The fluid stability of laser‐fusion targets is considered as a stability problem of a pseudo‐planetary atmosphere. Three atmospheric type modes are studied; acoustic, gravity, and Lamb modes. The changing character (i.e., growing, oscillatory, or growing‐oscillatory) of each is investigated as a function of the density‐gradient scale lengthHof the fluid. A growing class of modes is found which is distinct from the gravity (i.e., Taylor) mode if a gradient in entropy exists in the fluid. These modes are shown to be overstable Lamb modes. Also, the gravity mode is only stable for a distinct band of values ofH. These values, at which the density and Lamb modes change character, are derived from the dispersion relation for the modes. Finally, the consequences for laser targets are discussed.