The European Space Agency's Milky Way-mapping space mission Gaia, which involves UCL researchers, has completed its sky-scanning phase, racking up more than three trillion observations of two billion stars and other objects over a decade to revolutionise our view of the galaxy.
Launched on 19 December 2013, Gaia's fuel tank is now approaching empty - it uses about a dozen grams of cold gas per day to keep it spinning with pinpoint precision. But this is far from the end of the mission. Technology tests are scheduled for the weeks ahead before Gaia is moved to its 'retirement' orbit, and two massive data releases are tabled for around 2026 and the end of this decade, respectively.
ESA Director of Science, Professor Carole Mundell, said: "Today marks the end of science observations and we are celebrating this incredible mission that has exceeded all our expectations, lasting for almost twice its originally foreseen lifetime.
"The treasure trove of data collected by Gaia has given us unique insights into the origin and evolution of our Milky Way galaxy, and has also transformed astrophysics and Solar System science in ways that we are yet to fully appreciate. Gaia built on unique European excellence in astrometry and will leave a long-lasting legacy for future generations."
Gaia Project Scientist Dr Johannes Sahlmann said: "After 11 years in space and surviving micrometeorite impacts and solar storms along the way, Gaia has finished collecting science data. Now all eyes turn towards the preparation of the next data releases.
"I am thrilled with the performance of this incredible mission, and excited about the discoveries that await us."
Researchers at UCL's Mullard Space Science Laboratory played a critical role in the development of Gaia's Radial Velocity Spectrometer (RVS), which reveals the speed at which millions of stars are moving towards or away from us (their radial velocity).
Professor Steve Baker (Mullard Space Science Laboratory at UCL), current UK Primary Investigator for the Gaia RVS and leader of the MSSL team, said: "Although the Gaia instruments have stopped gathering new data our work is far from over. Gaia Data Release 4 (DR4) in 2026 will be by far the largest astrophysical data catalogue ever published and DR5, scheduled for 2030, will be more than twice as big.
"We are focused on delivering the radial velocities for the full 11-year survey, with greater accuracy and down to even fainter magnitudes than ever before."
Each CCD detector on Gaia has dedicated electronics to convert the faint signal levels to digital images. A team at UCL's Mullard Space Science Laboratory developed prototype electronics and then tested and calibrated each of the 106 electronic detectors used to capture all of Gaia's data. UCL researchers have also had a major role in the spectroscopic data processing.
The UK team involved in the Gaia mission is supported by the UK Space Agency and the Science and Technology Facilities Council.
Professor Baker added: "It is no exaggeration to say that Gaia has revolutionised the science of cosmology. The goldmine of Gaia data has given us a new understanding of the evolution of our Milky Way galaxy and fascinating new detail of its current motion and structure.
"Closer to home Gaia has provided precision orbits for more than 150,000 asteroids within our own Solar System. With each new catalogue release more exciting discoveries will be made - the best is yet to come."
Gaia delivers best Milky Way map
Gaia has been charting the positions, distances, movements, brightness changes, composition and numerous other characteristics of stars by monitoring them with its three instruments many times over the course of the mission.
This has enabled Gaia to deliver on its primary goal of building the largest, most precise map of the Milky Way, showing us our home galaxy like no other mission has done before.
As such, we now also have the best reconstructed view of how our galaxy might look to an outside observer. This new artist impression of the Milky Way incorporates Gaia data from a multitude of papers over the past decade.
Stefan Payne-Wardenaar, scientific visualiser at the Max Planck Institute for Astronomy, Germany, said: "It contains major changes from previous models, because Gaia has changed our impression of the Milky Way. Even basic ideas have been revised, such as the rotation of our galaxy's central bar, the warp of the disc, the detailed structure of spiral arms, and interstellar dust near the Sun.
"Still, the distant parts of the Milky Way remain educated guesses based on incomplete data. With further Gaia data releases our view of the Milky Way will become even more accurate."
