From ancient creeks of stars to the innards of white dwarfs, the Gaia Space Telescope has seen it all.
On Thursday, the European Space Agency's mission specialists will send the low-fuel Gaia into orbit around the Sun, turning it off to astronomers around the world after more than a decade of service.
Gaia has been charting the universe since 2014, creating a vast encyclopedia of the position and movement of celestial objects from the Milky Way and beyond. It is difficult to grasp the breadth of development and discovery that a spinning observatory is enabled. But here are some numbers: nearly 2 billion stars, millions of potential galaxies, and around 150,000 asteroids. These observations have led to over 13,000 studies by astronomers up until now.
Gaia changed the way scientists understand the universe, and that data became the reference point for many other telescopes on the ground and in the universe. Additionally, less than a third of the data collected has been released to scientists so far.
“It now supports almost everything in astronomy,” says Anthony Brown, an astronomer at Leiden University in the Netherlands, heading Gaia's data processing and analysis group. “If you were to ask my astronomy colleagues, I don't think they could have imagined that Gaia would have to do her research even if she wasn't there.”
Starting in 2013, Gaia's main goal was to uncover the history and structure of the Milky Way by constructing the most accurate, three-dimensional map of the position and velocity of 1 billion stars. With only a small portion of that data, astronomers have estimated the mass of the halos of dark matter that engulf our galaxy, identifying thousands of trespassing stars ingested from another galaxy 10 billion years ago.
Dr. Brown measured ongoing vibrations on the Milky Way disc and described them as a form of galactic seismology – bringing evidence of an encounter with satellite galaxies that have put themselves in orbit much more recently than scientists believed. That may be why the Milky Way appears to be distorted when viewed from the side.
Gaia's reach extends beyond what you can collect about galaxy addresses. The spacecraft helped us to observe the moon orbiting other worlds in our solar system, capturing Starcookes and spotted superfast stars zipped across the Milky Way. Within the stars catalog, astronomers have found hints for new planets and black holes, including the closest to Earth. Cosmologists have used the recording of Gaia, a pulsating star, to help us measure the expansion rate of our universe.
“Gaia is very important and very important to our understanding of the universe,” said Lisa Cartenegger, an astronomer at Cornell University in 2021, used Gaia's catalog to learn which alien worlds can see us.
The mission began recording data about six months after its release. For over a decade, it has slowly spinned in space, one million miles from Earth. There, gravity from the planet and the sun balance the satellite's movements.
Twin telescopes pointed in different directions on the spacecraft scanned the sky and captured striped optical light across its field of view. Three instruments accurately measured the position, velocity and color of stars and other celestial bodies. From this data, scientists inferred information on temperature, mass and chemical composition.
“They're the perfect time to learn about things,” said Joshua Wynn, an astrophysicist at Princeton University. But “it's really one of the most important astronomical projects of the past few decades.”
Dr. Wynn recently discovered a new exoplanet in Gaia's catalog. It is one of the few planets found using the method called Astrometry and helps to reveal a massive world orbiting far away from the host stars.
“Gaia is the first resource that we would have definitely been to find a bunch of planets through this technique,” Dr. Wynn said. “It's the beginning of what I think will be the next big step in discovering Exoporanet.”
Gaia closed her eyes to Starlight on January 15th. Since then, mission specialists have conducted final technical tests of spacecraft instruments that could be useful in future telescope operations. During these tests its orientation relative to the Sun changed, making the spaceship bright enough for amateur astronomers to find the night sky.
“It's a bittersweet moment when a mission stops collecting data,” said Johannes Sahlman, a physicist for the European Space Agency and a project scientist for Gaia. “But the mission itself should not be over.”
Despite its mission period, only what Gaia observes are available to astronomers, as it requires more time to process the vast amount of data it collects. The next data release for the spacecraft is set for 2026, with five and a half years of data. The final release, including the entire dataset, is scheduled for prior to 2030.
Many new spacecraft are expanding Gaia's scientific heritage by adjusting observations using mission stars catalogs. These include NASA's James Webb Space Telescope and European Space Agency's Euclidean mission. Future US-built Vera C. Rubin Observatory and the very large European telescopes will benefit from what Gaia saw in both Chile.
European scientists are already planning a successor spaceship that will then collect infrared light, rather than optical light, and take over Gaia's galaxy torch. Telescopes like this started earlier than in the 2040s and help astronomers peer into the dust that smears the center of the Milky Way.
In the meantime, Gaia will spend her days circling our home star. For mission scientists, there are no more weekly meetings with the flight control team and no new data comes in.
“That's a strange feeling,” said Dr. Brown, who was involved in the design of the mission in 1997.
