Summary and perspectives

A summary is given of the field of 'planetary' atoms, which have at least two highly excited electrons. The hyperspherical adiabatic and molecular adiabatic approaches of the quantum mechanical three-body Coulomb problem are discussed which lead to the discovery of quasi-separability of the quantum mechanical three body system. For very high double excited systems a semiclassical quantization is presented based on a one-to-one correspondence with the classical motion. Finally, methods for production of planetary atoms by electron scattering or photoabsorption are discussed. 30 refs.; 1 table