Theia Space Observatory

faint objects in motion: the new Astrometry frontier

Dark Matter

About 80% of the matter in the Universe is made of Dark Matter.
But its nature is unknown. 

Theia will probe the motions of stars inside Dark Matter small companion galaxies of the Milky Way. Theia will detect the gravitational perturbations of the galactic disk caused by Dark Matter halos passing through it. Theia will probe the shape of the Milky Way Dark Halo.

Theia is designed to study Dark Matter
down to micro arcseconds per year effects.

Habitable ExoEarths

Are there habitable Earths orbiting nearby Sun-like stars?

Theia is designed to probe tiny, sub-micro arcsecond, position variations of the ~50 nearest Solar-type stars. Theia will be capable of determining orbits and true masses of Earth twins in their habitable zones, where liquid water might exist.

By finding habitable Exo-Earths around our nearest Solar analogs, Theia will pave the way to future large exobiology missions.

Extreme conditions

The most extreme matter conditions are found in Neutron Stars and around Black Holes.

Theia is designed to determine distances and masses of the most extreme stellar objects in the Universe. It will reveal the neutron star interior and the state of matter at densities several times that of the atomic nucleus.

Theia will also allow us to learn about black holes properties from their hot-spots and shadows.

Open Observatory

15% of the mission time will be dedicated to an open call. 
Anyone can submit proposals.

Conceived as an infrastructure for the 2030s, Theia will bring precise Astrometry to the fingertips of general Astronomy&Astrophysics communities.

Theia will deliver Science-ready astrometric data – no need to struggle with complexities from satellite raw data and astrometric reduction. 


One telescope. One camera. Monitored.

Theia was designed to avoid complexity. It uses a single 0.8m diameter Korsch telescope, corrected for optical aberrations up to the third order. It also employs a single focal plane with 24 science detectors.

Theia's payload is continously monitored and calibrated at the picometer level with telescope and focal plane array interferometers and lambda/1000 wave-front sensors.


Astrometry, the foundation of Astronomy, lies at the very heart of Theia.

Theia is designed to perform differential astrometric measurements. Up to 30x more precise than the best measurements today. And by using the ESA/Gaia reference frame, these measurements can be made absolute.

For very bright stars, Theia can reach hundreds of nano-arcseconds. For very faint stars, tens of micro-arcseconds. This is why Theia will answer the most profound questions of modern Science.

The Collaboration

The Theia space mission was submitted to the ESA/M5 call for missions on the 5th October 2016. It is being conceived in a collaborative effort.

Before the open call for participation, the Theia Collaboration gathered 184 members from 22 countries.

The core team includes members from the UK, France, Italy, Sweden, Germany, Spain, Switzerland, Portugal and USA. Additional contributions come from Austria, Brazil, Canada, China, Denmark, Finland, Greece, Hungary, India, Israel, Japan, The Netherlands and Poland.

You can declare here if you wish to support Theia, or take an active role in future phases of Theia.