Superpuffs are planets with exceptionally low densities (rho less than or similar to 0.1 g cm-3) and core masses (M c less than or similar to 5M circle plus). Many lower-mass (M p less than or similar to 10M circle plus) superpuffs are expected to be unstable to catastrophic mass loss via photoevaporation and/or boil-off, whereas the larger gravitational potentials of higher-mass (M p greater than or similar to 10M circle plus) superpuffs should make them more stable to these processes. We test this expectation by studying atmospheric loss in the warm, higher-mass superpuff TOI-1420b (M = 25.1M circle plus, R = 11.9R circle plus, rho = 0.08 g cm-3, T eq = 960 K). We observed one full transit and one partial transit of this planet using the metastable helium filter on Palomar/WIRC and found that the helium transits were 0.671% +/- 0.079% (8.5 sigma) deeper than the TESS transits, indicating an outflowing atmosphere. We modeled the excess helium absorption using a self-consistent 1D hydrodynamics code to constrain the thermal structure of the outflow given different assumptions for the stellar XUV spectrum. These calculations then informed a 3D simulation, which provided a good match to the observations with a modest planetary mass-loss rate of 1010.82 g s-1 ( M p / M approximate to 70 Gyr). Superpuffs with M p greater than or similar to 10M circle plus, like TOI-1420b and WASP-107b, appear perfectly capable of retaining atmospheres over long timescales; therefore, these planets may have formed with the unusually large envelope mass fractions they appear to possess today. Alternatively, tidal circularization could have plausibly heated and inflated these planets, which would bring their envelope mass fractions into better agreement with expectations from core-nucleated accretion.

China has announced its ambitious targets towards carbon neutrality by 2060. The Guangdong-Hongkong-Macau (GHM) region, as a pilot demonstration area for China's reform and opening-up, faces dual pressures on providing low-carbon electricity for meeting its surging demand while limiting carbon emissions. Here, we develop an energy system optimization model with high spatio-temporal resolution that integrates investment planning and operation optimization to explore transition pathways for the GHM power system under various decarbonization scenarios. Power system operations in hourly resolution are included to quantify spatio-temporal variability of generation and demand. We show that reducing carbon emissions by 70%, 85%, and 100% in 2050 requires a total system cost of 619.1, 628.3, and 653.1 billion USD (values in 2021 USD), with an average decarbonization cost of 4.79, 5.27, and 7.11 USD per ton, respectively. Accelerating transition to carbon neutrality by 2035 incurs a total system cost of 686.9 billion USD and an average decarbonization cost of 9.11 USD per ton. Moreover, nuclear, offshore-wind, and imported electricity cover over 80% of electricity demand when achieving carbon neutrality and thus serve as cornerstones for supporting the GHM power system transition. Furthermore, we observe that a high fossil fuel price benefits emission mitigation, while reinforcing transmission networks considerably reduces system transition costs. Combing low renewable and storage prices, a high electricity import ratio, and transmission network expansion delivers a lower bound for system transition and a negative average decarbonization cost for the GHM region.

As the decarbonization of the electric power sector gathers pace, electric power systems will need to evolve in multiple ways: larger amounts of intermittent renewables will need to be deployed, as will dispatchable power generators, transmission lines, and energy storage solutions. Some of these resources could provide the electric power system with much-needed dispatchability, but the value of each will evolve over time and space, as will the impact of their deployment on economic costs and carbon emissions. This study systematically compares the roles that different sources of dispatchability could play in a power system's decarbonization and the evolution of its topology over the period from 2020 to 2060, with China as a case study. Results show that adding these resources to a system's operation yields multiple benefits for decarbonization. These include higher levels of renewables integration (+46 000 TWh, +19%), cost reductions (-5800 billion RMB, -13%), and lower GHG emissions (-23 billion tonnes, -23%). The role of different resources changes throughout the transition: transmission always plays the dominant role; dispatchable coal and nuclear generation reduces renewable curtailment up to 2030; pumped-hydro storage reduces curtailment from 2030 to 2040; and battery storage and concentrating solar power become critical after 2040. This evolution could redraw the economic and environmental maps of China by redistributing infrastructure, renewables integration and carbon emissions to less-developed, remote areas. These results help prioritize efforts to facilitate power system decarbonization over several decades; they also yield insights regarding the regional and sustainable development impact of the low-carbon transition.

Oxygen deficient zones (ODZs) account for about 30% of total oceanic fixed nitrogen loss via processes including denitrification, a microbially mediated pathway proceeding stepwise from NO3- to N-2. This process may be performed entirely by complete denitrifiers capable of all four enzymatic steps, but many organisms possess only partial denitrification pathways, either producing or consuming key intermediates such as the greenhouse gas N2O. Metagenomics and marker gene surveys have revealed a diversity of denitrification genes within ODZs, but whether these genes co-occur within complete or partial denitrifiers and the identities of denitrifying taxa remain open questions. We assemble genomes from metagenomes spanning the ETNP and Arabian Sea, and map these metagenome-assembled genomes (MAGs) to 56 metagenomes from all three major ODZs to reveal the predominance of partial denitrifiers, particularly single-step denitrifiers. We find niche differentiation among nitrogen-cycling organisms, with communities performing each nitrogen transformation distinct in taxonomic identity and motility traits. Our collection of 962 MAGs presents the largest collection of pelagic ODZ microorganisms and reveals a clearer picture of the nitrogen cycling community within this environment.