http://arxiv.org/abs/2209.12919
We explore the prospects for Twinkle to determine the atmospheric composition of the nearby terrestrial-like planet LTT 1445 Ab, including the possibility of detecting the potential biosignature ammonia (NH${3}$). At a distance of 6.9 pc, this system is the second closest known transiting system and will be observed through transmission spectroscopy with the upcoming Twinkle mission. Twinkle is equipped with a 0.45 m telescope, covers a spectral wavelength range of 0.5 – 4.5 $\mu$m simultaneously with a resolving power between 50 – 70, and is designed to study exoplanets, bright stars, and solar system objects. We investigate the mission’s potential to study LTT 1445 Ab and find that Twinkle data can distinguish between a cold Haber World (N$_2$-H$_2$-dominated atmosphere) and a Hycean World with a H$_2$O-H$_2$-dominated atmosphere, with a $\chi{\nu}^{2}$ = 3.01. Interior composition analysis favors a Haber World scenario for LTT 1445 Ab, which suggests that the planet probably lacks a substantial water layer. We use petitRADTRANS and a Twinkle simulator to simulate transmission spectra for the more likely scenario of a cold Haber World for which NH${3}$ is considered to be a biosignature. We study the detectability under different scenarios: varying hydrogen fraction, concentration of ammonia, and cloud coverage. We find that ammonia can be detected at a $\sim$ 3$\sigma$ level for optimal (non-cloudy) conditions with 25 transits and a volume mixing ration of 4.0 ppm of NH${3}$. We provide examples of retrieval analysis to constrain potential NH${3}$ and H${2}$O in the atmosphere. Our study illustrates the potential of Twinkle to characterize atmospheres of potentially habitable exoplanets.
C. Phillips, J. Wang, B. Edwards, et. al.
Wed, 28 Sep 22
12/89
Comments: (13 pages, submitted to MNRAS)
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