A rare Mars meteorite, discovered two years ago in Niger, sold for $4.3 million at Sotheby's in New York, sparking anger and an investigation from the Nigerien government which questions the legality of its export.

• The 24.7kg meteorite, scientifically named NWA 16788, is the largest ever found from Mars.
• Prof Paul Sereno, a palaeontologist, and Niger Heritage founder, asserts that Nigerien law was broken and the meteorite should be returned to Niger.
• Sotheby's maintains that all correct procedures were followed for its export, but Niger has launched an investigation into the sale and origin of the meteorite.