Masson Island or Mission Island is an ice-covered island about 27 kilometres (17 mi) long and rising to 465 metres (1,526 ft), lying 14 kilometres (9 mi) northwest of Henderson Island within the Shackleton Ice Shelf. Masson Island is located in the western part of Mawson Sea at (66°08′S96°35′E) and has an elevation of 465 metres (1,526 ft).