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Abstract We report initial observations aimed at the characterization of a third interstellar object. This object, 3I/ATLAS or C/2025 N1 (ATLAS), was discovered on 2025 July 1 UT and has an orbital eccentricity ofe ∼ 6.1, perihelion ofq ∼ 1.36 au, inclination of ∼175°, and hyperbolic velocity ofV_∞ ∼ 58 km s⁻¹. We report deep stacked images obtained using the Canada–France–Hawaii Telescope and the Very Large Telescope that resolve a compact coma. Using images obtained from several smaller ground-based telescopes, we find minimal light-curve variation for the object over a ∼4 day time span. The visible/near-infrared spectral slope of the object is 17.1% ± 0.2%/100 nm, comparable to other interstellar objects and primitive solar system small bodies (comets and D-type asteroids). Moreover, 3I/ATLAS will be observable through early 2025 September, then unobservable by Earth-based observatories near perihelion due to low solar elongation. It will be observable again from the ground in late 2025 November. Although this limitation unfortunately prohibits detailed Earth-based observations at perihelion when the activity of 3I/ATLAS is likely to peak, spacecraft at Mars could be used to make valuable observations at this time. 

Abstract Assessing the prevalence of atmospheres on rocky planets around M-dwarf stars is a top priority of exoplanet science. High-energy activity from M dwarfs can destroy the atmospheres of these planets, which could explain the lack of atmosphere detections to date. Volcanic outgassing has been proposed as a mechanism to replenish the atmospheres of tidally heated rocky planets. L 98-59 b, a sub-Earth transiting a nearby M dwarf, was recently identified as the most promising exoplanet to detect a volcanic atmosphere. We present the transmission spectrum of L 98-59 b from four transits observed with JWST NIRSpec G395H. Although the airless model provides an adequate fit to the data based on itsχ², an SO₂atmosphere is preferred by 3.6σover a flat line in terms of the Bayesian evidence. Such an atmosphere would likely be in a steady state where volcanism balances escape. If so, L 98-59 b must experience at least eight times as much volcanism and tidal heating per unit mass as Io. If volcanism is driven by runaway melting of the mantle, we predict the existence of a subsurface magma ocean in L 98-59 b extending up toR_p ∼  60%–90%. An SO₂-rich volcanic atmosphere on L 98-59 b would be indicative of an oxidized mantle with an oxygen fugacity offO₂ > IW + 2.7, and it would imply that L 98-59 b must have retained some of its volatile endowment despite its proximity to its star. Our findings suggest that volcanism may revive secondary atmospheres on tidally heated rocky planets around M dwarfs. 

Abstract Nongravitational accelerations in the absence of observed activity have recently been identified on near-Earth objects (NEOs), opening the question of the prevalence of anisotropic mass loss in the near-Earth environment. Motivated by the necessity of nongravitational accelerations to identify 2010 VL₆₅and 2021 UA₁₂as a single object, we investigate the problem of linking separate apparitions in the presence of nongravitational perturbations. We find that nongravitational accelerations on the order of 1 × 10^–9au day⁻²can lead to a change in plane-of-sky positions of ∼1 × 10³arcsec between apparitions. Moreover, we inject synthetic tracklets of hypothetical nongravitationally accelerating NEOs into the Minor Planet Center orbit identification algorithms. We find that at large nongravitational accelerations (∣A_i∣ ≥ 1 × 10⁻⁸au day⁻²) these algorithms fail to link a significant fraction of these tracklets. We further show that if orbits can be determined for both apparitions, the tracklets will be linked regardless of nongravitational accelerations, although they may be linked to multiple objects. In order to aid in the identification and linkage of nongravitationally accelerating objects, we propose and test a new methodology to search for unlinked pairs. When applied to the current census of NEOs, we recover the previously identified case but identify no new linkages. We conclude that current linking algorithms are generally robust to nongravitational accelerations, but objects with large nongravitational accelerations may potentially be missed. While current algorithms are well-positioned for the anticipated increase in the census population from future survey missions, it may be possible to find objects with large nongravitational accelerations hidden in isolated tracklet pairs. 

Abstract Stellar flares are short-duration (< hours) bursts of radiation associated with surface magnetic reconnection events. Stellar magnetic activity generally decreases as a function of both the age and Rossby number,R₀, a measure of the relative importance of the convective and rotational dynamos. Young stars (<300 Myr) have typically been overlooked in population-level flare studies due to challenges with flare-detection methods. Here, we select a sample of stars that are members of 26 nearby moving groups, clusters, or associations with ages <300 Myr that have been observed by the Transiting Exoplanet Survey Satellite at 2 minute cadence. We identified 26,355 flares originating from 3160 stars and robustly measured the rotation periods of 1847 stars. We measure and find the flare frequency distribution slope,α, saturates for all spectral types atα∼ −0.5 and is constant over 300 Myr. Additionally, we find that flare rates for starst_age= 50–250 Myr are saturated belowR₀< 0.14, which is consistent with other indicators of magnetic activity. We find evidence of annual flare rate variability in eleven stars, potentially correlated with long-term stellar activity cycles. Additionally, we crossmatch our entire sample with the Galaxy Evolution Explorer and find no correlation between flare rate and far- and near-ultraviolet flux. Finally, we find the flare rates of planet-hosting stars are relatively lower than comparable, larger samples of stars, which may have ramifications for the atmospheric evolution of short-period exoplanets. 

Abstract The discovery of two interstellar objects passing through the solar system, 1I/‘Oumuamua and 2I/Borisov, implies that a galactic population exists with a spatial number density of order ∼0.1 au⁻³. The forthcoming Rubin Observatory Legacy Survey of Space and Time (LSST) has been predicted to detect more asteroidal interstellar objects like 1I/‘Oumuamua. We apply recently developed methods to simulate a suite of galactic populations of interstellar objects with a range of assumed kinematics, albedos, and size–frequency distributions (SFDs). We incorporate these populations into the objectsInField algorithm, which simulates detections of moving objects by an arbitrary survey. We find that the LSST should detect between ∼0 and 70 asteroidal interstellar objects every year (assuming the implied number density), with sensitive dependence on the SFD slope and characteristic albedo of the host population. The apparent rate of motion on the sky—along with the associated trailing loss—appears to be the largest barrier to detecting interstellar objects. Specifically, a relatively large number of synthetic objects would be detectable by the LSST if not for their rapid sky motion (>0.°5 day⁻¹). Therefore, algorithms that could successfully link and detect rapidly moving objects would significantly increase the number of interstellar object discoveries with the LSST (and in general). The mean diameter of detectable, inactive interstellar objects ranges from ∼50 to 600 m and depends sensitively on the SFD slope and albedo. 

Abstract Tidal heating on Io due to its finite eccentricity was predicted to drive surface volcanic activity, which was subsequently confirmed by the Voyager spacecraft. Although the volcanic activity in Io is more complex, in theory volcanism can be driven by runaway melting in which the tidal heating increases as the mantle thickness decreases. We show that this runaway melting mechanism is generic for a composite planetary body with liquid core and solid mantle, provided that (i) the mantle rigidity,μ, is comparable to the central pressure, i.e.,μ/(ρgR_P) ≳ 0.1 for a body with densityρ, surface gravitational accelerationg, and radiusR_P; (ii) the surface is not molten; (iii) tides deposit sufficient energy; and (iv) the planet has nonzero eccentricity. We calculate the approximate liquid core radius as a function ofμ/(ρgR_P), and find that more than 90% of the core will melt due to this runaway forμ/(ρgR_P) ≳ 1. From all currently confirmed exoplanets, we find that the terrestrial planets in the L 98-59 system are the most promising candidates for sustaining active volcanism. However, uncertainties regarding the quality factors and the details of tidal heating and cooling mechanisms prohibit definitive claims of volcanism on any of these planets. We generate synthetic transmission spectra of these planets assuming Venus-like atmospheric compositions with an additional 5%, 50%, and 98% SO₂component, which is a tracer of volcanic activity. We find a ≳3σpreference for a model with SO₂with 5–10 transits with JWST for L 98-59bcd. 

Abstract In this paper, we investigate the nonprincipal axis (NPA) rotational state of 1I/‘Oumuamua—the first interstellar object discovered traversing the inner solar system—from its photometric light curve. Building upon Mashchenko, we develop a model which incorporates NPA rotation and Sun-induced, time-varying outgassing torques to generate synthetic light curves of the object. The model neglects tidal forces, which are negligible compared to outgassing torques over the distances at which ‘Oumuamua was observed. We implement an optimization scheme that incorporates the NPA rotation model to calculate the initial rotation state of the object. We find that an NPA rotation state with an average period of 〈P〉 ≃ 7.34 hr best reproduces the photometric data. The discrepancy between this period and previous estimates is due to continuous period modulation induced by outgassing torques in the rotational model, as well as different periods being used. The best fit to the 2017 October data does not reproduce the 2017 November data (although the later measurements are too sparse to fit). The light curve is consistent with there being no secular evolution of the angular momentum, which is somewhat in tension with the empirical correlations between nuclear spin-up and cometary outgassing. The complex rotation of ‘Oumuamua may be the result of primordial rotation about the smallest principal axis if (i) the object experienced hypervolatile outgassing and (ii) our idealized outgassing model is accurate. 

Abstract The nondetection of a coma surrounding 1I/‘Oumuamua, the first discovered interstellar object (ISO), has prompted a variety of hypotheses to explain its nongravitational acceleration. Given that forthcoming surveys are poised to identify analogs of this enigmatic object, it is prudent to devise alternative approaches to characterization. In this study, we posit X-ray spectroscopy as a surprisingly effective probe of volatile ISO compositions. Heavily ionized metals in the solar wind interact with outgassed neutrals and emit high-energy photons in a process known as charge exchange, and charge-exchange-induced X-rays from comets and planetary bodies have been observed extensively in our solar system. We develop a model to predict the X-ray flux of an ISO based on its chemical inventory and ephemeris. We find that while standard cometary constituents, such as H₂O, CO₂, CO, and dust, are best probed via optical or infrared observations, we predict strong X-ray emission generated by charge exchange with extended comae of H₂and N₂—species that lack strong infrared fluorescence transitions. We find that XMM-Newton would have been sensitive to charge exchange emission from 1I/‘Oumuamua during the object’s close approach to Earth, and that constraints on composition may have been feasible. We argue for follow-up X-ray observations of newly discovered ISOs with close-in perihelia. Compositional constraints on the general ISO population could reconcile the apparently self-conflicting nature of 1I/‘Oumuamua and provide insight into the earliest stages of planet formation in extrasolar systems. 

ABSTRACT A large fraction of white dwarfs (WDs) have metal-polluted atmospheres, which are produced by accreting material from remnant planetary systems. The composition of the accreted debris broadly resembles that of rocky Solar system objects. Volatile-enriched debris with compositions similar to long-period comets (LPCs) is rarely observed. We attempt to reconcile this dearth of volatiles with the premise that exo-Oort clouds (XOCs) occur around a large fraction of planet-hosting stars. We estimate the comet accretion rate from an XOC analytically, adapting the ‘loss cone’ theory of LPC delivery in the Solar system. We investigate the dynamical evolution of an XOC during late stellar evolution. Using numerical simulations, we show that 1–30 per cent of XOC objects remain bound after anisotropic stellar mass-loss imparting a WD natal kick of $${\sim}1 \, {\rm km \, s^{-1}}$$. We also characterize the surviving comets’ distribution function. Surviving planets orbiting a WD can prevent the accretion of XOC comets by the star. A planet’s ‘dynamical barrier’ is effective at preventing comet accretion if the energy kick imparted by the planet exceeds the comet’s orbital binding energy. By modifying the loss cone theory, we calculate the amount by which a planet reduces the WD’s accretion rate. We suggest that the scarcity of volatile-enriched debris in polluted WDs is caused by an unseen population of 10–$$100 \, \mathrm{au}$$ scale giant planets acting as barriers to incoming LPCs. Finally, we constrain the amount of volatiles delivered to a planet in the habitable zone of an old, cool WD. 

Abstract Cosmic rays produced by young stellar objects can potentially alter the ionization structure, heating budget, chemical composition, and accretion activity in circumstellar disks. The inner edges of these disks are truncated by strong magnetic fields, which can reconnect and produce flaring activity that accelerates cosmic radiation. The resulting cosmic rays can provide a source of ionization and produce spallation reactions that alter the composition of planetesimals. These reconnection and particle acceleration processes are analogous to the physical processes that produce flaring in and the heating of stellar coronae. Flaring events on the surface of the Sun exhibit a power-law distribution of energy, reminiscent of those measured for earthquakes and avalanches. Numerical lattice reconnection models are capable of reproducing the observed power-law behavior of solar flares under the paradigm of self-organized criticality. One interpretation of these experiments is that the solar corona maintains a nonlinear attractor—or “critical”—state by balancing energy input via braided magnetic fields and output via reconnection events. Motivated by these results, we generalize the lattice reconnection formalism for applications in the truncation region of magnetized disks. Our numerical experiments demonstrate that these nonlinear dynamical systems are capable of both attaining and maintaining criticality in the presence of Keplerian shear and other complications. The resulting power-law spectrum of flare energies in the equilibrium attractor state is found to be nearly universal in magnetized disks. This finding indicates that magnetic reconnection and flaring in the inner regions of circumstellar disks occur in a manner similar to the activity on stellar surfaces. These results, in turn, have ramifications for the spallation-driven injection of radionuclides in planetesimals, disk ionization, and the subsequent planetary formation process.