Transmission spectroscopy of an Earth-like planet orbiting a white dwarf. Left: transit geometry for an Earth-radius exoplanet in the WD 1856+534 system (observer’s perspective). The WD (white disk), planet (dark gray disk), and planetary atmosphere (blue annulus) are to scale. This geometry has a fractional flux decrement during transit, or transit depth, of ∼50%. Right: corresponding model transmission spectrum and synthetic JWST observations. The high-resolution model (R =  50,000, blue) is binned to a low resolution (R = 100, red) for comparison with simulated JWST NIRSpec Prism observations.