By BlueShift and AFP | 2025-03-27

After more than a decade mapping out our home galaxy, the European Space Agency (ESA) powered down the Gaia space telescope and sent it into "retirement orbit" around the Sun on Thursday (March 27).

Since launching in 2013, the telescope has been charting the positions, motion and properties of nearly two billion stars to create a vast map of the Milky Way, revealing many secrets of the cosmos along the way, the ESA said in a statement.

"[Gaia] has provided the largest, most precise multi-dimensional map of our galaxy ever created, revealing its structure and evolution in unprecedented detail," the statement said.

Gaia has uncovered evidence of massive galaxies slamming into each other, identified vast clusters of stars, helped discover new exoplanets and mapped millions of galaxies and blazing galactic monsters called quasars.

A study last year using Gaia data identified two streams of ancient stars at the Milky Way's heart thought to have formed around the galaxy's birth more than 12 billion years ago.

According to astronomers using Gaia, the Milky Way then swallowed other dwarf galaxies as it grew -- notably one called Gaia-Enceladus about 10 billion years ago.

Our home galaxy is still slowly devouring the Sagittarius dwarf galaxy, Gaia helped reveal.

The telescope also spotted more than 50 dwarf galaxies orbiting the Milky Way. Inside the galaxy, it tracked down 150,000 asteroids and detected several dozen black holes.

Gaia has been observing the universe from a stable orbit 1.5 million km from Earth called the second Lagrange point.

But the neighborhood has been becoming more crowded with the recent arrivals of powerful space telescopes, such as NASA's James Webb and ESA's Euclid.

To avoid causing any problems for the new kids on the block, the ESA's team on the ground gave the order for Gaia's engines to give a final push that will take the spacecraft into a distant orbit around the Sun.

Final goodbye

"Switching off a spacecraft at the end of its mission sounds like a simple enough job," Gaia spacecraft operator Tiago Nogueira said in a statement. "But spacecraft really don't want to be switched off."

"Gaia was designed to withstand failures such as radiation storms, micrometeorite impacts or a loss of communication with Earth," he said. "It has multiple redundant systems that ensured it could always reboot and resume operations in the event of disruption."

"We had to design a decommissioning strategy that involved systematically picking apart and disabling the layers of redundancy that have safeguarded Gaia for so long, because we don't want it to reactivate in the future and begin transmitting again if its solar panels find sunlight," Nogueira said.

So on Thursday, ESA engineers in Germany disconnected -- one by one -- all the satellite's systems that allow it to survive the perils of space.

The team at the European Space Operations Center in Darmstadt, Germany, then shut down Gaia's instruments before corrupting its on-board software.

Finally, they said their last goodbye, deactivating the spacecraft's communication system and central computer.

Now that Gaia is powered down, this "retirement orbit" will make sure it will remain at least 10 million km from Earth for the next 100 years.

Research continues

But Gaia's mission continues back on Earth.

Scientists are still sifting through the deluge of data the telescope sent back and are expected to deliver its fourth catalogue of the stars in 2026.

The final catalogue -- which will encompass 10 and a half years of observations -- is expected around 2030.

"Gaia's extensive data releases are a unique treasure trove for astrophysical research, and influence almost all disciplines in astronomy," said Gaia project scientist Johannes Sahlmann.

Data from Gaia "will continue shaping our scientific understanding of the cosmos for decades to come," he said.

Ultimately, Gaia's catalogue "will serve as a reference for astronomy for at least 30 to 40 years," Gaia engineer Jose Hernandez told AFP.

This fact means that even as Gaia distantly orbits the Sun in silence, what it observed will be feeding new discoveries for future generations.

Some of the astronomers who will make these breakthroughs using Gaia's data are "still in primary school," Hernandez said.