Why do unidentified objects seem to be popping up above North America all of a sudden?

Theappearance of a series of unidentified objects in the sky over a week that were subsequently shot down has prompted questions about why there seems to be asudden rash of such incidents. Since Feb. 4, when U.S. military personnel shot down what is believed to be a Chinese spy balloon off the coast of South Carolina, there have been three other objects shot from the sky over an eight-day period.

So far, only the first object shot down has been identified as aChinese spy balloon.The U.S. military said on Monday it had recovered key sensorsfrom the wreckage.

The otherobjects according toJohn Kirby, the U.S. National Security Council co-ordinator for strategic communications, didn't have propulsion and they weren't being manoeuvred.The U.S. therefore isn't sure if "they had a surveillance aspect to them," he said.

However, Prime Minister Justin Trudeau saidthere's reason to believe it's not a coincidencethat the four objects have been spottedover such a short time period.

"Obviously, there is some sort of pattern in there," he said. "The fact we are seeing this in significantdegree over the past week is a cause for interest and close attention, whichis exactly what we're doing."

CBC Explains ifmore objects are popping up in theNorth American skies, why they have been difficult to detect and what's being done to more easily discover them:

Are more unidentified objectspopping up in the sky over the U.S. and Canada lately?

It's difficult to say whether there are more unidentified objects hovering over the U.S. and Canada than in the past.

Thomas Lawson, former chief of defence staffwho also served as deputy commander of NORAD from 2011 to 2012, told CBC News Networkthat during his time at NORAD, he had "no indication that anything like this was floating all over continental North America."

"I thought it was remarkable that the current commander of NORADhad released his assessment that several of these [unidentified objects]over recent years have now been determined to have flown over continental North America," he said.

But, as noted byKirby, for many years, therehave been "unidentified aerial phenomena" thathave been reported without explanation or deep examination by previous governments.

"We are finally trying to understand them better now in light of the Chinese balloon program and this recent incursion into our airspace," he said in a news conference on Monday.

The White House has acknowledged that there were at least three incidents where balloons flew over U.S. territory during the Trump administration, and one incident during the Biden presidency, before the past week'sdiscoveries.

"This is what we assess as part of a larger Chinese surveillance balloon program,"Brig-Gen. Patrick S. Ryder, the Pentagon spokesperson, said in a news conference last week. "What we do know is that in some cases, whereas some of these balloons previously had not been identified, subsequent analysis, subsequent intelligence analysis did enable us to indicate that these were Chinese balloons."

Why do officials seem to be discovering more unidentified objects than in the past?

Since the U.S. shot down asuspected spy balloon from China on Feb. 4,therehas been closer scrutiny of the air space,Melissa Dalton,assistant secretary of defence for homeland defence and hemispheric affairs, said in a news conference last week.

WATCH: 'Obviously there is some sort of pattern': Trudeau

Obviously there is some sort of pattern,' Trudeau says of recent flying objects

2 years ago

Duration 0:32

Prime Minister Justin Trudeau says the objects that have been shot down over Alaska, Yukon and Lake Huron are 'a cause of interest and close attention.'

That has included enhancing the radar of the North American Aerospace Defense Command (NORAD)which, Dalton said,may at least partly explain the increase in objects that they've detected.

"One of the reasons that we think we're seeing more is because we're looking for more," Kirby said. "If you set the parameters in such a wayto look for something, it's more likely that you're going to find a certain something."

Riki M. Ellison, chairman andfounder of Missile Defense Advocacy Alliance, said he believes past administrations "tolerated" these objects flying in their airspace.

"Last week, they decided not to tolerate it anymore," he told CBC News in a phone interview.

Why has it been difficult to detect these objects?

For those tasked to look at radar screens, it can be "very overwhelming with all of the radar data coming at them," retiredmajor general Scott Clancy, who at one point served as deputy commander of the Alaskan NORAD Region, told CBC News Network.

"When yourprincipal threat are aircraft that are travelling at hundreds of miles an hour, you set the gain or filter to a level so that you're focused on those threats," he said.

And with so many gaps in the radar system over Alaska and without proper sensors to detect objects likespy balloons, it's like chasing "that needle in the haystack," Ellison said.

That's because slow-moving objects, such as balloons,at high altitudeare difficult to detect on radar, Kirby said.

"Even objects the size of the Chinese spy balloon had apayload the size of roughly three school buses were not picked up by previous administrations or other countries," he said.

Another issue is the temperature of the balloon itself. Slow-moving balloons don't give off heat that canbe detected at long-ranges, Ian Williams, deputy director of CSIS's Missile Defense Project, told Time magazine.

"They are not warm, typically. They kind of assume the temperature of the surrounding air for the most part; they don't have an engine burning or anything like that," he said.

What has NORAD done to locate more unidentified objects?

Gen. Glen VanHerck, commander of NORAD, said radar can be set to filter out "low-speed clutter" and latitude, but that has since been adjusted to "give us better fidelity on seeing smaller objects."

"So, with some adjustments, we've been able to get a bettercategorization of radar tracks now," he said."And that's why I think you're seeing these overall.Plus, there's a heightened alert to look for this information," he told reporters during a briefing at the Pentagon last week.

Ellison said that once they shot down the first object, that set a precedent which allowed NORAD to better calibrate theirsensors to start looking for patterns, and to look for a specific type of object.

"I think we've understood what the pattern is now, wherethesethings are going andwhat they're targeting," he said."That's why you're seeing more objects being taken down."