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One possible mechanism for Martian hemispherical dichotomy formation is excavation of the northern lowland basin in the existing crust by a single giant impact. Here we explore a related scenario in which the impact melt volume is sufficient to fill the excavated cavity, produce a thickened crust, and generate a topographic basin centered on the opposite side of the planet. We investigate this mechanism by formulating a model for viscous spreading of a partially molten layer over a spherical surface. We derive numerical solutions and calculate the final area of the spreading layer as a function of impactor size and shape of the layer boundary due to an initially asymmetric melt region. Results are compared with observations, including lowland basin size, shape of the dichotomy boundary, age difference between crustal provinces, and crustal thickness.

We use the long‐wavelength Venusian topography and geoid to constrain the global lithospheric thickness by assuming that the stagnant lid overlying the convective mantle is in isostatic equilibrium, the isostatic stagnant lid (ISL) approximation. Two‐dimensional and three‐dimensional numerical simulations of convection show that the ISL approximation is reasonably accurate in the tested parameter range of temperature‐dependant viscosity convection with bottom heating and internal heating. The errors in predicting the thickness of the stagnant lid (i.e., the lithosphere) are somewhat larger for internally heated convection. We attribute this to a flatter lid and, as a result, to a larger relative contribution to topography and geoid anomalies from the deeper parts of the layer. Application of the ISL approximation to Venus suggests that the average lithospheric thickness might be as large as 600 km, which is on the high end of previously proposed estimates. Key Points Thermal isostasy is a reasonably accurate model for a convecting system The magnitude of the dynamic topography is negligibly small Most of the Venusian topography can be explained by thermal isostasy

The isostatic stagnant lid (ISL) approximation is applied to the long‐wavelength Venusian topography and geoid to place constraints on the thickness of the crust and lithosphere. Previous studies showed that a purely thermal isostasy model of the lithosphere (the “stagnant lid”) accounts for a significant portion of the topography and geoid anomalies. Here we assume that the remaining discrepancy between the observed and model geoid is due to crustal thickness variations and that the crust, the lithosphere and the mantle are in a state of double isostatic equilibrium: the lithosphere is isostatically floating on top of the mantle and the crust is isostatically floating on top of the lithosphere. The addition of another variable, the crustal thickness, allows an exact fit to the observed topography and geoid. This also makes the solution non‐unique: an exact fit to topography and geoid can be achieved in a broad range of average lithospheric and crustal thicknesses. Additional constraints such as the gabbro‐eclogite phase transition and the existence of relatively young volcanism limit this range to some extent. The inferred variations in the crustal thickness are less sensitive to model assumptions and generally agree with the results obtained in previous studies. Key Points Venusian topography and geoid are fully explained by the crust and lithosphere A broad range of average thicknesses fit the observations Non‐uniqueness is reduced by additional constraints

Magnetic kagome metals are a promising platform to develop unique quantum transport and optical phenomena caused by the interplay between topological electronic bands, strong correlations, and magnetic order. This interplay may result in exotic quasiparticles that describe the coupled electronic and spin excitations on the frustrated kagome lattice. Here, we observe novel elementary magnetic excitations within the ferromagnetic Mn kagome layers in TbMn 6 Sn 6 using inelastic neutron scattering. We observe sharp, collective acoustic magnons and identify flat-band magnons that are localized to a hexagonal plaquette due to the special geometry of the kagome layer. Surprisingly, we observe another type of elementary magnetic excitation; a chiral magnetic quasiparticle that is also localized on a hexagonal plaquette. The short lifetime of localized flat-band and chiral quasiparticles suggest that they are hybrid excitations that decay into electronic states. S. X. M. Riberolles et al . study the kagome Chern insulator TbMn 6 Sn 6 via inelastic neutron scattering. They observe signatures of chiral and flat-band magnons, which are highly localized in real space and strongly damped in the time domain.

‘Sudden’ quantum quench and prethermalization have become a cross-cutting theme for discovering emergent states of matter1–4. Yet this remains challenging in electron matter5–9, especially superconductors10–14. The grand question of what is hidden underneath superconductivity (SC)15 appears universal, but poorly understood. Here we reveal a long-lived gapless quantum phase of prethermalized quasiparticles (QPs) after a single-cycle terahertz (THz) quench of a Nb3Sn SC gap. Its conductivity spectra is characterized by a sharp coherent peak and a vanishing scattering rate that decreases almost linearly towards zero frequency, which is most pronounced around the full depletion of the condensate and absent for a high-frequency pump. Above a critical pump threshold, such a QP phase with coherent transport and memory persists as an unusual prethermalization plateau, without relaxation to normal and SC thermal states for an order of magnitude longer than the QP recombination and thermalization times. Switching to this metastable ‘quantum QP fluid’ signals non-thermal quench of coupled SC and charge-density-wave (CDW)-like orders and hints quantum control beneath the SC.

Knowledge of magnetic symmetry is vital for exploiting nontrivial surface states of magnetic topological materials. EuIn 2 As 2 is an excellent example, as it is predicted to have collinear antiferromagnetic order where the magnetic moment direction determines either a topological-crystalline-insulator phase supporting axion electrodynamics or a higher-order-topological-insulator phase with chiral hinge states. Here, we use neutron diffraction, symmetry analysis, and density functional theory results to demonstrate that EuIn 2 As 2 actually exhibits low-symmetry helical antiferromagnetic order which makes it a stoichiometric magnetic topological-crystalline axion insulator protected by the combination of a 180 ∘ rotation and time-reversal symmetries: C 2 × T = 2 ′ . Surfaces protected by 2 ′ are expected to have an exotic gapless Dirac cone which is unpinned to specific crystal momenta. All other surfaces have gapped Dirac cones and exhibit half-integer quantum anomalous Hall conductivity. We predict that the direction of a modest applied magnetic field of μ 0 H  ≈ 1 to 2 T can tune between gapless and gapped surface states. Magnetic symmetry is a vital factor to determine exotic topological phases. Here, Riberolles et al. demonstrate a helical antiferromagnetic order in EuIn 2 As 2 which makes it a magnetic topological-crystalline axion insulator.

Intracellular pathogens and danger signals trigger the formation of inflammasomes, which activate inflammatory caspases and induce pyroptosis. The anthrax lethal factor metalloprotease and small-molecule DPP8/9 inhibitors both activate the NLRP1B inflammasome, but the molecular mechanism of NLRP1B activation is unknown. In this study, we used genome-wide CRISPR-Cas9 knockout screens to identify genes required for NLRP1B-mediated pyroptosis.We discovered that lethal factor induces cell death via the N-end rule proteasomal degradation pathway. Lethal factor directly cleaves NLRP1B, inducing the N-end rule–mediated degradation of the NLRP1B N terminus and freeing the NLRP1B C terminus to activate caspase-1. DPP8/9 inhibitors also induce proteasomal degradation of the NLRP1B N terminus but not via the N-end rule pathway. Thus, N-terminal degradation is the common activation mechanism of this innate immune sensor.

Symmetry plays a central role in conventional and topological phases of matter, making the ability to optically drive symmetry changes a critical step in developing future technologies that rely on such control. Topological materials, like topological semimetals, are particularly sensitive to a breaking or restoring of time-reversal and crystalline symmetries, which affect both bulk and surface electronic states. While previous studies have focused on controlling symmetry via coupling to the crystal lattice, we demonstrate here an all-electronic mechanism based on photocurrent generation. Using second harmonic generation spectroscopy as a sensitive probe of symmetry changes, we observe an ultrafast breaking of time-reversal and spatial symmetries following femtosecond optical excitation in the prototypical type-I Weyl semimetal TaAs. Our results show that optically driven photocurrents can be tailored to explicitly break electronic symmetry in a generic fashion, opening up the possibility of driving phase transitions between symmetry-protected states on ultrafast timescales. The authors demonstrate ultrafast symmetry breaking by optically driven photocurrents.

Noncoding RNA molecules (ncRNAs) have been implicated in numerous biological processes including transcriptional regulation and the modulation of protein function. Yet, in spite of the apparent abundance of ncRNA, little is known about the biological role of the projected thousands of ncRNA genes present in the human genome. To facilitate functional analysis of these RNAs, we have created an arrayed library of short hairpin RNAs (shRNAs) directed against 512 evolutionarily conserved putative ncRNAs and, via cell-based assays, we have begun to determine their roles in cellular pathways. Using this system, we have identified an ncRNA repressor of the nuclear factor of activated T cells (NFAT), which interacts with multiple proteins including members of the importin-beta superfamily and likely functions as a specific regulator of NFAT nuclear trafficking.