Gaia (spacecraft)

Gaia is a retired space observatory of the European Space Agency (ESA) that was launched in 2013 and operated until March 2025. The spacecraft was designed for astrometry: measuring the positions, distances and motions of stars with unprecedented precision, and the positions of exoplanets by measuring attributes about the stars they orbit such as their apparent magnitude and colour. As of 2026, the mission data processing continues, aiming to construct the largest and most precise 3D space catalogue ever made, totalling approximately 1 billion astronomical objects, mainly stars, but also planets, comets, asteroids and quasars, among others.

To study the precise position and motion of its target objects, the spacecraft monitored each of them about 70 times over the five years of the nominal mission (2014–2019), and about as many during its extension. Due to its detectors degrading more slowly than initially expected, the data acquisition phase of the mission was given an extension, lasting until March 27, 2025, when scientists at the ESA switched off Gaia after more than a decade of service. Gaia targeted objects brighter than magnitude 20 in a broad photometric band that covered the extended visual range between near-UV and near infrared; such objects represent approximately 1% of the Milky Way population. Additionally, Gaia was expected to detect thousands to tens of thousands of Jupiter-sized exoplanets beyond the Solar System using astrometry, 500,000 quasars outside this galaxy and tens of thousands of known and new asteroids and comets within the Solar System.

Even though the telescope was decommissioned in 2025, the Gaia mission continues to analyse the collected data to create a precise three-dimensional map of astronomical objects throughout the Milky Way and map their motions, which encode the origin and subsequent evolution of the Milky Way. The spectrophotometric measurements provide detailed physical properties of all stars observed, characterising their luminosity, effective temperature, gravity and elemental composition. This massive stellar census is providing the basic observational data to analyse a wide range of important questions related to the origin, structure and evolutionary history of the Milky Way Galaxy.