Tuesday, September 29, 2009

Friday Fireball Over the GTA

Last Friday evening—September 25th—a meteor streaked across the sky over southern Ontario and the Greater Toronto Area (locally abbreviated as the GTA). The event was seen just after 9 p.m. Eastern Daylight Time. Many described the light as a greenish color and that its brightness was greater than that of the full Moon—qualifying the object as a fireball. Some Toronto security cameras under the fireball's path actually caught the dramatic change in brightness at ground level as the fireball passed. One security camera actually caught a reflection of the fireball in the paint job of a parked van.

After a few seconds of fame, the meteor broke into reddish fragments and faded from view. Some described the meteor as a bolide since it broke up in flight. My understanding of a bolide is that the exposition would be more violent than what was reported, and that it would normally be accompanied by sonic boom-like sounds. Neither of these occurrances was reported in the story, but no matter. By whatever you call it, the event was spectacular.

So what do we really know about the object? When all is said and done, not much. But that has never stopped us before. Let’s pretend that we are a bunch of amateur astronomers sitting around a jolly table with a tasty beverage in hand. What can we guess about the object—and guessing is definitely what we are doing here.

Was this really a meteoroid or was it space junk? Good question. Since the newspapers did not report any official announcement of “something” expected to fall on that evening, I’m guessing that it was not space junk. If it was, though, shame on them for missing it. Let’s stay with the meteoroid guess.

About how big was it? Well, fireballs are thought to be the result of meteoroids that range in size from a basketball to a small car. At least, that would be the size range when it entered the atmosphere. It would have gradually broken up on its way down until it finally did that major breakup at the end.

What kind of meteor was it? Well, we don’t have details in the news story as to its direction, so we cannot even extrapolate an orbit that my suggest a possible family of Near-Earth asteroids, so we will have to let that one go. With regard to its composition, we can take a wild guess. The witnesses report that it was bright green. That is one of the usual colors seen of fireballs, along with blue, yellow, red, or even white. The color green can be an indication of the presence of the mineral nickel, so perhaps it was a nickel-iron meteoroid, and therefore produced nickel-iron meteorites.

Can we find the meteorites? Well, that depends on whether someone was close to the break-up point, and has a good idea of the general location. If they are nickel-iron meteorites, and that is a very wild guess, then they would be easier to spot than stony or stony-iron meteorites, which tend to blend in with the surrounding rocks. One think to look for is a crusty, charred exterior, as if someone took a large knife and carved big chunks out of the surface, creating interestingly shaped rocks. This carving appearance is the result of the ablation process as the meteoroid passes through the atmosphere. The surrounding air molecules are compressed, heat up, and ionize the gas around the meteoroid. As the outside of the meteoroid heats up, parts of the exterior pop off, taking the excess heat with them and allowing the larger body to survive intact for at least a little longer. If you do see a meteor, and if it comes down near your location, look around as best you can. If you do find something that you think might be a meteorite, take it to the nearest university, science museum or science center. Talk to the most knowledgeable person there on the subject of meteorites. Tell them all you can about the rocks and where you found them. If that person agrees with your opinion, they may need to send it off to someone for testing, or perhaps do the tests themselves. And if you’re lucky, you might have found a meteorite.

Why didn’t astronomers warn anybody about this one? Well, that goes back to its size. Official watch groups, like the participants in NASA’s Near-Earth Objects program, only look for bodies that are a kilometer in size or greater. The smaller stuff is just too small to consistently spot. And besides, statistics show that the smaller stuff usually breaks up well before hitting the ground, like this one did, or falls in water or in a remote area. The numbers say that bigger stuff is possible on the average of every one hundred years or so, like the Tunguska event over northern Russia on June 30, 1908. Wait, you say. It is now 2009. Are we statistically due for another Tunguska-sized event? Oh, I see you have been watching the History Channel. Me, too. Well, to be a concern, the body would have to affect a populated area, not a remote area or a body of water. Beyond that speculation, I’m not even going further. That topic is for the professionals.

If you really want to know about Near-Earth objects, then NASA’s Near Earth Object Program is definitely the place to check out. The folks in this group are constantly looking for bodies that might be a concern to Earth either now or in the future. As of September 27, 6,386 Near-Earth object have been discovered by them. These are bodies orbiting our Sun which come close to Earth every now and then. Knowing who our neighbors are and where our neighbors are is the first step in avoiding our neighbors, if you know what I mean. As I say these folks are dedicated and do a great job. And the site is very informative, too. Summing up, I would say that since these groups are diligently working away, it is a good chance that anything that would be a concern to us would be reported in the news well in advance of a possible problem. So please don’t worry your pretty little head about it.

Gee, that was fun. And I’m in need of another tasty beverage, so I’ll leave you now. But if you want to learn more about observing meteors and finding meteorites, or about Near-Earth objects, please check out these great sites:

American Meteor Society

International Meteor Organization

NASA's Near Earth Object Program


No comments: