Protecting the night sky from optical interference by satellites needs a standard that goes beyond a simple brightness limit to consider the aggregate impact of constellations. We discuss the infrastructure and tools required to achieve this.
The late stages of galaxy mergers—when two supermassive black holes (SMBHs) reach kiloparsec-scale separations—represent a critical phase for understanding SMBH growth, galaxy co-evolution and the progenitors of low-frequency gravitational waves. However, confirmed close-separation (<3 kpc) dual active galactic nuclei (AGNs) remain rare, particularly in the merger-rich early Universe. Here we report the discovery of LID-1166, a dual AGN with a projected separation of ~1.5 kpc at z ≈ 4.5. Spatially resolved James Webb Space Telescope/NIRSpec integral-field spectroscopy reveals two spatially and kinematically distinct narrow-line emission components with a line-of-sight velocity offset of ~−164 km s−1. Both components additionally exhibit broad Hα emission, including a compact off-nucleus component associated with the companion source, confirming two actively accreting SMBHs. Independent ALMA [C II] 158-μm observations reveal spatially and kinematically distinct cold-gas components associated with the same nuclei, demonstrating a gas-rich merger. While undergoing super-Eddington accretion during a late-stage merger, the SMBHs already lie on the local black hole–host mass relation for massive elliptical galaxies, suggesting that rapid, obscured growth may help establish this relation early in cosmic history. LID-1166 reveals a previously hidden phase of SMBH growth and points to a missing population of heavily obscured, merger-driven dual AGNs at high redshift. Observations reveal two rapidly growing supermassive black holes in a gas-rich galaxy merger just 1.3 billion years after the Big Bang. Both already lie on the black hole–host mass relation, indicating a period of early co-evolution.
Small planetary bodies record the processes that shaped the Solar System, but their surfaces and interiors often evolve in unexpected ways. Deimos, the potato-shaped, 12-km-diameter outer satellite of Mars, has a strikingly smooth surface covered by fine regolith, in contrast to its heavily cratered and grooved sibling, 22-km-diameter Phobos. Moreover, Deimos's topography is dominated by a single large south-polar depression, whose formation we simulate to constrain the moon's interior and surface geomechanical properties and to explain the origin and distribution of its regolith. Here we find that an oblique impact by a 320-m-diameter projectile can quantitatively account for this depression, the global regolith layer and surface features such as bright streaks and crater infill. Our results show that Deimos's upper layers are extremely weak and that its interior is highly porous and dissipative, resembling the recently visited rubble-pile asteroids rather than lunar regolith. This suggests that small dark moons and asteroids, despite their specific histories, may converge on similar physical states.
Trihydrogen cations ( H3+ ), a key diagnostic of atmospheric energy balance, are produced through ionization by solar radiation and particle impacts in hydrogen-rich planetary atmospheres. At Jupiter, H3+ is produced most efficiently in the auroral region through electron precipitation and has a leading role in magnetosphere-ionosphere coupling by regulating ionospheric conductance. Previously, the properties of H3+ have been determined from remote sensing, with plasma parameters retrieved from its infrared emissions, although these measurements are limited by line-of-sight integration and restricted altitude resolution. Here we report the unambiguous, direct in situ detection of H3+ plasma in the auroral region. Furthermore, intermittent H3+ outflows are measured high above the ionosphere, with upwards velocities exceeding Jupiter's escape speed, confirming atmospheric escape of H3+ . We propose that H3+ outflow originates in the auroral upwards electric current region, initially triggered by plasma-wave interactions and subsequently accelerated by the electric potential structure above the ionosphere. This study reveals a H3+ -mediated pathway for mass and energy transfer between the ionosphere and magnetosphere of Jupiter, constituting an atmospheric escape with a loss rate of order 1026 s-1. Similar mechanisms may operate at other planets with infrared aurorae and strong magnetic fields.
