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Did a meteorite impact near Thunder Bay Wednesday night?

Scott Sutherland
Meteorologist/Science Writer

Friday, December 15, 2017, 4:15 PM - Police in Thunder Bay are reporting a possible meteorite crash near the city on Wednesday night. Based on what's missing from the story, is that really what happened, though? Here's what we know.

At roughly 11 p.m. on Wednesday night, officers from the Thunder Bay Police Service were dispatched to investigate reports of an explosion, just to the southwest of the city. 

According to a Police Service press release, upon searching the area, along Highway 61, near Mount Forest Road, the officers discovered "a large round hole in the snow on the side of the road approximately two and a half feet around." 

In the centre of the hole, they said, was a pile of a "rock like substance".

Could this hole at the side of Hwy 61, near Thunder Bay, have been caused by a meteorite? Credit: Thunder Bay Police Services

The same hole, from a different angle, shows the size, and the depth of the crater. Credit: Thunder Bay Police Services

No footprints or tire tracks were found in the vicinity of the hole, according to the Police statement, and based on images taken at the scene, the hole was located on the shoulder of the asphalt road.

According to a report by CBC News, local resident Linda Pohole had called police after hearing an explosion.

"I called it in thinking that something happened in Mount Forest, and maybe a house exploded," she told CBC News. "It was that loud, and my son said he felt the house vibrate."

Dr. Stephen Kissin, Professor Aemeritus from Lakehead University, examines a hole in the ground that some say was caused by a meteorite. The original material that police found in the middle of the crater appears to have been removed. Credit: Lakehead University

Police Services contacted Lakehead University, and the following morning, Dr. Stephen Kissin, a Professor Aemeritus from the university's geology department, was on the scene to investigate. However, upon arriving, he found no meteorite present in the hole. Presumably, the "rock like substance" went missing overnight.

While there was some speculation that this may have been the result of the Geminid Meteor Shower, Dr. Kissin told CBC News that it was not likely, and that this was just a coincidence.

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What happens when a meteorite strikes the ground?

Although tonnes of meteoroids are swept up by Earth's atmosphere every day, most of them are bits of dust or ice crystals, with the occasional larger piece of rock or ice.

Any of the smaller meteoroids can create a brief flash of light in the sky, as they plunge into the atmosphere travelling at hundreds of thousands of kilometres per hour. The flash is produced as the air in the meteoroid's path is instantaneously compressed to the point where it glows, white hot. We had an excellent example of this over the past few days, due to the Tuesday night peak of the Geminid Meteor Shower. These small bits of matter are often vapourized by the hot, compressed air, however, and thus nothing survives to reach the ground.

Larger meteoroids are much more noticeable as they enter the atmosphere. They are travelling just as fast as the smaller bits, and their larger mass compresses more air, causing an even brighter flash of light. This is usually called a "fireball".

Some fireballs are so bright that they briefly light up the sky as if it were daytime, and a smaller subset can produce sonic booms. These meteoroids are far more likely to survive to reach the ground, often in pieces as they tend to break apart while they are still high up in the air.

On their way to the ground, larger meteoroids will pass into their "dark flight" phase. This is when the meteoroid has been slowed down by its interaction with the atmosphere so much that it's no longer compressing the air to the point of incandescence, and the meteoroid simply become a rock falling at somewhere around terminal velocity towards the ground. It can still cover plenty of distance across the map during this time, as it takes a ballistic trajectory towards the ground. When it hits, it's called a meteorite.

A primer on meteoroids, meteors and meteorites. Credits: Scott Sutherland / NASA JPL (Asteroids Ida & Dactyl) / NASA Earth Observatory (Blue Marble)

When it hits the ground, a dark flight meteoroid can still be travelling at around 500-600 km/h, so there's certainly the potential for it to produce a small crater. It's unlikely that the impact would cause an explosion, however. Any explosion, and resulting shaking of local residences, would result from the meteoroid breaking up, far above the ground.

For example, on March 26, 2003, the city of Chicago was pelted by hundreds of meteorites. One 15 centimetre-wide, 2.7 kg specimen managed to punch through the roof of a house, and the kitchen floor as well, ending up in a laundry pile in the basement. It did not, however, produce an explosion that shook nearby houses. According to a report by the Meteoritical Society, it did, however, produce a bright fireball that was visible in parts of Illinois, Indiana, Wisconsin and Ohio.

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Was this a meteorite, or something else?

Watch the video above, and you'll see a fairly good example of a bright fireball event.

So, what's missing for this event in the Thunder Bay area is the bright flash that should have accompanied it.

An object big enough to generate a sonic boom, which shakes houses on the ground in the vicinty, would have caused a very bright fireball, possibly even a bolide explosion. This is the kind of event where night suddenly turns into day for a brief moment, and this would have been clearly visible for hundreds of kilometres around. As of Friday, December 15, there have been no fireball reports from the Thunder Bay area for that night on the American Meteor Society website, which logs fireball reports from anywhere in the world.

Since the skies in the area were reasonably clear that night, the chances of a bright fireball going unnoticed, especially with the city of Thunder Bay only a short distance away, are slim.

Dr. Kissin is reportedly still examining the sample collected from the site, so no conclusions have yet been made. It will not be surprising, though, if something else - terrestrial and likely human-caused - is resopnsible for this event.

Sources: CBC News | TBPS | AMS Meteors | National Geographic

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