Letters in 2020

The Almahata Sitta 202 meteorite fragment hosts evidence of aqueous alteration at intermediate pressures and temperatures, indicative of a hitherto unknown Ceres-sized parent body. Such intermediate conditions, also seen in the Allende meteorite, might have been more common than our biased meteorite collection indicates.

The detection of three ultraviolet emission lines from GN-z11 can be interpreted as the [C iii] λ1907, C iii] λ1909 doublet and O iii] λ1666 at z = 10.957 ± 0.001, confirming GN-z11 as the most distant galaxy known to date and revealing the properties of its dense ionized gas.

A peculiar near-infrared transient with an observed duration shorter than 245 s, coincident with the luminous star-forming galaxy GN-z11 at z ≈ 11, might have arisen from a rest-frame ultraviolet flash associated with a long gamma-ray burst in GN-z11.

Solar imaging and spectral data indicate that impulsive heating through magnetic reconnection in transition region loops is responsible for observed transient brightenings, consistent with ion cyclotron turbulence due to strong currents at the reconnection sites.

The Milky Way disk is found to be moving with respect to the outer halo of the Galaxy as a result of the gravitational pull of the Large Magellanic Cloud as it falls into the Milky Way. Dynamical models of our Galaxy need to take this effect into account.

The change in growth of the lunar regolith thickness around 3.5 Gyr ago, a consequence of a change in population of the impactor bodies from planetesimals to asteroids, indicates that the instability of giant planets happened early.

LOFAR reveals diffuse radio emission in massive high-redshift clusters, whose high radio luminosities indicate magnetic field strengths similar to those in nearby clusters, suggesting fast magnetic field amplification in the early Universe.

Precision quantum sensor networks are a useful and viable tool in multi-messenger astronomy for the detection of exotic fields that go beyond standard model theories. They could, for example, detect intense bursts of exotic low-mass fields generated by high-energy astrophysical events.

The Stratospheric Observatory for Infrared Astronomy (SOFIA) looked at the Moon in the 6 µm wavelength region and found a signature of molecular water, distinguishing it from other forms of hydration. The authors estimate water abundances between 100 and 400 µg g⁻¹ at high latitudes, trapped within impact glasses or possibly in between grains.

The distribution of boulders on the surface of top-shaped asteroids such as Bennu or Ryugu tells us about the processes driving their evolution. A model shows that the spin-up induced by the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect can explain simultaneously both the latitudinal behaviour of the boulders and the regolith migration.

Soft X-ray observations of the southern Galactic sky with the HaloSat CubeSat indicate that the circumgalactic medium (CGM) of the Milky Way has a disk-like profile, with an extended spherical halo. Clumps in the CGM correlate with star-formation activity.

Realistic three-dimensional magneto-thermal simulations of magnetars with strong, large-scale toroidal magnetic fields accurately describe the observed light curves of 10 out of 19 magnetars in quiescence and allow their rotational orientation to be further constrained.

A shape evolution model shows that bilobed Arrokoth obtained its peculiar flattened shape by sublimation-driven mass loss. This process happened very early in the body’s history and may be a widespread shaping mechanism of Kuiper belt objects.

Six bright boulders of exotic material on near-Earth asteroid (101955) Bennu stand out from the average asteroidal surface. This unexpected record of impactors offers clues to the formation history of Bennu.

The Hayabusa2 team has discovered two types of bright boulder on the dark, carbonaceous asteroid Ryugu. One type has a spectrum consistent with material from an anhydrous silicate-rich asteroid, likely introduced by one or more collisions in Ryugu’s past.

The optical follow-up and analysis of two neutron star–black hole merger candidates with the Zwicky Transient Facility did not yield viable counterparts. However, state-of-the-art kilonova models constrain the ejecta properties of these mergers.

LTT 9779 b is Neptune-sized planet rotating around its star with a period of 0.79 days and an equilibrium temperature of 2,000 K. It is not clear how it retained its atmospheric envelope, which contains ~10% of H/He, as it should have been photoevaporated by now.

Three different layers can be distinguished in the first 500 metres of depth beneath the South Pole–Aitken basin on the Moon: a first layer made up by regolith and ejecta material from different craters, followed by a middle unit of mare basalts and finally a >200-m-thick layer of ejecta from the Leibnitz crater.

The detection of Lyman continuum emission with a high escape fraction from a low-mass clumpy galaxy at z = 1.42, in a redshift range where previously no similar sources were detected, opens up a new window to constrain the shape of the ionization spectrum.

Ten years of gamma-ray data reveal emission in the vicinity of the microquasar SS 433 that is co-spatial with an interstellar gas enhancement and varies periodically at the precessional period of SS 433, challenging existing theoretical models.