Wednesday, 7 January 2009
Can Comets Be Chondritic Meteors?
I am returning to a few thoughts on comets. Comets are percieved to be made of ice. Meteorites on the other hand are known to be made of stone. I don't quite understand why these very similar objects in space would be made from completely different materials. I suspect they are not different at all. Perhaps comets are made from the very same stuff as the meteors we recieve. I popped-out to Wiki's again -
"Most meteorites that fall on Earth are chondrites, which are characterized by the presence of round grains called chondrules (from Ancient Greek chondros, grain). Chondrules formed as molten or partially molten droplets in space before being accreted to their parent asteroids. Because chondrites represent the oldest solid material within our solar system and are believed to be the building blocks of the planetary system, it follows that an understanding of the formation of chondrules is important to understand the initial development of the planetary system.
Chondrites are stony meteorites that have not been modified due to melting or differentiation of the parent body. They formed when various types of dust and small grains that were present in the early solar system accreted to form primitive asteroids. Prominent among the components present in chondrites are the enigmatic chondrules, millimeter-sized objects that originated as freely floating, molten or partially molten droplets in space; most chondrules are rich in the silicate minerals olivine and pyroxene.
A carbonaceous chondrite or a C-type chondrite is a type of chondritic meteorite which contains high levels of water and organic compounds, representing only a small proportion (~5%) of known meteorites. Their bulk composition is mainly silicates, oxides and sulfides, while the minerals olivine and serpentine are characteristic. The presence of volatile organic chemicals and water indicates that they have not undergone significant heating (>200°C) since they formed, so their composition is considered to be representative of the solar nebula from which the solar system condensed."
"Meteorites are hardy, and the type known as chondrites are also primitive, dating back to the very early solar system. Chondrites contain a high density of so-called chondrules—roughly millimeter-sized spheres like the one shown here in polarized light—that were flash-melted at temperatures around 2000 K and subsequently cooled and incorporated into a meteorite's parent object, typically an asteroid. The heating mechanism is unknown but could involve shocks or lightning. Mostly made of silicate minerals such as olivine and pyroxene and of the metals iron and nickel, chondrules are expected to be deficient in volatile elements like sodium. But researchers at the Carnegie Institution of Washington, the US Geological Survey, and the American Museum of Natural History say it isn't so. Using electron microprobe spectroscopy, they studied 26 chondrules from the Semarkona meteorite that fell in India in 1940 and found significant sodium throughout."
"What is interesting about chondrules is that radiometric dating has put them among the first solids to have formed in the solar nebula. That is, they are the first things to have "frozen" out of the interstellar gas that eventually became our solar system. So by understanding the processes that affected chondrules, we'll gain insight as to what processes were taking place as solids first formed in the solar nebula which could have determined how the nebula as a whole evolved over time." Fred Ciesla, http://www.lpl.arizona.edu/~fciesla/work/chondrule/
A lot of people are convinced that the chondrite meteorites formed billions of years ago. This is because they are unable to explain the high temperatures needed to create the chondrules. Surely electrolysis explains the presence of chondrules. Electrolysis would also explain the behaviour of a comet - if the comet was made of the same stuff as a chondrite meteor. With the minerals that make up a meteor, we could imply that it becomes highly conductive under conditions where its salts have become molten. Where perhaps minerals and salts are expended under electrolysis, then a comet could fall out of its circuit with the Sun, and may even become a meteor.