Got a telescope? Bid farewell to ESA's retiring Milky Way mapper

The European Space Agency's (ESA) Milky Way mapper Gaia has completed the sky-scanning phase of its mission, racking up more than three trillion observations over the past decade.

Gaia was launched on December 19, 2013, with the aim to create a three-dimensional map of the Milky Way galaxy and beyond by surveying nearly two billion objects. The assignment was initially expected to last five and a half years yet Gaia has almost doubled that - now the fuel in the tank is virtually exhausted.

The spacecraft requires around a dozen grams of cold gas per day to keep it spinning and pointing correctly.

With science observations over, the next steps will be to perform some testing before the spacecraft is moved from its current orbit around Lagrange point 2, approximately 1.5 million km from Earth, to a heliocentric orbit far away from Earth's sphere of influence. According to ESA, "The spacecraft will be passivated on 27 March 2025, to avoid any harm or interference with other spacecraft."

During testing, Gaia's orientation will be adjusted, making it appear brighter and visible through small telescopes. Amateur astronomers will then be able to bid a final farewell to the spacecraft.

ESA shared some impressive statistics for the observatory. Gaia has observed almost two billion stars and other objects and logged 3,827 days of scientific observations. The observatory has also produced a three-dimensional map of 1.3 million quasars and provided precise orbits of more than 150,000 asteroids.

Over the years, 142TB of compressed data has been downloaded from the spacecraft and the scientific community was on the receiving end of multiple information dumps in the form of data releases. Gaia Data Release 4 is expected in 2026 and will consist of 500 TB of data products covering the first 5.5 years of the mission.

That said, it has not been entirely smooth sailing for the observatory. During the spacecraft's commissioning, it was discovered that the sky background observed by Gaia was "significantly higher than expected." Most of the blame for this was attributed to the fiber fabric used to reinforce the blankets of the sun shield. Some of these fibers had detached and were protruding, scattering sunlight behind the shield. It wasn't the end of the world, and engineers could mitigate the effect through methods that included tweaking the software.

Gaia was also struck by a micrometeoroid, which allowed more sunlight to seep in, it was hit by a failure in one of its charge-coupled devices (CCDs) that make up its "billion-pixel" camera and weathered a solar storm. Engineers could work around the issues on every occasion to keep the science data rolling in.

Rocio Guerra, Gaia Science Operations Team Leader based at ESA's European Space Astronomy Centre (ESAC), said, "Over the next months we will continue to downlink every last drop of data from Gaia, and at the same time the processing teams will ramp up their preparations for the fifth and final major data release at the end of this decade, covering the full 10.5 years of mission data."

There is, therefore, every chance that Gaia's discoveries will continue, even after the spacecraft has received its final command.

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In the meantime, there remains a chance to glimpse Gaia through a small telescope before its final retirement. Uwe Lammers, Gaia Mission Manager, said, "Gaia will treat us with this final gift as we bid farewell, shining among the stars ahead of its well-earned retirement.

"It's a moment to celebrate this transformative mission and thank all of the teams for more than a decade of hard work operating Gaia, planning its observations, and ensuring its precious data are returned smoothly to Earth." ®