On Thursday 27 March, the European Space Agency (ESA) sent its last messages to the Gaia Spacecraft. They told Gaia to shut down its communication systems and central computer and said goodbye to this amazing space telescope.
Gaia has been the most successful ESA space mission ever, so why did they turn Gaia off? What did Gaia achieve? And perhaps most importantly, why was it my favourite space telescope?
Artist’s impression of the Gaia spacecraft in front of the Milky Way.
ESA/ATG medialab; background: ESO/S. Brunier
Running on empty
Gaia was retired for a simple reason: after more than 11 years in space, it ran out of the cold gas propellant it needed to keep scanning the sky.
The telescope did its last observation on 15 January 2025. The ESA team then performed testing for a few weeks, before telling Gaia to leave its home at a point in space called L2 and start orbiting the Sun away from Earth.
L2 is one of five “Lagrangian points” around Earth and the Sun where gravitational conditions make for a nice, stable orbit. L2 is located 1.5 million kilometres from Earth on the “dark side”, opposite the Sun.
The Lagrange points around Earth and the Sun, including L2.
NASA, STScI, CSA
L2 is a highly prized location because it’s a stable spot to orbit, it’s close enough to Earth for easy communication, and spacecraft can use the Sun behind them for solar power while looking away from the Sun out into space.
It’s also too far away from Earth to send anyone on a repair mission, so once your spacecraft gets there it’s on its own.
Keeping L2 clear
L2 currently hosts the James Webb Space Telescope (operated by the USA, Europe and Canada), the European Euclid mission, the Chinese Chang’e 6 orbiter and the joint Russian-German Spektr-RG observatory. Since L2 is such a key location for space missions, it’s essential to keep it clear of debris and retired spacecraft.
A final status update from Gaia.
ESA, CC BY-SA
Gaia used its thrusters for the last time to push itself away from L2, and is now drifting around the Sun in a “retirement orbit” where it won’t get in anybody’s way.
As part of the retirement process, the Gaia team wrote farewell messages into the craft’s software and sent it the names of around 1,500 people who worked on Gaia over the years.
What is Gaia?
Gaia looks a bit like a spinning top hat in space. Its main mission was to produce a detailed, three-dimensional map of our galaxy, the Milky Way.
To do this, it measured the precise positions and motions of 1.46 billion objects in space. Gaia also measured brightnesses and variability and those data were used to provide temperatures, gravitational parameters, stellar types and more for millions of stars.