Much ado about Space Rocks
Time lapse of the night sky over Joshua Tree (Courtesy: Suli Yuan)
“Asteroids are our oldest and most numerous cosmic neighbors.”
It’s been a long while since I last went out just to look up at night sky full of dazzling stars. But, I had a chance to do so recently—and while I was night-dreaming, I was also hoping that I would catch a glimpse of a shooting star; but alas, it was, to answer Hamlet, not to be.
However, the thought of shooting stars made me wonder about the myriad of objects out in the sky and the Outer Space beyond. Apart from the stars, satellites, and space debris, there is also a whole family of different space rocks such as comets, asteroids, and meteors. But, it is also at that moment that I realized that I could not tell the difference among each of these types of space rock.
So like any other topic on this blog, I dug into these space rocks and this short post explains, at a basic level, what I have uncovered on this big family of space rocks.
The Big Family of Space Rocks
While all space rocks are made mostly of outer space dust, dirt, and metals, there are five main categories. They are: comets, asteroids, meteoroids, meteors, and meteorites, each distinguished by their own unique features.
Comets
Comets are composed of dust, dirt, and rocky materials that are engulfed in a shell containing ice, methane, ammonia, and other compounds. They orbit around the Sun and as they heat up, the shell sublimates (going directly from a solid state into a gaseous state) and forms the coma, an aura-like glow around its mass.
As comets move through Outer Space, the solar winds blow on the comas, forming the comets’ signature trailing tails. This tail is also what gives comet its name: deriving from the Latin word comēta, which comes from a Greek word meaning “wearing long hair.”
Comets’ orbits are highly elliptical. Depending on how long they take to complete an orbit around the Sun, comets are either categorized as long-period comets (taking more than 200 years to complete an orbit) or short-period comets (taking less than 200 years).
Asteroids
Asteroids are made of dust as well as rocky and metal materials. They generally come from the asteroid belt, which is situated between Mars and Jupiter. Asteroids are very much like comets except they don’t have the icy shells to form the coma or the tail. Additionally, asteroids’ orbits are more circular than the elliptical comets’ orbits.
Asteroids are usually the focus of disaster movies, and there is general scientific consensus that an asteroid, the Chicxulub Asteroid (named after its impact site), caused the extinction of the dinosaurs. And while the impact threat of an asteroid is real, a comet colliding with Earth is likely to be far more dangerous; this is due to the comet’s highly elliptical orbit, making its earthly impact more direct by coming from a more acute angle. Furthermore, comets can travel at three times the speed of asteroids, making their impact nine times more destructive (as impact energy is based on the square of the impact speed).
However, scientists still consider asteroids to be the greater threat since there are just so many more of them closer to Earth. In fact, the probability of an impact from an asteroid is 100 times greater than that of an impact from a comet of the same size.
Meteoroids
Meteoroids are just children of comets or asteroids; they are essentially metal or rocky chunks of each. While most of them originate in the asteroid belt, some do come from the Moon or Mars. In terms of size, meteoroids are bigger than a grain of sand but most are usually millimeters in size.
Meteors
Meteors are just meteoroids that enter the Earth’s atmosphere. The name “meteor” originated from the Greek word, meteōros, which means “high in the air.” Meteors are more commonly known as “shooting stars,” that flash of light you see in the night sky. This trail of light is the result of a meteor, usually the size of a pebble, burning up in the Earth’s atmosphere. Hence, meteor showers are just a collection of meteors that have hit the Earth; usually occurring as the Earth passes by a debris field left by a traveling comet.
Meteorites
And last, meteorites are just meteors that do not burn up in the Earth’s atmosphere and actually “lands” on Earth. Because meteorites are very small, they can be very dangerous as they are largely undetectable while traveling at a high rate of speed. But, not a lot of meteorites are in existence since the Earth’s atmosphere does a good job in vaporizing the meteors before they can turn into meteorites.
And so there you have it, a short and simple look at the big family of space rocks orbiting in the greater sky around us.
Resources
Infographic: What’s the Difference between a Comet, Asteroid and Meteor: https://www.universetoday.com/100075/infographic-whats-the-difference-between-a-comet-asteroid-and-meteor/
Less Than Five: What’s the Difference Between Comets, Asteroids, Meteoroids, Meteors and Meteorites? https://www.youtube.com/watch?v=dvd47rMYia0
Earth Impact: Are Comets a Bigger Danger Than Asteroids?: https://www.space.com/26264-asteroids-comets-earth-impact-risks.html
