(Proposal ID) S17B-120

(PI) Fukui, Akihiko

(Proposal Title)
Probing the Skies of the Potentially Habitable Planets

(Abstract)
Recently, the discovery of seven transiting Earth-sized planets (TRAPPIST-1b 
to h) around a nearby ultra-cool dwarf  was announced. Among them, at least 
three (TRAPPIST-1e, f, and g) are within the habitable zone, offering the 
first opportunity to probe the atmospheres of Earth-like planets in habitable 
zones. Although these planets should have strong XUV irradiation environments, 
they could still retain H_2-dominated atmospheres if they had accumulated 
substantial H/He gasses in their primordial atmospheres and they are relatively
young. In that case, we could detect rich atmospheric features even with 
current facilities. Here we propose to obtain optical-to-NIR transmission 
spectra of these three potentially habitable planets, TRAPPIST-1e, f, and g, 
by simultaneously using Gemini/GMOS-N for optical photometry and Subaru/MOIRCS 
or Keck/MOSFIRE for NIR spectro-photometry, in order to confirm if each of the 
planets has a clear H_2-dominated atmosphere or not. If any of the atmospheres 
are dominated by H_2, then this fact would provide valuable information about 
the formation, evolution, surface environments, and habitabilities of these 
planets. Even if we do not detect any spectral features, we could place 
meaningful constraints on their atmospheric natures.