What looked like a fireball streaked across the Texas sky on Sunday morning, leading many people to call authorities to report seeing falling debris.
"We don't know what it was," said Federal Aviation Administration spokesman Roland Herwig.
The Williamson County Sheriff's Office used a helicopter to search after callers said they thought they saw a plane crashing, a spokesman said.
"We don't doubt what people saw" but authorities found nothing, said spokesman John Foster.
The US Strategic Command said there was no connection to the sightings over Texas and Tuesday's collision of satellites from the US and Russia.
"There is no correlation between the debris from that collision and those reports of re-entry," said Maj. Regina Winchester, with STRATCOM.
The FAA notified pilots on Saturday to be aware of possible space debris after a collision Tuesday between U.S. and Russian communication satellites. The chief of Russia's Mission Control says clouds of debris from the collision will circle Earth for thousands of years and threaten numerous satellites.