What is an Asteroid Made of Exactly?


The OSIRIS-REx mission, launched by NASA in 2016, just made headlines due to its leaking of sample particles long before the spacecraft is expected to return to Earth in 2023.  The mission, which is part of the New Frontiers program launched by NASA back in 2003, is tasked with the role of collecting sample materials from Bennu, a prehistoric asteroid made from carbonaceous material.  Despite the hiccup, NASA expects to be fully capable of stowing the sample collector, known as TAGSAM, that exists on the spacecraft, in order to bring back to our planet a sample of the materials from which this asteroid is derived.

With this mission has come a new fascination regarding the nature of asteroids – more specifically, the materials of which they are composed.  Bennu is a unique asteroid, and the reason why it was selected for study is because it is believed to not have changed, material-wise, since prehistoric times.  What this means is that the materials that can be derived from it give us enormous insight into the development of the Solar System, including our planet, and even human life.  These organic materials, which are the earliest materials in existence, tell us how space objects gradually led to life as we know it.

The Materials of Asteroids

An asteroid is a relatively small space object made of rock, which orbits the sun.  They can be as small as dust particles, or they can be several hundred miles in diameter.  Each asteroid is unique, and asteroids are constantly colliding with one another to form more numerous, smaller ones.  Some asteroids have water, while others do not.

But, what all asteroids share in common is their base material, which is rock.  Now, rock is not a sole material in and of itself.  Many unique materials can make up rock, including metals and other organic elements.  Needless to say, the more metal found in a particular asteroid’s makeup, the stronger and more durable it is, and less likely to crumble.

Bennu, the asteroid that is currently being studied by NASA via the OSIRIS-REx mission and spacecraft, is a carbonaceous asteroid, meaning that it is derived mainly of carbon, and boasts unique organic compounds including amino acids.  Most asteroids in the Solar System are made up of at least 75 percent carbon.

In fact, there are three types of asteroids, which are classified according to their dominant materials.  C-type asteroids are made up mainly of chondrite, which is a carbonaceous material.  They’re darker in color, which comes from a combination of clay and silicate rocks.  S-type asteroids are stonier than C-types, and are made mainly of nickel-iron and silicate materials.  Finally, M-type asteroids are made from nickel-iron, which makes them metallic, and thus the most durable of all.

The reason why studying these materials is so important is because they allow us to learn more about how the Earth was made, and how life on Earth developed over time.  These materials contain organic compounds, as said earlier, and these organic compounds play a role in the development of living creatures.  The earliest living creatures had a symbiotic relationship with these materials, and this relationship can explain the evolution of the life that we know on our home planet.

Currently, the OSIRIS-REx is gathering a generous amount of material from the C-type asteroid Bennu, as C-types are believed to be the most primitive, and therefore the most informative when it comes to prehistoric Solar System development.  The mission is set to end in 2023, when the samples gathered will be brought home, so that we can study them closely.


The OSIRIS-REx is giving us more information into exactly what asteroids are made of.  While we know generally that they are composed of some combination of rock, metal and organic matter, studying the materials more intensively will answer a lot of questions about the development of our Solar System, and the development of humankind.

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