The Gaia Mission (2016): Mapping a Billion Stars in 3D

The Gaia mission paper, published in 2016 by the Gaia Collaboration and led by T. Prusti, describes ESA’s spacecraft for measuring the positions, distances and motions of more than a billion Milky Way stars. Gaia went on to build the most precise three-dimensional map of our galaxy ever made.

What was Gaia built to answer?

To understand how the Milky Way formed and evolved, astronomers need to know where its stars are and how they move, in three dimensions, for a large and fair sample. Gaia was the space telescope built to provide that for over a billion stars, roughly 1% of the galaxy’s total.

What the paper describes

• A long road to launch. ESA approved construction in 2006, after a study that swapped the original interferometer concept for direct imaging. European industry built the spacecraft and payload. A consortium of scientists, the Gaia Data Processing and Analysis Consortium (DPAC), was chosen in 2007 to turn the raw data into catalogs.
• Launch and orbit. Gaia launched on 19 December 2013 and reached its operating point a few weeks later near the Sun-Earth L2 point, about 1.5 million kilometers from Earth on the side away from the Sun.
• Commissioning. Tests of the spacecraft and instruments were completed on 19 July 2014.
• Scanning the sky. The nominal five-year mission began with four weeks of special scans near the ecliptic poles, then switched to repeated scanning of the full sky.
• Expected performance. The paper describes the as-built spacecraft, with special attention to the payload, and estimates its scientific performance from in-orbit operations.

How it works

Gaia’s method is astrometry, the precise measurement of star positions. The spacecraft scanned the whole sky again and again for years, so each star was measured many times. Two signals emerge from those repeats. Stars drift slowly across the sky, their proper motion. And nearer stars shift back and forth once a year as Gaia and Earth circle the Sun, an effect called parallax, which gives their distance by simple geometry. Combine both and you get a star’s position and motion in three dimensions.

Why it mattered

Gaia transformed nearly every field it touched, from the physics of individual stars to the Milky Way’s history. Its second data release revealed Gaia-Enceladus, a galaxy that merged with ours long ago, and in 2026 Vasily Belokurov, Amina Helmi and Rodrigo Ibata shared the Kavli Prize in Astrophysics for Gaia-based work on the Milky Way’s merger history. Gaia parallaxes also anchor the cosmic distance ladder: the SH0ES measurement of the Hubble constant calibrated its Cepheid stars with Gaia EDR3 parallaxes.

What we know now

Data Release 3, on 13 June 2022, contained information on more than 1.8 billion sources. Gaia ended science observations on 15 January 2025 and was switched off on 27 March 2025, after being moved into a retirement orbit around the Sun.

The data are still coming. Gaia DR4 opens on 2 December 2026, covering the first 5.5 years (66 months) of observations. It is expected to include the first large set of astrometric exoplanet candidates: planets revealed by the tiny wobble they cause in their star’s position on the sky (as of October 2026). Release news is tracked on our Gaia page.

Who wrote it

The paper is signed by the Gaia Collaboration, led by T. Prusti with J. H. J. de Bruijne and a long list of colleagues across Europe. It serves as the mission’s reference paper.

Read the original

Gaia Collaboration, Prusti, T., de Bruijne, J. H. J., et al. (2016). “The Gaia mission.” Astronomy & Astrophysics 595, A1. doi:10.1051/0004-6361/201629272

Free to read: arXiv preprint.