Resolved images of an unknown sector on the surface of Mercury

We took electronic photographs of Mercury on the side of the planet that was not photographed from the Mariner-10 spacecraft in 1973–1975 by the millisecond-exposure method in ground-based observations. Based on these photographs, we synthesized resolved images of the surface of unknown regions of the planet. The capabilities of the method are limited by the small angular size of the planetary disk (only 7.3 arcsec at average quadrature), specific difficulties of Mercury’s ground-based observations, their very limited duration, and the laboriousness of the subsequent computer-aided observational data processing. The millisecond-exposure method is complex, but a sufficient number of primary electronic photographs can be taken under good seeing conditions for the subsequent synthesis of Mercurian images with a resolution of no worse than the diffraction limit. A giant basin about 2000 km in diameter and other large structures are distinguished in the synthesized images of the planet. In the regions where radar data are available, these structures can be identified with previously found ones. In some measure, the synthesized images allow the relief of the longitude sector 210°–290° W to be reconstructed on Mercury. It can be asserted with caution that the large relief features are distributed asymmetrically over the surface of Mercury, much as observed on other terrestrial planets, the Moon, and many satellites of giant planets.