Bombardment of Venus with refined magnesium and calcium from off-world could also sequester carbon dioxide in the form of calcium and magnesium carbonates. About 8 kg of calcium or 5 kg of magnesium would be required to convert all the carbon dioxide in the atmosphere, which would entail a great deal of mining and mineral refining (perhaps on Mercury which is notably mineral rich). 8 kg is a few times the mass of the asteroid 4 Vesta (more than in diameter).