Letters in 2018

The identification and dating of ~30 cryovolcanic domes on Ceres from Dawn data shows that cryovolcanism has been continuous on the dwarf planet at least for the last 2.5 Gyr, but not at rates comparable with standard volcanism on terrestrial planets.

The mechanisms that sustain turbulence in a molecular cloud are not well understood. Using magnetohydrodynamic simulations, the effects of stellar winds on a cloud are studied, finding that energy can be efficiently transferred in magnetic waves generated by this stellar ‘feedback’.

The Patroclus–Menoetius Jupiter Trojan binary could survive its travel from the Kuiper belt to Jupiter’s orbit only if the giant planets’ migrations happened within ~100 Myr after the birth of the Solar System and not after ~700 Myr, as suggested instead by the Late Heavy Bombardment.

Probing the pre-explosion environments of hydrogen-poor superluminous supernovae is important for understanding how they exploded. Here, Lunnan et al. infer the presence of a fast-moving circumstellar shell around iPTF16eh through the detection of a resonance-line light echo, which indicates the massive progenitor experienced pulsational pair instability shell ejections.

Cosmochemical evidence is used to constrain models of Jupiter formation, which unfolds in three distinct phases: a rapid pebble accretion during the first Myr, followed by a slower growth controlled by larger planetesimals, ending in a runaway gas accretion stage.

A data-driven study of the too-big-to-fail problem of Milky Way dwarf spheroidals within the self-interacting dark matter paradigm finds a good description of their stellar kinematics and compatibility with the concentration–mass relation of pure cold dark matter simulations.

Precise measurements of the motion of Beta Pictoris obtained by Hipparcos between 1990 and 1993 and by Gaia ~24 years later allowed the mass of its planet Beta Pictoris b to be measured. The result of 11 ± 2 Jupiter masses supports ‘hot start’ formation models.

Star TYC 429-2097-1 contains the most lithium of any giant star, but lithium is too fragile to survive in the deep layers of a stellar atmosphere. How does the enrichment arise? Yan et al. rule out external sources (engulfment, accretion), favouring an internal process called ‘extra mixing’.

Double-shell planetary nebula HuBi 1 has an inner shell that emits in low ionization potential species, and an outer shell that emits in high-ionization species. This is the inverse of the usual case. The cause is the nebula’s rapidly fading central star that went through a ‘born-again’ event.

Noble gas abundances measured in the oldest calcium–aluminium-rich inclusions (CAIs) reveal a burst of intense solar irradiation early in the Solar System’s history, not recorded by CAIs that formed later. This result is consistent with a T Tauri phase for the Sun.

Thirty years after an initial, tentative detection, the molecule ²⁶AlF has now been firmly detected in space, by the observation of four different rotational transitions towards stellar merger remnant CK Vul. Curiously, CK Vul and similar objects are unlikely to be major sources of Galactic ²⁶Al.

A dark, ribbon-like structure at Jupiter’s magnetic equator marks a depletion of ionospheric H₃⁺ caused by a lack of photoelectrons. These photoelectrons, which collide with molecular hydrogen to form H₃⁺, are deviated away by magnetic field lines.

M31’s massive and metal-rich stellar halo appears to indicate that a single dominant merger with a large galaxy took place about 2 Gyr ago, co-temporal with M31’s global burst of star formation. M32 is likely to be the stripped core of the disrupted galaxy.

The X-ray-induced photodesorption of water from astrophysical ices, intact, has been little studied. However, it could be a key process in producing the cold water vapour that is seen in these regions. Here, the yield of such a mechanism is experimentally quantified.

The strong gravitational lensing signal around the massive cluster PSZ2 G099.86+58.45 indicates environment matter density in notable excess of the cosmological mean and implies that enhancing mechanisms around high-mass halos can be very effective.

Late-time optical and near-infrared observations of the binary neutron star merger GW170817 are at odds with kilonova models but match a Gaussian-structured relativistic jet, which would have launched a high-luminosity short gamma-ray burst to an aligned observer.

All inner main-belt asteroids, and not just those belonging to a specific family as previously thought, originate from the splintering of a few large asteroids. The history of such precursors determines the compositional variety we observe in asteroids and meteorites.

Using high-resolution spectra, the CARMENES survey detects a hydrogen atmosphere around KELT-9b, the hottest exoplanet ever discovered. This hydrogen envelope almost entirely fills the Roche lobe, indicating intense atmospheric loss.

Massive binary star Eta Carinae drives the strongest colliding wind shock in the solar neighbourhood. Using NuSTAR and XMM-Newton data, Eta Car has now been convincingly shown to accelerate non-thermal particles, contributing to the Galactic cosmic ray flux.

A method of atmospheric retrieval for exoplanets that uses supervised ‘random forest’ machine learning, less time-consuming than standard techniques, is presented. Tests on Hubble spectra of WASP-12b give results consistent with standard atmospheric retrievals.