Astronomy Article Summary

Descriptive Astronomy

1 May 2007

A Report on “Unlocking the Solar System’s Past”

         An August 2006 article in the Astronomy Magazine talked about the material in meteorites, and how precious these materials are, because they are older than the Earth. Tens of thousands of meteorites have been obtained from all over the world. The meteoriticists who study them categorize them in one of two ways: ones that preserve records of solar nebulas, and ones that give evidence of different planetary processes.

         Inside the meteorites are millimeter-sized spheres, called Chondrules. Inside the Chondrules are colored minerals that explain that these Chondrules used to be molten droplets in space. The two main components of Chondrules are olivine and pyroxene crystals. They are also two of the most abundant materials in the solar system. The texture of the crystals also shows that the chondrules were formed from dustballs that were melted in extreme temperatures. They show signs of being exposed to brief, high-temperature conditions, possibly due to “hot zones” in the solar system. Even though we have this thorough information, we still don’t know the nature of the “hot zones,” though there have been many suggestions.

         Chrondritic meteorites also contain refractory inclusions. At high temperatures, refractory elements will condense, so this tells us how hot the times were when the solar system was formed. On one hand, the temperatures got so high that dust evaporated, leaving the refractory elements. On the other hand, the temperatures became so low that new dust condensed. Both of the different materials have compositions which are unique, and contain calcium, aluminum, and titanium. It is unable to be said that the refractory inclusions and the chondrules were formed in the same area of the solar nebula. The refractory inclusions could possibly give us an earlier look at the solar system. Some studies suggest the refractory inclusions formed 4 billions years before the chondrules did.

         Meteorites also hold pieces of instellar matter left over from when our nascent star formed. Our solar system comes from a molecular cloud that had tons of dust and gas molecules. Hydrogen and helium dominated the cloud, but there are also hydrogen cyanide, water, ammonia, and formaldehyde, which were able to form because of cole temperatures. There were other cloud cores within the molecular cloud, one of which collapsed and became a disk, which is now our Sun. This collapse occurred in only 100,000 years. Some chondrules contain dust remnants from this old molecular cloud. The dust explains to us the types of stars and what was in the stardust of the area where our Sun was born.

         Meteorites also have traces of nuclear reactions that tell us clues about the stellar activity going on when the Sun was formed. Stardust and the isotopes, whose fingerprints are found in chondrules, but have long since been gone, suggest that the solar system was formed in very hot temperatures and among interstellar debris.

         Stellar birthplaces are very interesting and exciting places. Research suggests that there were fast-evolving high-mass neighbors, some even 15 times the mass of the Sun.

         The isotopes found before, plus longer-lived isotopes warmed the planets from the inside out as they formed. The smaller planets radiated the heat more efficiently than larger planets. The larger planets became self-insulating, and heated up, sometimes so much that they destroyed any clues we might find to their past. Some of the bodies came between the two extremes, and weren’t large enough to completely melt. The minerals in these heated, and the chemical compositions changed.

         All of these examples can be found in meteorites. These tell us that planets form quickly. Scientists have changed their old observations that small planets form in a quicker time than large planets. Now we think that small planets take less time to form than larger ones.

         The young solar system had many collisions within it, and it is believe that a body twice the size of the moon crashed into the Earth, and the debris flung off and formed our moon. Earth and the other planets were victims of flying asteroids and comet. The Cchicxulub impact, which occurred 65 million years ago, is said to be the reason dinosaurs no longer exist.

         When scientists first studied lunar samples, they found that the lunar crust had been transformed greatly 3.9 billion years ago, and that a lot of impact events produced the moon’s large impact basins. Scientists proposed the earth and the moon were impacted a number of times 4 billion years ago. There are also those that believe the evidence was biased, only coming from a couple of impact basins.

         Newly discovered lunar meteorites have back up the claim that our earth and moon were bombarded 4 billions years ago. They also show that this lasted about 20-200 million years. If this is true, it would coincide with the oldest rocks on earth, which are 3.85 billion years old.

         After analyzing a Martian meteorite, researchers found the same thing, impact at about 3.9 billion years ago. This suggests that perhaps the earth and moon weren’t the only bodies to be bombarded. It seems that the asteroid belts, and not comets, were responsible for these impacts.

         The impacts were not large enough that they would provide the water the earth has now, so this implies that the water on earth had already been formed. The conditions on the earth’s surface during the bombardment would have been extreme. It would have been hard, if not impossible, to maintain life on the planet at this time. The seas may have been temporarily vaporized. The bombardment did not last long enough to destroy the water though.

         It is believed that something big had to cause the asteroid belt to be disturbed and throw around debris. A leading theory says that resonances are to blame. It is possible that the same kind of process could occur in younger planetary systems as well. Studies show that planetary systems, similar to ours, have been formed. Hopefully soon we will have more information, although the meteorites have helped a great deal.