Gaia mapping the stars of the Milky Way

Status: In operation

Objective
A global space astrometry mission, Gaia will make the largest, most precise three-dimensional map of our Galaxy by surveying more than a thousand million stars.

Mission
Gaia will monitor each of its target stars about 70 times over a five-year period. It will precisely chart their positions, distances, movements, and changes in brightness. It is expected to discover hundreds of thousands of new celestial objects, such as extra-solar planets and brown dwarfs, and observe hundreds of thousands of asteroids within our own Solar System. The mission will also study about 500 000 distant quasars and will provide stringent new tests of Albert Einstein’s General Theory of Relativity.

What's special?

Gaia will create an extraordinarily precise three-dimensional map of more than a thousand million stars throughout our Galaxy and beyond, mapping their motions, luminosity, temperature and composition. This huge stellar census will provide the data needed to tackle an enormous range of important problems related to the origin, structure and evolutionary history of our Galaxy.

For example, Gaia will identify which stars are relics from smaller galaxies long ago ‘swallowed’ by the Milky Way. By watching for the large-scale motion of stars in our Galaxy, it will also probe the distribution of dark matter, the invisible substance thought to hold our Galaxy together.

Gaia will achieve its goals by repeatedly measuring the positions of all objects down to magnitude 20 (about 400 000 times fainter than can be seen with the naked eye).

For all objects brighter than magnitude 15 (4000 times fainter than the naked eye limit), Gaia will measure their positions to an accuracy of 24 microarcseconds. This is comparable to measuring the diameter of a human hair at a distance of 1000 km.

It will allow the nearest stars to have their distances measured to the extraordinary accuracy of 0.001%. Even stars near the Galactic centre, some 30 000 light-years away, will have their distances measured to within an accuracy of 20%.

The vast catalogue of celestial objects expected from Gaia’s scientific haul will not only benefit studies of our own Solar System and Galaxy, but also the fundamental physics that underpins our entire Universe.

Spacecraft

At its heart, Gaia contains two optical telescopes that work with three science instruments to precisely determine the location of stars and their velocities, and to split their light into a spectrum for analysis.

During its five-year mission, the spacecraft spins slowly, sweeping the two telescopes across the entire celestial sphere. As the detectors repeatedly measure the position of each celestial object, they will detect any changes in the object’s motion through space.

Journey

Gaia launched on a Soyuz-STB/Fregat-MT launch vehicle from the European Spaceport in Kourou, French Guiana.

After launch, Gaia unfolded a ‘skirt’ just over 10 m in diameter. This acts as both a sunshade to permanently shade the telescopes and allow their temperatures to drop to below –100°C, and as a power generator for the spacecraft. The underside of the shield is partially covered with solar panels and will always be facing the Sun, generating electricity to operate the spacecraft and its instruments.

Gaia is mapping the stars from an orbit around the Sun, at a distance of 1.5 million km beyond Earth’s orbit. This special location, known as the L2 Lagrangian point, keeps pace with Earth as we orbit the Sun. It offers a clearer view of the cosmos than an orbit around Earth, which would result in the spacecraft passing in and out of Earth's shadow and causing it to heat up and cool down, distorting its view. Free from this restriction and far away from the heat radiated by Earth, L2 provides a much more stable viewpoint.

History

Gaia has its roots in ESA’s Hipparcos mission (1989-1993), which catalogued more than 100 000 stars to high precision, and more than a million to lesser precision. Now, some 20 years later, Gaia will launch on its mission to catalogue a thousand million stars, measuring each star's position and motion 200 times more accurately than Hipparcos, and producing 10 000 times more data than its predecessor.

The Gaia mission was approved in 2000 as an ESA Cornerstone mission. It is a fully European mission.

The name ‘GAIA’ was originally derived as an acronym for Global Astrometric Interferometer for Astrophysics. This reflected the optical technique of interferometry that was originally planned for use on the spacecraft. However, the working method has now changed, and although the acronym is no longer applicable, the name Gaia remains to provide continuity with the project.

Partnerships

Gaia is a fully European mission.

The spacecraft is controlled from the European Space Operations Centre (ESOC, Darmstadt, Germany) using the three ground stations Cebreros (Spain), Malargüe (Argentina) and New Norcia (Australia). Science operations are conducted from the European Space Astronomy Centre (ESAC, Villafranca, Spain).

The Gaia Data Processing and Analysis Consortium (DPAC) process the raw data to be published in the largest stellar catalogue ever made.