The ESA Euclid mission will survey more than 14 000 deg2 of the sky in visible and near-infrared wavelengths, mapping the extragalactic sky to constrain our cosmological model of the Universe. Although the survey focusses on regions further than 15° from the ecliptic, it should allow for the detection of more than about 105 Solar System objects (SSOs). After simulating the expected signal from SSOs in Euclid images acquired with the visible camera (VIS), we describe an automated pipeline developed to detect moving objects with an apparent velocity in the range of 0.1–10″ h−1, typically corresponding to sources in the outer Solar System (from Centaurs to Kuiper-belt objects). In particular, the proposed detection scheme is based on SExtractor software and on applying a new algorithm capable of associating moving objects amongst different catalogues. After applying a suite of filters to improve the detection quality, we study the expected purity and completeness of the SSO detections. We also show how a Kohonen self-organising neural network can be successfully trained (in an unsupervised fashion) to classify stars, galaxies, and SSOs. By implementing an early-stopping method in the training scheme, we show that the network can be used in a predictive way, allowing one to assign the probability of each detected object being a member of each considered class.

The current standard model of cosmology successfully describes a variety of measurements, but the nature of its main ingredients, dark matter and dark energy, remains unknown. Euclid is a medium-class mission in the Cosmic Vision 2015–2025 programme of the European Space Agency (ESA) that will provide high-resolution optical imaging, as well as near-infrared imaging and spectroscopy, over about 14 000 deg2 of extragalactic sky. In addition to accurate weak lensing and clustering measurements that probe structure formation over half of the age of the Universe, its primary probes for cosmology, these exquisite data will enable a wide range of science. This paper provides a high-level overview of the mission, summarising the survey characteristics, the various data-processing steps, and data products. We also highlight the main science objectives and expected performance.

The surface of Mercury is exposed to extreme diurnal thermal variations caused by the high intensity of solar radiation, the radiative loss due to the planet’s lack of atmosphere, its eccentricity and its 3:2 spin - orbit resonance. This work presents an experimental study on terrestrial rocks used as Mercury analogues subjected to hermean conditions. We simulate the power density of a planetary surface at Mercury’s perihelion distance of 0.31 au using the Space and High-Irradiance Near-Sun Simulator (SHINeS) at Luleå University of Technology. The reflectance spectra were acquired in the visible and near-infrared wavelength range for every sample before and after irradiation. Permanent spectral changes are observed in all samples towards the longer wavelengths in the visible spectrum after only one thermal cycle. Darkening is evident in both the visible and near-infrared spectrum ranges, combined with reddening in the visible-to-near-infrared region in most of our samples. We propose that darker samples like boninite, basalt, and diorite are more likely to experience spectral changes due to their low albedo. 

Understanding the properties of planetary regolith is important for unravelling the origin and evolution of bodies in our solar system. On Earth, properties of regolith are identified in the laboratory through a variety of methods such as coring samples, shear tests, and triaxial tests. In space missions, these laboratory methods cannot be used, and one must rely on in-situ measurements for identifying soil mechanical properties. Penetrometers are perfect for this due to their small size, light weight and simple use. Penetrometers have been used on Earth to identify soil shear strength properties such as cohesion and angle of internal friction. However, results are highly dependent on the experimentally obtained data and the types of soil that are tested. In this paper, we use a model developed by Kang et al., that links penetrometry data to geotechnically relevant quantities such as the angle of internal friction, test this model using our own laboratory experiments, and compare this to known values as well as triaxial test results. We identified that for silica glass beads the effects of grain size and tip shape are very pronounced, with similar values of internal friction found in other sources and our triaxial tests. We observed that penetrometry can indicate similar angles of internal friction comparable to laboratory values for more irregular and angular sample materials such as the Phobos simulant used to prepare for JAXA's MMX mission. Our results suggest that a penetrometer could be used as a ‘poor man's triaxial test’ in planetary exploration.

We present the first polarimetric observations of the third discovered interstellar object (ISO), 3I/ATLAS (C/2025 N1, or 3I), obtained preperihelion with FORS2 at the Very Large Telescope, ALFOSC at the Nordic Optical Telescope, and FoReRo2 at the 2 m Ritchey-Chrétien-Coudé telescope, over a phase angle range of 7:7–22:4. This marks the second-ever polarimetric study of an ISO, the first distinguishing 2I/Borisov from most solar system comets by its higher positive polarization. Our polarimetric measurements as a function of phase angle reveal that 3I is characterized by a deep and narrow negative polarization branch, reaching a minimum value of −2.7% at phase angle 7^∘, and an inversion angle of 17^∘—a combination unprecedented among asteroids and comets, including 2I/Borisov. At very small phase angles, the extrapolated slope of the polarization phase curve is consistent with that of certain small trans-Neptunian objects and Centaur Pholus, consistent with independent spectroscopic evidence for a red, possibly water-ice-bearing object. Imaging confirms a diffuse coma present from our earliest observations, though no strong polarimetric features are spatially resolved. These findings may demonstrate that 3I represents a distinct type of comet, expanding the diversity of known interstellar bodies.

Characterising the mechanical properties of minor bodies is essential for understanding their origin and evolution. Past missions such as Hayabusa2 have landed on asteroids to sample and discover what these bodies are made of. However, there has been conflicting evidence and reports into the physical properties of the granular surface material of these bodies. With future missions such as Japan Aerospace eXploration Agency’s Martian Moons eXploration mission landing on Phobos, the understanding and identification of these physical properties is crucial to maximising the scientific output from these missions. Penetrometry, the determination of the reaction force that an object experiences as it penetrates a surface, can help to understand the essential properties of regolith, such as grain size, porosity and cohesion. Results of penetrometry experiments are largely analysed based on empirical models, which presents us with a challenge if we want to apply them to understand granular materials on asteroid surfaces because gravity cannot be eliminated in the laboratory. Hence, it is essential to verify penetrometry as a method and validate penetrometry instrument designs in microgravity. For this purpose, we conducted a microgravity experiment onboard a parabolic flight campaign. Our experiment tested the use of penetrometry in asteroid-analogue environments by investigating samples with varying properties, such as grain size distribution and shape, and then compared to 1 g experiments to understand the role microgravity plays. The experiment provided a substantial database for future analysis. This paper will focus on the design of the experiment and the parabolic flight campaign in which the experiments were conducted. The design decisions and the variables adjusted during the experiment will be discussed, evaluating how these influenced the campaign and its outcomes. We will also provide a snapshot of preliminary results of the data captured during this experiment. For example, we show the effect of cohesion on penetrometer reaction force, with more cohesive materials providing larger reaction forces nearly of the same magnitude of their 1 g counterparts. We also show that penetrometer tip shapes provide different reaction forces and that flat tips provide the largest reaction force compared to the others. The influence of penetration velocity will be investigated further with the aid of theoretical models. Early indications from the results seen so far are promising for future analyses and will provide key information for the analysis of penetrometry data on future missions.

Near-sun sky twilight observations allow for the detection of asteroids interior to the orbit of Venus (Aylos) and the Earth (Atiras) and comets. We present the results of observations with the Palomar 48-inch telescope (P48)/Zwicky Transient Facility (ZTF) camera in 30 s r-band exposures taken during evening astronomical twilight from 2019 Sep 20 to 2022 March 7 and during morning astronomical twilight sky from 2019 Sep 21 to 2022 Sep 29. More than 21,940 exposures were taken in evening astronomical twilight within 31° and 66° from the Sun with an r-band limiting magnitude between 18.0 and 20.8 (5th to 95th percentile), and more than 24,370 exposures were taken in morning astronomical twilight within 31° and 65° from the Sun with an r-band limiting magnitude between 18.2 and 20.9 (5th to 95th percentile). The morning and evening twilight pointings show a slight seasonal dependence in limiting magnitude and ability to point closer towards the Sun, with limiting magnitude improving by 0.5 magnitudes during the summer months and Sun-centric angular distances as small as 31–32° during the spring and fall months. In total, the one Aylo, (594913) ‘Ayló’chaxnim, and 4 Atiras, 2020 OV₁, 2021 BS₁, 2021 PB₂, and 2021 VR₃, were discovered in evening and morning twilight observations. Additional twilight survey discoveries also include 6 long period comets: C/2020 T2, C/2020 V2, C/2021 D2, C/2021 E3, C/2022 E3 and C/2022 P3, and two short period comets: P/2021 N1 and P/2022 P2 using deep learning comet detection pipelines. The P48/ZTF twilight survey also recovered 11 known Atiras, one Aylo, three short period comes, two long period comets, one interstellar object, 45,536 Main Belt asteroids, and 265 near-Earth objects. Additionally, observations from the GROWTH network of telescopes were used to recover the Aylo, Atira, and comet discoveries made during the ZTF twilight survey. Lastly, we discuss the future twilight surveys for the discovery of Aylos such as with the Vera Rubin Observatory which will have a twilight survey starting in its first year of operations and will cover the sky as within 45 degrees from the Sun. Twilight surveys such as those by ZTF and future surveys will provide opportunities for the discovery of asteroids inside the orbits of the terrestrial planets that would otherwise be unavailable in conventional sky survey observations.

This work examines the plausibility of a lunar origin of natural objects that have a negative total energy with respect to the geocenter, i.e. ET=potential＋ kinetic energy<0, while they are within 3 Earth Hill radii (RH), a population that we will refer to as ‘bound’. They are a super-set of the informally named population of ‘minimoons’ which require that the object make at least one orbit around Earth in a synodic frame rotating with Earth and that its geocentric distance be <RH at some point while ET<0. Bounded objects are also a dynamical subset of the population of Earth’s co-orbital population, objects in a 1:1 mean motion resonance with Earth or, less specifically, on Earth-like orbits. Only two minimoons have been discovered to date, 2006 RH120 and 2020 CD3, while 2024 PT5 and 2022 NX1 meet our condition for ’bound’. The likely source region of co-orbital objects is either the MB of asteroids, lunar ejecta, or a combination of both. Earlier works found that dynamical evolution of asteroids from the MB could explain the observed minimoon population, but spectra of 2020 CD3 and 2024 PT5 and Earth co-orbital (469219) Kamo‘oalewa are more consistent with lunar basalts than any MB asteroid spectra, suggesting that the ejection and subsequent evolution of material from the Moon’s surface contributes to the minimoon and, more generally, Earth’s co-orbital population. This work numerically calculates the steady-state size-frequency distribution of the bound population given our current understanding of the lunar impact rate, the energy of the impactors, crater-scaling relations, and the relationship between the ejecta mass and speed. We numerically integrate the trajectory of lunar ejecta and calculate the statistics of ‘prompt’ bounding that take place immediately after ejection, and ‘delayed’ bounding that occurs after the objects have spent time on heliocentric orbits. A sub-set of the delayed bound population composes the minimoon population. We find that lunar ejecta can account for the observed population of bound objects but uncertainties in the crater formation and lunar ejecta properties induce a many orders of magnitude range on the predicted population. If the bound objects can be distinguished as lunar or asteroidal in origin based on their spectra it may be possible to constrain crater formation processes and the dynamical and physical evolution of objects from the MB into near-Earth space.

As part of internal study efforts for a low-cost fast-schedule small spacecraft mission to take benefit of the close approach of Near-Earth Object (99942) Apophis in April 2029, graduate-level students from various space degree programs of Luleå University of Technology’s Kiruna Space Campus were tasked to contribute with a study on a fly-by mission concept utilising nano satellite technologies as part of a one-semester spacecraft design project course. The resulting mission – Utilisation of Nanosatellite Network for Apophis Measurements Exploration and Discoveries (UNNAMED) – aims to send four 16U CubeSat satellites to Apophis to map its surface in high resolution in both the optical and thermal spectrum. The mission is required to take place before and during the close approach of Apophis in April of 2029 and would provide an unique opportunity for European space science and research. The study concluded in the decision to utilise four nano satellites: each fully equipped with identical instruments and set up in order to reduce complexity. A small swarm of four satellite is proposed as a way to increase the redundancy level of the mission. The mission plans to employ mainly European Commercial Off The Shelf (COTS) components with Technology Readiness Level (TRL) 7+. It is designed to use a European launcher, with both dedicated and rideshare options assessed. In addition, European and in particular Nordic partners are planned as the operations providers. The paper will discuss the proposed mission and spacecraft design as well as the current planned scientific payload and launcher, cost, and schedule considerations.

Context. Gravitational waves from black-hole (BH) merging events have revealed a population of extra-galactic BHs residing in short-period binaries with masses that are higher than expected based on most stellar evolution models-And also higher than known stellar-origin black holes in our Galaxy. It has been proposed that those high-mass BHs are the remnants of massive metal-poor stars.

Aims. Gaia astrometry is expected to uncover many Galactic wide-binary systems containing dormant BHs, which may not have been detected before. The study of this population will provide new information on the BH-mass distribution in binaries and shed light on their formation mechanisms and progenitors.

Methods. As part of the validation efforts in preparation for the fourth Gaia data release (DR4), we analysed the preliminary astrometric binary solutions, obtained by the Gaia Non-Single Star pipeline, to verify their significance and to minimise false-detection rates in high-mass-function orbital solutions.

Results. The astrometric binary solution of one source, Gaia BH3, implies the presence of a 32.70a ±a 0.82aM- BH in a binary system with a period of 11.6 yr. Gaia radial velocities independently validate the astrometric orbit. Broad-band photometric and spectroscopic data show that the visible component is an old, very metal-poor giant of the Galactic halo, at a distance of 590 pc.

Conclusions. The BH in the Gaia BH3 system is more massive than any other Galactic stellar-origin BH known thus far. The low metallicity of the star companion supports the scenario that metal-poor massive stars are progenitors of the high-mass BHs detected by gravitational-wave telescopes. The Galactic orbit of the system and its metallicity indicate that it might belong to the Sequoia halo substructure. Alternatively, and more plausibly, it could belong to the ED-2 stream, which likely originated from a globular cluster that had been disrupted by the Milky Way.