ESA adopts galactic archaeology mission Arrakihs

Being adopted signifies that the examine section is full, the mission is proven to be possible, and ESA commits to implementing it. Within the upcoming growth section, the spacecraft and its scientific instrumentation can be constructed, built-in and extensively examined.  

Arrakihs is the second ‘quick’ or F-class mission of ESA’s Cosmic Imaginative and prescient programme, needing lower than ten years from its choice in November 2022 till launch. The choice to undertake it was made on the Science Programme Committee assembly on the Instituto Astrofísico de Canarias, Tenerife (10–11 June 2026). 

“Arrakihs is a ground-breaking and distinctive galactic archaeology mission. By uncovering hard-to-see galaxy haloes, it’s going to reveal new particulars of how galaxies type and whether or not the Milky Manner galaxy is exclusive. Its speedy growth showcases the pliability and breadth of ESA’s Science Programme,” says Professor Carole Mundell, ESA’s Director of Science. 

The mission title stands for Evaluation of Resolved Remnants of Accreted galaxies as a Key Instrument for Halo Surveys.

Uncovering galactic historical past 

Image a galaxy. You may think a glowing, spiralling disc of stars, fuel and mud. What you most likely don’t image is the a lot bigger ball-shaped area surrounding this disc, crammed with matter that’s a lot more durable to see. 

This area, referred to as the galaxy halo, is usually made up of invisible dark matter acting as the galaxy’s gravitational glue. The rest of the halo consists of normal matter, including stars and hot, charged gas. Arrakihs will observe diffuse stellar haloes and structures such as stellar streams – remnants of small galaxies that were torn apart by gravity. 

Importantly, a galaxy’s halo contains clear traces of how the galaxy formed and evolved over cosmic time. Scientists believe that galaxies grow over time by merging with others. Because galaxy haloes are so faint, we haven’t been able to study enough of them to be sure that our models of galaxy formation – and by extension the role of dark matter – are correct.  

By mapping stellar streams, Arrakihs will allow us to piece together the history of past mergers and give an estimate of the number of ‘lonely’ stars that were ripped away from their galaxies during mergers. 

In total, Arrakihs plans to investigate at least 80 galaxies with a similar mass to the Milky Way galaxy. This is a large enough number to get statistics on how a ‘typical’ galaxy forms, allowing us to understand how unique our home galaxy is.

Two pairs of European eyes

The mission needs to detect extremely faint objects with a ‘low surface brightness’. To do this, Arrakihs will carry one scientific instrument consisting of two pairs of ‘binocular telescopes’, a total of four cameras. Each camera is sensitive to a different band of wavelengths, spanning from the near-ultraviolet, through the visible spectrum, into the near-infrared.  

The instrument is being designed and developed by a consortium of ESA Member States led by Spain. Other core consortium partners are Switzerland, Austria, Belgium, Norway, Portugal and Sweden. Many of the instrument contributions are supported through ESA’s Prodex programme. 

Arrakihs will join ESA’s fleet of Cosmic Observers. These missions primarily address two top-level science themes of ESA’s Cosmic Vision 2015–2025, namely: What are the fundamental physical laws of the Universe? and How did the Universe originate and what is it made of? 

For more information, please contact   
ESA Media Relations   
media@esa.int