High-dispersion spectroscopy of extrasolar planets: from CO in hot Jupiters to O ₂ in exo-Earths

Abstract

Ground-based high-dispersion spectroscopy could reveal molecular oxygen as a biomarker gas in the atmospheres of twin-Earths transiting red dwarf stars within the next 25 years. The required contrasts are only a factor of 3 lower than that already achieved for carbon monoxide in hot Jupiter atmospheres today but will need much larger telescopes because the target stars will be orders of magnitude fainter. If extraterrestrial life is very common and can therefore be found on planets around the most nearby red dwarf stars, it may be detectable via transmission spectroscopy with the next-generation extremely large telescopes. However, it is likely that significantly more collecting area is required for this. This can be achieved through the development of low-cost flux collector technology, which combines a large collecting area with a low but sufficient image quality for high-dispersion spectroscopy of bright stars.

A review of exoplanetary biosignatures

“…The next generation of large ground-based telescopes such as the European Extremely Large Telescope (e.g. Snellen, [81]) will perform high resolution spectroscopy of Terrestrial exoplanets from the ground.…”

Laboratory spectra of hot molecules: Data needs for hot super-Earth exoplanets

“…Models suggest that magma-planet clouds and lower-atmospheres can be observed using secondary-eclipse spectroscopy [19] and that a photon-limited JWSTclass telescope should be able to detect SiO, Na and K in the atmosphere of 55 Cnc e with 10 hours of observations [61]. Furthermore, albedo measurements are possible at lower signal to noise; they may correspond to the albedo of clouds, or the albedo of the surface [74,75] High quality is also needed for complementary high-dispersion spectroscopic [15,17,76] (see Fig. 2, where the technique is illustrated using Doppler shifted TiO lines).…”

“…This is also true for retrievals of molecular abundances in exoplanets based on the use of transit spectroscopy which, thus far, has largely been performed using observations with fairly low resolving power (R < 3000) [11]. However, the situation is rather different with the high-dispersion spectroscopy developed by Snellen and co-workers [12,13,14,15,16], which is complementary to transit spectroscopy. This technique tracks the Doppler shifts of a large number of spectroscopic lines of a given species, by cross-correlating them to the reference lab data on the line positions.…”

ExoMol line lists – XXII. The rotation-vibration spectrum of silane up to 1200 K

“…Its quality (completeness and accuracy) should be sufficient, at least in principle, to detect silane in an atmosphere of a hot exoplanet from the transit spectroscopic observations, when combined with a proper atmospheric and radiative transfer models and providing that the abundance of SiH4 is sufficiently large to be detectable. However for high resolution detection techniques such as the highdispersion spectroscopy developed by Snellen (2014), our line positions might not be sufficiently accurate. This technique is based on the Doppler shifts of a large number of spectroscopic lines of a given species, which are cross-correlated to the reference lab data on the line positions.…”