ESA officially adopts ARRAKIHS as F2 Mission: Europe leads the exploration of the low surface brightness universe

Selected by ESA in 2022, ARRAKIHS (Analysis of Resolved Remnants of Accreted galaxies as a Key Instrument for Halo Surveys) was conceived to provide new insights into one of the major open questions in modern astrophysics: how galaxies form and evolve within the Standard Model of Cosmology.  

The decision marks the beginning of the next major phase of the mission, during which the spacecraft and its scientific instrumentation will be built, integrated and space-qualified. 

ESA’s adoption follows the successful completion of the conceptual and preliminary design milestones required for the mission, including the Preliminary Design Review (PDR) of the instrument and the delivery of the «Red Book», the definition study report describing the scientific, technical and programmatic implementation of ARRAKIHS. 

Revealing the faint Universe 

The low-surface-brightness diffuse-stellar halos around galaxies like the Milky Way preserve crucial information about how galaxies formed and evolved, revealing the combined effects of dark matter, galaxy mergers, and other processes that shape galaxies over cosmic time.  

"Many of these structures are extremely faint and difficult to study systematically with existing observations", explains Rebekka Coles-Bieri (UZH), the mission's Science Coordinator. 

ARRAKIHS will thus open a new observational window onto the largely unexplored low-surface-brightness Universe, enabling the study of previously hidden stellar components of the galaxy haloes. 

An international collaboration  

ARRAKIHS is developed through a collaboration between ESA and the ARRAKIHS Mission Consortium (AMC), led by Prof. Rafael Guzmán from the Instituto de Física de Cantabria (IFCA, CSIC–UC). 

The consortium includes more than 250 scientists and engineers from seven ESA member states led by Spain, including Austria, Belgium, Norway, Portugal, Sweden and Switzerland, together with additional contributions from institutions and companies in the United Kingdom, France, Denmark, the Netherlands, the United States, Taiwan and Thailand. 

At the University of Surrey, astrophysicists are leading the UK’s theoretical modelling work for the ARRAKIHS mission, helping scientists understand what the spacecraft’s observations will reveal about galaxies and dark matter. 

The Surrey team is developing methods that use faint stellar streams surrounding galaxies to map the gravitational field of the Milky Way analogues and study the shape of the invisible dark matter haloes around them.

From concept to adopted mission

Over the past few years, the international ARRAKIHS consortium has transformed a highly ambitious scientific concept into a fully established space mission within ESA’s Science Programme. This progress has been supported by major scientific and technological achievements, including developing new, high-resolution cosmological simulations and galaxy models, design of key subsystems of the flight instrument, the initial development of the ground-based infrastructure for scientific data and data analysis systems, and the operation of a ground demonstrator camera installed at the Javalambre Astrophysical Observatory, the acquisition of increasingly deep observations that further strengthen the mission’s scientific case. 

With its official adoption by ESA, ARRAKIHS is now entering the construction phase in preparation for its launch in 2030. 

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Notes to editors 

• Dr Denis Erkal is available for interview; please contact mediarelations@surrey.ac.uk to arrange.