Not Everything is a Spy Balloon or UFO. Here’s What Else Is Flying in Our Skies

Ever since Feb. 4, when the U.S. shot down a Chinese spy balloon off the coast of South Carolina, the military has been in something like skeet-shooting mode, blasting three more unidentified aerial objects out of the sky on Friday, Saturday, and Sunday (Feb. 10, 11, and 12). The first of the three, spotted by North American Aerospace Defense Command (NORAD) radar over the northern coast of Alaska was described by fighter pilots as a metallic, cylindrical airship; it was flying at about 40,000 ft.—low enough to menace civilian aircraft. How it stayed aloft was not clear.

“It could be a gaseous type of balloon inside a structure or it could be some kind of propulsion system,” said NORAD commander Gen. Glen VanHerck in a Sunday night news conference, reported by CNN.

The object shot down Saturday, also flying at 40,000 ft. over Canada’s Yukon territory, was a more traditional balloon with a metal payload hanging from it. Sunday’s object, flying at 20,000 ft. and shot down over Lake Huron, was the most mysterious of all, described as octagonal in shape with strings or cables hanging from it. Its means of staying aloft was unclear.

Either way, the shootdowns were both preemptive and unprecedented. “I believe this is the first time within the United States or American airspace that NORAD or United States Northern Command has taken kinetic action against an airborne object,” said VanHerck.

They also raised troubling questions about just how much hardware is flying around up there, what its origins are, and what its intent—hostile and military or scientific and benign—might be. Just how do we distinguish aerial friend from aerial foe, and have we entered a new phase of shooting first at whatever casts a radar shadow and asking questions later about what exactly we destroyed?

One concern that can be dispelled is that the recent flock of flying objects indicates that the U.S. is under a sudden assault from unknown sources. The fact is, objects like the three shot down over the weekend have been there all along. As the Airforce Technology website explains and as National Security Council spokesman John Kirby explained at a Monday, Feb. 13 briefing, in the wake of the Chinese balloon incursion, NORAD expanded the aperture of its radar coverage, looking not just for high-altitude, high-speed ordnance like missiles or fighter jets, but lower, slower moving objects like balloons and other less hostile aircraft. It was this sensitizing of the system—not the arrival of new invasive objects—that resulted in the recent detections.

“In light of the Chinese balloon program and this recent incursion into our airspace,” Kirby said, “the United States and Canada, through NORAD, have been more closely scrutinizing [North American] airspace, including enhancing our radar capabilities, which . . . may at least partly explain the increase in the objects that have been detected.”

The most common objects likely to set off NORAD’s new, lower-threshold tripwire are weather balloons—and there are a lot of them out there. The National Oceanic and Atmospheric Administration (NOAA) operates 92 weather balloon sites across North America and the Pacific Islands—69 of which are in the mainland U.S. and 13 of which are in Alaska. Each site launches an average of two balloons a day, one in the morning and one in the early evening.

“Sometimes they’ll launch them even more frequently if there is dynamic or severe weather,” says Marshall Shepherd, director of the atmospheric sciences program at the University of Georgia and past president of the American Meteorological Society. “Weather agencies around the globe do this as well because we need that information to feed our weather models.”

Weather balloons, unlike the Chinese spy balloons, do not have the ability to maneuver. “While they can drift as far as 180 miles, they typically travel only 30 to 35 miles downwind from their launch site,” said NOAA spokesperson Susan Buchanan in an email to TIME. “They do not hover over a location for an extended time.”

Weather balloons typically operate in the troposphere, which extends from 4 to 12 miles up; NASA operates its own balloons to study higher regions of the atmosphere and to test payloads in a near-space environment. Those objects ascend into the stratosphere, which reaches roughly 30 miles above the surface of the Earth.

“NASA often refers to these as suborbital platforms,” says Shepherd. “There are a host of suborbital platforms used in atmospheric research these days.”

NASA’s suborbital assets are not limited to balloons. The space agency also operates a fleet of drone-type aircraft that reach altitudes of 18 miles and are used for a range of purposes, including agricultural monitoring, telecommunications relays, Earth science studies, and tracking of severe storms.

All of NASA’s atmospheric assets could easily be detected by NORAD’s radar system, though none were among the recently sighted objects.

The private sector too might be contributing to the atmospheric traffic, though at Kirby’s Feb. 13 briefing he admitted that the government is only now beginning to look into that possibility—particularly whether commercial providers may be flying tests of broadband or Wi-Fi platforms. “I don’t know of any conversations right now,” he said, but added: “We know that a range of entities—including countries, companies, research, and academic organizations—operate objects at these altitudes for purposes that are not nefarious at all, including scientific research.” Kirby stressed that the three objects did not appear to be linked to China and could be “tied to some commercial or benign purpose.”

Then too there is always the possibility that some of the shootdowns are—or could be in the future—friendly fire incidents, with the U.S. military blasting its own assets out of the sky, according to Mark Baldwin, professor of climate sciences at the University of Exeter. “The U.S. likely has a spy balloon program similar to China,” he said in an email to TIME. “If so, the balloons will circle the globe many times—so that an individual U.S. balloon could be over the U.S. So if they shoot it down, they have to cover up the fact that it is a U.S. spy balloon.”

Nothing in the current circumstances indicates anything quite so cynical, though nothing in the current circumstances has any precedent either, so all explanations for what is causing all the air traffic are at least being considered—except for one: extraterrestrials.

“I just wanted to make sure we address this,” said White House press secretary Karine Jean-Pierre at Monday’s briefing. “I know there have been questions and concerns about this, but there is no—again, no—indication of aliens or extraterrestrial activity with these recent takedowns.”

Added Kirby straightforwardly: “I don’t think the American people need to worry about aliens, with respect to these craft. Period. I don’t think there’s any more that needs to be said there.”

Plenty more, however, will indeed be said concerning what the craft are—if not what they aren’t. For now, the origin of all but the Chinese spy balloon remains unknown. Questions will continue to be raised until the government, at last, provides some answers.