, a possibility within reach of current detectors, implies almost certainly that typically more than ∼ 100 signals of comparable radiated power cross the Earth, yet to be discovered.

The K2 mission will make use of the Kepler spacecraft and its assets to expand upon Kepler's groundbreaking discoveries in the fields of exoplanets and astrophysics through new and exciting observations. K2 will use an innovative way of operating the spacecraft to observe target fields along the ecliptic for the next 2-3 years. Early science commissioning observations have shown an estimated photometric precision near 400 ppm in a single 30 minute observation, and a 6-hr photometric precision of 80 ppm (both at V = 12). The K2 mission offers long-term, simultaneous optical observation of thousands of objects at a precision far better than is achievable from ground-based telescopes. Ecliptic fields will be observed for approximately 75 days enabling a unique exoplanet survey which fills the gaps in duration and sensitivity between the Kepler and TESS missions, and offers pre-launch exoplanet target identification for JWST transit spectroscopy. Astrophysics observations with K2 will include studies of young open clusters, bright stars, galaxies, supernovae, and asteroseismology.