It gave us the best map of the Milky Way. Now the Gaia spacecraft is orbiting into retirement

After more than a decade of delivering groundbreaking discoveries from the far reaches of our galaxy, the Gaia spacecraft officially completed its mission and was shut down on March 27 due to its depleted fuel supply. 

For its team on the ground, it was a bittersweet moment. 

“I’ve been working with the spacecraft sending data back for the past 11 years or so, so it’s quite a change,” Anthony Brown, a Dutch astronomer who leads Gaia’s data processing and analysis group, told As It Happens host Nil Köksal. 

“On the other hand, it’s also nice [that] something is closed off, and there’s still plenty of work to look forward to in terms of processing all the data that is still freshly coming up.” 

Gaia, launched in 2013 by the European Space Agency (ESA), was stationed some 1.5 million kilometres away, in a region known as ​​the second Lagrange point (L2). There, it orbited the sun and had an optimal vantage point for observing the universe.

Carrying two telescopes, the spacecraft’s mission was to map the Milky Way, offering insights into the composition of our home galaxy and how it evolved, formed and is structured. 

Unlike the James Webb Space Telescope that’s also orbiting in L2, which produces illustrious pictures, Gaia gave us detailed measurements of stars across the galaxy. 

“Missions that produce images like the James Webb Space Telescope … they speak much more directly to people’s imaginations, so there’s a good chance that they will have heard of those missions and maybe not of Gaia,” said Brown. 

But he says Gaia’s contributions have “exceeded most people’s expectations.” 

What Gaia reported back 

What was originally intended to be a five-year mission doubled in length.

Over the course of that mission, Gaia scanned the sky and recorded data of nearly two billion stars by precisely measuring their position, distance, movement, chemical composition and brightness. 

“If you want to know something about a star in the sky, just look it up in the Gaia catalog,” said Brown. 

But the spacecraft also delivered several surprising findings.  

Gaia’s data revealed possible causes of the Milky Way’s warped shape, identified new star clusters, and contributed to the discovery of planets outside our solar system and black holes. It also mapped millions of galaxies, and tracked hundreds of thousands of asteroids and comets. 

“I think it already outperformed what we had expected,” said Brown. 

It also fulfilled its primary goal of drawing the biggest and most precise map of the Milky Way, providing the clearest reconstructed view of how our galaxy might appear to an outside observer.

Leaves behind legacy in retirement 

Astronomers have been releasing Gaia’s data in batches since 2016, and its final set will be released no earlier than 2030.  

Sarah Gallagher, the director of the Institute for Earth and Space Exploration at Western University in London, Ont., who was not involved in the expedition, says Canadian researchers have been analyzing Gaia’s data. 

“What’s really exciting about having these long missions with beautiful data sets that are then shared around with anyone in the world, is that people are going to find stuff that nobody expected,” said Gallagher. 

“I have a student who’s working with Gaia data right now … he’s going to find some really cool stuff.” 

Its legacy will also live on through the follow-up missions that will continue the work Gaia has done, says Gallagher. 

On the day Gaia was shut down, and before all communication was cut off, the crew sent Gaia — now moved into its retirement orbit around the sun, a final word. 

Brown’s message was: “Farewell to an amazing spacecraft that revolutionized 21st century astronomy.”