![Injection–recovery calibration (173 runs). Left: fraction of truths inside the central credible interval against its level, per parameter; calibrated posteriors follow the diagonal, within the grey 95% binomial range. Right: posterior quantile of the true period against the true period in units of the baseline (1733–1902 d), coloured by the total signal-to-noise ratio S; dashed lines bound the 95% interval. For true periods just below one baseline the posterior tends to lie above the truth (points near q = 0): such periods tend to be overestimated, while q near 1 means it is underestimated.-- [astro-ph.IM]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/11/ExoPlanetLab.png?fit=1200%2C676&ssl=1)
[astro-ph.IM] Gaia Data Release 4 (DR4) provides epoch astrometry from which thousands of giant planets and many substellar and stellar companions can be characterised.
We present ExoPlanetLab, an open-source package for Bayesian orbit inference from Gaia epoch astrometry, radial velocities (RVs) and relative astrometry, validated on simulated and real data.
The model orbit is compared with the epoch residuals after removing the part absorbed by the single-star fit. A Student-t likelihood describes heavy-tailed data. A robust Keplerian periodogram with bootstrap false-alarm probabilities gives starting values for a joint fit. Five samplers are available: tempered ensemble MCMC, two nested samplers and two reversible-jump samplers. Evidences for a fixed number of companions select that number.
Acceleration and scan-angle models test whether an orbit is warranted. The samplers agree within 0.1 sigma on a simulated two-planet system. In 180 injections all fits converge, and all signals with signal-to-noise ratio S >= 10 are detected. The posteriors show no significant bias, but the period coverage is below nominal: 90% of the true periods lie within their 95% credible intervals. None of 30 companion-free data sets gives a false detection.
On DR4 pre-release data the orbit of Gaia BH3 is recovered within 1.4 sigma of published solutions. The Student-t model brings the astrometric period and eccentricity of HD 114762 onto its RV orbit.
Eight simulated relative positions narrow the period’s credible interval to 0.27 of its width, and Octofitter agrees within 0.2 sigma on the same data. The code is validated for single sources with DR4-like epoch astrometry, with or without RVs. Relative astrometry is tested on simulated data only. The main limits are an uncorrelated noise model and the computing cost, which grows linearly with the number of measurements and steeply with the number of companions.
David Hobbs
Comments: 17 pages, 9 figures, 5 tables. Code: https://github.com/hobbsSe/ExoPlanetLab, archived at https://zenodo.org/records/24101622
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2611.13770 [astro-ph.IM] (or arXiv:2611.13770v1 [astro-ph.IM] for this version)
https://doi.org/10.48550/arXiv.2611.13770
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Submission history
From: David Hobbs
[v1] Tue, 10 Nov 2026 09:09:59 UTC (383 KB)
https://arxiv.org/abs/2611.13770
Astrobiology,
