Direct High-Resolution Imaging of Earth-Like Exoplanets

TL;DR

This paper evaluates various methods for high-resolution imaging of Earth-like exoplanets, concluding that the Solar Gravitational Lens is uniquely capable of achieving true resolved imaging with current or near-future technology.

Contribution

It provides a comprehensive analysis of existing and proposed imaging techniques, highlighting the limitations and proposing the Solar Gravitational Lens as the most feasible solution for resolved exoplanet imaging.

Findings

Most conventional methods are far from achieving the necessary resolution and photon budget.

Technological and fundamental barriers prevent current methods from mapping Earth analogs.

The Solar Gravitational Lens can potentially provide the required resolution and photon collection for resolved imaging.

Abstract

We have surveyed all conventional methods proposed or conceivable for obtaining resolved images of an Earth-like exoplanet. Generating a 10 x 10 pixel map of a 1 R_E world at 10 pc demands ~0.85 uas 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 telescopes 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); (7) diffraction occultation by Solar System bodies. Even though these approaches serve their primary goals -- exoplanet discovery and initial coarse 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 angular-resolution and photon-budget thresholds 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 ~1e10 and inherent uas-scale focusing once an imaging spacecraft reaches heliocentric distances beyond >= 550 AU -- is uniquely capable of simultaneously meeting both the resolution and photon-budget requirements. Once mission-specific risks (coronal calibration, focal-plane scanning, deconvolution) are retired, the SGL enables true, resolved surface images and spatially resolved spectroscopy of Earth-like exoplanets in our stellar neighborhood.