# Ariel by European Space Agency

Canonical page: https://technooptimist.io/spaceflight/ariel
Frontier: [Spaceflight](https://technooptimist.io/spaceflight.md) · Field: Space telescopes · Company: [European Space Agency](https://technooptimist.io/companies/esa.md)
Stage: Proto (2 of 5: Research → Proto → Pilot → Deploy → Scaling)
Updated: last update 2026-03-16, facts checked 2026-10-11
Goal: Find out what planets around other stars are made of and how that depends on their star, by measuring the atmospheres of about 1,000 known planets instead of a few dozen.
Status: Payload under test with Airbus building the spacecraft; launch on Ariane 6 now listed for 2031.
Next milestone: Whole payload assembled and tested together, target 2026

## Milestones

| Status | Milestone | Date | Slip |
| --- | --- | --- | --- |
| Done | Selected as ESA's fourth medium-class science mission | Mar 2018 |   |
| Done | Adopted: moves from study to implementation | Nov 2020 |   |
| Done | Airbus signs contract to build the spacecraft | 6 Dec 2021 |   |
| Done | Payload passes preliminary design review | May 2023 |   |
| Done | Spacecraft design passes review; construction starts | 5 Dec 2023 |   |
| Done | Structural model assembled and shake-tested | Oct 2024 |   |
| Current | Whole payload assembled and tested together | 2026 |   |
| Planned | Launch on Ariane 6 to Sun-Earth L2 | 2031 | +24 mo (originally 2029) |

## Upcoming events

- **2026**: Whole payload assembled and tested together
- **2031**: Launch on Ariane 6 to Sun-Earth L2 (slipped 24 mo)

## Most important updates

- **16 Mar 2026**: Ariel payload assembled for testing; launch now more likely in 2031 than 2029. Ariel's multinational payload was assembled as a whole for the first time and is being tested to show it can survive launch and the cold vacuum of space. ([our story](https://technooptimist.io/stories/ariel-payload-assembled-for-testing-launch-now-more-likely-in-2031-than-f00117f2.md) · [original source](https://www.iflscience.com/ariel-a-revolutionary-1000-exoplanet-mission-is-getting-tested-iflscience-got-an-exclusive-look-82869))
- **5 Dec 2023**: Ariel passes its design review and moves into construction. Ariel's spacecraft design passed its preliminary design review after a 19-month phase, moving the mission from drawing board to construction. ([our story](https://technooptimist.io/stories/ariel-passes-its-design-review-and-moves-into-construction-f3c9f394.md) · [original source](https://www.esa.int/Science_Exploration/Space_Science/Ariel/Ariel_moves_from_drawing_board_to_construction_phase))
- **7 Dec 2021**: Airbus signs contract to build ESA's Ariel exoplanet telescope. ESA and Airbus signed the contract to design and build Ariel at ESA headquarters in Paris. ([our story](https://technooptimist.io/stories/airbus-signs-contract-to-build-esa-s-ariel-exoplanet-telescope-d662daf0.md) · [original source](https://www.esa.int/Science_Exploration/Space_Science/Airbus_will_build_ESA_s_Ariel_exoplanet_satellite))

## Current obstacles

- **Launch slipping to 2031**: Planned for 2029 when the contract was signed, launch is now listed by ESA for 2031.
- **A payload from many countries**: Over 50 institutes in 16 to 17 European countries, plus NASA and Canada, supply parts that must work together; the mirror was still to be added in 2026.

## Physics limits

- **An atmosphere is a thin ring of light**: Only a thin shell of gas around the planet filters starlight, so the signal is a tiny fraction of the star's light; small rocky planets give the weakest signals of all.
- **Only planets that cross their star**: Transit spectroscopy needs the orbit to be seen edge-on. Most planets never line up, so Ariel can study only the known transiting ones.
- **Stars are not steady lamps**: Starspots and flares change the star's colour and brightness, and can mimic or hide molecules in a planet's atmosphere.

## How it works

### Transit spectra: Starlight through a planet's air

When a planet crosses its star, a sliver of starlight filters through its atmosphere. Water, carbon dioxide and methane each absorb their own colours.

### Visible + infrared: Many colours at the same moment

Ariel observes visible and infrared light at once, so it can tell a planet's atmosphere apart from flickers and spots on the star.

### Cold metal mirror: An all-aluminium telescope

Mirror and structure are one metal, so they shrink equally when cooled to about 55 K and the telescope stays in focus.

### Survey: A census, not a handful

Instead of studying a few planets deeply, Ariel looks at about 1,000, from hot gas giants to rocky worlds, to find patterns linked to their stars.

## Spec sheet

| Spec | Ariel | Provenance |
| --- | --- | --- |
| Planets to survey | About 1,000 | reported |
| Primary mirror | 1.1 × 0.7 m, all-aluminium | reported |
| Collecting area | 0.64 m² | reported |
| Infrared spectrometer range | 1.95–7.8 µm | reported |
| Telescope temperature | About 55 K (−218 °C) | reported |
| Launch mass | 1,400 kg | reported |
| Time per planet system | 10 hours to 3 days | reported |
| Initial mission | 4 years | reported |

Provenance: reported = stated by the company; estimated = our estimate; sample = a sample figure.

## About European Space Agency

ESA is the European intergovernmental space agency with 23 member states. It operates Earth observation systems, the International Space Station, deep-space missions and the Ariane rocket family. The Hera mission is ESA's planetary-defence follow-up to NASA's DART impact test.

- Develops Ariane rockets and Copernicus Earth-observation satellites; participates in the International Space Station.
- Hera mission to asteroid Didymos measures how NASA's 2022 DART impact deflected it, validating planetary defence.
- Multinational agency with 23 European member states; 2026 budget €8.26 billion.

- Founded: 1975
- Headquarters: FR
- Status: government
- Website: https://www.esa.int
- Partners, customers, investors: NASA (partner); Airbus Defence and Space (supplier); Thales Alenia Space (supplier)

Company page: https://technooptimist.io/companies/esa.md

## Related programs

More from European Space Agency:

- [Hera](https://technooptimist.io/spaceflight/hera.md) (Deploy)
- [ExoMars Rosalind Franklin rover](https://technooptimist.io/spaceflight/rosalind-franklin-rover.md) (Pilot)
- [PLATO](https://technooptimist.io/spaceflight/plato.md) (Proto)
- [JUICE (Jupiter Icy Moons Explorer)](https://technooptimist.io/spaceflight/juice.md) (Deploy)
- [Euclid](https://technooptimist.io/spaceflight/euclid.md) (Deploy)
- [Ramses](https://technooptimist.io/spaceflight/ramses.md) (Proto)

Everything in Spaceflight: https://technooptimist.io/spaceflight.md

---

The Techno Optimist tracks every frontier of technology, program by program: https://technooptimist.io/ (a Markdown version of any page: add .md to its URL; site map for agents: https://technooptimist.io/llms.txt).
Data API (JSON, realtime stream): https://technooptimist.io/developers. People read 5 pages free, then Reader $10/month; these Markdown pages are open to agents.