Caloris latitude: 31.5°N; longitude: 162.7°E
The great Caloris impact basin, visible in this enhanced-color image as a large, circular, orange feature.
Tolstoj latitude: -16.28°N; longitude: 198.4°E
Tolstoj impact basin is approximately 350 km in diameter.
Rembrandt latitude: -43.32°N; longitude: 75.38°E
Rembrandt, the second largest basin on Mercury at 715 km (444 mi), is easy to spot with its light crater floor that contrasts with the surrounding darker material.
Impact basins are depressions in the surface of a planet caused by large, high-velocity asteroids or comets crashing into the planet. What distinguishes impact basins from impact craters is simply their size – impact basins are larger, and since they are larger, impact basins can often have multiple rings. On Mercury, there are 46 basins with a diameter greater than 300 km (186 mi). To put this in perspective, Earth has nearly seven times the surface area of Mercury, but is believed to have only two basins with the same enormity. To be fair, basins on Earth are subject to far more erosion and other forces due to global tectonics, so some have likely been erased over time. Many of Mercury’s basins have been subjected to volcanic lava flows and later impact events, so their features can be very subtle and can be difficult to see on a global mosaic. Caloris basin, in the left image, is one of the largest basins in the solar system with a diameter of 1525 km (948 mi) and is therefore very easy to spot on an image of Mercury!