GenAI impression of the Time Domain Telescope: rows of robotic unit telescopes in open enclosures on a desert ridge at dusk, each projecting an orange laser guide star beam into the sky.

Global spectroscopic telescope array

Time Domain Telescope

Adaptive, fast, and smart: hundreds of spectroscopic eyes on the time-domain sky.

Spectra when you need them. Anywhere, anytime.

GenAI impression of the TDT unit telescopes.

TDT at a glance

  • 100 × 2 mUnit telescopes with extreme adaptive optics in the core array at ESO
  • g ≈ 25 in 30 minWith the full array, at signal-to-noise 10 and R = 5000
  • 0.35–1.8 µmSimultaneous u to H coverage, at resolutions up to R = 105
  • < 1 minTo reconfigure the array for a new alert

The road to ESO’s Expanding Horizons

The TDT consortium is preparing a proposal to ESO’s call for a transformational facility for the 2040s.

  1. Completed: Q4 2024

    Kick-off meeting, The Hague

  2. Completed: Q3 2025

    ESO opens the call

  3. Completed: December 2025

    Community white papers

  4. Completed:

    Collaboration meeting, Hamburg

  5. Next milestone:

    Letter of Intent

  6. Upcoming:

    Full proposal

Full timeline

Go big or go wide

Each TDT unit telescope is individually steerable and permanently instrumented, and many units feed shared clusters of fibre-fed spectrographs. The array can observe as one large telescope on a single faint target, as many independent telescopes on many targets, or anything in between, and it can switch within a minute when the sky changes. A core of 100 units at ESO, with partner stations around the globe, will deliver spectra around the clock.

More about the TDT concept

Four science themes

Stellar deaths and cosmic elements

What is the origin of the elements?

Gravitational-wave mergers, supernovae and gamma-ray bursts, and stellar furnaces.

Powering the Universe

What powers the Universe?

Accretion on all scales from YSOs to QSOs, stellar mergers including LISA sources, and the growth of supermassive black holes.

The history of the Universe

What is the expansion history of the Universe?

Type Ia supernovae, gravitational-wave sirens, the cosmic distance ladder, and the nature of dark matter.

Exoplanets and the Galaxy

How has the formation history of the Galaxy shaped planetary systems and their habitability?

Exoplanet atmospheres and their host stars, planets around stellar remnants, and the outer Solar System.

Explore the project

The TDT concept

The array, its adaptive optics, fibres and spectrographs, performance and operations, at a glance.

Science cases

Four science themes, from stellar deaths and cosmic elements to exoplanets and the Galaxy.

Technology

Extreme adaptive optics in the optical blue, near-read-noise-free detectors, and agentic scheduling.

News & documents

Join the TDT working groups

The TDT is being shaped by an open community of astronomers. Register your interest in a science working group to help define the facility.