There is no doubt in Jim Wentworth’s mind about what caused the flash of light and building-rattling boom Friday night.
Wentworth’s Fire in the Sky Observatory near Nisswa is a registered research facility with the Minor Planets Center of the Harvard Smithsonian Center for Astrophysics. Friday, Wentworth had just left the observatory for his house when he saw a flash of light off his home’s deck. Sixty seconds later, a sonic boom.
“It surely shook my house,” Wentworth said.
The source, he said, was a bolide. They arrive with such velocity, Wentworth said, they are hard to track. They may come from the sun or a blank area of space. NASA describes a bolide or fireball as an exceptionally bright meteor spectacular enough to be seen across a very wide area. Objects causing fireball events can exceed one meter in size.
“Fireballs that explode in the atmosphere are technically referred to as bolides although the terms fireballs and bolides are often used interchangeably,” NASA reports. Friday’s sighting in southern Minnesota and northern Iowa fit the bill.
Wentworth, a retired electrical engineer and former Central Lakes College astronomy instructor, said the bolide in the Brainerd area may have been the size of a car or truck or even larger.
Most of the asteroids around Earth, some up to a half-mile in diameter, are known. But the smaller ones may arrive without fanfare. On Feb. 15, 2013, the Chelyabinsk meteor in Russia measured 19.8 yards across and was traveling an estimated 41,600 mph. It broke windows, injured more than a thousand people and damaged buildings. The meteor over Russia broke apart about 14 miles above the Earth’s surface with the explosion’s energy exceeding 470 kilotons of TNT, NASA reported quoting Peter Brown, Western Ontario professor of physics. The Chelyabinsk meteor strike was the most powerful since the Tunguska, Siberia, event of 1908 that flattened millions of trees and knocked people out of their chairs 40 miles away from the impact zone, NASA reported.
Wentworth looks for such bolides, searching space for fast-moving objects. Often it turns out to be space debris in high orbit around the Earth. The bolide by Brainerd on Friday was a random event, Wentworth said.
“It’s amazing what things can happen,” Wentworth said. On Friday, his wife said the boom sounded like a bomb. If it didn’t break up or come in with glancing blow, it could have provided a significant impact crater. “I’ve lived up here 40 years and can never remember it happening.”
Wentworth said the bolide released a lot of energy with the bright light flash the first indication and an explosion as it explodes and breaks up into smaller particles. Ninety percent of it burns up before it hits the ground. If it’s big enough, made of rock or iron, and retains its mass so it is big enough to penetrate the atmosphere it can create a huge crater.
Those are the dangerous ones, Wentworth said.
“Every day the Earth is accumulating many tons of debris,” Wentworth said. “These things — they become very unpredictable.”
Wentworth said he once saw a meteor, perhaps the size of a basketball, illuminate the summer night sky so much he could see variations in the color of the grass.
“It was like a continuous lightning bolt,” he said. Looking up he could see the fireball. When it exploded, it was like a fireworks rocket with sparkles. It’s not a frequent event but it’s an attention getter when it happens, he said.
“We’re in a shooting gallery and we know not when somebody pulls the trigger on us,” Wentworth said. Could there be another event here? It’s unpredictable. The probability is low, Wentworth said, but it’s not zero. On Friday, Wentworth remembers his exact words to his wife: “I said, ‘whew that was a close call.’”