By Patricia Zengerle
WASHINGTON (Reuters) - An unprecedented spate of mysterious flying objects over North America - including a Chinese spy balloon shot down on Feb. 4 after floating over much of the United States - has transfixed Americans and Canadians, prompted political outrage and raised a host of national security questions.
Here is what we know - and do not know - about the objects:
WHAT ARE THE OBJECTS?
The first of the four objects was a 200-foot-tall (60-meter-high) aerial intruder that set off the frenzy when it was spotted two weeks ago. It has been identified by U.S. officials as a balloon that China was using to spy on the United States.
Beijing denies the balloon was for surveillance and says it was a civilian research craft.
The other three remain officially unidentified, as crews work to retrieve and identify debris.
They include an object about the size of a small car shot down over sea ice near Dead Horse, Alaska, on Friday, another similar in shape but smaller than the Chinese spy balloon brought down over Canada's Yukon on Saturday and an octagonal object shot down over Lake Huron on Sunday.
WHERE DID THEY COME FROM?
U.S. officials have not yet announced any point of origin for the devices. On Sunday the U.S. Air Force general overseeing North American airspace said he would not rule out aliens or any other explanation, although another U.S. official said later there was no evidence that extra-terrestrials were involved.
WHY ARE WE SEEING SO MANY NOW?
The U.S. military adjusted its radar to find slower flying objects at different altitudes after the first balloon was spotted and the government announced that several Chinese spy balloons had visited the United States undetected in recent years.
U.S. officials said U.S. North American Aerospace Defense Command (NORAD) has been adjusting the filters and algorithms it uses to examine radar data, making them sensitive enough to detect the smaller objects whose ability to stay aloft and move with the wind is confounding U.S. officials.
HOW DID THE MILITARY TAKE THEM DOWN?
On Feb. 4, an F-22 fighter jet shot down the first balloon over the Atlantic Ocean off of South Carolina. F-22s also shot down the objects over Alaska on Friday and Canada on Saturday. The device over Lake Huron was blown out of the sky on Sunday by an F-16.
All four were hit with Sidewinder missiles, which each cost hundreds of thousands of dollars.
The military considered using guns, but this was deemed too difficult given the small targets. Guns would also be more dangerous for the pilot, since debris can more easily hit an aircraft firing at close range than one launching a missile from a distance.
WHAT THREAT DO THE OBJECTS POSE?
The objects, especially those spotted near military installations, have raised fears of surveillance by U.S. adversaries and have raised tensions between the United States and China, which both accuse the other violating sovereign airspace.
Some also few at altitudes where they could pose a danger to civilian aircraft. The incidents have prompted repeated closures of airspace to commercial craft to avoid possible collisions between fighter jets and civilian aircraft.
IS THE UNITED STATES SENDING BALLOONS OVER CHINA?
China has accused Washington of sending high-altitude balloons over its airspace without permission more than 10 times since the beginning of 2022.
U.S. officials denied the accusation.
WHAT ABOUT OTHER COUNTRIES?
The United States accuses China of conducting a high altitude surveillance balloon program for intelligence collection that has violated the sovereignty of more than 40 countries across five continents.
Washington said another Chinese balloon had been spotted over Latin America. Close U.S. ally Britain said it would review its security in the wake of the U.S. China balloon incident.