The phase 0/A study of the ESA M3 mission candidate EChO

Abstract

EChO, the Exoplanet Characterisation Observatory, has been one of the five M-class mission candidates competing for the M3 launch slot within the science programme Cosmic Vision 2015-2025 of the European Space Agency (ESA). As such, EChO has been the subject of a Phase 0/A study that involved European Industry, research institutes and universities from ESA member states and that concluded in Exp Astron EChO is a concept for a dedicated mission to measure the chemical composition and structure of hundreds of exoplanet atmospheres using the technique of transit spectroscopy. With simultaneous and uninterrupted spectral coverage from the visible to infrared wavelengths, EChO targets extend from gas giants (Jupiter or Neptune-like) to super-Earths in the very hot to temperate zones of F to M-type host stars, opening up the way to large-scale, comparative planetology that would place our own solar system in the context of other planetary systems in the Milky Way. A review of the performance requirements of the EChO mission was held at ESA at the end of 2013, with the objective of assessing the readiness of the mission to progress to the Phase B1 study phase. No critical issues were identified from a technical perspective, however a number of recommendations were made for future work. Since the mission was not selected for the M3 launch slot, EChO is no longer under study at ESA. In this paper we give an overview of the final mission concept for EChO as of the end of the study, from scientific, technical and operational perspectives.

The EChO science case

“…The frequency band over which the requirement applies is between 2.8×10 −5 Hz and 3.7 mHz, or~5 min to 10 h [60,122,127,187]. This implies having the capability to remove any residual systematics and to co-add the elementary observations from many repeat visits to a given target.…”

“…The photometric stability budget is described by Puig et al [127], Pascale et al [122], and Waldmann and Pascale [187]. To achieve the required performance, particular attention is required to:…”

“…The first approach taken is based on a static radiometric model that takes the required performance figures for the payload to 'size' the mission. This model has been used to calculate the number of transit/occultation revisits necessary to achieve a specified SNR in the transit spectral features and the possible revisits during a given mission lifetime [127]. The second approach is to construct a model that simulates the actual performance of the mission as realistically as possible (EChOSim).…”

The Long wave (11–16 μm) spectrograph for the EChO M3 Mission Candidate study

“…At these wavelengths, thermal emission from both the telescope and the instrument module, combined with the astrophysical background, can form a large fraction of the signal at the detector (e.g. [10]). The design described in this paper includes features to minimise these contributions, and also describes options for optimising the resolving power λ/Δλ (nominally R=30 defined in the study [10]) of the instrument.…”

“…[10]). The design described in this paper includes features to minimise these contributions, and also describes options for optimising the resolving power λ/Δλ (nominally R=30 defined in the study [10]) of the instrument. Given the limited availability of high performance detectors with high technology-readiness and operating temperatures of>7 K, a study that targets specific molecules (e.g.…”