Vincent B. Wickwar
Lidar observations on the night of 19-20 February 2004 at Logan, Utah (41.74 N, 111.81 W) revealed a strange thin layer which descended from roughly 55 km to 30 km over seven hours. Approximations are made for the dimensions and descent rate of the layer. Although the particle radius and density are unknown, a range can be determined from the descent rate and reference to the sizes of known particles. Several possible sources for the layer are explored, concluding that an object entering the Earth’s atmosphere was the most probable cause.
Bentley, Houston D. "Investigation of an Unusual Thin Layer Descending Through the Upper Stratosphere." 2018, pp. 1-8.