William Herbst is Professor of Astronomy at Wesleyan University and James Greenwood is Assistant Professor of Earth and Environmental Sciences at Wesleyan University. This article was originally published under The Conversation. The article contributed to Space.com's Expert Voices: Op-Ed & Insights .
William Herbst Professor of Astronomy, Wesleyan University and James Greenwood Assistant Professor of Geological and Environmental Sciences, Wesleyan University
The April 26, 1803 was an unusual day in the small town of L & # 39; Aigle in Normandy, France ̵
Over 3,000 of them fell from the sky. Fortunatly nobody was hurt. The French Academy of Sciences investigated and proclaimed that they came from outer space based on many eyewitness accounts and the unusual appearance of the rocks.
Related: Photos: Fireball Drops Meteorites on California
The earth is constantly being hit with stones while it orbits the sun and carries around 50 tons daily Mass of our planet at . Meteorites, as these rocks are called, are easy to find in desert areas and on the ice levels of the Antarctic, where they stick out like a sore thumb. You can even land in backyards, treasures hidden between ordinary terrestrial rocks. Amateurs and professionals collect meteorites, and the more interesting people make it to museums and laboratories around the world to exhibit and study. They are also bought and sold on eBay .
Despite decades of intensive study by thousands of scientists, there is no general consensus on how most meteorites formed. As Astronomer and Geologist we have recently developed a new theory of what happened during the Solar System's birth to create these precious relics of our past. As planets are formed by collisions of these first rocks, this is an important part of Earth's history.
The mysterious chondrules
About 10% of the meteorites are made of pure iron. These are formed by a multi-step process in which a large molten asteroid has enough gravity to cause iron to sink into its center. This forms an iron core, just like Earth's. After this asteroid has solidified, it can be smashed by collisions with other objects in meteorites. Iron meteorites are as old as the solar system itself and prove that large asteroids that formed quickly and completely melted were once abundant.
The other 90% of the meteorites are called "chondrites" because they are full of mysterious, tiny particles of rock spheres called "chondrules". There is no such thing as a chondrule in any terrestrial rock. It is clear that during a short period of intense heating, chondrules formed in space when temperatures reached the melting point of the rock for less than an hour, about 3000 degrees Fahrenheit (19459006). What could that explain?
Researchers have made many hypotheses over the last 40 years. However, no consensus has yet been reached on how this brief warming spurt has gone.
The Chondrule problem is so difficult and controversial that a few years ago we announced to our colleagues that we were working on it. shake their heads and send their condolences. After suggesting a solution, we are preparing for a more critical response, which is all right as science progresses in this way.
The flyby model
Our idea is quite simple . The radioactive dating of hundreds of chondrules shows that they formed between 1.8 and 4 million years after the solar system began – about 4.6 billion years ago. During this time, there were plenty of molten asteroids, the parent bodies of iron meteorites. Volcanic eruptions on these asteroids released enormous amounts of heat into the space around them. For smaller objects that pass during an outbreak, a short, intense heat wave would occur.
To test our hypothesis, we split the challenge. Astronomer Herbst nibbled the numbers to see how much heat was needed and how long chondrules should be produced. Then geologist Greenwood used a furnace in our Wesleyan lab to replicate the predicted conditions and see if we can create our own chondrules.
The experiments were quite successful.
We put some particulate earth dust with compositions similar to room dust into a small capsule, put it in our oven and turned the temperature through the predicted area. It came out a good-looking synthetic Chondrule. Case closed? Not so fast.
There were two problems with our model. First, we ignored the larger question of how chondrules became part of the entire meteorite. How do you relate to the substance between chondrene matrix? In addition, our model seemed a bit too chic. Only a small part of primitive matter is heated in the way we have suggested. Would it be sufficient to consider all these meteorites with many chondrules on earth?
Production of Whole Meteorites
To address these issues, we have expanded our original model Warming of a larger object up to a diameter of several kilometers in flyby , As this material approaches a hot asteroid, parts of it evaporate like a comet, resulting in an atmosphere rich in oxygen and other volatile elements. This is exactly the kind of atmosphere in which Chondren forms from previous detailed chemical studies.
We also expect that heat and gas pressure will transform the passing object into a whole meteorite by hardening the process known as Hot Isostatic Pressing which is used commercially to make metal alloys. When the chondrules melt into small balls, they release gas to the matrix, which captures these elements as the meteorite hardens. When chondrules and chondrites form together in this way, we expect the matrix to be improved in exactly the same elements as the chondrules are depleted. This phenomenon, known as complementarity has been observed for decades, and our model provides a plausible explanation for this.
Perhaps the most recent addition to our model is that it directly associates the formation of chondrules with the hardening of meteorites. Since only well-hardened objects from space can penetrate the Earth's atmosphere, we would expect the meteorites in our museums to be as full of chondrules as they are. But hard meteorites full of chondrules would be the exception and not the rule in space, as they form through a relatively unusual process – the hot flyby. We should know soon enough whether this idea contains water, since it is predicted that chondrules on asteroids will be rare. Both Japan and United States have ongoing missions to nearby asteroids that will return samples in the next few years.
When these asteroids are full of chondrules, like the hardened meteorites If we make it to the surface, our model can be discarded and the search for a solution to the famous chondrule problem can continue. If chondrules on asteroids are rare, however, the Flyby model passed an important test.
This article was re-published in The Conversation under a Creative Commons license. Read the original article.
Track all the questions and debates of Expert Voices and become part of the discussion on Facebook and Twitter . The views expressed are those of the author and do not necessarily reflect the views of the publisher.