Table 2.

Transit vs. Phase Curve Observations of GJ 1132b with JWST

Method	Observation Time	Signal (ppm)	Noise (ppm)	S/N
Single transita	one transitb = 90 minutes	19.9	19.7	1
Stacked   transitsa	13 transits = 19.5 hr	19.9	5.5	4
Thermal phase   curvec	one half-orbit = 19.5 hr	373	84	4

Notes. Transit spectroscopy and thermal phase curve measurements of a planet like GJ 1132b will require similar amounts of JWST observation time. The shown signal-to-noise ratios (S/N) are estimates for the most basic observational goals: detecting molecular features in low-resolution near-IR transit spectra, and detecting the day–night thermal emission contrast of a bare rock in the mid-IR. We compute signals following Cowan et al. (2015) and Koll & Abbot (2015). We estimate noise assuming photon-limited precision, but include imperfect instrument throughput for MIRI (see Section 8).

^a1–4 μm, NIRSpec, R ~ 25, CO₂-dominated atmosphere.

^bWe assume a measurement lasts 45 minutes in-transit, plus 45 minutes out-of-transit baseline.

^c16.5–19.5 μm, MIRI, broadband.