ESA Greenlights 'Arrakihs' Space Mission to Solve the Mystery of How Galaxies Like the Milky Way Formed

Level 2 — Elementary

The European Space Agency officially adopted a new space mission called Arrakihs on June 10 and 11, 2026. The decision was made at a meeting of ESA's Science Programme Committee in Tenerife, Spain. The mission will be the first ever designed specifically to photograph the faint outer halos of galaxies similar in size to the Milky Way.

Galaxies have a bright centre with many stars, but they also have an outer halo that is much harder to see. These halos contain important clues about how the galaxy formed over billions of years. When smaller galaxies collide with a larger one, they leave traces in the halo. Arrakihs will be designed to detect these traces.

The spacecraft will carry two binocular-style telescopes with four cameras in total. The cameras will observe light in four different wavelengths, from the near-ultraviolet to the near-infrared. Arrakihs will study at least 80 galaxies that are similar in mass to our own Milky Way. By collecting data from so many galaxies, scientists will be able to find patterns.

The mission is planned to launch by the end of 2030. It is led by a team from Spain and supported by a group of European countries. The name Arrakihs stands for Analysis of Resolved Remnants of Accreted galaxies as a Key Instrument for Halo Surveys. It is also a playful reference to Arrakis, the desert planet from Frank Herbert's famous Dune science fiction novels.

wavelength: the distance between waves of light or other radiation, which determines its colour or type

near-infrared: a type of light just beyond red that is invisible to the human eye but can reveal cool stars and structures

ultraviolet: a type of light with shorter wavelengths than visible light, often linked to energetic young stars

accretion: the gradual collection of matter by a galaxy or star pulling in smaller objects through gravity

remnant: a small part left over from a larger object or event that has mostly disappeared

low surface brightness: describing extremely faint astronomical structures that are difficult to detect even with powerful telescopes

data: information collected by scientists through experiments or observations

binocular: having two optical elements placed side by side to observe together

Level 3 — Intermediate

The European Space Agency's Science Programme Committee formally adopted the Arrakihs mission at its meeting at the Instituto Astrofísico de Canarias in Tenerife on June 10 and 11, 2026. Arrakihs, an acronym for Analysis of Resolved Remnants of Accreted galaxies as a Key Instrument for Halo Surveys, will be the first satellite mission dedicated entirely to capturing the ultra-faint low surface brightness structures that surround galaxies similar in mass to the Milky Way.

Galaxy haloes are the outermost and least luminous components of a galaxy. When a large galaxy like the Milky Way swallows smaller satellite galaxies over billions of years, the dissolved stars and debris are deposited in streams and shells throughout the halo. These fossil structures preserve a record of a galaxy's assembly history. Astronomers call the study of such signatures galactic archaeology, but observing them requires unprecedented sensitivity to extremely faint light, since halo structures can be thousands of times dimmer than the galaxy's bright central disc.

Arrakihs addresses this challenge with an instrument built around two binocular telescopes housing four cameras in total, covering a spectral range from the near-ultraviolet through visible light to the near-infrared. By surveying at least 80 Milky Way-mass galaxies, scientists can build a statistically significant sample, revealing whether our own galaxy's merger history is typical or exceptional. The mission is the first to target low surface brightness science as its primary objective rather than treating it as a secondary byproduct of observations aimed at something else.

The mission is led by a consortium of ESA member states under Spanish scientific leadership and is targeted for launch no later than the end of 2030. Adoption by the Science Programme Committee is a critical milestone that unlocks funding for the detailed design phase. The name Arrakihs pays homage to Arrakis, the desert world of Frank Herbert's Dune, a nod to the idea that the mission will reveal hidden riches obscured beneath the vast darkness of the cosmos.

low surface brightness: an astronomical term for extremely faint structures whose light is spread thinly across a large area of sky

spectral range: the span of electromagnetic wavelengths that an instrument can detect and measure

galactic archaeology: the study of the history and formation of galaxies through the remnants left by past mergers and accretion events

satellite galaxies: smaller galaxies that orbit around and are gravitationally bound to a larger galaxy

fossil structure: a remnant of an ancient event that has survived to the present and preserves information about the past

consortium: a partnership of organisations working together on a shared project

statistically significant: describing results that are unlikely to have occurred by chance and can be relied upon as meaningful

assembly history: the sequence of mergers, accretions, and events through which a galaxy grew to its present form

Level 4 — Advanced

ESA's Science Programme Committee voted to adopt the Arrakihs mission at its plenary session at the Instituto Astrofísico de Canarias, Tenerife, on June 10 and 11, 2026, formally committing the agency to the first space observatory built from the ground up around the challenge of low surface brightness (LSB) photometry. Arrakihs, an acronym for Analysis of Resolved Remnants of Accreted galaxies as a Key Instrument for Halo Surveys, moves immediately into the detailed design phase, with a launch window at the end of 2030 as the binding contractual milestone.

The scientific imperative is rooted in a deep gap in observational cosmology. The Lambda-CDM standard model predicts that Milky Way-mass galaxies should display rich networks of stellar streams, shell structures, and tidal debris fields in their haloes, as residual evidence of the hierarchical accretion process by which large galaxies cannibalise smaller companions across cosmic time. Ground-based imaging surveys and the Hubble Space Telescope have confirmed such structures in only a handful of well-studied galaxies because the surface brightnesses involved fall below 28 to 30 magnitudes per square arcsecond, a regime where atmospheric scattering, scattered light from bright stars, and detector systematics conspire to obliterate the signal.

Arrakihs circumvents the ground-based ceiling by placing its instrument package, comprising two co-pointing binocular telescope units with a total of four cameras spanning near-ultraviolet through near-infrared wavelengths, in a space environment where the zodiacal light foreground is stable, thermal systematics are controlled, and scattered-light paths are fully characterised. The survey strategy targets at least 80 Milky Way-mass galaxies out to distances where resolved stellar populations remain accessible, providing the large statistical ensemble needed to discriminate between galaxy formation models with substantially different merger-rate histories.

Scientifically, the mission poses a direct test of whether the Milky Way is a typical or outlier member of its mass class, a question with ramifications for our understanding of structure formation, feedback processes, and the distribution of dark matter within galaxy-scale potential wells. Catherine Vollgraff Heidweiller, ESA's Head of Science Strategy, emphasised that Arrakihs exemplifies the agency's commitment to long-horizon science that is not commercially driven, an orientation that distinguishes it from commercially-focused space ventures. The name, a deliberate homage to the planet Arrakis in Frank Herbert's Dune, frames the mission's goal metaphorically as the extraction of riches, in this case cosmological knowledge, from a universe whose most telling features are hidden in plain darkness.

Lambda-CDM model: the standard cosmological model describing the universe's composition and evolution, incorporating dark energy and cold dark matter

surface brightness: the amount of light emitted per unit area of an astronomical object's apparent surface, measured in magnitudes per square arcsecond

tidal debris field: material stripped from a smaller galaxy by the gravitational tidal forces of a larger one during a close encounter

arcsecond: a unit of angular measurement equal to one-sixtieth of an arcminute, used to describe tiny angles on the sky

zodiacal light: a faint diffuse glow in the night sky caused by sunlight scattered off dust in the inner solar system

hierarchical accretion: the cosmological process by which small structures merge under gravity to build progressively larger ones over time

potential well: a region of space where an object's gravitational or other potential energy is lower than in surrounding regions

feedback processes: astrophysical mechanisms such as supernova explosions or active galactic nuclei that regulate star formation within a galaxy

Level 1 — Absolute Beginner

Level 2 — Elementary

Level 3 — Intermediate

Level 4 — Advanced

ESA Greenlights 'Arrakihs' Space Mission to Solve the Mystery of How Galaxies Like the Milky Way Formed

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