The European Space Agency (ESA) has announced the end of the Gaia mission. After more than a decade of operation, the space observatory was switched off on command from Earth.
Gaia’s main achievements
The Gaia observatory was launched by ESA at the end of 2013. Its key mission was to make a detailed map of the Milky Way. During the operation, it observed 2 billion stars and other objects, measuring their brightness, distance, and direction of motion. This has allowed the construction of the largest and most accurate three-dimensional map of our galaxy, revealing its structure and evolution in unprecedented detail.
The mission has found evidence of past galactic mergers, identified new star clusters, contributed to the discovery of exoplanets and black holes, mapped millions of quasars and galaxies, and tracked hundreds of thousands of asteroids and comets. It also provided a better visualization of what our galaxy might look like to an outside observer.
But Gaia’s achievements don’t stop there. Over the years, the telescope has discovered many objects, from asteroids in the Solar System to distant galaxies and quasars. The telescope has also discovered several exoplanets and hypervelocity stars leaving our Milky Way. In total, Gaia has collected 500 terabytes of data over the course of its operation.
Retirement for Gaia
Gaia was designed for a nominal lifetime of five years. In reality, the observatory operated for more than ten years. Unfortunately, by January 2025, Gaia has nearly exhausted the nitrogen reserves used for its orientation and targeting. As a result, ESA decided to retire the telescope.
The solution to this problem turned out to be more complicated than it may seem. Gaia worked in the vicinity of the L2 Lagrangian point of the Sun-Earth system. It’s a very valuable orbital position for science — and ESA wanted to eliminate the possibility of an unguided telescope interfering with other missions in the future.
Therefore, Gaia was put into a stable orbit around the Sun. It should minimize the likelihood of it coming within 10 million kilometers of Earth for at least the next century. After that, it was time to turn off the telescope.
How to break a space telescope
“Switching off a spacecraft at the end of its mission sounds like a simple enough job,” said Gaia mission operator Tiago Nogueira. “But spacecraft really don’t want to be switched off.”
Gaia was designed to withstand radiation, solar storms, being hit by micrometeorites or losing contact with Earth. “The observatory is equipped with multiple redundant systems to ensure that it can always reboot and resume operations in the event of a failure.”
Therefore, engineers have developed an entire strategy for decommissioning Gaia that involves systematically shutting down all redundancy layers. This is required to eliminate the possibility that when light hits the solar panels of the vehicle, it will recharge its batteries and start transmitting again.
After deactivating and disabling Gaia’s instruments and subsystems one by one, the team intentionally corrupted its onboard software. This was required to ensure that the machine would never restart again. The communications subsystem and the central computer were the last to be shut down. On March 27, Gaia transmitted its last set of data, after which it went permanently silent.
The final commands have been sent to Gaia. This is the last time that the spacecraft will ever hear from its team on Earth. The final commands include those to shut down the spacecraft's communication systems and central computer.
— ESA Operations (@operations.esa.int) 27 марта 2025 г. в 10:56
[image or embed]
But although this is the end of Gaia’s operation, the observatory’s contributions to astronomy will continue to shape research for many decades to come. Its vast archive of data remains a veritable treasure trove for scientists to refine knowledge about galactic archaeology, stellar evolution, exoplanets, and more.
According to ESA
