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Asteroids: What are They Made Of?

written by: pms19650•edited by: Rebecca Scudder•updated: 9/11/2010

This article explores what asteroids are made of - and why it matters to life on Earth. Did you know that the iron behemoths are more dangerous? Will a one kilometer asteroid hit the Earth in 2019?

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    What Are Asteroids Made Of And Why It Matters

    Rocky Asteroid (Courtesy PBS) 

    Asteroid is a term that is used to define a large range of objects. Most novices used the term quite liberally regardless of whether reference is to a Near Earth Object (NEO), a Tran-Neptunian Object (TNO) or a planetoid. Typically asteroid is a term reserved for objects in the inner solar system. Casual observers don’t differentiate between the types of objects but there is a lesson to be learned in orbital differentiation as well as the materials that make them up.

    Most asteroids are made of carbon, silica or iron. These three materials tend to be the majority of the composition, so typically there isn’t a mixture of elements. This is not good news for protecting the Earth from a deadly dinosaur killer. A half kilometer asteroid made almost entirely of iron could devastate our planet.

    While it is theorized that the dinosaur killer was the size of Mount Everest, an iron asteroid doesn’t need to be that big to change our planet. Significant challenges to life can start at a much smaller size. Carbonaceous asteroids (carbon) and stony asteroids (silica) make up 92% of all asteroid bodies. Luckily these bodies would have a pretty tough time punching through our atmosphere. These two classes of asteroids will tend to break up and explode above the planet, minimizing damage. How do we know? It has happened in modern times. It happened over Indonesia on October 19th 2009. A ten-meter near earth object exploded with the power of 15,000 pounds of TNT. It was almost twice as powerful as the bomb dropped on Hiroshima. The explosion triggers nuclear explosion test ban monitors more than 10,000 kilometers away. The stony or carbon asteroids tend to explode in air. This is a circumstance that protects life on Earth. The deadly eight percent of asteroids made of iron can successfully punch through the atmosphere and hit the planet.

    Understanding asteroids is a critical factor. A group of astronomers are trying to classify and count all near earth objects. The idea is that we can prepare for explosions like the one the happened over Indonesia. That asteroid was undetected. Luckily it was not a metal asteroid and it never hit the ground. Please note that some stony masses can hit the earth if they are large enough.

    Assessments can be made by the amount of light that reflects back from the object. This data can help astronomers make calculations if risk needs to be assessed on a “planet killer". An example of this type of asteroid is 2002 NT7. This asteroid is supposedly on a collision course with Earth in 2019. Most astronomers believe this asteroid will miss the planet but NASA is carefully monitoring it.

    Asking what an asteroid is made of is a great question. Asking whether one will hit us is a far more intriguing question.






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