United States President Joe Biden says the three mysterious objects shot down by US fighter jets over North America do not appear to have been used for spying.
They are also likely not linked to China's spy balloon program — but there are limited theories as to what they actually were.
Here's what we know.
What does the United States think the objects were?
Recovery efforts are still underway, but US officials have so far labelled the three objects as likely "benign" and "not nefarious".
Mr Biden said on Wednesday local time: “We don’t yet know exactly what these three objects were, but nothing right now suggests they were related to China’s spy balloon program or that they were surveillance vehicles from any other country.
"The intelligence community’s current assessment is that these three objects were most likely balloons tied to private companies, recreation or research organisations studying weather or conducting other scientific research.
“When I came into office, I instructed our intelligence community to take a broad look at the phenomenon of unidentified aerial objects.
"We know that a range of entities including countries, companies and research organisations operate objects at altitudes for purposes that are not nefarious, including legitimate scientific research."
White House national security spokesperson John Kirby said earlier this week that the leading theory is the balloons are tied to a "commercial or benign" purpose.
What other theories are there for the mystery objects?
Scientists and atmospheric experts have suggested everything from civilian drones, weather balloons and non-military aerial gadgets.
The US National Weather Service launches weather balloons at about 90 different locations across the country every single day. The balloons study wind patterns, air quality and more, and can travel hundreds of kilometres.
Michigan Technological University's atmospheric physicist Raymond Shaw said for scientists, balloons are "a nice way to make atmospheric measurements without spending a bunch of money.
"Worldwide, there are hundreds, probably close to 1,000 balloons launched every day for meteorological observations for countries all over the world."
The object downed over Alaska was described as being the size of a small car — the same size as some large consumer or commercial drones, even though these are banned from flying higher than 121 metres.
Research drones are also sometimes used instead of satellites in Arctic regions close to where these objects were shot down.
Why were 'benign' flying objects picked up on military radars?
The United States upgraded its radar capabilities recently.
This means "slow-moving" objects that would otherwise have gone unnoticed are now being picked up on the radar and flagged. Officials say there is no evidence of any sudden increase in unidentified objects.
Mr Biden said on Wednesday there would be "sharper rules" to deal with objects moving forward.
"[This includes] distinguishing between those that are likely to pose safety and security risks that necessitate action and those that do not," he said.
United States senators have also called for transmitting devices to be mandated on weather and research balloons.
Arizona Democrat Mark Kelly said: "If we require transponders on them we would make the military's life a lot easier — we don't want to be firing AIM-9X [missiles] at a NASA weather balloon."
Could aliens be to blame?
There is no evidence any extra-terrestrials were involved.
But conspiracy theories continue to run rampant across social media, with posts about aliens increasing by almost 300 per cent since the first balloon was downed, according to a San Francisco media intelligence group.
"I don't think the American people need to worry about aliens with respect to these crafts, period," Mr Kirby said earlier this week.
ABC/Reuters
