The European Space Agency (ESA)’s Gaia mission is creating the most detailed map ever of our galaxy, the Milky Way. In December 2020, it delivered the position, brightness, color, and proper motion of 1.8 billion stars. Now ESA is releasing the full data, revealing a true treasure trove of observations that spans from the Solar System to some of the furthest reaches of the cosmos. 

The full release, which is accompanied by 50 different scientific papers, includes the classification of 1.5 billion stars in our galaxy, which can already tell us a lot about the objects in question. But Gaia went further by providing a huge database of chemistry for millions of stars; the spectrum of light of a star tells us the chemical components and can be used to work out age, temperature, color, mass, metallicity, the speed at which they move toward or away from us, and more. 

Thanks to this signature, Gaia was even able to recognize and track stars that did not form in the Milky Way but were taken in during past galaxy mergers, as our own galaxy snacked and cannibalized several of its numerous galactic satellites.  

“Our galaxy is a beautiful melting pot of stars,” Dr Alejandra Recio-Blanco of the Observatoire de la Côte d’Azur in France, and member of the Gaia collaboration, said in a statement.  

“This diversity is extremely important, because it tells us the story of our galaxy’s formation. It reveals the processes of migration within our galaxy and accretion from external galaxies. It also clearly shows that our Sun, and we, all belong to an ever-changing system, formed thanks to the assembly of stars and gas of different origins.” 

The mission also reports the largest catalog yet of binary stars, with detailed observations of 813,000 binary stars and measurements of their position, distance, orbit, and mass. And that’s not all. Gaia not only tracks how the stars move but also how they change in themselves. It measured the variation in brightness in 10 million variable stars.

One of the most surprising discoveries is Gaia is so powerful it has been able to detect "starquakes" (motions on a star's surface) for thousands of stars, something that it was not actually designed for. 

“Starquakes teach us a lot about stars, notably their internal workings. Gaia is opening a goldmine for ‘asteroseismology' of massive stars,” added Conny Aerts of KU Leuven in Belgium and member of the Gaia collaboration.

It’s not just stars that "star" in this map. Gaia has used the light of 470 million stars to produce a 3 million pixel map of the dust in the Milky Way. It has also observed 156,000 asteroids near our planet, all the way out beyond the orbit of Neptune, and targeted 31 moons of the giant planets and Mars. Beyond our galaxy, it measured 1.9 million quasars and 2.9 million galaxies. 

“Unlike other missions that target specific objects, Gaia is a survey mission. This means that while surveying the entire sky with billions of stars multiple times, Gaia is bound to make discoveries that other more dedicated missions would miss," explained Dr Timo Prusti, Project Scientist for Gaia at ESA. "This is one of its strengths, and we can’t wait for the astronomy community to dive into our new data to find out even more about our galaxy and its surroundings than we could’ve imagined."

Usually, the mission will end with the fourth and final data release, which will make all these observations even more precise. However, there’s the possibility of a two-year extension and a fifth data release coming no sooner than 2027.