Proyecto ARRAKIHS

This is the first mission of the European Space Agency (ESA) Science Programme to be coordinated by Spain.

Approved by ESA's Science Programme Committee (SPC) as an F-class space mission in November 2022, it will focus on the study of dark matter by analysing its gravitational effects on satellite galaxies orbiting larger Milky Way-type galaxies.

The main objective of the ARRAKIHS project (Analysis of Resolved Remnants of Accreted Galaxies as a Key Instrument for Halo Surveys) is to study dark matter in the Universe, which, based on different cosmological observables, could be up to five times more abundant than ordinary matter. Due to its properties, dark matter is very difficult to detect directly and, at present, we are only aware of its existence due to its gravitational effects. It is these effects on satellites orbiting in the halo of galaxies like the Milky Way that ARRAKIHS aims to discover and characterise to shed light on the nature of dark matter.

For this purpose, ARRAKIHS will use a set of two binocular telescopes mounted on a minisatellite (about 300 kg) in low polar orbit. These telescopes will permit observation of galactic halos and faint stellar streams around 115 galaxies with very low surface brightness located between 82 and 130 million light-years away. Studying the nature and number of these structures will make it possible to test different models of dark matter.

Rafael Guzman Llorente, Research Professor at the Spanish National Research Council (CSIC), attached to the Institute of Physics of Cantabria (IFCA), leads an international scientific consortium spanning ten countries. In addition to Spain's participation, ARRAKIHS collaborates with researchers from several countries, including Switzerland, Sweden, Austria, Belgium, the United Kingdom and the United States.

Regarding Spain, in addition to IFCA, the Institute of Space Studies of Catalonia (IEEC), the Institute of Astrophysics of Andalusia (IAA), the Centre for the Study of Cosmos Physics of Aragon (CEFCA), the Complutense University of Madrid (UCM), the Institute of Astrophysics of the Canary Islands (IAC), the Spanish Astrobiology Centre (CAB) and the National Institute for Aerospace Technology (INTA) are also participating in the project.

The ARRAKIHS satellite is expected to be launched on a Vega-C or similar rocket in 2031. Before announcing tenders for the study and construction of the satellite, the ARRAKIHS design needs to be finalised, which is currently in the definition phase between the scientific consortium (which will provide the instrumentation as an in-kind contribution from the participating countries) and the ESA.

The mission study phase (A/B) will run for three years in order to perform tasks to demonstrate the scientific and technological feasibility of the mission. Once this phase has been completed in 2026, ARRAKIHS will be formally adopted by the SPC.