As a large Chinese balloon traversing the United States reached North Carolina on Saturday, Chinese officials were sticking by their claims that the vessel wasn’t being used for spying, but “for scientific research such as meteorology.”

But experts say that the balloon, which is being closely monitored by US officials, looks nothing like a typical weather balloon.

“The reported characteristics of this balloon don’t really match anything that we’re familiar with,” Jonathan Porter, the chief meteorologist at Accuweather, tells TIME.

US defense officials suspect that the balloon, first spotted on Feb. 1 above Montana, is a “high-altitude surveillance device,” posing as a civilian weather balloon. The Biden administration is considering a plan to shoot down the balloon once it is above the Atlantic Ocean where the remnants could potentially be recovered, the Associated Press reported on Saturday, citing four US officials who spoke on the condition of anonymity to discuss the sensitive operation.

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Around the world, thousands of government-operated and privately owned weather balloons are launched daily to collect information about temperature, winds and moisture in the atmosphere. Porter explains that this balloon was detected so quickly and raised alarms because of its massive size. A typical weather balloon grows in size as it ascends through the atmosphere, starting off at about six feet wide, and expanding to roughly 20 feet in diameter as it rises. The Chinese balloon clocks in at around 90 feet wide, or the length of three buses, according to U.S. defense officials.

“The kinds of weather balloons that are launched twice a day from Weather Service offices are typically just a little box that has a temperature sensor, relative humidity sensor, pressure sensor and then a little tiny transmitter,” Alexandra Anderson-Frey, a professor of atmospheric science at the University of Washington, tells TIME. “Based on the photos that have been going around, there’s obviously a lot more equipment on this one.”

Chinese officials have said that the balloon wound up over the U.S. when it blew off course, but experts question the validity of that claim, especially considering how far the balloon has traveled. U.S. defense officials estimate the balloon traversed the Pacific Ocean, from China to Alaska to Canada, before reaching the continental U.S. The Pentagon has said the balloon appears to be “traveling at an altitude well above commercial air traffic.”

“This has been traveling at a much longer distance than what would be these standard weather balloons. They go up over one particular place and up to about 50,000 feet in the atmosphere, and then that’s it, they’re done,” Porter says. “They don’t travel large distances, so I think that there’s pretty significant differences between typical weather balloons and this reported balloon.”

Secretary of State Antony Blinken deemed the alleged spy balloon “unacceptable and irresponsible,” and proceeded to cancel his upcoming trip to China from Feb. 5 to Feb. 6, which was set to be the first high-level meeting between the U.S. and China in years. A second balloon with similarly suspicious characteristics was detected moving over Latin America on Friday.

Although China is notorious for keeping its technological research private, that likely would not explain the unusual characteristics of the balloon gliding over America, says Anderson-Frey. Most weather technology is consistent globally, she says, so the idea of China making such dramatic upgrades to one of its weather balloons would be very surprising.

“Weather technology that is currently in use has been in use for a very long time. A lot of the sensors have become a little more sophisticated, but relatively unchanged since the 70s, or 80s,” she says. “I haven’t heard word of any brand new developments in the weather world on the technology side of things.”

The scientist also expresses the confusion most experts have about why Chinese officials didn’t expect the balloon to cross the U.S. or face detection. “With the prevailing winds being the way they are, it was inevitable that this balloon would wind up over the United States, just with the way the wind speeds at those levels are right now,” Anderson-Frey says. “It shouldn’t have come as a surprise on their end.”