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We explore the prospects for Twinkle to determine the atmospheric compositionof the nearby terrestrial-like planet LTT 1445 Ab, including the possibility ofdetecting the potential biosignature ammonia (NH$_{3}$). At a distance of 6.9pc, this system is the second closest known transiting system and will beobserved through transmission spectroscopy with the upcoming Twinkle mission.Twinkle is equipped with a 0.45 m telescope, covers a spectral wavelength rangeof 0.5 - 4.5 $\mu$m simultaneously with a resolving power between 50 - 70, andis designed to study exoplanets, bright stars, and solar system objects. Weinvestigate the mission's potential to study LTT 1445 Ab and find that Twinkledata can distinguish between a cold Haber World (N$_2$-H$_2$-dominatedatmosphere) 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 Worldscenario for LTT 1445 Ab, which suggests that the planet probably lacks asubstantial water layer. We use petitRADTRANS and a Twinkle simulator tosimulate transmission spectra for the more likely scenario of a cold HaberWorld for which NH$_{3}$ is considered to be a biosignature. We study thedetectability under different scenarios: varying hydrogen fraction,concentration of ammonia, and cloud coverage. We find that ammonia can bedetected at a $\sim$ 3$\sigma$ level for optimal (non-cloudy) conditions with25 transits and a volume mixing ration of 4.0 ppm of NH$_{3}$. We provideexamples of retrieval analysis to constrain potential NH$_{3}$ and H$_{2}$O inthe atmosphere. Our study illustrates the potential of Twinkle to characterizeatmospheres of potentially habitable exoplanets.

Is LTT 1445 Ab a Hycean World or a cold Haber World? Exploring the Potential of Twinkle to Unveil Its Nature