Interferometric Space Missions for Exoplanet Science: Legacy of Darwin/TPF

Abstract

DARWIN/TPF is a project of an infrared space-based interferometer designed to directly detect and characterize terrestrial exoplanets around nearby stars. Unlike spectro-photometric instruments observing planetary transits, an interferometer does not rely on any particular geometric constraints and could characterize exoplanets with any orbital configuration around nearby stars. The idea to use an infrared nulling interferometer to characterize exoplanets dates back to Bracewell (1978), and was extensively studied in the 1990s and 2000s by both ESA and NASA. The project focuses on the mid-infrared regime (5-20 µm), which provides access to key features of exoplanets, such as their size, their temperature, the presence of an atmosphere, their climate structure, as well as the presence of important atmospheric molecules such as H 2 O, CO 2 , O 3 , NH 3 , and CH 4 . This wavelength regime also provides a favorable planet/star contrast to detect the thermal emission of temperate (∼ 300 K) exoplanets (10 7 vs 10 10 in the visible). In this chapter, we first review the scientific rationale of a mid-infrared nulling interferometer and present how it would provide an essential context for interpreting detections of possible biosignatures. Then, we present the main technological challenges identified during the ESA and NASA studies, and how they have progressed over the last 10 years. Finally, we discuss which technologies remain to be developed before flying such an instrument, and possible ways to make DARWIN/TPF a reality in the mid-term future.

Exoplanet Biosignatures: A Framework for Their Assessment

“…They found that the red edge detectability ranged from 1% to 12% in observations and models. For space-based telescopes such as the Terrestrial Planet Finder/Darwin concepts (Beichman et al, 2007;Defre `re et al, 2017), the exposure times would be *100 h to reach a sufficient spectral precision (<3%) with a spectral resolution (k/Dk) of 25 for an Earth at 10 parsecs distance (Arnold et al, 2002). If detected, seasonal variations would be especially informative.…”

Kernel-nulling for a robust direct interferometric detection of extrasolar planets

“…They are listed along with their predicted observational properties in Table 3. The size of this sample doubles (Defrère et al 2018b), if one assumes a tighter inner working angle of 1 mas (0.25 × λ/B), which brings in potentially warmer planets with more favorable contrasts. A more detailed characterization of the true VIKiNG discovery and characterization potential is beyond the scope of this paper that only aims at introducing a new instrument concept.…”

Atmospheres of Rocky Exoplanets

“…The proposed facilities would use a variety of technologies to achieve the high contrast and high angular resolution required for direct imaging of other Earths: starlight suppression with a coronograph or a starshade, or interferometry. These projects build on the heritage of many previously studied missions, notably the Terrestrial Planet Finder/Darwin concepts (Defrère et al 2018). Now that the occurrence rate of temperate rocky planets is known (Dressing & Charbonneau 2015;Bryson et al 2021), the time is ripe to pursue a flagship mission to characterize them in more detail.…”