Direct Multipixel Imaging and Spectroscopy of an Exoplanet With A Solar Gravity Lens Mission

Direct multipixel imaging of exoplanets requires significant light amplification and very high angular resolution. With optical telescopes and interferometers, we face the sobering reality: i) to capture even a single-pixel image of an “Earth 2.0” at 30 parsec (pc), a \~90 kilometer (km) telescope aperture is needed (for the wavelength of λ = 1 µm); ii) interferometers with telescopes (\~30 m) and baselines (~1 km) will require integration times of ~105 years to achieve a signal-to-noise ratio, SNR=7 against the exozodiacal background. These scenarios involving the classical optical instruments are impractical, giving us no hope to spatially resolve and characterize exolife features.

To overcome these challenges, in our NIAC Phase II study we examined the solar gravitational lens (SGL) as the means to produce direct high-resolution, multipixel images of exoplanets. The SGL results from the diffraction of light by the solar gravitational field, which acts as a lens by focusing incident light at distances >548 AU behind the sun (Figure 1 in report). The properties of the SGL are remarkable: it offers maximum light amplification of ~1011 and angular resolution of ~10−10 arcsec, for λ = 1 µm. A probe with a 1-m telescope in the SGL focal region (SGLF), namely, in its strong interference region, can build an image of an exoplanet at 30 pc with 10-km scale resolution of its surface, which is not possible with any known classical optical instruments. This resolution is sufficient to observe seasonal changes, oceans, continents and surface topography.

We reached and exceeded all objectives set for our Phase II study: We developed a new wave-optical approach to study the imaging of exoplanets while treating them as extended, resolved, faint sources at large but finite distances. We designed coronagraph and spectrograph instruments needed to work with the SGL. We properly accounted for the solar corona brightness. We developed deconvolution algorithms and demonstrated the feasibility of high-quality image reconstruction. We identified the most effective observing scenarios and integration times.

As a result, we are now able to estimate the SNR for light from realistic sources in the presence of the solar corona. We have proven that multipixel imaging and spectroscopy of exoplanets up to 30 pc are feasible. By doing so, we were able to move the idea of applications of the SGL from a domain of theoretical physics to the practical mainstream of astronomy and astrophysics. Under a Phase II NIAC program, we confirmed the feasibility of the SGL-based technique for direct imaging and spectroscopy of an exoplanet, yielding technology readiness level (TRL) of TRL 3.