JWST/NIRISS Reveals the Water-rich "Steam World" Atmosphere of GJ 9827 d

With sizable volatile envelopes but smaller radii than the solar system ice giants, sub-Neptunes have been revealed as one of the most common types of planet in the galaxy. While the spectroscopic characterization of larger sub-Neptunes (2.5─4 R <SUB>⊕</SUB>) has revealed hydrogen-dominated atmospheres, smaller sub-Neptunes (1.6─2.5 R <SUB>⊕</SUB>) could either host thin, rapidly evaporating, hydrogen-rich atmospheres or be stable, metal-rich "water worlds" with high mean molecular weight atmospheres and a fundamentally different formation and evolutionary history. Here, we present the 0.6─2.8 μm JWST/NIRISS/SOSS transmission spectrum of GJ 9827 d, the smallest (1.98 R <SUB>⊕</SUB>) warm (T <SUB>eq,A=0.3</SUB> ∼ 620 K) sub-Neptune where atmospheric absorbers have been detected to date. Our two transit observations with NIRISS/SOSS, combined with the existing HST/WFC3 spectrum, enable us to break the clouds─metallicity degeneracy. We detect water in a highly metal-enriched "steam world" atmosphere (O/H of ∼4 by mass and H<SUB>2</SUB>O found to be the background gas with a volume mixing ratio of >31%). We further show that these results are robust to stellar contamination through the transit light source effect. We do not detect escaping metastable He, which, combined with previous nondetections of escaping He and H, supports the steam atmosphere scenario. In water-rich atmospheres, hydrogen loss driven by water photolysis happens predominantly in the ionized form, which eludes observational constraints. We also detect several flares in the NIRISS/SOSS light curves with far-UV energies of the order of 10<SUP>30</SUP> erg, highlighting the active nature of the star. Further atmospheric characterization of GJ 9827 d probing carbon or sulfur species could reveal the origin of its high metal enrichment.

How solar prominences form

Prominences are cool plasma structures extending several thousand kilometers in the Sun’s hot corona. Some persist for weeks.

Review of Solar Energetic Particle Prediction Models

Solar Energetic Particle (SEP) events are interesting from a scientific perspective as they are the product of a broad set of physical processes from the corona out through the extent of the heliosphere, and provide insight into processes of particle acceleration and transport that are widely applicable in astrophysics. From the operations perspective, SEP events pose a radiation hazard for aviation, electronics in space, and human space exploration, in particular for missions outside of the Earth's protective magnetosphere including to the Moon and Mars. Thus, it is critical to improve the scientific understanding of SEP events and use this understanding to develop and improve SEP forecasting capabilities to support operations. Many SEP models exist or are in development using a wide variety of approaches and with differing goals. These include computationally intensive physics-based models, fast and light empirical models, machine learning-based models, and mixed-model approaches. The aim of this paper is to summarize all of the SEP models currently developed in the scientific community, including a description of model approach, inputs and outputs, free parameters, and any published validations or comparisons with data.

Deployed Electromagnetic Radiation Deflector Shield Creating a Zone of Minimum Radiation and Magnetic/Plasma Effects for Spacecraft - NASA Technical Reports Server (NTRS)

Spaceflight outside of the Earth's protective magnetic field is dangerous from a cosmic radiation perspective. Inside Earth's magnetic field, where the manned International Space Station (ISS) orbits, the radiation encountered is minimal and almost all is deflected by our planet's magnetic fields. However, outside that protective shield, the Sun's solar wind (high energy radiation, solar energetic particles or SEPs) consisting of protons, electrons, alpha particles and plasmas continuously bombards the spacecraft for the months or years of spaceflight. On occasion the Sun produces a CME (Coronal Mass Ejection) that vastly increases the energy and volume of this radiation. These particles damage human DNA as well as living tissue and can destroy sensitive electronics. The Deployed Electromagnetic Radiation Deflector Shield (DERDS) provides a magnetic field that will deflect SEPs and CMEs and other harmful solar and cosmic rays away from a manned spacecraft, robotic spacecraft, or manned extra-planetary base stations using an electromagnet that is deployed between the spacecraft/station and the source of radiation and creates a magnetosphere or zone of minimal radiation in which the spacecraft or base station would reside.

Where to Search For Life: Evidence from narrative sources with established predictive efficacy

The search for habitable planets, and even for ``Earth 2.0'', is a major driver in contemporary astronomy. However selecting target fields to prioritise for such searches presents a challenge. Here we establish a statistical analysis of the appearance of constellation names in science fiction magazines of the pulp era, evaluating the most commonly mentioned constellations and thus those which the science fiction community collectively identify as the most likely locations to find life. Given that the predictive power of science fiction is well established, we suggest that these locations might be prioritised by searches for extrasolar biospheres.

UK Solar Physics

The Luminosity Function and Stellar Evolution.

The evolutionary significance of the observed luminosity function for main-sequence stars in the solar neighborhood is discussed. The hypothesis is made that stars move off the main sequence after burning about 10 per cent of their hydrogen mass and that stars have been created at a uniform rate in the solar neighborhood for the last five billion years. Using this hypothesis and the observed luminosity function, the rate of star creation as a function of stellar mass is calculated. The total number and mass of stars which have moved off the main sequence is found to be comparable with the total number of white dwarfs and with the total mass of all fainter main-sequence stars, respectively.