Today astronomers are saying goodbye to a remarkable spacecraft: a telescope that has observed nearly two billion stars in its 12-year life. The Gaia Observatory from the European Space Agency (ESA) has now been powered down and sent into a “retirement orbit” around the sun — but data from the mission will continue to be released and analyzed for years to come.
Gaia’s goal was to create a 3D map of our entire galaxy, and so far it has revealed the structure of the Milky Way in the greatest detail ever obtained. It has uncovered evidence that our galaxy was formed from past galactic mergers, spotted new and previously unknown star clusters, and helped to discover objects like exoplanets and black holes. The enormous trove of data collected by the telescope has been the subject of three data releases so far, with the most recent in 2022, but there will be more data to come in future with a fourth data release planned for 2026.
The originally planned lifespan of the spacecraft was just five years, but its mission was extended until its fuel reserves dipped too low. When that happened, the Gaia team had to plan a way to safely end the mission without the spacecraft drifting and potentially disrupting other spacecraft in the L2 orbit around the sun.
“Switching off a spacecraft at the end of its mission sounds like a simple enough job,” said Gaia Spacecraft Operator Tiago Nogueira. “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. It has multiple redundant systems that ensured it could always reboot and resume operations in the event of disruption,” Nogueira explained. “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.”
As the team were saying farewell to Gaia, they added a personal touch. The spacecraft’s onboard software was deliberately corrupted so that it wouldn’t start back up again, and the team took this opportunity to overwrite the software with a farewell message and the names of thousands of people who have worked on the mission.
As part of this process, some of Gaia's onboard software is being overwritten using farewell messages from its team on Earth, as well as the names of around 1500 people that have contributed to the mission over the years.
— ESA Operations (@operations.esa.int) 2025-03-27T08:34:48.875Z
“Today, I was in charge of corrupting Gaia’s processor modules to make sure that the onboard software will never restart again once we have switched off the spacecraft,” says Spacecraft Operations Engineer, Julia Fortuno. “I have mixed feelings between the excitement for these important end-of-life operations and the sadness of saying goodbye to a spacecraft I have worked on for more than five years. I am very happy to have been part of this incredible mission.”
The final messages sent to Gaia will continue to be carried out into space as the observatory sleeps, and as data from it continues to contribute to astronomy. As Gaia Mission Manager Uwe Lammers put it: “We will never forget Gaia, and Gaia will never forget us.”
