Presentation #403.05 in the session Into the Unknown: Astrobiology and Habitability.
We present work on studying the atmospheric composition and detecting a potential biosignature, ammonia (NH3), in the nearby terrestrial-like planet LTT 1445 Ab. At a distance of 6.9 pc, this system is the second closest known transiting system and will be observed for transmission spectroscopy with the upcoming Twinkle mission. Twinkle is equipped with a 0.45m telescope, covers a spectral wavelength range of 0.5–4.5 microns simultaneously with a resolution between 50–70, and is designed to study exoplanet, bright stars, along with solar system objects. Twinkle is scheduled to launch in 2024, and will have a 7 year mission lifetime. We investigate and conclude that Twinkle data can distinguish between a Cold Haber World and a Hycean World with a H2O-H2-dominated atmosphere. We use petitRADTRANS and a Twinkle simulator to simulate observed transmission spectra for the more likely scenario of a Cold Haber World with a N2-H2-dominated atmosphere, for which NH3 is considered to be a biosignature. We study the detectability under different scenarios: varying hydrogen fraction, concentration of ammonia, and cloud coverage. Given the spectro-photometry uncertainty across the Twinkle wavelength range for 25 transits, and a volume mixing ration of 4.0 ppm of NH3, we find that transmission spectroscopy with Twinkle, would detect ammonia at a ~ 3 sigma level, for an optimal non-cloudy atmospheric conditions.