Volume 3 Issue 6, June 2019

Astrobiologists hope to detect signs of life on ocean worlds such as Europa. But the major challenge will actually come if such detections are successful — how to prove they are real and not artefacts of contamination or exotic chemistry?

Although a major objective in Mars exploration is the search for life, there are many scenarios that could lead to the recovery of lifeless samples. What could lifeless samples tell us about Mars and its habitability?

A pioneer of millimetre-wave astronomy, Norio Kaifu was an incomparable leader, person of spirit, colleague and friend.

The first detection of emission from carbon monoxide molecules in a circumstellar envelope delivered a tool for estimating numerous physical characteristics of evolved stars, not least the amount of gas and dust they return to the interstellar medium of a galaxy.

Measurement of the diffraction pattern of starlight during an asteroid occultation opens up new territory in stellar angular size determinations.

The stellar initial mass function (IMF) is the key to understanding the matter cycle in the Universe. Edwin Salpeter’s paper of 1955 founded this research field. Evidence today, however, challenges the initial mass function as an invariant probability distribution function.

Although dark matter cannot be seen, it can be studied by the gravitational effect of dark objects on the light from background stars. New observations of the nearby Andromeda galaxy probe the possibility that the dark matter could be small black holes.

The future of Solar System exploration lies in the subsurface of rocky bodies, including planets. Robots provide a relatively cost-effective and safe method of probing the subsurface; this Perspective summarizes recent efforts in robotic drilling and regolith-sampling methods, concluding with a summary of China’s future space exploration plans.

Li and Be isotopic measurements of calcium–aluminium inclusions (CAIs) in the Efremovka meteorite suggest that the solid and gaseous precursors of CAIs were irradiated by a superflare during the last stages of the pre-main-sequence evolution of the Sun.

Three mysterious features at Titan’s northern polar region appear as lakes when observed with Cassini’s radar during winter but as land when observed in the infrared during spring, providing evidence of liquid removal on Titan at seasonal scale.

Using large-aperture Cherenkov telescopes, Benbow et al. have measured the angular sizes of two stars through timely occultations by asteroids, achieving an order of magnitude improvement in resolution over the lunar occultation method.

High-angular-resolution observations of 1.3 mm continuum and H30α recombination line emission identify a binary star system in formation, with protostars apparently separated by 180 au. The velocity difference between the two protostars constrains the orbital period and total mass of the system.

The abundance of primordial black holes in the Galactic halo is constrained through their microlensing of stars in M31. Despite monitoring tens of millions of stars, only a single candidate event is found, providing stringent upper bounds on their abundance.

Bathymetric radar measurements of several lacustrine features on Titan’s northern polar region were obtained during the last Cassini flyby in April 2017. These 100-m-deep and methane-dominated lakes are probably carved and replenished by local rainfall and regulated by subsurface flows.

A coupled thermal, geophysical and dynamical simulation covering 4.5 Gyr of evolution of Saturn’s inner mid-sized moons shows that, with the possible exception of Mimas, they formed early in Saturn’s history. A complex game of resonances has impacted the four older moons, shaping their geology and interior.

Low-mass, low-metallicity cool subdwarf stars are rare in the solar neighbourhood, and therefore their properties are not well constrained observationally. Here the authors report both a mass and radius determination of a cool subdwarf in an eclipsing binary system, providing a valuable data point.

Ultracompact stellar clusters in the Galactic Centre are likely to be major contributors to the Galactic cosmic ray flux in the multi-TeV energy range. Observations of the diffuse gamma-ray emission from the Galactic Centre and two young massive star clusters correlate with the cosmic-ray distribution.

By conducting chemical reactions involving a single pair of reactants within helium nanodroplets, Henning and Krasnokutski have measured the energetics of simple reactions relevant to astrochemistry. This approach allows the reaction pathways of surface reactions to be predicted with more accuracy than before.

The 4-metre Multi-Object Spectroscopic Telescope (4MOST) is a versatile optical survey instrument that will be installed on the VISTA telescope in 2022, offering medium- and high-resolution spectra and an innovative operations mode, explains Principal Investigator Roelof de Jong on behalf of the 4MOST Consortium.