Context. Robust impact monitoring of near-Earth objects is an essential task of planetary defense. Current systems such as NASA's Sentry-II, NEODyS's CLOMON2, and ESA's Aegis have been highly successful, but independent approaches are essential to ensure reliability and to cross-validate predictions of possible impacts, probabilities, and paths on Earth. Aims. We present NEOForCE (Near-Earth Objects' Forecast of Collisional Events), a new independent monitoring system for asteroid impact prediction. By relying on orbital solutions from DynAstVO at Paris Observatory and using an original methodology for uncertainty propagation, NEOForCE provides an alternative line of verification for future impact assessments and strengthens the overall robustness of planetary defense. Methods. As other monitoring systems do, NEOForCE samples several thousand so-called "virtual asteroids" from the uncertainty region and integrates their orbits up to 100 years into the future. Instead of searching for close approaches of the virtual asteroids themselves with the Earth, our system looks for times when the Earth comes close to the "realistic" uncertainty regions around them, which are mostly stretched along the osculating ellipses of virtual asteroids. For every virtual asteroid and every possible collision time, we also estimate the maximal impact probability, and only if this value is large enough (>5 & times; 10(-8)) do we continue to the next step. In this second step, we compute how the original asteroid orbit should be slightly modified so that the new trajectory leads to an Earth impact, which allows us to confirm the possible collision and estimate the impact probability. Results. We tested NEOForCE against NASA's Sentry-II system on five representative asteroids with a high impact probability and significant number of possible collisions: 2000 SG344, 2005 QK76, 2008 JL3, 2023 DO, and 2008 EX5. NEOForCE successfully recovered almost all of the possible collisions reported by Sentry-II with impact probabilities above 10(-7), demonstrating the robustness of our approach. In addition, NEOForCE identified several potential impacts at the 10(-7)-10(-6) level that Sentry-II did not report.

The 2029 close encounter of near-Earth asteroid (99942) Apophis, at approximately 38,000 km from Earth center, offers a unique opportunity to advance planetary science, defense, and public engagement. This rare event enables real-time observations of tidal effects, surface displacement, spin changes, and dust ejection, deepening our understanding of rubble-pile asteroids and improving models of their evolution. Detailed data will refine predictions of the Yarkovsky and YORP effects, enhancing asteroid dynamics research. From a planetary defense perspective, Apophis provides a critical test case for impact risk assessment and mitigation strategies, informing rapid-response reconnaissance missions. Public outreach during the event will raise awareness of asteroid science and planetary safety, fostering interest in space exploration. International collaborations, including NASA’s OSIRIS-APEX and ESA’s RAMSES missions, along with the potential contributions from China, aim to maximize scientific returns, making the 2029 Apophis flyby a milestone in global planetary exploration and defense efforts.

The method of weighted least squares is widely used in parameter estimation problems such as asteroid orbit determination. A frequent difficulty is the realistic treatment of observational uncertainties, especially when combining heterogeneous datasets with very different precision. We propose a quick and simple reweighting scheme that adjusts the contribution of each measurement group to ensure a statistically consistent least-squares solution. The method consists of three steps: (i) estimating the error standard deviations for each observational subset, (ii) rescaling their weights by the corresponding variances, and (iii) performing a weighted least-squares fit using the adjusted weights. We apply this approach to heliocentric orbit fitting of asteroids using combined ground-based astrometry and high-precision Gaia measurements. We validated the method by fitting each orbit to a restricted observation set and comparing its predictions with the complete set of measurements. For 7 objects, the reweighted solutions provide significantly improved agreement with older data. The most dramatic case is asteroid (21) Lutetia, where increasing the effective uncertainty of Gaia observations by a factor of 17 yields a substantially better fit, indicating the importance of accounting for possible systematic biases in high-precision datasets. We further apply the scheme to the recently discovered near-Earth asteroid 2024 YR4, where we grouped observations by the visual magnitude. The reweighted orbit produces smaller uncertainty regions and a more stable solution, reducing predicted impact probabilities by roughly an order of magnitude. All computed probabilities remain below 0.5%, under the 1% International Asteroid Warning Network (IAWN) alert threshold. This reweighting procedure provides a practical way to combine measurements of heterogeneous quality, improving the reliability of least-squares solutions in orbit determination and impact-risk assessment. The method is general and can be readily applied to other parameter estimation problems involving mixed-precision data.

We report on the observation and measurement of astrometry, photometry, morphology, and activity of the interstellar object 3I/ATLAS, also designated C/2025 N1 (ATLAS) with the NSF-DOE Vera C. Rubin Observatory. Comet 3I/ATLAS, the third known interstellar object, was discovered on UT 2025 July 1. Rubin Observatory had coincidentally collected images of the object's region of the sky during routine commissioning. Facilitated by Rubin's high resolution and large aperture, we successfully recovered object detections from Rubin observations spanning UT 2025 June 21 (10 days before discovery, when 3I/ATLAS was 4.5 au from the Sun) through the date of discovery, and we acquired additional images through UT 2025 July 20 as part of commissioning. We measure on-sky locations of 3I/ATLAS in Rubin ugrizy bands, with a typical precision of similar to 70 mas, and briefly describe the reason this is coarser than our measured static source astrometric precision of similar to 3 mas in Rubin images. We measure grizy magnitudes of 3I/ATLAS photometry at similar to 0.01 mag precision, detecting no short-term photometric variability above 0.01 mag. We derive an estimated near-nucleus dust-to-nucleus scattering cross-sectional ratio of eta greater than or similar to 13 on UT 2025 July 2 based on Rubin photometry and an upper limit nucleus size computed from Hubble Space Telescope observations. We find Rubin colors of g - r = (0.657 +/- 0.013) mag, r - i = (0.235 +/- 0.018) mag, i - z = (0.147 +/- 0.042) mag, and z - y = (0.047 +/- 0.052) mag. These data represent the earliest observations of this object by a large (greater than or similar to 8 m class) telescope and illustrate the type of measurements (and discoveries) Rubin's Legacy Survey of Space and Time will provide after it begins in early 2026.

In a previous article, we obtained the first-ever list of astrometric binary asteroid candidates. Some of these candidates have now been confirmed. In that previous work, however, the details of the statistical methods were not provided. Our first aim is to provide methodological details and performance evaluation of the approach used for detecting binaries. Our second aim is to establish an updated list of binary asteroid candidates from Gaia FPR astrometric residuals exploration, where we account for the statistical properties of FPR data. We account for the astrometric uncertainties from FPR and we refine the statistical model of the data, which we use in MC simulation to evaluate the strength of the individual detections; we set up a trend detection method in the residuals and apply a dedicated period search algorithm; we update the statistical selection process to build the list of candidates; we set up a method for detecting objects in multiple windows of consecutive observation; we refine the method for confidence interval estimation of these parameters and we better constrain the physical parameter selection. We detect 343 binary asteroid candidates corresponding to 410 windows of consecutive observations in the astrometric data. We show that in noise-only control simulations, the typical number of detections is 88

Context. The spectral properties and albedo of near-Earth asteroid (153201) 2000 WO107 are consistent with a taxonomic type M. This implies that it might have a high metal abundance and higher density. Aims. We combined different methods to investigate the asteroid rotation, determine its shape, and use it to estimate its density. Methods. We carried out photometric observations of the asteroid during the 2020 apparition. We then created a program to simulate the light curves, and used it within a Markov chain Monte Carlo (MCMC) algorithm to reconstruct the asteroid shape model from the observational data. The Goldstone radar observations of the asteroid were used as an additional constraint on the asteroid model in the MCMC algorithm. The estimated shape and rotation rate of the contact binary were used to compute its density. Results. The photometric observations of (153201) 2000 WO107 obtained at a wide range of the phase angles from 5 to 68 degrees in the time interval of November 28 - December 8, 2020, show light curves typical for contact binary asteroids, which agrees with the results of the radar data. The light curves have a maximum amplitude of up to 1.24 mag. The best-fit modeled shape of the asteroid is composed of two ellipsoidal lobes with axes of 0.68 x 0.38 x 0.36 km and 0.44 x 0.42 x 0.16 km. Its sidereal rotation period is determined to be 5.017 +/- 0.002 h. The most probable solution for the angular velocity vector of the asteroid indicates ecliptic coordinates of lambda = 96 degrees +/- 8 degrees and beta = -78 degrees +/- 1 degrees, but another less probable solution of around lambda = 286 degrees +/- 11 degrees, beta = -76 degrees +/- 2 degrees cannot be disregarded. The estimated density of the asteroid rho = 4.80(-0.63)(+0.34) g/cm(3) is consistent with a possible metallic composition. From the orbital simulation of this potentially hazardous asteroid, we find that its integral probability of colliding with the Earth in the next 10 000 years is 7 10(-5).

Estimating the probability of a collision of asteroids with the Earth is an important task for planetary defense. There are systems that compute impact probabilities of near-Earth asteroids with the Earth on a regular basis: Sentry (Nasa, Jet Propulsion Laboratory) and CLOMON-2 (originally University of Pisa, now ESA). Here we present NEOForCE (Near-Earth Objects Forecast for Collisional Events) a new monitoring system developed at Institut de mécanique céleste et de calcul des éphémérides (IMCCE, Paris Observatory). This system is original and independent. As ephemeris of major planets and the Moon we use INPOP [1]. The asteroids’ orbits and covariance matrices are taken from DynAstVO database [2]. For computing the impact probability we use the Line Of Variation (LOV) sampling method [3] but with significant modifications. The longest axis of the confidence ellipsoid is chosen to be sampled obtaining virtual asteroids. Each virtual asteroid’s orbit is propagated from the time of discovery 100 years ahead with variational equations. Each virtual asteroid is a representative of its small vicinity and we apply the Partial Banana Mapping method (PBM) [5] for each of this vicinity to look for possible collisions. Then the results are combined and the procedure to find explicitly the initial conditions of the collisional trajectory is launched.The main differences with the existing monitoring systems are: usage of INPOP ephemeris of major planets instead of DE, having our own orbit fitting and propagation procedure of asteroids from DynAstVO, and implementation of Partial Banana Mapping method. Hence the system provides an independent assessment of the impact probability, which in case of risks is crucial. [1] Fienga, A., et al. (2020) INPOP new release: INPOP19a. Astrometry, Earth Rotation, and Reference Systems in the GAIA era. p. 293-297.[2] Desmars J., et al. (2017) DynAstVO: a Europlanet database of NEA orbits. European Planetary Science Congress. 2017. p. EPSC2017-324.[3] Milani A., et al. (2005) Nonlinear impact monitoring: line of variation searches for impactors. ICARUS, V. 173, p. 362-384.[4] Vavilov D.E. (2020) The partial banana mapping: a robust linear method for impact probability estimation. MNRAS, V. 492, p. 4546–4552.

Context. Near-Earth asteroids that orbit in the vicinity of the Earth have regular close approaches with our planet, and some of the asteroids can even collide with it. Several methods exist to compute an impact probability (IP). They include linear methods that can promptly give an estimate, but only provide reliable results when the two-body formalism is not strongly perturbed. Nonlinear methods are more robust, but several thousand asteroid orbit clones have to be integrated for a reliable result.Aims. We developed a semilinear method that is reliable for IP computations and is fast enough. On one hand, it is robust and can handle perturbations from close encounters with planets, and on the other hand, it only requires the numerical integration of several orbits.Methods. We modified the partial-banana mapping (PBM) method (which we developed in earlier work), which uses a special curvilinear coordinate system to approximate the curved shape of the uncertainty region in physical 3D space. As in PBM, at the time of the possible collision, we determine the closest point to the Earth along the main axis of the uncertainty region. Based on this, we determine the initial condition in orbital space at the epoch of observations that leads to this point, integrate this orbit, and finally, compute the impact probability. The scheme can be iterated until the procedure converges. This approach allowed us to take gravitational perturbations into account.Results. The method was applied on 16 test cases and showed that virtual impactors were determined for 15 cases in the first run (without iterations). The computed impact probabilities agreed with the Monte Carlo results that were taken as reference, and they were more accurate than the results of linear methods for a similar computing time. The method worked even for the possible collision of (99942) Apophis in 2036 and successfully handled the close approach in 2029 (the Apophis orbit in the test was obtained from observations in 2004-2006). For one of the 16 cases, the collisional orbit was too far from the nominal orbit, and the impact probability was zero (which agrees with the Monte Carlo result), while the estimates from the linear methods for the impact probability were about 5%.Conclusions. The method we developed successfully fills in the gap between fast linear methods with a numerical integration of the nominal orbit alone, which are of limited usage for an almost pure two-body problem, and time-consuming nonlinear methods that sample the uncertainty region with a numerical integration of several thousand orbits.

We combine different methods to investigate the rotation, determine the shape and estimate the density of near-Earth asteroid (153201) 2000 WO_107. We carried out photometric observations of the asteroid during the 2020 apparition. Then we created a program able to simulate the lightcurves, and used it within a Markov chain Monte Carlo (MCMC) algorithm to reconstruct the asteroid shape model from the observational data. The Goldstone radar observations of the asteroid were used as an additional constraint on the asteroid model in the MCMC algorithm. The estimated shape and rotation rate of the contact binary were used to compute its density. The photometric observations of (153201) 2000 WO_107 obtained at a wide range of the phase angles from 5 to 68 degrees in the time interval November 28 – December 8, 2020, show lightcurves typical for contact binary asteroids, which agrees with the results of the radar data. The lightcurves have a maximum amplitude of up to 1.24 mag. The best-fit modelled shape of the asteroid is composed of two ellipsoidal lobes with the axes 0.68× 0.38 × 0.36 km and 0.44 × 0.42 × 0.16 km. Its sidereal rotation period is determined to be 5.017± 0.002 hr. The most probable solution for the angular velocity vector of the asteroid points at the ecliptic coordinates λ=96^∘± 8^∘ and β=-78^∘± 1^∘, whereas another less probable solution around λ=286^∘± 11 ^∘, β=-76^∘± 2 ^∘ cannot be disregarded. The estimated density of the asteroid ρ=4.80^+0.34_-0.63 g/cm^3 is consistent with its possible metallic composition. From the orbital simulation of this potentially hazardous asteroid, we find that its integral probability of colliding with the Earth in the next 10,000 years is 7· 10^-5.

Introduction In the framework of the Virtual European Solar and Planetary Access (VESPA) of Europlanet, we have developed two new data services for planetary moons: MoonsProp and VOccDB. Both services are encoded using the Europlanet-Table Access Protocol (EPN-TAP) and can be accessed from the VESPA portal (https://vespa.obspm.fr/). The portal enables interoperability between planetary science data services in the Virtual Observatory context, but other access modes are available (see Erard et al 2024, "Virtual European Solar & Planetary Access (VESPA) 2024: Legacy", EPSC2024-355, this conference). 1. MoonsProp: physical and dynamical properties of natural satellites Considering that it is difficult to access the physical and dynamical properties of natural satellites or moons for direct use in workflows, we have developed a specific database. This database, MoonsProp, provides up-to-date physical and dynamic characteristics of natural satellites. It concerns 288 satellites in total (Earth’s Moon, 2 satellites of Mars, 95 of Jupiter, 146 of Saturn, 28 of Uranus, 16 of Neptune). Users can access the size, mass, rotational properties, magnitude, albedo and orbital elements of all planetary satellites (see https://epn.imcce.fr/moonsprop.html for more details). These quantities are extracted from various publications, peer-reviewed papers and articles, books, or possibly web pages, all cited in a list of references (database parameter: bib_reference).All quantities can hence be extracted for use by other VESPA planetary service necessitating reference value on global physical parameters. One can also derive graphs on statistical properties as shown in Fig. 1.Figure 1. Distribution of some of the orbital elements distribution of satellites of giant planets in MoonsProp database. Circles and squares are proportional to the square root of the diameter. 2. VOccDB: prediction of stellar occultations by natural satellites The VOccDB database provides the predictions of stellar occultations of bright GaiaDR3 stars by natural satellites of Jupiter, Saturn and Uranus over the period 2024-2033. All events up to visual magnitude 12 for the four biggest Galilean satellites, and magnitude 15 for other satellites are described: circumstances and observational data, including visibility maps (see Fig. 2), date and timing of the occultation, star position and magnitude, duration, etc. (see https://epn.imcce.fr/voccdb.html for more details) and additional information on the proximity of the Moon and the planet. All general circumstances were computed with the planetary and satellites ephemerides available at IMCCE. These data are given in TDB time scale and with present (2024) TDB-UTC; they will be updated as soon as new theories of natural satellites are published.Figure 2. Example of graphic showing the path of the satellite umbra (here Carme) during a stellar occultation with a Gaia DR3 star on 13 Nov. 2024.Currently, 4485 events are published in the database. The EPN-TAP format can provide a global view of these predictions. The occurrence of these events naturally increases with the density of the star fields crossed by the satellites. We can therefore see this effect in this database when we plot the histogram of these events showing the transits of Jupiter, Saturn and Uranus in the Milky Way (see Fig.3).Figure 3. Histogramme of events showing the increase of events during the cross of the Milky Way by the different planets. Acknowledgements: The Europlanet-2024 Research Infrastructure project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 871149.

Gaia is a space mission from the European Space Agency (ESA) that was launched in 2013. The mission opens a window to explore the unprecedented high precision astrometric data for a large population of solar system objects. Its latest data release – the Focused Product Release (Gaia FPR) published in October 2023 – contains 66 months of data, for about 160,000 asteroids. By covering a main-belt asteroid’s typical orbital period, it has been shown that the Gaia data alone can provide very precise heliocentric orbits [1]. Thanks to this unprecedented precision, Gaia data is able to reveal the astrometric signature of binary asteroids. This is the case for the recently discovered binary (4337) Arecibo system, analyzed with the Gaia DR3 data [2]; where an astrometric wobble was clearly detected in a time window of several days covering successive transits. In this study, we continue the research on the Arecibo system, taking into account all the Gaia FPR observations. We begin by fitting the heliocentric orbit. These residuals contain the binary signal, which is proportional to the relative orbit with a scaling factor related to the flux ratio and the mass ratio of the components (see [3], [4] for the analytical formula). We then fit the relative orbit to derive the relevant parameters. We obtain an estimate of the component masses, their density ratio, and flux ratio. With an estimation of the volume, a bulk density of ρ1 ≈ 1.2 and ρ2 ≈ 1.6, for the primary and secondary, is derived. The results are consistent with an ice-rich body in the outer main belt. The high accuracy of Gaia's astrometric solutions enables us, for the first time, to estimate the individual masses and therefore the density of each component of a Small Solar System binary, which generally offer valuable insights into the formation of the Solar System, as well as its collisions and dynamic evolution. Moreover, with the orbital parameters, we are able to predict future mutual events and stellar occultations that will provide additional constraints on the individual density. [1] Gaia Collaboration, David, P., Mignard, F., et al. 2023, A&A, 680, A37[2] Tanga, P., Pauwels, T., Mignard, F., et al. 2023, A&A, 674, A12[3] Pravec, P. & Scheirich, P. 2012, Planet. Space Sci., 73, 56[4] Lindegren, L. 2022

Gravitational waves from black-hole 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. 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. 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. The astrometric binary solution of one source, Gaia BH3, implies the presence of a 32.70 \pm 0.82 M\odot 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. 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.

Introduction:Gaia observations (DR1-DR3) confirmed that the solar system will experience a close flyby of the K-type star Gliese 710 in about 1.3 Myrs. This 0.6 solar mass star will pass through the Oort cloud at a velocity of ~14.4 km/s, an inclination of ~150° with respect to the ecliptic and approach the Sun up to approximately 10,000 au (according to Gaia DR3 release). Earlier studies predicted flyby distances between 12000 and 4300 au (see e.g. Berski and Dybczynski 2016; Bailer-Jones et al. 2018; De la Fuente Marcos and De la Fuente Marcos 2018). The stellar passage will perturb the comets outside Neptune’s orbit, especiallyobjects entering the sphere of influence of Gliese 710.Assuming that there are 10¹² Oort cloud objects between 100 to 100000 au from the Sun (resulting in a mean object density of 0.0002 comets/au³), it is obvious that numerical calculations of such a system are not within the realms of possibility even if a numerical code allows orbit calculation of tens of millions of (non-interacting) objects.Numerical study:Using our recently developed GPU based N-body code GANBISS (Zimmermann & Pilat-Lohinger 2023) we studied the orbits of some hundred million test-comets in the outer solar system for the time of the flyby of Gliese 710 which takes about 64000 years. 50 million comets were distributed in each of the six zones around the hyperbolic trajectory of the passing star. The cross section of this (red) tube is defined by the sphere of influence of Gliese 710. Figure 1 shows the six zones of the Oort cloud: a flat disk (purple) from 50 to 5000 au (i < 1°), a flared disk (green) from 5000 to 10000 au (i < 45°) and a spherical cloud between 10000 and 100000 au (0° < i < 180°) which has been divided into four zones.Results:When looking at the changes in the orbital parameters of the comets due to the stellar flyby in the individual zones, the (a,e) diagrams show V-structures (see Pilat-Lohinger et al. 2022a, 2022b) that disappear when the entire area of the Oort cloud is considered at once.The passage of a star thus produces two branches of comets: an inward-facing branch that can transport comets towards the inner solar system, and an outward-facing branch that might scatter objects into the interstellar region. Moreover, the inward-facing branch shows higher eccentricities than the outward-facing branch, particularly in case of comets of the outer spherical cloud.Assuming that the radius of Gliese 710's sphere of influence is about 2000 au -- resulting in an average object density of 0.00017 obj/au3 in the tube around the trajectory -- our calculations show that after the stellar flyby more than 4500 comets have their pericenter within 5 au and more than 108 million comets were scattered into interstellar space.Conclusion:Our numerical study shows that the star Gliese 710 -- which will pass through the Oort Cloud up to a distance of 10000 au from the Sun in about 1.3 million years -- will scatter several thousand comets towards the inner solar system, increasing the number of comets crossing Earth’s orbit and the risk of encounters with planet Earth.Figure 1: Sketch of Gliese 710's flybyFigure 2: Semi-major axis – eccentricity map of the comets after the stellar flyby. The different colors denote the different zone (see Fig.1). Note that the map shows a reduced number of comets.

Here we describe the novel, multi-point Comet Interceptor mission. It is dedicated to the exploration of a little-processed long-period comet, possibly entering the inner Solar System for the first time, or to encounter an interstellar object originating at another star. The objectives of the mission are to address the following questions: What are the surface composition, shape, morphology, and structure of the target object? What is the composition of the gas and dust in the coma, its connection to the nucleus, and the nature of its interaction with the solar wind? The mission was proposed to the European Space Agency in 2018, and formally adopted by the agency in June 2022, for launch in 2029 together with the Ariel mission. Comet Interceptor will take advantage of the opportunity presented by ESA’s F-Class call for fast, flexible, low-cost missions to which it was proposed. The call required a launch to a halo orbit around the Sun-Earth L2 point. The mission can take advantage of this placement to wait for the discovery of a suitable comet reachable with its minimum V capability of 600 ms^-1 . Comet Interceptor will be unique in encountering and studying, at a nominal closest approach distance of 1000 km, a comet that represents a near-pristine sample of material from the formation of the Solar System. It will also add a capability that no previous cometary mission has had, which is to deploy two sub-probes – B1, provided by the Japanese space agency, JAXA, and B2 – that will follow different trajectories through the coma. While the main probe passes at a nominal 1000 km distance, probes B1 and B2 will follow different chords through the coma at distances of 850 km and 400 km, respectively. The result will be unique, simultaneous, spatially resolved information of the 3-dimensional properties of the target comet and its interaction with the space environment. We present the mission’s science background leading to these objectives, as well as an overview of the scientific instruments, mission design, and schedule.

The Gaia space mission provides highly precise astrometric data about 160,000 solar system objects. Because the object is extended and Gaia observes at a non-zero solar phase angle, the measurement is subject to a photocentre-barycentre shift effect. In other words, astrometry records the centre of the illuminated part (photocentre) of the celestial body instead of the actual centre of mass. This displacement is determined by the surface properties, size, spin and shape of the target [1]. The effect can be shown by statistically significant residuals after the fitting of heliocentric or planetocentric orbits using Gaia astrometric data. The typical magnitude of the offsets for the largest bodies (with diameters > 100km) is of a few mill-arcseconds, larger than the Gaia precision. In this work, we used two approaches to correct the effect. The first is to assume that the body is a sphere and use an analytical formula to estimate the offset [2], which is a valid approximation for dwarf planets or planetary satellites. Secondly, we directly used the simulated displacement from a complex shape model by reconstructing the Gaia-object-Sun geometry at the observation epoch. This is done by using an updated spin and shape topographic model derived from photometric data (including Gaia DR3 photometry) using the Sage method [3,4]. In the presentation, we will show the effect of the photocentre correction using both methods on a selection of large asteroids and Jovian satellites. [1] L. Lindegren, “Meridian observations of planets with a photoelectric multislit micrometer.,”, vol. 57, no. 1-2, pp. 55–72, May 1977[2] D. Hestroffer, “Photocentre displacement of minor planets: analysis of HIPPARCOS astrometry,”, vol. 336, pp. 776–781, Aug. 1998.[3] P. Bartczak and G. Dudziński, “Shaping asteroid models using genetic evolution (SAGE),”, vol. 473, no. 4, pp. 5050–5065, Feb. 2018. doi: 10.1093/mnras/stx2535. arXiv: 1904.08940 [astro-ph.EP].[4] P. Bartczak et al, “Synergy between SAGE and SHAPE algorithms for modelling the physical parameters of asteroids,” in European Planetary Science Congress, Sep. 2024, EPSC2024.

Context. Binary asteroids are present in all populations of the Solar System, from near-Earth to trans-Neptunian regions. As is true for the small Solar System bodies (SSSBs), binary asteroids generally offer valuable insights into the formation of the Solar System, as well as its collisions and dynamic evolution. In particular, the binaries provide fundamental quantities and properties of these SSSBs, such as mass, angular momentum, and density, all of which are often hidden. The direct measurement of densities and porosities is of great value in revealing the gravitational aggregates and icy bodies that form the asteroid-comet continuum. Aims. Several observation techniques from space and ground-based platforms have provided many results in this regard. Here we show the value of the Gaia mission and its high-precision astrometry for analysing asteroid binaries and for individually deriving the masses of the components. Methods. We focus on the binary asteroid (4337) Arecibo, a member of the Themis family. We analysed the astrometry obtained in the Gaia FPR catalogue release, and performed orbital fitting for both the heliocentric orbit of the system and the relative orbit of the binary components. Results. We obtain an estimation of the component masses and their flux ratio, and derive bulk densities rho1 = 1.2 and rho2 = 1.6 for the primary and the secondary, respectively. The results are consistent with an ice-rich body in the outer main belt. They also show a significantly denser secondary or a less closely packed primary. Constraints on these densities and on macroscopic porosities are nevertheless limited by our poor knowledge of the sizes of the components. Observations of future mutual events, and of stellar occultations predicted in 2024 - 2025, will be essential for improving our knowledge of this system and its formation.

IntroductionEstimating the probability of a collision of asteroids with the Earth is an important task for planetary defense. There are systems that compute impact probabilities of near-Earth asteroids with the Earth on a regular basis: Sentry (Nasa, Jet Propulsion Laboratory) and CLOMON-2 (originally University of Pisa, now ESA). Here we present NEOForCE (Near-Earth Objects Forecast for Collisional Events) a new impact monitoring system which is being developed at Institut de mécanique céleste et de calcul des éphémérides (IMCCE, Paris Observatory).Partial Banana Mapping methodThe core of the new system is the Partial Banana Mapping method (PBM) [1] with the extension of a direct search for initial state vector that leads to a collision [2]. The basic principle of the Partial Banana Mapping method (PBM) is that the covariance matrix in curvilinear coordinate system, as described in [3] or in orbital elements much better represent the actual shape of the uncertainty region (see Fig.1) in the two-body formalism. To find the possible collision we can find on the main axis of the curvilinear uncertainty region the point, which is closest to the Earth (point B). In the extension of the PBM method we then are finding a state vector from the original uncertainty region (at epoch of observations) that leads to point B. Then we propagate the orbit of the found state vector until the time of possible collision and compute its probability. This approach can successfully find the virtual asteroid that leads to a collision.Figure 1: The scheme of the banana shaped uncertainty region of the asteroid. Point A is the nominal position of the asteroid, point B — the virtual asteroid of the main axis of the uncertainty region, which is closest to the Earth. The bold line is the nominal asteroid’s orbit. The dashed arrow is the direction of the Earth’s relative velocity.Line Of Variations approachIf the asteroid has close approaches with major planets then the linear analysis of collisions (like Partial Banana Mapping) can fail and nonlinear analysis is required. In NEOForCE we apply the concept of Line of Variations sampling to deal with it.The uncertainty region of an asteroid at the epoch of observations is quite small and well represented by an ellipsoid (6 dimensional ellipsoid, since we have uncertainty in coordinates and velocities). The idea of Line of Variations approach [5,6] is to sample virtual asteroid on the main axis of this 6-dimensional uncertainty ellipsoid and integrate their orbits forward in time separately.In NEOForCE each of the virtual asteroid is considered to be a representative of its vicinity of the uncertainty region (see Fig.2). The vicinity is found by dividing the largest eigen value of the covariance matrix that represents the uncertainty of the orbit. Then we proceed the analysis by the improved Partial Banana Mapping approach for each of the virtual asteroid.Fig. 2. The schematic illustration of the uncertainty region at the epoch of observations. The horizontal line is the main line of the uncertainty ellipsoid (Line of Variations) and the black dots are the virtual asteroids. The green area is the vicinity of virtual asteroid that it represents.ConclusionThe NEOForCE monitoring system will be using orbits of asteroids from DynAstVO database [6] and planetary ephemerids INPOP [7] from Institut de mécanique céleste et de calcul des éphémérides (IMCCE, Paris Observatory). The system has original approach of collisional analysis based on Partial Banana Mapping method. Hence the system provides an independent assessment of the impact probability, which is crucial for planetary defense campaign.AcknowledgmentsThis project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 101068341 “NEOForCE”.References:[1] D. E. Vavilov (2020) MNRAS 492(3), 4546.[2] D. E. Vavilov (2023) in Planetary Defense Conference 2023.[3] D. E.Vavilov, et al. (2015) MNRAS 446(1),705.[4] A. Milani, et al. (2002) Asteroid Close Approaches: Analysis and Potential Impact Detection 55–69.[5] A. Milani, et al. (2005) Icarus 173(2),362.[6] J. Desmars, et al. (2017) in European Planetary Science Congress EPSC2017–324.[7] A. Fienga, et al. (2021) Notes Scientifiques et Techniques de l’Institut de Mecanique Celeste 110.

Introduction The knowledge of the current dynamic of Near Earth Asteroids (NEAs) is essential. Accurate astrometric measurements acquired over a large time span are important to provide reliable orbits and impact probability. With growing number of observations and a large number of already existing data, a rapid and accurate algorithm for follow-up and precovery of NEAs is required.In this work we focus on precovery of asteroids. The New Astrometric Reduction of Old Observations (NAROO) program is dedicated to the measurement of astrophotographic plates and the analysis of old observations [1]. It has access to a collection of more than ten thousand plates from 1949 to 2000. Photographic plates consist of a substantial source of old observations of NEAs but they can be difficult to retrieve, as positions predicted back in time from orbit propagation can be highly imprecise and the objects are generally faint.Basic principlesThe orbits of most of the NEAs, and in particular newly discovered ones, are not precise, therefore the accurate positions of these asteroids are unknown. In the majority of cases the trajectory itself is quite well defined, but there is an uncertainty in the position along the orbit. Over time, this uncertainty grows and can reach even the whole orbit (the mean anomaly is undefined). Because of that, our nominal prediction of the spherical coordinates of an asteroid on a photographic plate can be far from the real one. It is also possible that the nominal orbital solution tells us that the object is not on the plate, however, a significant part of the uncertainty region is, and, hence, there is still a probability that the object can be found on the plate.Partial banana mapping methodIn order to find if a Near-Earth Object can be on the photographic plate, we use a modification of a Partial Banana Mapping method [2]. In Fig. 1 one can see a schematic illustration of the method. The idea is that we take a covariance matrix of the asteroid in equinoctial orbital elements and consider the largest eigen vector of the matrix (which corresponds to the main axis of the curvilinear uncertainty region). Then we take several samples on this line (virtual asteroids) and project them onto celestial sphere with their uncertainties. This approach will give us the uncertainty region of the asteroid on the celestial sphere. If the region intersects with the plate, it means there is a chance of the object being on the plate and we can even provide the probability. We also estimate the length of the uncertainty region as well as visual magnitudes of the virtual asteroids.Fig. 1. The scheme of the banana shaped uncertainty region of the asteroid. Point A is the nominal position of the asteroid. The bold line is the nominal asteroid’s orbit. ComputationsWe tested the method with asteroid 2015 UM67 (506074) Svarog. In the test we simulated the scenario that it is the end of 2015 year, so we only have 3 months arc observations of the object. The result can be found in Fig. 2.Fig. 2. Possible position (blue dots) of asteroid (506074) Svarog on 1990/03/01 06:00:00. The purple square represents the photographic plate. The orange dot is the nominal position of the object. The red dot in the plate is the position where the object was actually found. The green line is the uncertainty region of the nominal position constructed only from the covariance matrix in right ascension and declination. As one can see the method could successfully predict the possible positions of the object and the actual observation is exactly in the 5 uncertainty region. This region is indeed curved, as one can compare it to the straight green line, directly obtained from the local covariance matrix. On the other hand, we can not get accurate predictions of the asteroid position using only the nominal position with its covariance matrix.It took approximately 0.359 seconds to compute these results for asteroid Svarog on a PC with 12th Gen Intel(R) Core(TM) i7-12700H 2.30 GHz processor. On the contrary the Monte Carlo approach is required to integrate at least 1000 orbits of virtual asteroids and it takes 109.51 seconds (305 times longer!). This proves that our method is an efficient technique for asteroid follow-up and precovery.To crossmatch all the NEAs with about 9000 photographic plates, available at Paris observatory, it takes only 1 day of computation.Acknowledgments This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 101068341 “NEOForCE”. This study shows outcomes from the NAROO program which was supported by the DIM-ACAV of Ile-de-France region, PSL Research University, the Programme National GRAM and the Programme National de Planétologie (PNP) of CNRS/INSU with INP and IN2P3, co-funded by CNES.References:[1] Robert, V., Desmars, J., Lainey, V., et al. 2021, A&A, 652, A3.[2] Vavilov D. E. (2020) MNRAS, 492, 4546–4552.

We present the third data release of the European Space Agency's Gaia mission, GDR3. The GDR3 catalogue is the outcome of the processing of raw data collected with the Gaia instruments during the first 34 months of the mission by the Gaia Data Processing and Analysis Consortium. The GDR3 catalogue contains the same source list, celestial positions, proper motions, parallaxes, and broad band photometry in the G, G$_{BP}$, and G$_{RP}$ pass-bands already present in the Early Third Data Release. GDR3 introduces an impressive wealth of new data products. More than 33 million objects in the ranges $G_{rvs} < 14$ and $3100 <T_{eff} <14500 $, have new determinations of their mean radial velocities based on data collected by Gaia. We provide G$_{rvs}$ magnitudes for most sources with radial velocities, and a line broadening parameter is listed for a subset of these. Mean Gaia spectra are made available to the community. The GDR3 catalogue includes about 1 million mean spectra from the radial velocity spectrometer, and about 220 million low-resolution blue and red prism photometer BPRP mean spectra. The results of the analysis of epoch photometry are provided for some 10 million sources across 24 variability types. GDR3 includes astrophysical parameters and source class probabilities for about 470 million and 1500 million sources, respectively, including stars, galaxies, and quasars. Orbital elements and trend parameters are provided for some $800\,000$ astrometric, spectroscopic and eclipsing binaries. More than $150\,000$ Solar System objects, including new discoveries, with preliminary orbital solutions and individual epoch observations are part of this release. Reflectance spectra derived from the epoch BPRP spectral data are published for about 60\,000 asteroids. Finally, an additional data set is provided, namely the Gaia Andromeda Photometric Survey (abridged)

Gaia Data Release 3 (DR3) provides a wealth of new data products for the astronomical community to exploit, including astrophysical parameters for a half billion stars. In this work we demonstrate the high quality of these data products and illustrate their use in different astrophysical contexts. We query the astrophysical parameter tables along with other tables in Gaia DR3 to derive the samples of the stars of interest. We validate our results by using the Gaia catalogue itself and by comparison with external data. We have produced six homogeneous samples of stars with high quality astrophysical parameters across the HR diagram for the community to exploit. We first focus on three samples that span a large parameter space: young massive disk stars (~3M), FGKM spectral type stars (~3M), and UCDs (~20K). We provide these sources along with additional information (either a flag or complementary parameters) as tables that are made available in the Gaia archive. We furthermore identify 15740 bone fide carbon stars, 5863 solar-analogues, and provide the first homogeneous set of stellar parameters of the Spectro Photometric Standard Stars. We use a subset of the OBA sample to illustrate its usefulness to analyse the Milky Way rotation curve. We then use the properties of the FGKM stars to analyse known exoplanet systems. We also analyse the ages of some unseen UCD-companions to the FGKM stars. We additionally predict the colours of the Sun in various passbands (Gaia, 2MASS, WISE) using the solar-analogue sample.