Bright green meteor explodes in the night sky Monday, see it
Monday, February 6, 2017, 2:15 PM - Night owls throughout the U.S. Midwest and southern Ontario were treated to a spectacular show, as a bright green meteor fireball blazed through the sky over the western shores of Lake Michigan on Monday morning.
We've been hearing about a few close asteroid flybys as of late, with some of these measuring up to 10-20 metres in size, but very early Monday morning, around 2:27 a.m. EST, something much smaller plunged into Earth's atmosphere.
The bright green fireball produced by this object flashed high in the sky over eastern Wisconsin, along the shores of Lake Michigan, but was seen by many observers in Illinois as well, and was spotted all the way from New York State to Iowa, and as far south as Kentucky.
The observers map for the Feb 6, 2017 meteor sighting, showing the locations of the witnesses, and the trajectory deduced from their reports. Credit: American Meteor Society
The American Meteor Society (AMS) has logged over 220 reports from people who witnessed this event, and it's very likely to have been seen by many more. Fortunately, for those of us who missed it, it was captured by webcams and dashcams throughout the area.
The view in the video that leads off the story is from a police dashcam, from the Lisle, Illinois Police Department, and the following videos caught it as well.
A security camera from Plover, Wisconsin:
The rooftop camera from the Atmospheric, Oceanic & Space Sciences Building on the University of Wisconsin-Madison campus:
Even more remarkably, it's quite possible that this meteoroid was caught on Doppler radar as it sped through the air:
Meteor likely detected by NWS Doppler radar. Radar capture at 1:29 AM. pic.twitter.com/zeUKCQ3zAU— Jeff Last (@JeffLast) February 6, 2017
It's difficult to be absolutely certain that this blip on the radar was caused by the meteoroid, simply because it's difficult to know exactly where it was at any time, and even the exact timing matters. The trajectory and timing on record for this event, as they stand now, are based on a collection of the eye witness reports. So, there is some uncertainty involved. Still, this is very close to the timing of the meteor, and right along its projected trajectory, so there's a good chance we're seeing it here.
So, why was it green?
The bright light of this meteor was produced as a meteoroid - a chunk of space rock potentially as old as our solar system - entered the atmosphere, travelling at tens of thousands of kilometres per hour. At that speed, the rock compressed the air molecules in its path to the point where they were so hot, they glowed. At the same time, as the meteoroid was pushing on the air molecules, the air molecules pushed back, slowing the meteoroid down. The glow of the meteor persisted only as long as the meteoroid was travelling fast enough to apply sufficient compression to the air. Once it had slowed down enough, the light went out and and the meteoroid - or at least the remaining fragments of it - entered what's known as their "dark flight" for the rest of their journey to the surface.
Why do I say "at least the remaining fragments"? Because the bright, intermittent flashes seen in the video were caused by the meteoroid succumbing to the forces being exerted on it by the air it is compressing. Although some meteoroids can be made of some very tough materials, many of them have the same consistency as rocks you would find on the ground. As they compress the air in their path, the air pushes back, and this applies immense pressure to the meteoroid. Effectively, it gets squeezed, and when the rock matrix of the meteoroid can't withstand this squeezing any more, it gets crushed. Each time that happens, the release of energy causes a bright flash of light. The final flash in the videos, just before the meteor went dark, was the meteoroid exploding into multiple fragments.
The green colour of this meteor comes from the heated air - which can reach temperatures of over 1,700oC - melting the outer layer of rock, and is a likely indication of the presence of nickel in the meteoroid's mass. Many of these space rocks have metal in them - usually a mix of nickel and iron - which accounts for why nearly all of them are magnetic. In meteorites, we see a few different ways this can happen. It can simply be flecks or veins of metal inside a rocky meteorite's matrix. It could be like we see in one of the rarer meteorites, known as Pallasites, which contain olivine crystals trapped inside a nickel-iron lattice. It could, possibly, even be a completely metallic mass, like we see in nickel-iron meteorites.
Finding meteorite fragments from this mass would confirm its type, but that seems unlikely, given its trajectory. Based on the AMS's analysis, the potential impact site is in the middle of Lake Michigan:
Updates: In addition to the radar imagery, reports have NASA scientists estimating that the object that caused this was a fragment of a larger asteroid, which may have been up to 5 metres wide when it first entered the atmosphere, but had been reduced down to closer to 30 centimetres wide by the time it hit the ground. Also, based on this, the scientists estimated that there could be hundreds of meteorites lying at the bottom of Lake Michigan from this event.