How scientists know the New Year's Day boom over Pittsburgh was an exploding meteor

Story Transcript

The new year started with a bang in Pittsburgh.

Astronomer Diane Turnshek was in her kitchen on Saturday morning when she heard a "humongous crash" that rattled all the suncatchers on her window. 

She wasn't alone. People all over the city reported hearing the boom.

After ruling out the weather or any kind of local phenomenon, she came to the same conclusion that NASA and the National Weather Service (NWS) would eventually reach — this was a meteor exploding over the Earth.

"A meteor just makes total sense," Turnshek, a lecturer at Carnegie Mellon University, told As It Happens guest host Helen Mann.

Ruling everything else out 

When she heard and felt the impact at about 11:26 a.m. ET, Turnshek's mind instantly turned to the stars.

"As an astronomer, my immediate thought is it's something celestial," she said.

But first, she says she had to eliminate all other possibilities. For example, could it have been some kind of local incident? A car accident, a shooting or fireworks, perhaps? 

That didn't make sense. A quick online search showed that people as far as 80 kilometres away from her had reported hearing the boom.

"It ruled out any local explosions or train wreck or car accident or anything that had a close source," she said.

What about an earthquake?

"I work at Allegheny Observatory and we have a very sensitive seismograph," she said. "The seismograph didn't show anything whatsoever."

Meanwhile, officials at the NWS and NASA were busy investigating. 

Shannon Hefferan, an NWS meteorologist in Pittsburgh, said they were able to rule out lightning using GOES-16, a weather satellite operated by NASA and the National Oceanic and Atmospheric Administration.

The NWS tweeted on Saturday that a meteor was "the most likely explanation."

That was just an educated guess, Hefferan said, but NASA later used the same satellite to confirm it was, indeed, a meteor — specifically a chunk of rock from an asteroid.

"The way we know this is a meteor is that it was moving directly north to south," William J. Cooke, head of NASA's Meteoroid Environment Office, said. "All the data points were in a straight line, and lightning does not behave that way. Only meteors behave that way."

NASA was able to glean more information about the fireball thanks to scientists at Western University in London, Ont., who examined data from an infrasound station in Pennsylvania that captured the sound wave.

They estimated the meteor was hurtling at 72,420 kilometres per hour.

Had it not been cloudy in Pittsburgh on Saturday, people would have seen it illuminate the sky with a light 100 times brighter than a full moon, Cooke wrote in on the NASA Meteor Watch Facebook page. 

NASA estimates it was about a metre in diameter with a mass of around 450 kilograms. Cooke says a meteor that size crashes to Earth 100 times a year, once every three or four days, but it's extremely rare in Pennsylvania. 

'It was terrifyingly loud'

Turnshek spends a lot of time star gazing, and says she's never seen anything like it. 

"I've seen bolides [large meteors] before at night. They do make a sizzling noise and you can sometimes hear a repercussion in the air," she said. "But I didn't think that there could be one that large, that big [and] that noisy. I mean, it was terrifyingly loud."

The next step, she says, is to search for the meteor's remnants. It definitely would have crashed to Earth, she said, but it's hard to say whether it would have broken into tiny shards spread over a large area, or if there are some "fair-sized chunks" somewhere out there.

"I want to go on a hunt," she said. 

She says a nice chunk of meteorite could be worth a pretty penny, but for her, that's beside the point.

"I've bought and given away hundreds of meteorites to my students over the years, and I just think it's wonderful to have someone touch a piece of rock that was out in space," she said. "That's the value of it to me, is here's a celestial wonder right in your hand."

Written by Sheena Goodyear. Interview produced by Chris Harbord.