ARRAKIHS Mission
Contents
The ARRAKIHS mission
Mission scope
ARRAKIHS consortium
The ARRAKIHS mission
ARRAKIHS (Analysis of Resolved Remnants of Accreted galaxies as a Key Instrument for Halo Surveys) is a cutting-edge mission of the European Space Agency (ESA) proposed by the ARRAKIHS Mission Consortium to investigate the nature of dark matter and galaxy formation on small scales. Selected as an F-mission (fast mission) in November 2022, it is currently in phases O/A/B, with an adoption decision expected in mid-2026.
ARRAKIHS is designed to explore how well the Λ-Cold Dark Matter (ΛCDM) model aligns with observations of smaller-scale structures, such as galaxy halos. One of its main goals is to investigate potential mismatches between what the model predicts, and what we observe in the real world. In particular, the mission aims to determine whether these mismatches point to the need for alternative dark matter models or refinements to baryonic physics in galaxy formation simulations.
ARRAKIHS will conduct deep simultaneous visible and infrared imaging of a statistically representative sample of nearby halos of Milky Way-type galaxies in the local Universe, reaching unprecedented low surface brightness levels. ARRAKIHS will provide key tests with statistical significance to determine whether the reported tensions arise from selection effects or small number statistics. However, if these tensions are confirmed, ARRAKIHS will highlight inconsistencies in the current theoretical models of MW-like galaxy formation, highlighting the need for refinements or alternative frameworks.
The ARRAKIHS mission has three primary observational goals: to provide robust statistics on the numbers and shapes of tidal stellar structures, characterise the shape and extent of the diffuse stellar halo, and determine the abundance and locations of satellite galaxies across a comprehensive sample of MW-like galaxies beyond the Local Group.
Mission Scope
The mission’s scope involves imaging a vast expanse of the sky during three years, covering around 100 square degrees in each of two visible and two near-infrared bands simultaneously, down to an unprecedentedly low surface brightness (SB). In particular we will include red and blue visual filters which, together with the near-infrared, are critical to separate components and characterize the observed physical properties. ARRAKIHS will capture ultra-detailed images of nearby Milky Way-like galaxies, focusing on the faint outer regions of their halos. These halos hold crucial information about how galaxies form and evolve, but because they are so faint, studying them from Earth is nearly impossible due to the effects of the atmosphere.
To achieve its goals, ARRAKIHS will use an innovative binocular telescope assembly designed specifically to achieve ultra-low surface brightness imaging. The instrument will be mounted on a small satellite in a Sun-Synchronous Low Earth Orbit at an altitude of approximately 800 km. The mission is planned to launch in the early 2030s and will complete its survey within three years of operation. The survey will culminate in the creation of a unique catalogue of ultra-low surface brightness extragalactic images, focusing on a volume-limited and mass-limited sample of galaxies akin to our own Milky Way.
ARRAKIHS will achieve an unparalleled surface brightness sensitivity, capturing details beyond 30 mag/arcsec².
The data collected will provide a statistically significant test of the Λ-Cold Dark Matter (ΛCDM) model and its predictions about galaxy formation. If ARRAKIHS reveals discrepancies with the model, it could lead to important advances in our understanding of the Universe, including new theories about dark matter or improved models of how stars and gas interact.
ARRAKIHS Consortium
The ARRAKIHS Mission Consortium (AMC) is a collective of junior and senior researchers collaborating to achieve the common goal of launching this fast space mission with the scientific objective of understanding the nature of dark matter. Comprising scientists, engineers, PhD students, technical and management professionals, the Consortium continuously expands in both size and expertise.
The AMC members belong to different research institutes and companies representing six European countries (Spain, Austria, Belgium, Sweden, Switzerland, Norway, Portugal, and United Kingdom). These countries are collectively referred to as the “Member States” and they are responsible for the Science, Instrument and Science Data Center funding, design and operation.
The ARRAKIHS Mission Consortium includes technological companies across Europe, led by the Spanish company Satlantis, the prime contractor for the instrument. Additionally, the consortium collaborates with research institutes from: the Netherlands, France, Denmark, the United States, Thailand, and Taiwan.