posted on Oct, 23 2009 @ 05:07 PM
Originally posted by internos
I'd say that some possible explanation would be the on-going orionid meteor shower which will reach its peak tonight
Actually internos, it's likely that this event was not
connected to the Orionids or any other cometary
meteor shower. The Orionids,
which are mostly dust ejected from Halley's Comet, like other cometary meteoroids, are composed of extremely fragile material, which is
unlikely to survive long enough to be able to cause the effects that people observed.
Usually when people report sonic booms/shaking from a meteor, that is a good indicator that something survived below about 50km, since above 50km the
air is not dense enough for sound waves to propagate down to people on the ground. If something made it down that far, it likely dropped meteorites to
Since there has never been a case before where cometary material has been recovered after such an event, it remains highly unlikely that this even was
connected with a cometary source.
Asteroids on the other hand are a much more likely culprit, since they make up 100% of all recovered meteorite falls.
By far the most prevalent parent body of meteoroids, cometary meteoroids form about 95% of the total meteor population, and include nearly ALL of the
shower meteor population. These parent bodies are composed of frozen methane (CH4), ammonia (NH3), water (H2O), and common gases (such as carbon
dioxide, CO2), carbon dust and other trace materials. As a comet passes near the sun in its orbit, the outer surface exposed to sunlight is vaporized
and ejected in spectacular jets and streams, freeing large amounts of loosely aggregated clumps of dust and other non-volatile materials.
These freshly generated cometary meteoroids, often called "dustballs" will roughly continue to follow the orbit of the parent comet, and will form a
Based upon photographic fireball studies, cometary meteoroids have extremely low densities, about 0.8 grams/cc for class IIIA fireballs, and 0.3
grams/cc for class IIIB fireballs. This composition is very fragile and vaporizes so readily when entering the atmosphere, that it is called
"friable" material. These meteoroids have virtually no chance of making it to the ground unless an extremely large piece of the comet enters the
atmosphere, in which case it would very likely explode at some point in its flight, due to mechanical and thermal stresses.
These parent bodies are the smaller asteroids, constructed of denser and less volatile materials than the comets. Small meteoroids of this type are
produced through collisions. This class of parent bodies generate about 5% of the total meteor population, generally as part of the non-shower, or
"sporadic" meteors. These meteoroids can make it through the atmosphere, and as meteorites, they make up about 84% of all falls.
Stony meteorites from this source are called Chondrites, due to the rounded nodules of material found within their structure, which are called
chondrules. Chondrite meteorites have two major groupings:
The first group, the Class II fireballs, are the carbon-rich Chondrites, or Carbonaceous Chondrites, which help bridge the gap between comets and
asteroids. They make up about 4% of all observed falls, and have densities of around 2.0 grams/cc. They are characterized by the presence of 2% or
more carbon, partly present as complex hydrocarbons, and of considerable hydrogen (hydroxyl groups, OH-1, and water, H2O).
The second group, the Class I fireballs, are what is called the Ordinary Chondrites, making up about 80% of all observed falls. They have an average
density of 3.7 grams/cc, and generally fall into two general types: Olivine-Bronzite Chondrites (about equal amounts of bronzite and olivine) and
Olivine-Hypersthene Chondrites (less pyroxene than olivine).
These asteroids are physically the largest parent body for meteoroids, but generate only a small fraction of the overall meteor population: less than
1%, and have no fireball classification. Due to their hardier composition, however, they make up about 16% of the observed falls. A
differentiated asteroid is one with sufficient size to cause internal temperatures high enough to melt and stratify the asteroid. The higher density
materials (mainly iron) gather in the core, the lighter basalt/silicate materials gather in the outer layers, with thinner layers of various
concentrations of other materials stratified in between. Small meteoroids of these types have been produced by what must have been spectacular
collisions, breaking up even the iron core of the asteroid.
The three major groups for these meteors are:
1. Achondrites (Basalt/Silicate non-chondritic stones); with a 3-4 grams/cc density, and comprising about 8% of observed falls. These formed in
the outer and crustal layers of the asteroid.
2. Siderolites (Stony-Irons); with a 5-7 grams/cc density, and comprising about 2% of observed falls. These formed a thin layer between the core
and outer layers of the parent bodies. They generally consist of round, translucent green crystals of olivine imbedded in a matrix of iron.
3. Siderites (Irons); with a 7.9 grams/cc density, and comprising about 6% of observed falls. These are the remains of the core of a
differentiated asteroid, and show signs of extremely slow cooling (1-10 deg C per million years), and extremely high shock stresses, presumably from
collisions. These meteorites weather so well once on the ground, they make up 54% of all meteorite finds despite their small percentage of the fall
Source: The American Meteor Society
Originally posted by internos
it found place even as APOD
As above, this fireball likely had no connection with the Orionids or any other cometary meteor shower. There is certainly no mention of it there on