Direct High-Resolution Imaging of Earth-Like Exoplanets

We have surveyed all conventional methods proposed or conceivable for obtaining resolved images of an Earth-like exoplanet. Generating a 10 × 10 pixel map of a 1 R⊕ world at 10 pc demands ≈ 0.85 µas angular resolution and photon-collection sufficient for SNR 5 per “micro-pixel.” We derived diffraction-limit and photon-budget requirements for: (1) large single-aperture space tele- scopes with internal coronagraphs; (2) external-starshades; (3) space-based interferometry (nulling and non-nulling); (4) ground-based ELTs with extreme AO; (5) pupil-densified “hypertelescopes”; (6) indirect reconstructions (rotational light-curve inversion, eclipse mapping, intensity interferometry); and (7) diffraction-occultation by Solar System bodies. Even though these approaches serve their primary goals—exoplanet discovery and initial corse characterization—each remains orders of magnitude away from delivering a spatially resolved image. In every case, technology readiness falls short, and fundamental barriers leave them 2–5 orders of magnitude below the astrometric resolution and photon-budget thresholds needed to map an Earth analog even on decadal timescales. Ultimately, an in situ platform delivered to 0.1 AU of the target could, in principle, overcome both diffraction and photon-starvation limits—but such a mission far exceeds current propulsion, autonomy, and communications capabilities. By contrast, the Solar Gravitational Lens—providing on-axis gain of ∼10^10 and inherent µas-scale focusing once a spacecraft reaches 550 AU—remains the only near-term, scientifically and technologically viable means to acquire true, resolved surface images and spatially resolved spectroscopy of Earth-like exoplanets in our stellar neighborhood.