MICROMETEORITES EVERYWHERE MICROMETEORITES belong to the oldest matter there is. They are mineral remnants from before the planets were formed and may even contain particles older than the sun that have traveled farther than anything else on Earth. We are just beginning to explore these microscopic alien stones, yet they are everywhere. WHAT IS A SPHERULE? Most micrometeorites retrieved on Earth are cosmic spherules. A spherule is a rounded object, a solidified melt droplet of stone and/or metal. The sphere is nature’s efficient solution for maximum volume and minimum surface. Surface tension while the micrometeorite is still in a liquid state bends the object into a sphere. Raindrops are also formed this way. In nature, rock can melt and create spherules in three ways: by volcano, lightning, and meteorite. On an uninhabited world, we would only have to distinguish these three types of naturally occurring spherules from one another to identify the extraterrestrial particles. HOW DO WE FIND A MICROMETEORITE hidden among billions of other particles? Micrometeorites offer two clues that will help us in the process. First, most micrometeorites contain small amounts of iron and nickel. These we can extract from the rest of the particulate we gather with our weapon of choice: a magnet. In the cosmic spherule collection from the South Pole, for example, approximately 80 percent of the micrometeorites are magnetic. The remaining 20 percent of spherules are nonmagnetic. Here, the metal content has been evaporated completely by the frictional heat created during atmospheric flight. These spherules we have to search for in a different way, which we will get to later. Meanwhile, the short road to finding 80 percent of micrometeorites is a magnet. Any type will do, but the stronger the better. I use a handheld neodymium magnet that measures 40 millimeters in diameter and has a hook in the center that serves as a grip. The magnet shown on page 20 is the one I have used to find all the urban micrometeorites in my collection. WHAT WE FIND IN THE DUST The Micrometeorites Cryptocrystalline (CC) micrometeorites are statistically the second-most common type you will find in a field sample. They are mainly glassy particles with fine-grained crystallites too small to recognize as individual grains. Extraterrestrial, But Not Micrometeorites Chondrules are millimeter-sized igneous droplets found in primitive meteorites. They formed in flashheating events in the Solar Nebula around 4.56 billion years ago (160 million years older than the oldest mineral fragment found on Earth). Most coarse-grained micrometeorites are thought to originate from chondrules. Industrial Spherules Magnetic I-type cosmic spherules are iron oxides, mainly magnetite and wüstite. They are resistant to weathering but rare, amounting to only around 2 percent of the overall number of melted micrometeorites found. In deep-sea collections, however, they occur more frequently than 2 percent due to the lower weathering resistance of stony micrometeorites in that environment. Naturally Occurring Spherules Searching for micrometeorites with a magnet is the best path to success. There is, however, one mineral that will occur practically everywhere, and it is also the most magnetic of all naturally occurring minerals on Earth: magnetite. When sampling for micrometeorites in road dust, beach sand, desert sand, mountains, and even on roofs, magnetite particles are abundant and will get caught by the magnet, like the crystals shown here.
✔ Author(s): Jon Larsen
✔ Title: On the Trail of Stardust: The Guide to Finding Micrometeorites: Tools, Techniques, and Identification
✔ Rating : 4.8 out of 5 base on (114 reviews)
✔ ISBN-10: 0760364583
✔ Language: English
✔ Format ebook: PDF, EPUB, Kindle, Audio, HTML and MOBI
✔ Device compatibles: Android, iOS, PC and Amazon Kindle
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