Light pollution affects every region on Earth, including at the poles and even above us in low-Earth orbit. That isn’t news. But the extent of the problem, laid out in our Focus on dark skies, is startling and should turn us all into activists.

Harnessing the power of citizen science and machine learning, this study takes in 20 years of Hubble Space Telescope images, of which 2.7% show satellite streaks, and predicts that this fraction will increase by up to an order of magnitude in the next decade.

The arrangement of dwarf galaxies in a thin plane surrounding the Milky Way has been thought to contradict the prevailing cosmological model of cold dark matter in the Universe. New work suggests that this arrangement may just be a temporary alignment, bringing our galaxy back into agreement with theoretical expectations once the radial distribution of satellites is taken into account.

The unusual radar properties of icy satellites appear to be correlated and distributed along a spectrum of values. Only modelling including the coherent backscatter opposition effect can reproduce this behaviour.

The returned samples from Hayabusa2 show that C-type asteroid Ryugu experienced various steps of mineralogical alteration within only 1–2 million years after accretion.

Models for night sky brightness are used to characterize sites for astronomical observatories, but in the presence of artificial light pollution, certain assumptions regarding aerosol shapes mean that the estimates are systematically underestimated, particularly at low altitudes.

The brightness at the tip of the red giant branch in the Magellanic Clouds sets the scale of the Universe and has been debated. Here a number of samples are drawn from across the Clouds and composited, providing sub-per-cent level agreement and measurements consistent with independent geometric constraints.

A nested orbit-to-ground approach for microbial landscape patterns at different scales, tested in the high Andes, provides a machine learning-based search tool for detecting biosignatures on terrestrial planets.

Laboratory measurements reveal highly efficient formation of H₂ at temperatures up to 250 K on a carbonaceous surface. This process should lead to a high rate of H₂ formation on the surfaces of polycyclic aromatic hydrocarbons in both nearby and high-redshift galaxies, bolstering the contribution of H₂ to the cooling of warmer gas.

Low Earth orbits are increasingly congested, impacting astronomical observations and dark skies. Globally coordinated regulatory policies and mitigation strategies are among urgent next steps to protect this shared environment and intangible heritage.

Light pollution affects every region on Earth, including at the poles and even above us in low-Earth orbit. That isn’t news. But the extent of the problem, laid out in our Focus on dark skies, is startling and should turn us all into activists.

Unfettered access to dark night skies is rapidly diminishing, due to light pollution and satellite constellation tracks. Scientists should do more to stand up to ‘big light’ and ‘big space’ and preserve this natural resource.