Space missions like Hipparcos and Gaia have transformed astrometry, achieving precision down to tens of microarcseconds and revolutionizing our understanding of the Milky Way, stellar dynamics, and exoplanetary systems. The next frontier, sub-microarcsecond astrometry, could answer two of the most fascinating questions in modern astronomy: the detection of Earth-like exoplanets in the habitable zones of nearby stars and the role of dark matter in shaping galactic structures. NASA’s upcoming flagship mission, the Habitable Worlds Observatory (HWO), and the proposed M-class mission Theia from the European Space Agency (ESA) are expected to address these challenges by using differential astrometry. This technique measures the relative positions of stars within a field of view of several arcminutes to minimize systematic errors and offer a precision enhancement of two orders of magnitude.

Differential astrometry is particularly powerful for detecting the minuscule stellar wobble produced by an Earth-mass exoplanet orbiting a Sun-like star 10 parsecs away. Achieving this level of precision requires the meticulous calibration of both the detector and the optical system. Modern approaches, such as interferometric calibration using Young’s fringes, enable micro-pixel mapping of detector. Meanwhile, high-order polynomial models are able to correct for optical distortions that can displace stellar positions by hundreds of pixels. Our proposed astrometric instrument for HWO or Theia uses features a gigapixel-scale focal plane made up of stitched CMOS detectors and a detector calibration unit that projects the laser fringes for continuous and picometer-scale calibration.

For exoplanet research, sub-microarcsecond astrometry offers the unique ability to measure true planetary masses and three-dimensional orbits, essential for interpreting atmospheric spectra and assessing habitability. In dark matter studies, it provides a direct probe of the distribution and properties of dark matter, from the inner density profiles of halos to the detection of invisible subhalos through their gravitational effects on stellar motions. Technically, these ambitions demand advancements in detector technology, optical metrology, and spacecraft stability, as well as innovative data processing pipelines to correct for instrumental drifts and astrophysical noise.

This PhD thesis will focus on developing and validating the calibration and data analysis techniques required to achieve sub-microarcsecond precision in differential astrometry. Through laboratory experiments, simulations, and the analysis of astrometric data, the research will address the interplay between detector calibration, optical distortion modeling, and observational strategies. The goal is to optimize the error budget for HWO and contribute to the broader framework of ESA’s M-class missions, ensuring that the next generation of astrometric instruments can unlock groundbreaking discoveries in exoplanetary science and dark matter research.

The thesis will take place at IPAG (Institute for Planetology and Astrophysics in Grenoble) where the lab demonstration is being held in close connection with the international consortium and the industrial partners. The objective of the thesis will be to demonstrate the performance of the high precision astrometry method in lab as well as the functionality of the new very large detectors. The PhD student will also be involved in the science definition of the missions either on the exoplanet part or the dark matter part.  The student should have a good knowledge of physics, in particular in optics and should have an appetite for setting up laboratory experiments and analyzing experimental data with astrophysical finality.

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For more Information about the topics and the co-financial partner (found by the lab!); contact Directeur de thèse - Fabien.Malbet@univ-grenoble-alpes.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!