THESEUS

Transient High-Energy Sky and Early Universe Surveyor

Mission type	Space observatory
Operator	European Space Agency
Spacecraft properties
Power	115 W [1]
Start of mission
Launch date	2037 (proposed) [2]
Rocket	Vega-E [1] (baseline)
Orbital parameters
Regime	Low Earth orbit
Altitude	600 km [1]
Inclination	5° (equatorial) [1]
Main
Diameter	Infrared: 70 cm; Cassegrain type [1]
Wavelengths	Infrared, Gamma-rays and X-rays
Cosmic Vision M-class ←  ARIEL

Transient High-Energy Sky and Early Universe Surveyor (THESEUS) is a space telescope mission proposal by the European Space Agency that would study gamma-ray bursts and X-rays for investigating the early universe. ^{[1] [3]} If developed, the mission would investigate star formation rates and metallicity evolution, as well as studying the sources and physics of reionization.

Overview

THESEUS is a mission concept that would monitor transient events in the high-energy Universe across the whole sky and over the entirety of cosmic history. In particular, it expects to make a complete census of gamma-ray bursts (GRBs) from the Universe's first billion years, to help understand the life cycle of the first stars. ^[4] THESEUS would provide real-time triggers and accurate locations of the sources, which could also be followed up by other space- or ground-based telescopes operating at complementary wavelengths.

The space observatory would study GRBs and X-rays and their association with the explosive death of massive stars, supernova shock break-outs, black hole tidal disruption events, and magnetar flares. This can provide fundamental information on the cosmic star formation rate, the number density and properties of low-mass galaxies, the neutral hydrogen fraction, and the escape fraction of ultraviolet photons from galaxies. ^[1]

Project history

The concept was selected in May 2018 as a finalist to become the fifth Medium-class mission (M5) of the Cosmic Vision programme by the European Space Agency (ESA). The other finalist was EnVision, a Venus orbiter. The winner, EnVision, was selected in June 2021 for launch in 2031. ^[5]

In November 2023, following a new selection process (2022) and a Phase-0 study (2023), THESEUS was selected by ESA for a new 2.5 year Phase-A study as one of the three candidates M7 missions under the new Voyage 2050 framework (together with M-Matisse and Plasma Observatory). ^[6]

Scientific payload

The conceptual payload of THESEUS includes: ^[1]

• Soft X-ray Imager (SXI), sensitive to 0.3-6 keV is a set of 4 lobster-eye telescope units, covering a total field of view (FOV) of 1 sr with source location accuracy <1-2 arcmin.
• InfraRed Telescope (IRT), sensitive to 0.7-1.8 μm is a 0.7 m NIR telescope with 15x15 arcmin FOV, for fast response, with both imaging and moderate spectroscopic capabilities (R~400). Mass: 112.6 kg.
• X-Gamma ray Imaging Spectrometer (XGIS), sensitive to 2 keV-20 MeV, is a set of coded-mask cameras using monolithic X-gamma ray detectors based on bars of silicon diodes coupled with CsI crystal scintillator, granting a 1.5 sr FOV, a source location accuracy of 5 arcmin in 2-30 keV and an unprecedentedly broad energy band. Mass: 37.3 kg.

See also

• Gamma-ray astronomy
• List of proposed space observatories
• X-ray astronomy
• List of European Space Agency programmes and missions

References

1. The THESEUS space mission concept: science case, design and expected performances. (PDF). Lorenzo Amati, et al. March 2018. doi : 10.1142/9789813226609_0421
2. ESA names space mission concepts in running for Cosmic Vision mission slot. David Szondy, New Atlas. 7 May 2018.
3. The Transient High Energy Sky and Early Universe Surveyor (THESEUS). Lorenzo Amati, Paul T. O'Brien, Diego Götz. Proceedings Volume 9905, Space Telescopes and Instrumentation 2016: Ultraviolet to Gamma Ray; 18 July 2016. doi : 10.1117/12.2231525
4. ESA selects three new mission concepts for study. European Space Agency. Published by PhysOrg. 8 May 2018.
5. "ESA selects revolutionary Venus mission EnVision". ESA . 10 June 2021. Retrieved 10 June 2021.
6. science.esa.int