Overview
Almost all of the exoplanets known today were found with time-domain techniques, chiefly radial velocities and photometric transits. We are now entering the era of characterising planetary systems in their Galactic environment. Transmission spectroscopy is revealing the composition of exoplanet atmospheres, increasingly common multi-planet systems invite a quantitative comparison with the Solar System, and planets around stellar remnants offer a glimpse of the Solar System’s future, with planetary debris torn apart and accreted onto white dwarfs. Combined with the star formation history of the Milky Way, this lets us ask how planetary systems and their habitability have changed over the lifetime of the Galaxy. Closer to home, time-domain surveys of the Solar System are raising new questions about the structure and history of its outer regions.
Why the TDT?
The TDT will bring transmission spectroscopy of planetary atmospheres to a wide range of settings and host stars, in particular Solar-system analogues. Its strict time scheduling makes it possible to observe many exoplanets repeatedly and to study exoplanet weather and climate cycles, with simultaneous photometry from units equipped with photometers. At R = 105 the full 100-unit array reaches a signal-to-noise ratio of about 200 per resolution element in one hour on a g = 16 host star, matching the photometric depth of TESS and PLATO. The transit of an Earth-like planet around a Sun-like star lasts about 13 hours, and stellar activity and surface inhomogeneities mean many transits are needed per target, so the global coverage of the TDT and its long lifetime as an ESO facility are essential.
Science themes
Exoplanet atmospheres and their host stars
Planets around stellar remnants
The outer Solar System
Observing requirements
| Requirement | Value |
|---|---|
| Target classes and magnitude range | Transiting-planet host stars, especially Solar-system analogues (e.g. g = 16); planets around stellar remnants; bodies in the outer Solar System |
| Cadence and monitoring duration | Repeated transits over several years; an Earth-analogue transit lasts about 13 hours, needing continuous coverage across the global array |
| Spectral resolution | R = 105 (signal-to-noise ratio about 200 per resolution element in 1 hour on g = 16 with the full array) |
| Number of unit telescopes per target | The full array (100 units), with simultaneous photometry from photometer-equipped units |