ARRAKIHS (Analysis of Resolved Remnants of Accreted galaxies as a Key Instrument for Halo Surveys) is an F-class space mission of the European Space Agency (ESA), selected as the second Fast mission (F2) within the Cosmic Vision programme. The mission aims to test the Λ-Cold Dark Matter (ΛCDM) model by analysing discrepancies between theoretical predictions and observations of small-scale structures, such as tidal stellar streams and dwarf satellite galaxies. It is specifically designed to explore the low-surface-brightness Universe, targeting the faintest and most diffuse structures in galaxies across a statistical sample of nearby Milky Way-like galaxies.

With a projected launch in 2030, the mission is led by Spain, with important contributions from Switzerland, Belgium, Austria, Sweden, Norway, Portugal, and the United Kingdom. It is named after the planet Arrakis from science fiction novel Dune. The name is a backronym of "Analysis of Resolved Remnants of Accreted galaxies as a Key Instrument for Halo Surveys".

The faint structures targeted by the mission include the diffuse stellar halo surrounding a galaxy, tidal stellar streams and shells, and other very low-brightness features, all of them difficult to detect with conventional astronomical surveys. Together, these faint galaxy components preserve evidence of past accretion and merger events, providing a fossil record of galaxy assembly. As such, they provide valuable constraints on galaxy assembly and formation processes, as well as on the role of dark matter in shaping galactic halos, linking the observable properties of galaxies to their underlying gravitational structure.

ARRAKIHS will investigate how galaxies assemble and how dark matter and baryonic processes shape their outskirts through deep visible and near-infrared observations of a statistically representative sample of nearby Milky Way-mass galaxies. By combining unprecedented depth with homogeneous observations across a large sample, the mission will move beyond studies of individual systems and enable population-level investigations of galaxy assembly. The ARRAKIHS design and survey strategy is optimized to achieve unprecedented sensitivity to faint diffuse emission while minimizing systematic observational effects.

By reaching surface-brightness limits beyond those achieved by existing wide-field surveys, ARRAKIHS will reveal and characterise faint structures that until now have been studied in detail in a small number of nearby galaxies. By extending such studies beyond our Local Group, the mission will place these galaxies in a broader galactic context, helping to constrain the mass assembly history of Milky Way-like galaxies, improve our understanding of galaxy formation processes, and investigate how stellar streams can be used to probe the properties of dark matter halos.

The ARRAKIHS mission's primary payload is a dual binocular telescope system with a modified Maksutov Cassegrain design equipped with two visible-wavelength and two infrared cameras, optimized for low surface brightness astronomy. Developed by the Spanish aerospace company Satlantis, the prime contractor for the instrument's design and manufacturing, the system is designed to detect extremely faint stellar structures surrounding galaxies with high sensitivity and precision. The spacecraft's wide-field imaging system has continuous wavelength coverage from 280 to 1600 nm across four photometric bands (VIS1 and VIS2 in the visible, and NIR1 and NIR2 in the near-infrared).

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