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Two double-sun exoplanets have been discovered by the Kepler spacecraft, establishing a new class of ‘circumbinary’ exoplanets and suggesting that at least several million such systems exist in our Galaxy.

A 4.8σ exomoon candidate is found around gas giant Kepler-1708 b, which orbits at 1.6 au around its star. It is the only candidate from a dedicated survey that analysed 70 cool giant exoplanets discovered by Kepler. Kepler-1708 b-i has a radius of 2.6 Earth radii and orbits its planet at 12 planetary radii.

Two exoplanets of Earth’s size have been discovered in orbit around the star Kepler-20.

When an extrasolar planet passes in front of its star (transits), its radius can be measured from the decrease in starlight and its orbital period from the time between transits. This study reports Kepler spacecraft observations of a single Sun-like star that reveal six transiting planets, five with orbital periods between 10 and 47 days plus a sixth one with a longer period. The five inner planets are among the smallest for which mass and size have both been measured, and these measurements imply substantial envelopes of light gases.

Transit timing reveals the masses for the three small planets orbiting the star Kepler-138.

A comprehensive study of the Kepler-138 system reveals the twin nature of Kepler-138 c and d and the presence of a fourth planet. Remarkably, the warm-temperate planet Kepler-138 d is probably composed of 50% volatiles by volume, indicative of a water world, rather than a rocky world, despite its small ~1.5 R_⊕ size.

Kepler-107 b and c have the same radius but, contrary to expectations, the outermost Kepler-107 c is much denser. This difference cannot be explained by photoevaporation by stellar high-energy particle flux and it suggests that Kepler-107 c experienced a giant impact event.

A fast-evolving luminous transient (FELT) has been detected with a rise time to peak luminosity of only 2.2 days. This implies that the light-curve of this FELT cannot be powered by the decay of radioactive elements, as with type Ia supernovae.

Using Kepler, this study identifies a compact multiplanetary system that is not flat, where gravitational interactions cause its planets’ periods to change by nearly a day per cycle and their orbital planes to tilt back and forth.

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.

An outstanding discrepancy between observations and models of stellar limb darkening is resolved here by the inclusion of stellar surface magnetism in models. This will enable an improved characterization of transiting exoplanets.

Stellar data from the Kepler spacecraft are used to infer the existence of a sub-Mercury-sized exoplanet, the smallest yet discovered, in orbit around a Sun-like star.

The radial-velocity technique could detect a small gas giant orbiting a binary star and determine its mass: 65.2 ± 11.8 Earth masses. The system also hosts a smaller inner planet, making it one of the few known multiplanetary circumbinary systems.

The explosion of a type Ia supernova could be triggered either by accretion from a companion—which should be indicated by brightening caused by interaction of supernova ejecta with the companion—or by a merger with a white dwarf or other small star; here observations by the Kepler mission of three type Ia supernovae reveal no such brightening, leading to the conclusion that they were triggered by a merger.

Data from the Kepler spacecraft and the HARPS-N ground-based spectrograph indicate that the extrasolar planet Kepler-78b has a mean density similar to that of Earth and imply that it is composed of rock and iron.

Transit timing variations of the four-planet system Kepler-223 are used to compute the long-term stability of the system, which has a chain of resonances; the results suggest that inward planetary migration, rather than in situ assembly, is responsible for the formation of some close-in sub-Neptune systems.

An analysis of 1,055 planets around main sequence stars identifies three subsamples of star–planet synchronization: subsynchronized, dominant for periods shorter than 6.2 days; supersynchronized, for periods longer than 13.5 days; and a transitional regime in between. Synchronized systems are a minority, contrary to eclipsing binaries.

An analysis of transits of planets over starspots on the Sun-like star Kepler-30 shows that the orbits of the three planets are aligned with the stellar equator; this configuration is similar to that of our Solar System, and suggests that high obliquities are confined to systems that experienced disruptive dynamical interactions.

Theory predicts a deficit of super-Earth sized planets, which orbit close to their host star. Here, Lundkvist et al. use data from the NASA Kepler mission to show that this deficit is also seen in observations, thereby providing new insight into exoplanetary 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.

Space telescope observations of the transmission spectrum of the extrasolar planet HAT-P-11b, which is about the same size as Neptune, reveal water vapour absorption at a wavelength of 1.4 micrometres and indicate that the planetary atmosphere is predominantly clear down to an altitude corresponding to about 1 millibar.

Automatic extraction of consistent governing laws from data is a challenging problem. The authors propose a method that takes as input experimental data and background theory and combines symbolic regression with logical reasoning to obtain scientifically meaningful symbolic formulas.

A weak magnetic field regulates magnetically gated accretion of gas from a companion star onto the white dwarf in the binary system MV Lyrae, previously labelled as a ‘non-magnetic’ system.

Superflares are large explosive events on stellar surfaces, much larger than solar flares, but it remains unclear whether they share the same origin. Here, the authors analysed 48 superflare stars and determine the relation between their chromospheric activity and the occurrence of superflares.

Measuring acoustic oscillations in 27 stars within the M67 cluster presents evidence of a rapidly evolving convective zone as stars evolve from subgiants to red giants.

An analysis of the 3.45-Gyr-old volcanic sediments from the Kitty’s Gap Chert in Australia shows the presence of microfossils and highlights the difficulty of determining the biotic nature of structures in future extraterrestrial samples.

TOI-500 hosts at least four planets, the innermost of which is an Earth-sized ultra-short-period body with a density similar to Earth. The architecture of the TOI-500 system can be explained by a slow, secular, low-eccentricity migration scenario.

Analysis of Kepler data has yielded the smallest known mass for an exoplanet orbiting a normal star. Its mass and size are similar to those of Mars, setting a benchmark for the properties of exoplanets smaller than Earth. See Letter p.321

Whereas large planets, such as gas giants, are more likely to form around high-metallicity stars, terrestrial-sized planets are found to form around stars with a wide range of metallicities, indicating that they may be widespread in the disk of the Galaxy.

Three examples of a new family of planets, which orbit a pair of stars rather than a single one, have been discovered. The Milky Way may contain millions of these circumbinary planets. See Letter p.475

The pulsation spectra of intermediate-mass stars (so-called δ Scuti stars) have been challenging to analyse, but new observations of 60 such stars reveal remarkably regular sequences of high-frequency pulsation modes.

Leveraging asteroseismology, stellar abundances and kinematics to derive precise ages for a sample of 95 stars, Montalbán et al. determine that the Milky Way was already host to a substantial population of stars when it was just 3.8 billion years old, at the time of the Gaia-Enceladus accretion event.

Observations of six transiting planets around the bright nearby star HD 110067 show that they follow a chain of resonant orbits, with three of the planets inferring the presence of large hydrogen-dominated atmospheres.

This study presents high-resolution imaging of the ultracool dwarf LSR J1835 + 3259 at 8.4 GHz, demonstrating that its quiescent radio emission is spatially resolved and traces a double-lobed and axisymmetrical structure with properties consistent with radiation belt observations and modelling.

Red giants are evolved stars that have exhausted the supply of hydrogen in their cores and instead burn hydrogen in a surrounding shell. Once a red giant is sufficiently evolved, the helium in the core also undergoes fusion. However, it is difficult to distinguish between the two groups. Asteroseismology offers a way forward. This study reports observations of gravity-mode period spacings in red giants using high precision photometry obtained by the Kepler spacecraft. It is found that the stars fall into two clear groups, making it possible to distinguish unambiguously between hydrogen-shell-burning stars and those that are also burning helium.

The age of a young to middle-aged star can be determined from how quickly or slowly it rotates, but the relationship breaks down for old stars; models now show that old stars are rotating much more quickly than expected, perhaps because magnetic winds are weaker and therefore brake the rotation less effectively.

Two planets around the post-red-giant star KIC 05807616 are shown to have survived being engulfed by the former red giant

The use of IL-17/IL-23 blocking therapy for rare inflammatory skin diseases needs proof of principle data for larger clinical trials. Here the authors show that patients with Darier disease have enhanced Th17 cells and, using IL-17/IL-23 blockers, they show that the immune gene signatures are altered in localised skin biopsies.

The magnetic field structure of the protoplanetary disk around HD 142527 is derived from dust polarization observations. A magnetic field strength of 0.3 mG and its three-dimensional components were calculated using the distributions of the polarization vectors.

Using asteroseismology to measure the spin axes of stars in two old open star clusters, Corsaro et al. find alignment between significant numbers of stars. It is thought that this is an imprint of the original angular momentum of the parent molecular cloud.

Star DMPP-1 hosts a compact, four-planet system comprising three irradiated super-Earth-mass planets and one Neptune-mass planet, discovered through radial velocity measurements and the star’s anomalously low chromospheric emission.

Suppression of dipolar oscillation modes by strong magnetic fields in the cores of intermediate-mass red giant stars reveals that powerful magnetic dynamos were very common in the previously convective cores of these stars.

In this Stage 2 Registered Report, Buchanan et al. show evidence confirming the phenomenon of semantic priming across speakers of 19 diverse languages.