Global images of Earth's ultraviolet dayglow as gained with an imaging photometer on board Dynamics Explorer 1 exhibit transient decreases, or atmospheric holes, in the dayglow intensities over areas with diameters ∼50 km. Features of these atmospheric holes include (1) preferential motion in the east‐to‐west direction across the sunlit face of Earth, (2) similar diurnal variations in occurrence rates as those for radar meteors, (3) correlation of the occurrence rates with the nonshower rates as determined with forward scatter radar, and (4) larger angular diameters for these atmospheric holes when the spacecraft approaches Earth during its perigee passes. A significantly less extensive series of images of Earth's ultraviolet dayglow with the Viking spacecraft also provides evidence of these atmospheric holes. The atmospheric holes are interpreted in terms of obscuration of the dayglow by water clouds from the disruption and subsequent vaporization of small comets at low altitudes above the atmosphere. Supporting evidences for the existence of these small comets are given by telescopic sighting of these objects at greater altitudes before disruption and the detection of water bursts in Earth's upper atmosphere. We summarize the current status of this small‐comet hypothesis and its relationship to conventional wisdom concerning geophysical, lunar, and interplanetary ph