Letters

The abundance of Be and V isotopes in calcium–aluminium-rich inclusions (CAIs), the oldest solids in the Solar System, shows that CAIs were irradiated by a gradual flux of radiation from solar flares when the Sun was young and more energetic, for a short time (300 yr) and at close distance (≈0.1 au).

Cassini’s RADAR has surveyed a region close to Enceladus’s ‘tiger stripes’. It finds a temperate subsurface with warm cracks, indicating that the moon’s icy crust is only a few kilometres thick at these points. A dormant crack hints at episodic geological activity.

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.

The key ingredients for a massive cloud of gas to collapse and directly form a black hole without fragmenting and forming stars are a strong ionizing background emission and a closely timed burst of star formation in its vicinity.

A magnetohydrodynamic model for outflows around supermassive black holes can also reproduce the X-ray properties of an outflow around a stellar black hole. This indicates that magnetic forces have a universal role to play in driving these winds.

The authors find that a nearby planetary system has two terrestrial planets that transit in front of their star (from our perspective). Transiting terrestrial planets are sought after, as they can be characterized in detail, including their atmospheres. Having two in the same system is very rare.

A selected group of intermediate-redshift galaxies appear similar to primeval galaxies. Analysing spectra of these nearer analogues for chemical abundances and ionization levels gives an improved understanding of galaxies that are too faint to study well.

The roughly spherical outer regions and aspherical inner regions of protoplanetary nebulae — here imaged by ALMA — are explained in terms of an embedded binary system with stars on eccentric orbits.

Environments where stars are abundantly formed are more conducive to stellar tidal disruption events, as evidenced by the detection of the remains of a star being accreted by a supermassive black hole within a starburst galaxy.

A binary system containing a ‘polluted’ white dwarf must host a stable, rocky, circumbinary debris disk, argue Farihi and colleagues. Therefore large planetesimal formation, and potentially terrestrial planet formation, must be robust and common in such systems.

An uncharacteristically long stellar disruption from a supermassive black hole has been unravelling over the last decade. Spectral information implies very efficient accretion but recent observations hint at a transition to a less extreme accretion mode.

The authors present evidence that the lunar soil contains oxygen ions from Earth that escape our atmosphere and reach the Moon through the Earth’s magnetospheric wind. The lunar surface possibly contains clues about the history of Earth’s atmosphere.

The presence of a large underdensity, the dipole repeller, is predicted based on a study of the velocity field of our Local Group of galaxies. The combined effects of this super-void and the Shapley concentration control the local cosmic flow.

Isotopic analyses of stardust have yet to single out a specific stellar origin for it. A revision of the proton-capture rate of ¹⁷O has helped to identify intermediate mass stars (4–8 solar masses) as the source of a large fraction of meteoritic stardust.

The New Horizons spacecraft revealed a large dark reddish area along Pluto’s equatorial region, probably made up by organics. Here the authors show that it could be formed by the very same giant impact that created Pluto’s biggest satellite, Charon.

Heck et al. provide the first experimental evidence that the composition of meteorites falling on the Earth changes with time. The distribution of meteorites 470 million years ago is significantly different from today — an effect linked to events happening in the asteroid belt.

Our currently accepted model of a hierarchically growing, dark-matter dominated Universe predicts rare isolated groups of dwarf galaxies. The discovery of seven such systems may point to the building blocks of present-day intermediate-mass galaxies.

Multi-wavelength data from a cluster–cluster merger reveals that relativistic electrons ejected from near an actively accreting black hole are efficiently re-accelerated at a cluster shock to produce characteristically diffuse radio emission.

Measurements of cold molecular gas from galaxies with stellar masses and star formation rates similar to those of the main progenitor of the Milky Way 8.5 billion years ago show similar physics of star formation to that seen now.

An experimental apparatus using a single optical atomic clock to detect dark matter topological defects (like strings) is proposed. Tests show it can constrain the dark matter–Standard Model coupling strength ~3 orders of magnitude better than previous limits.