Volume 3 Issue 10, October 2019

In 1919 scientists from rival nations collaborated to test predictions made by Albert Einstein’s general theory of relativity during a solar eclipse expedition.

Present-day Mars is thought to be unsuitable for life as we know it. However, a thin coating of silica aerogel on the Martian surface may be enough to induce local, potentially habitable subsurface environments.

A substantial population of previously unknown massive dusty galaxies during the first two billion years after the Big Bang have been identified with submillimetre observations. They may solve some outstanding puzzles related to the formation and evolution of most massive galaxies in the Universe today.

Large-scale structures can probe the laws of gravity at scales that they have not yet been tested at, but these tests demand accurate modelling of complex galaxy formation processes in competing gravitational theories.

The peculiar carbon isotopic compositions of carbonates in the Tagish Lake meteorite suggest that D-type asteroids accreted in the outer part of the protoplanetary disk — beyond 10 au — before being dispersed sunwards to the main asteroid belt.

A Kavli Institute for Theoretical Physics workshop in July 2019 directed attention to the Hubble constant discrepancy. New results showed that it does not appear to depend on the use of any one method, team or source. Proposed solutions focused on the pre-recombination era.

To what extent do small-scale processes, such as star formation and black-hole accretion, affect global galaxy properties such as stellar masses, star formation rates and chemical abundances?

A combination of laboratory experiments and numerical modelling shows that a 2–3 cm-thick layer of silica aerogel deployed over the temperate regions of Mars could maintain a surface environment conducive to liquid water all year round. Such an approach would create a habitable setting for photosynthetic life.

The Juno spacecraft’s observations of magnetic field perturbations in Jupiter’s polar regions show Birkeland currents associated with aurorae that are weaker than anticipated and filamentary in nature. An asymmetry is observed between the northern and southern auroras.

The uniformly high ¹³C/¹²C ratios of the Tagish Lake meteorite, whose parent body is a D-type asteroid, indicate that at least some D-type asteroids were formed in the cold outer Solar System from a ¹³C-rich CO₂ ice reservoir and subsequently migrated inwards.

Contractional features such as scarps, ridges and fractures from thrust faults are typical of large silicate bodies such as Mercury and Mars. Evidence for similar features on Ceres suggests the possibility of large-scale contraction on this icy body.

The superbubble containing the Sun is filled with sparse, very hot matter. Creating a three-dimensional map of this Local Bubble using the diffuse interstellar bands (DIBs), Farhang et al. show that, surprisingly, two DIB carriers exist within the bubble itself. The λ5,780 DIB carrier, compared with λ5,797, is the hardier.

Of the 72 known fast radio burst (FRB) sources only two have been observed to emit repeat bursts. By calculating the volumetric occurrence rate of non-repeating FRBs, Vikram Ravi shows that there are not enough candidate cataclysmic progenitor events for most FRBs to be one-off phenomena, and therefore most FRBs must repeat.

Stars in the Milky Way halo are older than those in its thick disk, with their ten-billion-year age distribution cutoff marking the accretion of Gaia-Enceladus to the Milky Way. The red-sequence halo stars are those formed first in the Milky Way progenitor, constituting its long-sought in situ halo.

Combining gravitational-wave and electromagnetic data with new radio observations of GW170817, an improved measurement of \(H_0 = 70.3_{-5.0}^{+5.3}\, {\mathrm{km}}\, {\mathrm{s}}^{-1}\,{\mathrm{Mpc}}^{-1}\) is derived. Fifteen more GW170817-like events with radio data could resolve the Hubble constant tension.

Full cosmological hydrodynamical simulations employing modified gravity find that disk galaxies can form and their stellar properties are only mildly affected. Modified gravity leaves signatures on large-scale structure observable with the Square Kilometre Array.