The status of observations and current theories of spacecraft-induced optical emission (ram glow) from the Atmospheric Explorer-C satellite to the most recent shuttle missions is reviewed. To resolve the discrepancy between the observed spectral continuum and the most likely gas-phase emitter, the NO2 continuum, a second continuum is proposed, lying further to the red and due to true surface emission (chemiluminescence) as a consequence of atomic and molecular oxygen adsorption. An altitude variation modelled on the basis of this mechanism, using laboratory data, offers good agreement with observations by the AE-E satellite, and is capable of producing the quantitative intensities in general.