WASHINGTON — Days after a Chinese spy balloon was shot down by the U.S. military off the coast of South Carolina, AI startup Synthetaic backtracked the balloon’s trajectory across the continental United States using Earth imaging data from Planet Labs satellites. Synthetaic founder Corey Jaskolski said this is a novel way to use commercial satellite imagery to track aerial vehicles that might not be seen by radar or by ground observers. It’s also another way to exploit open-source data to independently confirm where the Chinese balloon or other objects came from, he said. “The map we put together overlays our...