The elemental compositions of exoplanets encode information about their formation environments and internal structures. While volatile ratios such as carbon-to-oxygen (C/O) are used to trace formation location, the rock-forming elements-magnesium (Mg), silicon (Si), and iron (Fe)-govern interior mineralogy and are commonly assumed to reflect the host star's abundances. Yet this assumption remains largely untested. Ultra-hot Jupiters, gas-giant exoplanets with dayside temperatures above 3000 K, provide rare access to refractory elements that remain gaseous. Here we present high-resolution thermal emission spectroscopy of the exoplanet WASP-189b ( T e q = 335 4 - 34 + 27 K) obtained with the Immersion Grating Infrared Spectrometer (IGRINS) on Gemini South. We detect neutral iron (Fe I), magnesium (Mg I), silicon (Si I), water (H2O), carbon monoxide (CO), and hydroxyl (OH) at signal-to-noise ratios exceeding 4, and retrieve their elemental abundances. We show that the Mg/Si, Fe/Mg, and Si/Fe ratios are consistent with stellar values, while the refractory-to-volatile ratio is enhanced by roughly a factor of 2. These findings demonstrate that giant-planet atmospheres can preserve stellar-like rock-forming ratios, providing an empirical validation of the stellar-proxy assumption that underpins planetary composition and formation models across exoplanet systems.

Precise stellar ages (uncertainties ≲ 1 Gyr, or ∼ 20% at solar age) are required to discern evolutionary trends in atmospheric biosignatures of terrestrial habitable zone exoplanets surveyed by the Habitable Worlds Observatory (HWO) and will aid in constraining planetary interior evolution and target prioritization. We present a catalog of stellar ages for Tier 1 and Tier 2 targets in the HWO Target Stars and Systems (TSS) sub-working group's TSS25 list, compiling published literature ages derived from high-precision methods. The sample comprises 659 stars likely to be observed by HWO, independent of the final mission architecture. This initial catalog focuses on asteroseismology and gyrochronology, which can achieve ∼ 20% precision for the majority of these stars. We find that only ∼ 5% of the sample have asteroseismic ages and ∼ 20% have gyrochronal ages, with just ∼ 2% having constraints from both methods. For stars with multiple published measurements, the median reported statistical uncertainties are slightly smaller than the systematic uncertainties: ∼ 9% versus ∼ 12% for asteroseismology and ∼ 16% versus ∼ 18% for gyrochronology. The scarcity of precise stellar ages in this sample highlights the need for a concerted effort to obtain robust age constraints in advance of HWO; this catalog is intended as a living resource that will be regularly updated in the lead-up to the mission.

Future direct imaging space telescopes, such as NASA’s Habitable Worlds Observatory (HWO), will be the first capable of both detecting and characterizing terrestrial exoplanets in the habitable zones (HZs) of nearby Sun-like stars. Since this will require a significant amount of time and resources for even a single system or exoplanet, the likelihood that a system will host detectable life should be considered when prioritizing observations. One method of prioritization is to estimate the likelihood that an exoplanet has remained continuously within the HZ long enough for life to emerge and make a detectable impact on the atmosphere. We utilize a Bayesian method to calculate the likelihood that a given orbital radius around a star is currently in the 2 Gyr continuous habitable zone (CHZ 2 ), the approximate time it took life on Earth to significantly oxygenate the atmosphere. We apply this method to the 164 stars in the NASA Exoplanet Exploration Program Mission Star List for HWO, representing a preliminary sample of Sun-like stars with HZs most accessible to a future direct imaging mission. By considering the CHZ 2 likelihood at all orbital radii outside a hypothetical inner working angle for HWO, we define a metric for prioritizing targets according to the accessibility and total extent of the CHZ 2 . We find that the CHZ 2 metric peaks between 3 and 4 Gyr for late F and early G dwarfs, but tentatively determine that stars earlier than ∼F3 or hotter than ∼6600 K are unlikely to have a CHZ 2 at the time of observation.

Stars and their associated planets originate from the same cloud of gas and dust, making a star’s elemental composition a valuable indicator for indirectly studying planetary compositions. While the connection between a star’s iron (Fe) abundance and the presence of giant exoplanets is established, the relationship with small planets remains unclear. The elements Mg, Si, and Fe are important in forming small planets. Employing machine learning algorithms like XGBoost, trained on the abundances (e.g., the Hypatia Catalog) of known exoplanet-hosting stars (NASA Exoplanet Archive), allows us to determine significant “features” (abundances or molar ratios) that may indicate the presence of small planets. We test on three groups of exoplanets: (1) all small, R _P < 3.5 R _⊕ ; (2) sub-Neptunes, 2.0 R _⊕ < R _P < 3.5 R _⊕ ; and (3) super-Earths, 1.0 R _⊕ < R _P < 2.0 R _⊕ —each subdivided into seven ensembles to test different combinations of features. We created a list of stars with ≥90% probability of hosting small planets across all ensembles and experiments (“overlap stars”). We found abundance trends for stars hosting small planets, possibly indicating star–planet chemical interplay during formation. We also found that Na and V are key features regardless of planetary radii. We expect our results to underscore the importance of elements in exoplanet formation and machine learning’s role in target selection for future NASA missions, e.g., the James Webb Space Telescope, the Nancy Grace Roman Space Telescope, and the Habitable Worlds Observatory—all of which are aimed at small-planet detection.

Core collapse supernovae are thought to be one of the main sources in the galaxy of elements heavier than iron. Understanding the origin of the elements is thus tightly linked to our understanding of the explosion mechanism of supernovae and supernova nucleosynthesis. X-ray and gamma-ray observations of young supernova remnants, combined with improved theoretical modeling, have resulted in enormous improvements in our knowledge of these events. The isotope Ti-44 is one of the most sensitive probes of the innermost regions of the core collapse engine, and its spatial and velocity distribution are key observables. Hard x-ray imaging spectroscopy with the Nuclear Spectroscopic Telescope Array (NuSTAR) has provided new insights into the structure of the supernova remnant Cassiopeia A (Cas A), establishing the convective nature of the supernova engine. However, many questions about the details of this engine remain. We present here the concept for a balloon-borne follow-up mission called A SuperConducting ENergetic x-ray Telescope (ASCENT). ASCENT uses transition edge sensor gamma-ray microcalorimeter detectors with a demonstrated 55-eV full-width half maximum energy resolution at 97 keV. This 8- to 16-fold improvement in energy resolution over NuSTAR will allow for high-resolution imaging and spectroscopy of the Ti-44 emission. This will allow for a detailed reconstruction of gamma-ray line redshifts, widths, and shapes, allowing us to address questions such as, What is the source of the neutron star kicks? What is the dominant production pathway for Ti-44? Is the engine of Cas A unique?

There are currently many large-field surveys that are operational and are being planned including the powerful Vera C. Rubin Observatory Legacy Survey of Space and Time. These surveys will increase the number and diversity of transients dramatically. However, for some transients, like supernovae (SNe), we can gain more understanding by directed observations (e.g., shock breakout and γ -ray detections) than by simply increasing the sample size. For example, the initial emission from these transients can be a powerful probe of these explosions. Upcoming ground-based detectors are not ideally suited to observing the initial emission (shock emergence) of these transients. These observations require a large field-of-view X-ray mission with a UV follow-up within the first hour of shock breakout. The emission in the first 1 hr to even 1 day provides strong constraints on the stellar radius and asymmetries in the outer layers of stars, the properties of the circumstellar medium (e.g., inhomogeneities in the wind for core-collapse SNe and accreting companions in thermonuclear SNe), and the transition region between these two areas. This paper describes a simulation for the number of SNe that could be seen by a large field-of-view lobster-eye X-ray and UV observatory.

The ideal exoplanets to search for life are those within a star’s habitable zone. However, even within the habitable zone, planets can still develop uninhabitable climate states. Sustaining a temperate climate over geologic (∼gigayear) timescales requires a planet to contain sufficient internal energy to power a planetary-scale carbon cycle. A major component of a rocky planet’s energy budget is the heat produced by the decay of radioactive elements, especially 40K, 232Th, 235U, and 238U. As the planet ages and these elements decay, this radiogenic energy source dwindles. Here we estimate the probability distribution of the amount of these heat-producing elements that enter into rocky exoplanets through Galactic history by combining the system-to-system variation seen in stellar abundance data with the results from Galactic chemical evolution models. From this, we perform Monte Carlo thermal evolution models that maximize the mantle cooling rate, thus allowing us to create a pessimistic estimate of lifetime a rocky, stagnant-lid exoplanet can support a global carbon cycle through Galactic history. We apply this framework to a sample of 17 likely rocky exoplanets with measured ages, seven of which we predict are likely to be actively degassing today, despite our pessimistic assumptions. For the remaining planets, including those orbiting TRAPPIST-1, we cannot confidently assume that they currently contain sufficient internal heat to support mantle degassing at a rate sufficient to sustain a global carbon cycle or temperate climate without additional tidal heating or undergoing plate tectonics.

Earth and Space Science Open Archive Presented WorkOpen AccessYou are viewing the latest version by default [v1]Continuous Habitable Zones: Pairing a GCM and Bayesian Framework to Predict Habitable Zone EvolutionAuthorsAustinWareiDNancyKiangiDPatrickYoungiDSee all authors Austin WareiDCorresponding Author• Submitting AuthorArizona State UniversityiDhttps://orcid.org/0000-0003-2828-0334view email addressThe email was not providedcopy email addressNancy KiangiDNASA Goddard Institute for Space StudiesiDhttps://orcid.org/0000-0002-5730-924Xview email addressThe email was not providedcopy email addressPatrick YoungiDArizona State UniversityiDhttps://orcid.org/0000-0003-1705-5991view email addressThe email was not providedcopy email address

The number of potentially habitable planets continues to increase, but we lack the time and resources to characterize all of them. With ∼30 known potentially habitable planets and an ever-growing number of candidate and confirmed planets, a robust statistical framework for prioritizing characterization of these planets is desirable. Using the ∼2 Gyr it took life on Earth to make a detectable impact on the atmosphere as a benchmark, we use a Bayesian statistical method to determine the probability that a given radius around a star has been continuously habitable for 2 Gyr. We perform this analysis on nine potentially habitable exoplanets with planetary radii <1.8 R ⊕ and/or planetary masses <10 M ⊕ around nine low-mass host stars (∼0.5–1.1 M ⊙) with measured stellar mass and metallicity, as well as Venus, Earth, and Mars. Ages for the host stars are generated by the analysis. The technique is also used to provide age estimates for 2768 low-mass stars (0.5–1.3 M ⊙) in the TESS Continuous Viewing Zones.

Understanding stellar composition is fundamental not only to our comprehension of the galaxy, especially chemical evolution, but it can also shed light on the interior structure and mineralogy of exoplanets, which are formed from the same material as their host stars. Unfortunately, the underlying mathematics describing stellar mass fractions and stellar elemental abundances is difficult to parse, fragmented across the literature, and contains vexing omissions that makes any calculation far from trivial, especially for non-experts. In this treatise, we present clear mathematical formalism and clarification of inherent assumptions and normalizations within stellar composition measurements, which facilitates the conversion from stellar mass fractions to elemental abundances to molar ratios, including error propagation. We also provide an example case study of HIP 544 to further illustrate the provided equations. Given the important chemical association between stars, as well as the interdisciplinary relationship between stars and their planets, it is vital that stellar mass fractions and abundance data be more transparent and accessible to people within different sub-fields and scientific disciplines.

The detection of two transition metals in the remnant of a supernova lends support to a mechanism for the explosion of a massive star called the neutrino-driven convective supernova engine, where a plume of hot material re-invigorates a stalled shockwave.

Introduction: Our Sun was likely born as a protostar in a dense star forming region, in the vicinity of several massive (>8 M) stars. Very early in its history, the protoplanetary disk around the proto-Sun was impacted by debris from the supernova (SN) explosions of some of these massive stars. This caused an enrichment of the disk with short-lived radionuclides, the daughter products of which we observe in meteorites today. Injection of r-process nuclides resulting from SN events led to observed excesses of Cr, Ti, and r-process Mo in calciumaluminum-rich inclusions (CAIs) [1−3]. In one scenario that can explain these r-process enrichments, these earliest solids derived their compositions from infalling material from a heterogenous molecular cloud, followed by inward transport to the inner disk, where CAIs condensed [4]. In addition, it is often surmised that the onset of our solar system was triggered by such an event [e.g., 5]. In this study, we investigate whether SN ejecta are intrinsically heterogeneous in r-process nuclides (Cr and Ti), and whether it is possible to inject r-process nuclides alone into a young protoplanetary disk. We also explore the chemistry and timeline by which rprocess nuclides mix and pollute the protoplanetary disk, and compare it to the accreted s-process nuclides. Finally, we compare the known Cr and Ti isotopic compositions of stardust in meteorites to the ejecta compositions in core collapse supernova (CCSN). Methods: The CCSN nucleosynthetic yields were determined by a 3D, spherically symmetric, CCSN simulation introduced in [6,7]. This model, called 15S, is based on a 15 M progenitor star which is evolved using the 1D stellar evolution code TYCHO [8]. After core collapse and shock revival, the star is mapped into the 3D smoothed-particle hydrodynamics (SPH) code SNSPH [9,10] for 43 simulated hours until it is postprocessed and isotope yields are captured using the Burnf code [11]. To avoid isotope abundances being influenced by rounding errors, only isotope mass fractions higher than 10 (relative to the mass of each of the roughly 1 million SPH particles) are included. Maps of the SN ejecta were created using the SPH visualization software SPLASH [12] and plots were created in MATLAB. To ensure that the interior of the explosion can be investigated, cross-sections were formed which have a width of approximately 4.5 au in the Y direction. Additionally, SPH particles in the hydrogen envelope contain neither Ti nor Cr, we consider only the inner 6 au of the supernova ejecta. Results and Discussion: Stardust enriched in rprocess nuclides. Oxide stardust <100 nm in size shows large excesses in Cr and Ti [13−15]. The reported δCr values of SiC stardust in acid leachates, on the other hand, tend to be indistinguishable from the terrestrial values within the experimental uncertainties [16], although Ti excesses have been observed [17,18]. Marhas et al. [19] reported 300-600 ‰ Cr excess in one unique SiC X grain. Graphite stardust exhibits large enrichments of Ti [20], although Cr isotopes have not been explored. Figure 1. Comparison of observed Cr and Ti isotope ratios in oxide stardust with isotopic compositions predicted by 3D CCSN model 15S. The excellent correlation makes CCSN potential sources of such stardust grains.

We present the isotope yields of two post-explosion, three-dimensional 15 core-collapse supernova models, 15S and 15A, and compare them to the carbon, nitrogen, silicon, aluminum, sulfur, calcium, titanium, iron, and nickel isotopic compositions of SiC stardust. We find that these core-collapse supernova models predict similar carbon and nitrogen compositions to SiC X grains and grains with 12C/13C < 20 and 14N/15N < 60, which we will hereafter refer to as SiC ‘D’ grains. Material from the interior of a 15 explosion reaches high enough temperatures shortly after core collapse to produce the large enrichments of 13C and 15N necessary to replicate the compositions of SiC D grains. The innermost ejecta in a core-collapse supernova is operating in the neutrino-driven regime and undergoes fast proton capture after being heated by the supernova shockwave. Both 3D models predict 0.3 Al/27Al < 1.5, comparable to the ratios seen in SiC X, C, and D grains. Models 15S and 15A, in general, predict very large anomalies in calcium isotopes but do compare qualitatively with the SiC X grain measurements that show 44Ca and 43Ca excesses. The titanium isotopic compositions of SiC X grains are well reproduced. The models predict 57Fe excesses and depletions that are observed in SiC X grains, and in addition predict accurately the 60Ni/58Ni, 61Ni/58Ni, and 62Ni/58Ni ratios in SiC X grains, as a result of fast neutron captures initiated by the propagation of the supernova shockwave. Finally, symmetry has a noticeable effect on the production of silicon, sulfur, and iron isotopes in the SN ejecta.

Mixing above the proto-neutron star is believed to play an important role in the supernova engine, and this mixing results in a supernova explosion with asymmetries. Elements produced in the innermost ejecta, e.g., 56 Ni and 44 Ti, provide a clean probe of this engine. The production of 44 Ti is particularly sensitive to the exact production pathway and, by understanding the available pathways, we can use 44 Ti to probe the supernova engine. Using thermodynamic trajectories from a three-dimensional supernova explosion model, we review the production of these elements and the structures expected to form under the “convective-engine” paradigm behind supernovae. We compare our results to recent X-ray and γ -ray observations of the Cassiopeia A supernova remnant.

The catalog of stellar evolution tracks discussed in our previous work is meant to help characterize exoplanet host stars of interest for follow-up observations with future missions like the James Webb Space Telescope . However, the utility of the catalog has been predicated on the assumption that we would precisely know the age of the particular host star in question; in reality, it is unlikely that we will be able to accurately estimate the age of a given system. Stellar age is relatively straightforward to calculate for stellar clusters, but it is difficult to accurately measure the age of an individual star to high precision. Unfortunately, this is the kind of information we should consider as we attempt to constrain the long-term habitability potential of a given planetary system of interest. This is ultimately why we must rely on predictions of accurate stellar evolution models, as well a consideration of what we can observably measure (stellar mass, composition, orbital radius of an exoplanet) in order to create a statistical framework wherein we can identify the best candidate systems for follow-up characterization. In this paper we discuss a statistical approach to constrain long-term planetary habitability by evaluating the likelihood that at a given time of observation, a star would have a planet in the 2 Gy continuously habitable zone (CHZ 2 ). Additionally, we will discuss how we can use existing observational data (i.e., data assembled in the Hypatia catalog and the Kepler exoplanet host star database) for a robust comparison to the catalog of theoretical stellar models.