A Marauder leaking cesium fuel as it approaches Moya
Cesium fuel is a green, phosphorescent fuel used in many Peacekeeper vessels, including Marauders. The Leviathan biomechanoid hybrid known as Talyn also used cesium fuel, due to the Peacekeeper technology bred into him.
Cesium fuel is derived from the metal cesium, an alkali metal, and is extremely flammable. Damaged vessels leaking cesium are especially at risk of being caught in an explosion, and sometimes it becomes necessary for vessel to vent cesium in order to prevent that risk.
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Cesium fuel is seen in Farscape.