Thomas Müller

The asteroid 2024 YR ₄ is a potentially hazardous Apollo-type near-Earth object. Its highly eccentric orbit produces close Earth-Moon encounters roughly every 4 years. Based on the astrometry collected during the discovery apparition, the asteroid had a 4% probability of a lunar impact on 2032 December 22. A collection of light curves, including JWST-NIRCam data, allowed us to constrain the rotation period, spin pole, and convex shape solutions for the object. We analyzed two sets of JWST-MIRI observations obtained in three filters on 26 March 2025. The extracted photometry reveals rotationally driven thermal flux variations. The combination of a spin-shape model from light-curve inversion and the absolutely calibrated three-band mid-infrared light curves is well reproduced by a convex spin-shape solution with a spin pole at ( λ _ecl , β _ecl ) = (232 ±1°, −11 ±3°), a sidereal period of 19.4633 (± 0.0001) min, and axis ratios of a/b ≈ 1.28 and b/c ≈ 1.45. The corresponding equivalent-volume diameter is 60.8 _−3.6 ^+1.8 m, with a geometric V-band albedo of p _V = 0.11 _−0.03 ^+0.05 (assuming H _V = 24.14 ±0.25 mag). A high thermal inertia Γ > 500 J m ⁻² K ⁻¹ s ^−1/2 and low surface roughness are required to explain the observed MIRI data. The rapid rotation, in combination with the high thermal inertia, leads to significant heat transport to the night side, producing a broad nearly isothermal equatorial band. The near-Earth asteroid thermal model has limited reliability for this object, requiring an extreme beaming parameter η > 3, whereas the fast-rotating model and a full thermophysical model provide consistent and reliable estimates of the size and albedo. The combination of high eccentricity and high thermal inertia implies seasonal skin depths of up to ~3 m and radiative timescales of weeks to months. Although seasonal heating is negligible for the March 2025 observations because of the near-equator-on viewing geometry, the seasonal Yarkovsky drift is expected to be dominant over the diurnal component and might become measurable during future encounters. Although JWST astrometry from February 2026 rules out any possible impact on the Earth or the Moon for at least 100 years, the spin, shape, and radiometric constraints presented here provide an important benchmark for future potentially hazardous objects.

Present models of the zodiacal light (scattered sunlight from interplanetary dust in the visible) and zodiacal emission (thermal emission in the mid-infrared) are primarily constrained by surface-brightness measurements obtained at relatively large solar elongations ( ϵ ≳ 60°). As a result, their predictive accuracy at smaller elongations remains uncertain. This is particularly relevant for solar elongations of ϵ ≈ 30°–60°, where next-generation near-Earth-object discovery missions such as NEO Surveyor and NEOMIR are designed to operate. To evaluate the reliability of these models at small solar elongations, we compile and reanalyze the available small-elongation zodiacal-light and zodiacal-emission measurements and provide the first systematic validation of modern zodiacal-light models in a regime where they have never been independently tested. We compare two models derived from the COBE/DIRBE survey: one constrained primarily by the spatial and temporal variation of the monochromatic sky brightness, and another that additionally uses interband color information and fixes the absolute normalization by requiring the minimum high-latitude residual at 25 μ m to vanish. We find that the former reproduces the observations significantly better. At wavelengths most relevant to infrared near-Earth-object surveys (∼8–10 μ m), it typically agrees with measurements to within ∼10% at ϵ ≈ 40°–60°. Although it also performs better at ϵ ≈ 30°, significant discrepancies remain. These results show that zodiacal emission at small solar elongations is still only weakly constrained and that its absolute brightness remains uncertain. New mid-infrared observations are required to improve background estimates for future infrared survey missions.

Aims. The Beam Expander Testing X-ray (BEaTriX) facility is an advanced experimental setup designed to test silicon pore optics mirror modules (SPO MMs) for the NewAthena telescope at the energies 4.51 keV and 1.49 keV. The 4.51 keV energy line has been operational since 2022, while the other is under developement. Its novel design allows measurements of the point spread function (PSF) and of the effective area with the required accuracy. The 4.51 keV line at BEaTriX can be operated in two configurations: one with higher flux used for the effective area measurement and another with tighter beam collimation used for the half-energy width (HEW) measurement. In this paper, we present a deconvolution–based method to mathematically derive the PSF of a perfectly collimated X-ray beam, using the PSF information acquired with the high-flux configuration. This approach offers the possibility to primarily use the high-flux configuration for the MM characterization. Methods. We used the Richardson–Lucy deconvolution algorithm to reconstruct the PSF of a perfectly collimated X-ray beam. The deconvolution kernel, which models the angular distribution of the BEaTriX beam, was derived from a Hartmann test in high-flux configuration, accounting for the finite source size, dispersivity of the beam expander, figure errors of the collimating mirror, and misalignments. Using this kernel and performing a deconvolution to the measured high-flux image, we are able to obtain the intrinsic PSF of the MM for an ideally collimated beam. Results. The images reconstructed using the deconvolution method were used to calculate the qualification parameters (i.e., full width at half maximum, FWHM, and HEW) for an SPO MM. To validate the reliability of the reconstruction approach, the mathematically deconvolved image is convolved back to the modeled beam kernel. This operation, as expected, yields the experimental PSF obtained in the high-flux configuration. As a further validation, the deconvolved PSF was compared with independent measurements acquired at the PANTER X-ray test facility, demonstrating a very good agreement.

Wildfire detection and characterization from space critically depend on accurate thermal infrared measurements across a wide dynamic range. OroraTech’s SAFIRE payloads feature mid-wave infrared (MWIR) and long-wave infrared (LWIR) bands optimized for this purpose, yet the volume and power constraints of many CubeSat platforms preclude the use of onboard calibration sources. This reflects a broader limitation of current Earth observation systems: the absence of robust calibration and validation methodologies at high brightness temperatures relevant to active fires. We evaluate the potential of using thermophysical models (TPM) of the Moon as a vicarious calibration reference for calibration transfer between instruments. The Moon reaches surface temperatures of up to 400 K, offering a stable target in the thermal domain that is visible from many different orbits. Previous research has established the use of TPMs for Moon observations in the infrared; however, uncertainties in surface properties remain, particularly in the mid-wave infrared. We investigate these effects using SAFIRE observations of the lunar surface acquired over a wide range of lunar phase angles (from waxing -81.5° to waning +122.2°). We constrain the TPMs using observations from the Sentinel-3 Sea and Land Surface Temperature Radiometer (SLSTR) fire channels and uncover a 5.2 % inter-sensor disagreement in the MWIR between Sentinel-3A and Sentinel-3B at high brightness temperatures, corresponding to ~2.2 K at 400 K. Applying the same methodology to observations of our SAFIRE payloads bounds the calibration transfer error at 5.8 % in the MWIR and 4.2 % in the LWIR for lunar phase angles within ±45°. These results establish lunar vicarious calibration as a viable approach in the thermal domain for high-temperature applications, providing a pathway toward improved fire radiative power retrievals and enhanced global wildfire monitoring.

Recent stellar occultations indicate that Quaoar's apparent shape is consistent across all observed events, suggesting that the body is close to a Maclaurin spheroid rather than a triaxial ellipsoid. Such a nearly axisymmetric figure naturally implies a single-peaked rotational light curve with a period of ∼8.8 h, instead of the previously proposed double-peaked 17.7 h period. In this work, we investigate which patterns of surface albedo variation can reproduce the observed visible and infrared thermal emission light curves under this faster rotation scenario. We further show that while standard tidal evolution can explain Weywot's present orbit, it cannot explain Quaoar's 17.7 h rotation period. If the true rotation period is instead close to half this value, the tension largely disappears, and Quaoar's figure, primordial rotation, and the long-term tidal influence of Weywot become mutually consistent. Moreover, the dynamical evolution of Quaoar's inner ring provides independent constraints that could be tested using sufficiently high-resolution occultation measurements.

Asteroids are remnants of the early Solar System and are possible reservoirs of organic compounds that can be delivered to planets. Besides, collisions with asteroids can alter the evolution of planets and their moons and pose a threat to life on Earth. We will present our project on detecting and characterising asteroids via their thermal emission using the JWST Mid-Infrared Instrument (MIRI) in the context of Solar System science and planetary defence. JWST MIRI opened up a new window to detect small and cool asteroids by observing at mid-infrared wavelengths (5 - 28 micron) with unprecedented sensitivity. After four years in operation, a wealth of archival MIRI imaging data is available for mining. As a first step, we focused on the images acquired via the MIRI Mid-INfrared Disk Survey (MINDS) which is part of the MIRI European Consortium Guaranteed Time Observation program. We detected 18 asteroids in this data set. Most of them were unknown, and these are fainter and smaller than the known ones. We will present our method to search for asteroids, show the results obtained so far, and describe our plan to extend it to the whole MIRI archive. One component will be to develop a citizen science project to identify asteroids. This search is complementary to those conducted at visible and near-infrared wavelengths with facilities such as VST/OmegaCAM, HST, Euclid, and LSST: their combination helps build the spectral energy distribution of asteroids which constrain their temperatures, sizes, and surface properties. Overall, this study will help understand the physical properties of asteroids, their role in the formation of the Solar System and of planetary systems in general, and will contribute to assessing the risk of future collisions with Earth.

D-type asteroids are among the most primitive, organic-rich objects in the Solar System and are widely thought to have originated in the outer regions of Solar System, being them key witnesses to early Solar System chemistry and volatile delivery. (162998) 2001 SK162 is a Near-Earth Asteroid (NEA) belonging to the Apollo group and designated as a Potentially Hazardous Asteroid (PHA). Discovered by the LINEAR program in 2001, the object follows an eccentric orbit (e ~ 0.47) with a small orbital inclination of 1.7° and a perihelion distance of ~1.01 au. Some previous studies showed that this asteroid is possible D/T types [1,2,3,4]. These orbital and spectral characteristics led to its selection as the D-type primary target of the Japanese Next Generation Small-body Sample Return mission (NGSR-D) [5]. Precise knowledge of the target’s fundamental physical properties—in particular its geometric albedo, diameter, rotation state, and shape—is essential for mission planning, including spacecraft navigation, approach trajectory design, and sample acquisition operations. However, these properties remain poorly constrained: previous photometric and thermal-infrared observations [7,6] have yielded significant uncertainties that could directly impact mission design and operations.To address this, we conducted a coordinated, multi-technique observing campaign of 2001 SK162 between October 2025 and March 2026, using a worldwide network of facilities: lightcurve photometry with the Two-meter Twin Telescope (TTT) at Teide Observatory; visible multi-band photometry with MuSCAT3/4 on the Las Cumbres Observatory (LCO) 2-m telescopes at Haleakala Observatory and with the Pirka 1.6-m telescope at Nayoro Observatory; visible spectroscopy with OSIRIS on the 10.4-m Gran Telescopio Canarias (GTC) at Roque de los Muchachos Observatory (ORM); NIR multi-band photometry with MOSFIRE on Keck I and polarimetry with the Subaru Telescope at Maunakea Observatories and the 2.5-m Nordic Optical Telescope (NOT) at ORM. In parallel, we reanalyzed archival WISE and Spitzer thermal-infrared data to independently constrain the size and albedo.Lightcurves were obtained with TTT over 37 nights between 2025-10-21 and 2025-12-22. Periodogram analysis yields a rotational period of ~178 h, much longer than the previous estimate [8] and placing 2001 SK162 firmly in the slow-rotator regime. The lightcurve shows a peak-to-peak amplitude of 0.34 mag, indicating a moderately elongated shape. Combining our TTT photometry with archival ZTF data, we fit the H–G phase function and obtain H_V = 18.04 mag and G = 0.10, consistent with the photometric behavior of dark, primitive asteroids.Visible multi-band photometry with MuSCAT3/4 (LCO 2-m) and Pirka 1.6-m telescope and visible spectroscopy with OSIRIS/GTC consistently reveal a featureless, red visible reflectance spectrum. Within the recent taxonomic framework of Mahlke et al. [9], the spectrum is best classified as D- or Z-type, although the color variation with different rotational phase is little. This confirms the spectral classification on which the NGSR-D target selection was based and reinforces the scientific case for sampling 2001 SK162. Moreover, we also obtained the near infrared reflectance at Y, J, and K bands by MOSFIRE/Keck I.Because the geometric albedo of 2001 SK162 has been poorly constrained, we performed polarimetric observations with Subaru and NOT to discriminate between high- and low-albedo solutions, and reanalyzed archival WISE and Spitzer thermal-infrared data to provide an independent estimate of the geometric albedo and effective diameter. Joint analysis of these complementary techniques is ongoing and will be presented at the meeting, with the goal of delivering a self-consistent set of physical parameters for the NGSR-D mission. Together, these results provide the first comprehensive physical characterization of (162998) 2001 SK162. The combination of an unusually long rotation period, elongated shape, and primitive D/Z-type spectral classification makes this object a scientifically compelling target for NGSR-D. [1] Binzel et al. (2004) MAPS 39, 351, [2] Ye (2011) AJ 141, 32, [3] Thomas et al. (2014) Icarus 228, 217, [4] Marsset et al. (2022) AJ 163, 165, [5] Okada, T. et al. (2026) EPSC 2026, [6] Mainzer et al. (2011) AJ 743, 156, [7] Mueller et al. (2011) AJ 141, 109, [8] Pravec, P. et al. (2005) https://space.asu.cas.cz/~ppravec/neo.htm, [9] Mahlke, M., Carry, B., & Mattei, P.A. (2022) A&A 665, A26.

Trans-Neptunian objects are distant bodies that retain valuable information about the origin and evolution of the Solar System. Many of these objects constitute binary systems. Studying binaries allows us to further characterise this primitive population and is critical for determining mass densities, a key but elusive physical property. Nevertheless, satellite detection can be challenging. This study aims to constrain the presence of close-in satellites around a selection of ten trans-Neptunian objects, including four known binary systems used for methodology validation. We developed a methodology independent of primary-secondary separation. We exploit the combination of occultation-derived sizes and thermal emission data from the 'TNOs are Cool' key project. We model the thermal emission from a binary system to explain the thermal excess that cannot be reproduced by a single body of the occultation-derived size. Herschel Space Observatory We obtain satisfactory constraints for the validation targets , , , and . We find that , , and are likely binary systems, which was previously unknown. We report size estimates for their putative satellites. For , , and we find that no sizable satellite is needed to reconcile thermal and occultation data.

The Euclid Ecliptic Survey was conducted during the calibration phase of the mission, from 23 to 31 December 2023, as a campaign to study Solar System objects. We used data from this survey to analyse more than 23 000 appeareances of 2321 known asteroids. Due to their high apparent angular motion relative to the background stars (5–60″ h ⁻¹ ), these objects appear as streaks in VIS long-exposure images. We set out to estimate their spin periods, since only 7% of them have periods published in the literature. We used multiple apertures along each streak to increase the time resolution of our light curves. Our method combines a Lomb–Scargle approach with a Markov chain Monte Carlo (MCMC) algorithm to characterise the posterior distributions. Some asteroids show multimodality in the MCMC search, indicating period aliases; in these cases, we report all aliases and their likelihoods. We validate our pipeline by comparing our fitted periods with 48 published periods, including period harmonics. We find that 44% of our periods are within 1% of those published and 98% are within 15%, and we establish that with 98% confidence the best solution can be found among the first three aliases. All reliable periods reported are in agreement with our current understanding of the spin-period distribution for asteroids. We find 16 periods below the spin barrier of 2.2 h with absolute magnitudes below 19, and thus 16 candidate super-fast rotators. We provide light curves for all 2321 objects observed and 889 high-quality periods in an open-access catalogue. The asteroids with reported periods include five Mars crossers, four Cybeles, four Hildas, three Hungarias, and 877 asteroids in other regions of the main belt. Our results represent the first batch of spin periods extracted from light curves and include the first-ever period measurements for 93% of the objects.