Mission
1. Objectives
The Gaia mission is fundamentally transforming the study of Small Solar System Bodies (SSSBs) through its unprecedented astrometric, photometric, and spectrophotometric precision. Covering a wide range of heliocentric distances, Gaia provides a homogeneous dataset that is reshaping the understanding of asteroid and comet dynamics. The FPR release has demonstrated over a reduced subset of asteroids that Gaia data alone over 5 years can produce highly accurate orbits and reveal subtle dynamical effects (David et al. 2023 A&A 680). The forthcoming ten-year dataset, including approximately 400,000 asteroids, will enable new advances in dynamical and physical modelling, through the combined analysis of astrometric and photomletric data, and complementary ground-based observations.
2. Methodology and Technical Approach
Large-scale statistical and dynamical analyses of Gaia’s datasets require new computational tools capable of managing heterogeneous and high-volume data. Combining multi-gigabyte astrometric and photometric datasets of different precision (space vs. ground) necessitates advanced computational methods and high-performance computing (HPC) resources. These methodologies are applicable to future large-scale surveys such as LSST, CSST, and Gaia-NIR, and will be integrated into the pôle petits-corps at CNES, and the SE-OP webservice at Paris Observatory.
Although Gaia achieves 0.2–10 milliarcseconds (mas) astrometric precision, systematic effects remain for bright objects (G < 12), primarily due to their size, shape, and motion. In addition, background stellar contamination can bias centroiding in the DPAC automatic processing pipeline. To address these issues, systematic searches and corrections will be applied to maintain sub-mas accuracy. Besides, current DPAC models use simple triaxial ellipsoids, and Gaia data alone to estimate photocentre offsets. Improved results will be obtained through combination of space- and ground-based data. Moreover a joint inversion of astrometric and photometric data will enable recovery of complex shape models, spin states, sizes, and surface scattering parameters. New genetic and AI-based inversion algorithms, implemented on GPU architectures, will be developed to support these combined analyses.
3. N-body Dynamical Modelling and Orbit Determination
The combination of Gaia and ground-based astrometry over long time spans allows enhanced orbit determination and the detection of mutual gravitational perturbations and non-gravitational effects. A new heteroscedastic weighting scheme will ensure the consistent combination of heterogeneous datasets, yielding a robust orbital solution. Mutual asteroid–asteroid perturbations, often neglected before Gaia, need to be taken into account. They can moreover be exploited to derive asteroid masses (Mouret et al. 2007 A&A 472), improve NEO trajectories, and refine impact probability (IP) calculations. Using the ten-year Gaia dataset and past observations, an HPC-based GPU N²-body propagation will identify past and future close encounters, enabling systematic mass determination through global N-body parameter estimation. These updated orbits and masses will be incorporated into the INPOP planetary ephemerides for global dynamical consistency.
4. Archival Data Exploitation
Historical photographic plate collections are a treasure-trove for SSSB studies, particularly for investigating secular variations and non-gravitational dynamics (e.g., Yarkovsky drift, cometary activity). The NAROO digitization facility at the Paris Observatory, coupled with Gaia’s reference frame, enables sub-arcsecond re-reduction of historical data. Measurements of non-gravitational accelerations and shape parameters will inform models of thermal and surface properties, supported by AI-driven techniques (Zhao et al. 2025 A&A 691). These archival datasets also facilitate precovery and recovery of Near-Earth Objects (NEOs), extending their observational arcs and improving impact probability estimates: a critical aspect of planetary defence. Within the DynaAstVO and NEOForce projects (Desmars et al. 2016 DPS48; Vavilov et al. 2024 EPSC), positions and uncertainty regions can be predicted using large ensembles of orbital clones and parallelized IP computations on HPC systems. We will develop a systematic search on archive plates can, provide new refined orbits, and dedicated fast IP computation on parallel computing.
5. Fundamental Physics and Perspectives
The comprehensive analysis of about 400,000 Solar System Objects within a coherent dynamical framework will enable new tests of fundamental physics, including constraints on Parametrized Post-Newtonian (PPN) and Standard-Model Extension (SME) parameters, and further tests of General Relativity. Additionally, linking the dynamically non-rotating reference frame of SSOs to Gaia’s kinematically non-rotating reference frame of QSOs will provide a unique empirical test of Mach’s principle.
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For more Information about the topics and the co-financial partner (found by the lab!); contact Directeur de thèse - daniel.hestroffer@obspm.fr
then, prepare a resume, a recent transcript and a reference letter from your M2 supervisor/ engineering school director and you will be ready to apply online before March 13th, 2026 Midnight Paris time!