The ESA space observatory launched in 2013 that measures stellar positions for astrometric exoplanet searches is Gaia. Instead of waiting for a planet to transit, Gaia can detect a star’s minute back-and-forth motion caused by the gravitational pull of an orbiting planet.
Gaia was launched on 19 December 2013 from Kourou, French Guiana, aboard a Soyuz rocket. It was placed near the Sun–Earth L2 point, about 1.5 million kilometres from Earth, a location that provides a stable observing environment and keeps the spacecraft’s view largely away from Earth’s interference.
The mission’s main goal was to create an extraordinarily precise three-dimensional map of the Milky Way. By repeatedly measuring stellar positions, distances and motions, Gaia also provides the astrometric information needed to search for large exoplanets, particularly those with relatively long orbits.
Planck and Herschel were also ESA observatories, but they served different purposes: Planck studied the cosmic microwave background, while Herschel observed the infrared universe. Gaia is the mission associated with precision stellar astrometry.