Last week, after the Air Force shot down a Chinese surveillance balloon, examination of its wreckage revealed that it could not only take images, but also scoop up radio and cellphone communications. The balloon, the U.S. military said, was part of a bigger global program by China to collect information about military operations.Since then the U.S. has shot down three other objects from the skies over North America — apparently without knowing much about them.Guest: Julian E. Barnes, a national security reporter for The New York Times.Background reading: The U.S. and Canada are investigating three unidentified flying objects shot down over North America in recent days. Militaries have adjusted radars to try to spot more incursions.A timeline of the unidentified flying objects that have been brought down this month.Here is what we know about the objects and the Chinese spy balloon.For more information on today’s episode, visit nytimes.com/thedaily. Transcripts of each episode will be made available by the next workday.