The European Space Agency has officially adopted a mission named Arrakihs that will hunt for the faintest light around galaxies, aiming to rewrite what we know about how galaxies are born and grow. Planned for launch by the end of 2030, Arrakihs will peer into the dim haloes surrounding nearby galaxies, regions so faint they have largely escaped observation until now. The mission was given the green light at a Science Programme Committee meeting held at the Instituto Astrofísico de Canarias in Tenerife on 10–11 June 2026.
What a galaxy halo hides about the past
When most people picture a galaxy, they imagine a bright, spinning disc of stars, gas and dust. But surrounding that disc is a much larger, ball-shaped region called the galaxy halo, filled with matter that is extremely hard to see. Most of that halo is made of invisible dark matter, which acts as the galaxy’s gravitational glue, while the rest contains normal matter including stars and hot, charged gas. Arrakihs will focus on diffuse stellar haloes and structures known as stellar streams, which are the shredded remains of small galaxies torn apart by gravity over billions of years.
Scientists believe that galaxies grow by merging with other galaxies over cosmic time. Because galaxy haloes are so faint, researchers have not been able to study enough of them to confirm whether current models of galaxy formation and the role of dark matter are correct. Arrakihs will map stellar streams to piece together the history of past mergers and count the number of “lonely” stars that were ripped away from their original galaxies during those violent events.
A fast mission with a big target list
Arrakihs is the second “fast” or F-class mission in ESA’s Cosmic Vision programme, meaning it must go from selection to launch in less than ten years. It was selected in November 2022, and adoption means the study phase is complete, the mission is shown to be feasible, and ESA commits to building it. The spacecraft and its scientific instruments will now be built, integrated and extensively tested before launch.
The mission plans to investigate at least 80 galaxies with a mass similar to the Milky Way. That sample is large enough to produce statistics on how a typical galaxy forms and to help answer whether our home galaxy is unique. The name Arrakihs stands for Analysis of Resolved Remnants of Accreted galaxies as a Key Instrument for Halo Surveys.
Why this matters for understanding our own galaxy
By capturing the unseen light from galaxy haloes, Arrakihs will dig up cosmic history and reveal how galaxies like our own form and evolve. The mission’s rapid development, as ESA’s Director of Science Carole Mundell noted, showcases the flexibility and breadth of ESA’s Science Programme. For people on Earth, the mission offers a chance to learn whether the Milky Way is a typical galaxy or something rarer, and to see the faint ghosts of galaxies that were consumed long ago.
