Deep under the Paciﬁc Ocean in the Marianas Trench lies the Challenger Deep -- the deepest place on earth. Despite immense pressure, frigid water and near darkness, this unimaginably hostile environment holds diverse life forms. Manned exploration poses challenges similar to those of space exploration. Challenger Deep impressionistically depicts the deep ocean's remarkable, wonderful, bizarre, magniﬁcent environment and its rarely-witnessed life forms. The score features unusual harmonies employing the deepest sonorities of the contrabass and cello sections. The upper strings' moving lines depict darting sea creatures and objects slowly dropping for miles underwater. Several musical devices convey the idea of enormous depth, including chromatic passages with lowered notes and themes that gradually transpose lower and lower.