The mysterious substance “containing a very small amount of enriched uranium” was found at an altitude of 7km (4.3 miles) above Alaska’s Aleutian Islands, according to a report issued by the Journal of Environmental Radioactivity.
It is the first time the group of US scientists has detected enriched uranium-235 in their 20-year study. They were making no special attempt to sample radioactive material, when they came across it during a routine flight to check atmospheric conditions in August 2016.
The scientists are now struggling to find the prime source of the unusual finding and how it got there. The study only vaguely suggests that “the particle could have originated from a variety of areas across Asia” without elaborating. However, it is clear that the particle is “definitely not from a natural source,” according to one of the authors, Dan Murphy, cited by Gizmondo.