Here's why mysterious flying objects are suddenly popping up all over the place, according to the military command that's been shooting them down

• Four suspicious flying objects have been shot down over North American skies in recent days.
• The commander of NORAD and NORTHCOM explained why more of these objects seem to suddenly be popping up.
• NORAD changed its radar filters to help spot smaller, slower objects after a Chinese spy balloon drifted over the US.

A US Air Force general overseeing a bilateral command tasked with defending US and Canadian airspace explained that there's a reason mysterious flying objects seem to suddenly be popping up all over the place. The command has changed the way it looks for them and is now finding more of these objects.

Four objects, one Chinese surveillance balloon and three other smaller objects, were shot down in the span of about a week, and the North American military command that's been involved in shooting down these objects flying over the US and Canada revealed in a briefing Sunday that the uptick in discovery and engagement follows a tweak of its radar filters after the Chinese spy balloon drifted across the continental US earlier this month.

Gen. Glen VanHerck, the commander of North American Aerospace Defense Command and US Northern Command, said that NORAD started searching for much smaller, slower-moving flying objects, while also making adjustments to filtration based on altitude. Typically, NORAD's radar detection is searching for fighter jets or bombers, which move at high speeds.

"What we're seeing is very, very small objects that produce a very, very low radar cross-section," VanHerck said. "These are very, very slow objects in the space, if you will, going at the speed of the wind essentially."

VanHerck said he believes the increased ability to detect these objects can be attributed to the radar adjustments and that operators are on "heightened alert" and looking more closely for these smaller and slower objects. Since the US Air Force shot down the Chinese balloon in early February, fighter jets have downed three additional airborne objects.

An F-22 Raptor, a stealth fifth-generation fighter jet, fired a single AIM-9X Sidewinder air-to-air missile to down the Chinese surveillance balloon off the coast of South Carolina on February 4, sending the large system plummeting over 60,000 feet into the Atlantic Ocean. 

Just days later, on February 10, an F-22 used an AIM-9X to down an unidentified object over Alaska. US officials said this object was flying at an altitude of 40,000 feet and posed a threat to civilian aircraft. On February 11, the next day, an F-22 fired an AIM-9X to take down an object over northern Canada. 

The F-22, which notched its first three air-to-air kills after nearly two decades in service, was finally given a rest on Sunday, when an F-16 — still using the AIM-9X — took down an object over Lake Huron that was flying at a low altitude of 20,000 feet, well below the cruising altitude of many commercial airliners. 

While the US identified the first object as a high-altitude Chinese surveillance balloon, North American militaries have yet to explain publically what the other objects are — aside from offering a few details about size and shape — and what purpose they serve. 

Melissa Dalton, the assistant secretary of defense for homeland defense and hemispheric affairs, said on Sunday that although the US has not been able to identify what these recent objects were from over the weekend, the decision to shoot them down was still made out of an "abundance of caution to protect our security and interests." 

She added that the recent objects did not pose a "kinetic military threat," but they were traveling in proximity to "sensitive" US military sites and that their relatively low altitude could possibly threaten civilian aircraft. 

"We have been more closely scrutinizing our air space at these altitudes, including enhancing our radar, which may at least partly explain the increase in objects that we've detected over the past week," Dalton noted. "We also know that a range of entities, including countries, companies, research organizations operate objects at these altitudes for purposes that are not nefarious, including legitimate research." 

As recovery teams work to collect debris from the downed objects, it's not immediately clear where they all came from. Pentagon Press Secretary Brig. Gen. Pat Ryder told reporters at a briefing last week that China operates a global network of surveillance balloons that extends across five continents and multiple regions, but it is unclear if the objects that were downed in the wake of the Chinese spy balloon were also of Chinese origin.