Mystery still surrounds the latest flying objects shot down by the US over northern Alaska, Canada’s central Yukon territory and Lake Huron in Michigan in the last week.
Unlike the suspected Chinese surveillance balloon that was shot down off the coast of South Carolina on 4 February, US authorities have been mostly unwilling to speculate on where the last three objects originate from – or even to characterise what they are.
However, according to CBS’s veteran national security correspondent, David Martin, officials have apparently not ruled out whether at least some of the unidentified aerial objects were so-called “sky trash”.
What is sky trash?
Sky trash – much like space trash – encompasses a variety of objects within the stratosphere, anywhere from 8km to 40km above our heads.
“All kinds of stuff has been launched over the years. Normally it falls to Earth but some accumulates,” says Jonathan McDowell, an astronomer at Harvard-Smithsonian Center for Astrophysics.
These objects – predominantly balloons – are used to monitor the weather, conduct scientific research that can’t be done on the ground or to check things on Earth that can’t be seen by a satellite.
“The simple fact is they’re cheaper to fly than a satellite, you can put up many more … and resolution can be better because they’re closer to Earth,” says Brad Tucker, an astrophysicist and an astronomer at the Australian National University.
These balloons are launched by governments all over the world, as well as by scientific research groups and private companies.
How much is up there?
“I think there’s a lot up there,” says Tucker. “It could be anything purposefully put up: balloons to high-altitude drones. Or rubbish trapped in currents, like plastic bags and party balloons.”
To take just one example: every day 1,800 weather balloons are launched worldwide, according to the US National Weather Service, 92 of which are in the US alone. Each one carries an instrument to measure pressure, temperature and relative humidity. Of the tens of thousands launched every year, only 20% of these instruments are ever recovered.
Private companies are also responsible for launching thousands of balloons into space. Until 2021, Google launched hundreds of self-navigating balloons the size of tennis courts into the sky to beam internet to rural and remote areas.
The company behind the project, Loon, had some successes: in 2017 the balloons were used to deliver internet to 100,000 people in Puerto Rico in the weeks after a natural disaster. But there were also a number of incidents of Loon balloons blowing off course and crashing down on to farms or power lines.
Loon balloons over Puerto Rico supplementing wireless coverage on the island.
— Flightradar24 (@flightradar24) January 22, 2018
Read more about Project Loon and how to track them at https://t.co/npC7OtbfvT pic.twitter.com/fP5oE4UgN2
Balloons are in fact such a ubiquitous presence in the stratosphere that there is an icon to monitor them on the Flight Radar website used to track aircraft.
“Most come down,” says McDowell. Those that do blow off course, “you’d expect them to lose pressure, leak a bit. Like with a party balloon, after a couple of months it’s not going to be well inflated.”
Can anyone send balloons up into the sky?
In the US you need to comply with Federal Aviation Administration (FAA) regulations.
“You need transponders so planes know where you are. You need to provide a flight path. You’re in contact with regional airlines and you’re monitoring airspace,” Tucker says.
With a potential risk to planes, experts say the practice is well regulated, which is what makes these most recent examples so unusual.
Flying at above 20km, the Chinese balloon was close in altitude to most scientific and weather balloons, according to McDowell. “Airlines fly at 10km-12km, so they are well below where that was.”
But the more recent objects – shot down over the past week – have been lower.
“They were at a lot lower altitude of about 15km,” says Brad Tucker. “So at 15km you’re getting a bit too close.”
Tucker says the last three objects could have been old balloons that someone lost control of, experimental balloons or something more pernicious.
Every country abides by International Air Transport Association (IATA) standards, including for balloons. These standards cover everything from launch conditions to the altitude at which they’re allowed to fly.
“Either these weren’t meeting those standards because they were allowed to, or they were working outside normal protocol,” says Tucker.
Why are we only talking about it now?
The sudden flurry of objects is at least partly explained by heightened vigilance. Since the discovery of the giant balloon, the Pentagon has scrutinised high altitudes more and radar system have been made more sensitive.
“In the past, the US just hasn’t paid much attention to those balloons, but this Chinese balloon was a gamechanger. And now, certainly, the Biden administration does not feel it can simply let these other objects pass through American airspace,” David Martin said on CBS’s Face the Nation.
“A month ago they might have looked at these things and said, that’s boring let’s ignore it,” says McDowell.
“A lot of the stuff they’re shooting down now will be found to be boring. Stuff from companies or government.”
Why are the most recent objects not being called balloons?
On Sunday, Gen Glen VanHerck, who is tasked with safeguarding North American airspace, said the military had not been able to identify what the three most recent objects were, how they stayed aloft, or where they were coming from.
He said they were being called, “objects, not balloons, for a reason”.
“It may be that they’re being cautious,” says McDowell. “You might infer it’s a balloon but don’t know it’s a balloon. It’s hard to see what else it could be though.”
VanHerck also raised eyebrows when asked whether he had ruled out extraterrestrials. “I’ll let the intel community and the counterintelligence community figure that out. I haven’t ruled out anything.”
Experts, have however ruled out aliens. Tucker says that it’s likely “a lot of reports of UFOs could just be this sky trash we’re talking about.”
