![Distributions of planetary mass, mass of the host star and semi-major axis of all confirmed exoplanets listed at exoplanet.eu. The planets are color-coded according to method used for their discovery. The dashed gray line marks the deuterium-burning mass limit of 13 MJup. [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/09/Characterization-1.png?fit=1200%2C667&ssl=1)
[astro-ph.EP] Astrometry is the oldest method used to search for extrasolar planets. This technique provides key information about a planetary system, like the true mass of planets and its three-dimensional orbital architecture.
Nowadays, the space-based mission Gaia, on one hand, and ground-based interferometry at infrared and radio wavelengths, on the other hand, can achieve astrometric accuracies of tens of micro-arseconds.
Thanks to this unprecedented level of accuracy, the number of astrometrically discovered exoplanets has started to grow. In this chapter, I review the basic principles for orbital characterization of unseen planetary companions using astrometric data.
I also review the properties of the exoplanets discovered so far with astrometric methods and comment on the contributions that this technique can make to the exoplanet field.
Gisela N. Ortiz-Leon
Comments: This work is a peer-reviewed chapter contribution to an edited volume
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2609.26664 [astro-ph.EP] (or arXiv:2609.26664v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2609.26664
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Submission history
From: Gisela Ortiz
[v1] Tue, 22 Sep 2026 16:26:37 UTC (777 KB)
https://arxiv.org/abs/2609.26664
Astrobiology,
