The destructive power of an impacting asteroid is primarily estimated by knowledge of its size. Asteroid 2024 YR4 reached a peak 2032 impact probability with Earth of 3%, motivating a desire to determine its size. Owing to its infrared capabilities, JWST is uniquely suited for such assessment, especially for decameter-scale objects. We used JWST to observe 2024 YR4 and find a diameter of 60 ± 7 m. This size range corresponds to an albedo for 2024 YR4 of 8%–18%, consistent with observation that it is an S-type asteroid (International Asteroid Warning Network, https://iawn.net/obscamp/2024YR4/index.shtml), if at the low-albedo end of that asteroid taxon. Future observations through 2025 May will help further refine the asteroid's thermophysical model.

The first eruption of the periodic nova T CrB for eighty years is anticipated soon, though with an unknown date. A refinement of the future eruption date is investigated. The investigation is based on the combination of the previous eruption dates and on the orbital ephemeris of the binary system, without any hypothesis on the eruption mechanism. It is predicted that the next eruption should appear around 2025 March 27 or November 10, or later.

Near-Earth objects (NEOs) that follow horseshoe paths, and approach our planet at close range and low relative velocity, may undergo mini-moon events in which their geocentric energy becomes negative for hours, days or months, but without completing one revolution around Earth while bound. An example of NEO experiencing such a temporarily captured flyby is 2022 NX₁, which was a short-lived mini-moon in 1981 and 2022. Here, we show that the recently discovered small body 2024 PT₅ follows a horseshoe path and it will become a mini-moon in 2024, from September 29 until November 25.

We highlight the announcement by the IAU Minor Planet Center of 128 new irregular moons of Saturn discovered in our CFHT imaging acquired in 2023. We were able to link 83 of the new moons to detections from our earlier 2019–2021 study. Of the 58 new retrograde moons with multiyear arcs, 46 are likely in the Mundilfari subgroup. This large fraction is in line with the steep size distribution of the subgroup and the idea that it was created by a recent collision. Also, by more than tripling the number of Kiviuq subgroup members, the new discoveries have confirmed that this subgroup is a very tightly grouped collisional family, although likely much older.

Past solar activity is of great interest for astrophysical and geophysical studies. Systematic searches over the last four centuries have detailed the evolution of the solar cycle. Brief comments on solar activity for periods with sparse records, such as the year 1791, are crucial. Lorenzo Hervás y Panduro, a Jesuit intellectual, noted in his 1793 book that sunspots were seen almost daily from 1791 January 1 to April 20. This would suggest a solar activity level estimated at a sunspot number of around 70.

TOI-2285 b is a sub-Neptune-sized planet orbiting a nearby M dwarf, discovered through the TESS photometric survey and ground-based follow-up observations. The planet was initially reported to have an orbital period of 27.27 days, making it one of the lowest temperature sub-Neptunes transiting a bright M dwarf. However, additional TESS data reveal that its true orbital period is 13.64 days, half the original value, resulting in a warmer equilibrium temperature (358 K) than previously estimated (284 K). The misidentification likely resulted from the low signal-to-noise ratio of individual transit signals and the limited number of transits observed by TESS at that time. This case highlights the importance of carefully considering harmonic solutions for similar cases. The additional TESS data also reveal another planetary candidate with an orbital period of 9.67 days and a radius of 1.5 R_⊕, requiring validation in future studies.

As a star evolves, its radius expands and can surpass the semimajor axis of an orbiting planet in a planetary engulfment event. In this project, we obtain time-dependent radius values for various stellar masses using Modules for Experiments in Stellar Astrophysics and compare the results to known exoplanet systems to predict if/when host stars will swallow their planets, assuming no further dynamical evolution of the systems. Our models predict that 61% of exoplanets are planetary engulfment candidates, with most events occurring just before the onset of helium fusion, near the first dredge-up. This finding suggests that resulting stellar lithium enrichment may be quickly erased, leaving enhanced angular momentum as a more reliable tracer for engulfment. We also find an inverse correlation between the mass of the host star and the probability of planetary engulfment.

The tidal disruption of a rocky planet by a red dwarf results in a stream of molten rock, with half the material eventually landing on the surface of the star. Since the mean density of a ∼0.1M_⊙ star is ∼10² g cm⁻³, the rocky debris with a density of ∼3 g cm⁻³ would lead to lava rivers or lakes floating on the surface of the red dwarf. These would be observable as stellar spots, owing to their high opacity. Advanced technological civilizations could design ships that float on the surface of red dwarfs and constitute a new type of technological signatures.

We report the cometary activity of the Centaur 2023 RS₆₁ (RS61) evident in our UT 2025 January 2 observations with the Lowell Discovery Telescope, showing a coma and a ∼59-long tail. The archival observations from the Pan-STARRS1 survey reveal two previously unnoticed activity episodes in 2017 and 2023, suggesting SR61 could be a rare outbursting Centaur similar to 174P/Echeclus. The outburst on UT 2017 October 10 at r_H = 13.5 au makes RS61 the second-most distant active Centaur after 95P/Chiron. We estimate a nucleus size between 4.7 km ≤ r_n ≤ 7.0 km, assuming typical Centaur geometric albedos, an upper-limit Afρ ≤ 245 cm and dust production rate  kg s⁻¹. As RS61 approaches the perihelion in 2028 its activity will likely increase, making this object an exciting observing target.

Turbulent radiative mixing layers (TRMLs) may play a crucial role in driving multiphase gas formation in galactic outflows and the circumgalactic medium. Magnetic fields pervade these regions and can be amplified by shear-driven turbulence and cooling-induced compression. However, strong magnetic fields inhibit mixing. We present three-dimensional magnetohydrodynamic simulations of ∼transonic, TRMLs, beginning with a weak uniform magnetic field (10⁻¹² G). Adiabatic simulations show essentially no change in magnetic-field strength during the first Kelvin–Helmholtz time, as one would expect. In contrast, simulations with radiative cooling boost the magnetic-field strength by a factor of 3–10. Allowing cooling to molecular temperatures appears to promote a sustained enhancement of magnetic-field strength, which may be aided by turbulent mixing. Our work helps to disentangle the driving mechanisms of magnetic-field amplification in turbulent mixing layers, which impact the survival of cold gas clouds in galactic winds.

Fifteen Anomalous Cepheid (ACeph) candidates were recently identified in the dwarf galaxy Crater II via an extended survey done with the Dark Energy Camera at the 4 m Blanco Telescope at Cerro Tololo Inter-American Observatory (CTIO). Using various Period–Luminosity relationships found in the literature, we anchor these candidates to the nearby RR-Lyrae stars' distances to confirm 14 of the candidates as not only being ACephs, but as confidently belonging to Crater II rather than the field within the line-of-sight.

Our ability to electromagnetically detect and characterize astrophysical black holes depends crucially on their accretion of gas. We used the Eulerian grid codes FLASH, Athena, and Athena++ to perform fluid dynamic simulations, studying black hole accretion. Our findings demonstrate that, in viscous conditions, all three codes produce similar accretion rates, while, in non-viscous conditions, Athena++ appears to generate much smaller accretion rates. Nevertheless, our results give insight on the purely numerical variability of black hole accretion.

Magnetic fields exist in and around galaxies, but the properties of these fields have not been fully explored due to the challenges inherent in observing and modeling them. In this Note, we explore the differences in magnetic field strength of central and satellite galaxies from the magnetohydrodynamic TNG100 simulation. We find that on average, magnetic fields in satellite galaxies are roughly an order of magnitude stronger than those of central galaxies with comparable masses. The difference is greater for satellites that have already approached within 1R₂₀₀ of their host galaxies. These results indicate that magnetic fields in satellite galaxies are amplified by environmental processes as they fall into a host halo.

Despite their long history, a complete inventory of Galactic novae has remained incomplete due to severe dust extinction. Recent ground-based near-infrared (NIR) as well as space-based mid-infrared (MIR) searches are providing a new window into discovering heavily obscured Galactic novae. Even with its slow cadence, archival photometric searches for large-amplitude, fast fading outbursts in the NEOWISE survey were previously used to identify Galactic nova candidates between 2014 and 2020. In this paper, we demonstrate the efficacy of the method with the discovery and NIR spectroscopy of WTP 21aaeuqd—a bright (peak W2 AB flux ≈10.5 mag), rapidly evolving (t₂ ≈ 120 days) MIR Galactic outburst (at ). The reduced spectrum exhibits broad (≈800 km s⁻¹) emission lines of H i and C i, confirming its classification as a missed Fe ii nova. This result confirms that archival infrared photometric searches are an effective way to identify nova candidates missed in optical searches.