• In our interview with NASA chief scientist Ellen Stofan (10 January, p 26), we printed a rough estimate of the distance travelled on Mars by the Opportunity rover. The latest figure from NASA is 41.8 kilometres, double the distance stated.
• We understated the nitrogen content of Earth’s atmosphere by a fair margin (24 January, p 13). It does of course account for 78 per cent by volume of dry air.
