Letters

An ab initio closed-form analytical solution for the geometric albedo and the integral phase function, which is valid for any law of reflection provided that it depends only on the scattering angle, is proposed. Such solutions can be applied to determine the scattering properties of planetary atmospheres or surfaces.

The nearby Ophiuchus star-forming region should be able to give us insight into the incorporation of short-lived radionuclides into the early Solar System. These radionuclides, such as ²⁶Al, originated from multiple sources and gently warmed the protosolar disk over an extended period. Another heating event, therefore—perhaps an FU Orionis-type outburst—presumably led to the resetting of the radiogenic clock.

Like a seismograph, Saturn’s rings are sensitive to oscillations coming from the planet’s interior. State-of-the-art modelling shows that Cassini’s measurements of ring waves point to a convectively stable diffuse core within Saturn, which extends for 60% of its radius and contains 17 Earth masses of ice and rock.

The spectral properties of a short gamma-ray burst indicate that, contrary to expectations, it arose from the collapse of a massive star rather than from a compact binary merger. This discovery also confirms that most collapsars do not produce ultra-relativistic jets.

A gamma-ray burst (GRB) is reported to show a sharp 1-second spike, characteristic of short GRBs, but with other observational properties resembling those of long GRBs. This burst may belong to a class of core-collapse-origin GRBs with genuinely short durations.

The millimetre image of the Centaurus A nucleus by the Event Horizon Telescope reveals a highly collimated, asymmetrically edge-brightened jet. The source’s event horizon shadow should be visible at terahertz frequencies, consistent with the universal scale invariance of black holes.

Chandra X-ray spectroscopy reveals a 10⁸ K plasma outflow in the low-luminosity active galactic nucleus M81. Magnetohydrodynamical simulations show this energetic wind to originate from a hot accretion flow and impact its host galaxy.

A full 2D radiation–hydrodynamic model of a protoplanetary disk shows that rocky planets can be formed early, and not tens of million years after the dispersal of the gas disk as usually assumed, by means of gas-driven migration of planetesimals around 1 au. The model reproduces well the structure of the inner Solar System.

Three planets orbit the Sun-like star ν² Lupi. CHEOPS data show that all of them are transiting and show remarkable diversity. In particular, dry and gas-poor inner planet b has experienced extensive atmospheric loss, while planets c and d are water rich and have a small gaseous envelope of primordial origin.

Electron-capture supernovae are thought to come from progenitors with a narrow range of masses, and thus they are rare. Here the authors present six indicators of an electron-capture supernova origin, and find that supernova 2018zd fulfils all six criteria.

The Hayabusa2 spacecraft found dark boulders with very high porosity (>70%, as high as cometary nuclei) at the bottom of small craters on Ryugu. Such boulders are probably the most pristine parts of the planetesimals that formed Ryugu’s parent body and might have been captured by Hayabusa2 sampling.

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.

The Voyager 1 spacecraft is now probing interstellar space beyond the heliopause. Here, measurements from the Plasma Wave System reveal au-scale density fluctuations that trace interstellar turbulence without the need for solar shock-generated plasma oscillation events.

Fast-moving pulsars and neutron stars in general may have received a kinetic ‘kick’ from an asymmetric element in the supernova explosion that formed them. Here, the spin axis of a pulsar is determined to lie along the three-dimensional direction of the pulsar’s motion, providing a challenging constraint on supernova explosion modelling.

The complex evolutionary dance of the strongly magnetic white dwarf in a compact binary system can be effectively modelled by considering spin evolution, core crystallization and a rotation-driven dynamo similar to that in planets and low-mass stars.

Two sub-arcsec double quasars at z > 2 are discovered from a targeted search with a novel astrometric technique. They could be the long-sought kpc-scale dual supermassive black holes or sub-arcsec gravitationally lensed quasar images.

Gravitational lensing is detected in the light curve of a gamma-ray burst. The inferred lens mass, while dependent on the unknown lens redshift, provides evidence for an intermediate-mass black hole at a false alarm probability of 0.6% with trial factors.

Following HAWC observations of the Cygnus Cocoon, massive star-forming regions can now be considered to be sources of very-high-energy (TeV to PeV) Galactic cosmic rays.

Using a new infrared spectropolarimeter at Palomar Observatory, the geometry of a number of supernova ejecta have been assessed, revealing a potential similarity in geometry between SN 2018hna and SN 1987A.

Gamma-ray emission up to and above 100 TeV is detected from the supernova remnant G106.3+2.7. The emission above 10 TeV is associated with a molecular cloud rather than the pulsar PSR J2229+6114, favouring a hadronic origin via the π⁰ decay caused by accelerated relativistic protons.