Star Metro - Space telescope Gaia sent into 'retirement' but legacy endures

Since launching in 2013, the telescope has been charting the positions, motion and properties of nearly two billion stars to create an unparalleled map of our home galaxy, according to the European Space Agency.

Gaia has been peering into the universe from a stable orbit 1.5 million kilometres (930,000 miles) from Earth called the second Lagrange point.

But the neighbourhood has been getting more crowded with the recent arrivals of the powerful James Webb and Euclid space telescopes.

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

This "retirement orbit" will make sure the spacecraft will remain at least 10 million kilometres from Earth for the next century.

Over nearly 11 years, 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 around 10 billion years ago.

Our home galaxy is still slowing 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.

- Final goodbye -

On Thursday, ESA engineers in Germany disconnected -- one-by-one -- all the satellite's systems that allow it to survive the perils of space, such as radiation storms or being struck by tiny meteorites.

"The spacecraft are designed so that they cannot be killed -- it is very difficult to disconnect them," ESA operations engineer Tiago Nogueira told AFP.

The team at the European Space Operations Centre in the city of Darmstadt 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.

But Gaia's mission will continue 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.

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 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.

Ch.Levesque--SMC