In my recent studies regarding comets and asteroids, some of the terminology about even what a meteoroid, meteor and meteorite are, were also very confusing; let alone the difference between an asteroid and a comet. So what exactly are these objects and where do they come from? What happens when they hit Earth and what kind of damage can they cause, if any? These are some of the common questions I will try to answer and hopefully articulate it in a comprehensive way that all readers can comprehend.
Looking up at the night sky on a clear evening is a glimpse into the past. Every single point of light that one’s eyes can see took time to travel from its origin all the way across space and time, just to reach your human sense of eyesight. Because of the vast distance, even our own Sun’s light takes around 8 minutes to be seen and experienced from the time the photons leave and start their journey at light-speed in our direction.
Stars appear all over the night sky and in previous centuries, many people believed that they also fell into Earth and coined them a misnomer name as, “falling stars” or “shooting stars“. We know today however, that these are no stars at all, but the remnants of stars in the form of dust, ice, rocks, metals and larger clumps of material that we have assigned more accurate names to.
What is a “Falling Star”?
A Falling Star is simply an ancient term used to describe what appears as a long and fast streak of light across the sky, sometimes with an explosion or fireball. Although they may resemble distant actual stars in the background of the night sky, these are in fact what’s scientifically called a meteor. A meteoroid on the other hand, is a small body that enters Earth’s atmosphere while an asteroid and comet are larger bodies that can sometimes enter Earth’s atmosphere. When one of these objects gets close enough to Earth and within the layers of our atmosphere as already mentioned, friction then causes the object to break and burn up as it approaches Earth’s surface at speeds of around 40,000 to 70,000 mph. Because of its trajectory and speed, particles of the object leave trails for long distances behind it that can extend for hundreds of miles across the celestial sky. Oh and by the way, if the object does not completely obliterate on it’s journey through Earth’s atmosphere and some leftover fragment manages to make contact with the ground, then this leftover piece is commonly referred to as a meteorite at that point.
A meteoroid is defined as an object smaller than 1 meter in size but not smaller than 1 millimeter. At that point it’s considered cosmic dust. Meteoroids are often fragments of asteroids and comets. However, an asteroid is defined as an object larger than 1 meter in space and is made up of mostly rock, iron and nickel. While a comet is more defined as a chunk of dust and ice and sometimes comets and asteroids can be the same size, but again have different formation structure materials.
A star however, is a different beast all in itself and has a mass of over a million times that of Earth. Our host star we call the Sun could fit 1.3 million Earths inside of it for a comparison. So as you can clearly see, there are no actual stars falling into Earth or you and me and everyone else would not be around to talk about them. Furthermore, larger objects don’t technically fall into smaller objects. Instead, it’s exactly the opposite.
Where do Meteors come from?
Now that you know that no stars actually fall into Earth, then you’re probably also wondering where in the world do meteors come from? Well I can assure you that they don’t come from anywhere of this world; Earth that is. However, they are our planetesimal neighbors. Wait, what? What exactly is a planetesimal first off? A planetesimal is basically a failed protoplanet. I know, I know! So many things to understand in order to get to the point. Stay with me though; this will all make sense as you read on.
When the solar system was just a bunch of gas and dust clouds floating along in space, essentially everything started to collapse into shape at this time; around 4.6 billion years ago. Hydrogen and Helium formed together relatively quickly and started to craft the Sun as the other bodies in this nebula also started to develop simultaneously. Some objects clumped together faster than others and as the Sun began to generate and emit radiation and generate a huge gravitational field at the same time, the smaller formations were then cleaning out their orbital neighborhoods of what the sun left them as scraps to fight over. It is said that at one time we may have had up to 20 planets in our young solar system, but that’s another article for another day. For now, let’s stay focused on what’s going on with the solar system’s early formation days.
What are Planetesimals and Protoplanets?
In a time of just 10-20 million initial years, most of the planets already took their shapes and sizes as we know today. The terrestrial–or rocky–planets were the closest to the Sun and include Mercury, Venus, Earth and Mars. The next region of space if just a swirling disc of planetesimals and protoplanets, but you probably know them better as meteoroids and asteroids. These are embryo-like planet formations that just couldn’t quite get enough mass to form into a more defined planet. Oh and you can challenge your friends by telling them that asteroids are also referred to as minor planets.
A protoplanet is the next step up from those tiny planetesimals that we call asteroids and has to be at least 1 kilometer in size. A protoplanet is a planet 1 km in size and can be of any size above that. However, once protoplanets get big enough to take on more of a spherical shape, orbit the sun, but still can’t quite clear their neighborhood of debris, it may then be referred to as a dwarf planet.
The Asteroid Belt
Okay so remember where we’re at? Mercury, Venus, Earth, Mars, Asteroid Belt, then come the Jovian (Gas Giant) Planets. In the following order you have Jupiter, Saturn, Uranus and finally Neptune. Jupiter is the largest planet in our solar system as you probably already knew from early education as a child. But did you know that Jupiter is likely the reason there’s an asteroid belt in between Mars and Jupiter itself? Jupiter’s gravitational field is so strong compared to the rest of the planets that this likely disrupted the formation of Ceres from graduating from a Dwarf Planet into one that we could actually call a real planet. Ceres is considered a protoplanet, dwarf planet and an asteroid. It’s actually the largest asteroid in the asteroid belt. I didn’t mention Ceres until now because there are moons bigger and smaller than this object. Big enough to be a moon, yet orbits no planet so classified as a dwarf planet instead…barely.
This asteroid belt, in between Mars and Jupiter, is where some of the asteroids and meteoroids that eventually hit Earth come from. These are called Near Earth Objects or NEOs once they come within a defined certain distance. Sometimes these rocky/iron/nickel mixed asteroids get gravitationally bumped out of their orbits and pushed into Earth’s orbit for a fantastic collision. These rarely make contact with Earth in case you were wondering so no need to stock up on doomsday supplies just yet. In fact, it’s so rare of collisions that we just call these sporadic meteors when they actually come in contact with Earth because they are not what you usually see during a meteor shower. We’ll get to where meteor showers come from in a moment, but first a quick word from our sponsors…..just kidding. No commercials for this literature podcast, although you may eventually see side ads to help this student writer pay for his time on these fantastic–average–articles that everyone–2 or 3 people–is/are talking about.
What are Meteoroids, Meteors and Meteorites?
Anyways, you perhaps already figured out something interesting so far. Although wandering meteoroids and asteroids later hit Earth’s atmosphere and become a Meteor, most of them will usually completely burn up. However, the iron asteroids are the objects that have the highest potential to leave their Meteorite fragments on the ground for people like you and me to stumble upon easily either by trained eyesight or with the aide of a metal detector. Comets, Asteroids and Meteoroids are technically classified as different objects based on their size and composition right up until the enter Earth’s atmosphere. It’s at this point they are all technically referred to as a Meteor and if any fragments remain intact when they reach the surface, they are then known as a meteorite.
The Kuiper Belt
Now that you know more about the objects from the nearby Asteroids Belt, lets delve further into space right up Uranus axis towards Neptune and beyond. This leaves us near Pluto, the bullied little guy who just couldn’t quite make the Solar System softball team as a real planet. Since the 1970’s it’s been discussed by scientists around the world if Pluto should be reclassified into something else due to its smaller size as discovered with newer technology and methods since it was first discovered. Several years later on January 5, 2005 a new further object was discovered that we named Eris which is the Greek goddess of strife and discord and would soon display an example of that at her discovery. Measurements of Eris revealed that it’s actually 27% more massive than Pluto which caused a dilemma. Eris was quickly named the 10th planet by NASA until International Astronomical Union (IAU) stepped in and said, “Whoa whoa whoa, wait a minute, let’s actually define what a planet really is.” or something like that. So by August of 2006, Planets would then be discerned as a new term called Dwarf Planets with clear definitions. Dwarf planets are protoplanet-mass objects in space that do not clean out their orbital neighborhood and also do not revolve around other planetary objects. R.I.P. Pluto 1930 – 2006. Pluto got demoted to a Dwarf Planet and the Solar System suddenly only has 8 planets after the history books were already written. Thanks a lot Eris, goddess of strife and discord! A name well lived up to.
In this same region that Pluto orbits is where we are going next to learn about where meteor showers come from. But wait! How can Earth have showers of meteors raining down on it from a place so incredibly distant and thought of as void where no more planets call home? What is this mysterious zone that is the origin of meteor showers here on Earth, you ask? Well nothing short of what we like to call the Kuiper Belt. The kuiper belt is a region of space beyond Neptune where many comets, asteroids and other small icy objects are located.
The main difference between the Asteroid belt between Mars and Jupiter and the Kuiper belt at the outside region of the planets is heat. As you can imagine the kuiper belt is a very cold area because it is so distant from the Sun. This is where ice and dust clump together much like dirty snowballs of many shapes and sizes. Keep in mind that the comets and asteroids are all mostly the same age as the sun and other planets. Around 4.5 to 4.6 billion years old. Here’s the region of space where some of the inner comets come from as you may have guessed. However, did you know there is yet an additional, even more distant place where outer comets come from and will sometimes cross paths with Earth’s orbit.
The Oort Cloud
Outer comets come from a place much much further than the kuiper belt. If you thought the kuiper belt was a long ways away from home, guess again. On September 5, 1977 a satellite called Voyager 1 was launched into space and sent on a one way trip into deep space. Voyager 1 finally got past the kuiper belt 35 years later on August 25, 2012 and is now considered interstellar, but that’s not technically true just yet. It still has yet another 300 years of travel to get to the beginning layer of what we call the Oort Cloud. The Oort cloud totally surrounds our disc shaped solar system in a much larger spherical shape with even colder and bigger comets. It will take Voyager 1 yet another incredible 30,000, yes 30 thousand years to get past this entire thick region of space to finally be in true outer space. However, this cloud of comets around us isn’t exactly like you think. The objects are spaced so far apart that the distance between these objects is about the same distance as the Sun and Saturn are apart. In other words, these Oort cloud objects are on average about 930 million miles apart from each other. Yet this area is so incredibly vast that it reaches half way to the next nearest star, Alpha Centauri which is 4 light years away from us. This Oort cloud is thought to have been close enough to another star in the past that the gravity of the other neighboring star is likely what bumped some of these distant comets into Earth’s direction. Another hypothesis is that there might be an actual large Planet 9 or even a binary dead star in this region. Okay so it’s likely not actually a dark binary star despite what some people speculate, but something of pretty good mass is giving us evidence that whatever it is, it has enough mass to be disrupting the outer comets in the Oort cloud and sending them our way. This incredibly distant region of space is where outer comets come from and some can be the size of large mountains.
Meteor Showers
No matter where the icy-dust balls we call comets come from, near or far, as these objects go rogue and cross paths with Earth’s orbit, they push through space with what we call a Coma in front of them and 2 tails behind them. One tail is a gas tail while the other tail is a dust and debris tail. The coma of a comet is like the windshield of the comet that forms as it plows through space and gets nearer to the sun. It is calculated that some of these comas can reach a width of nearly 1 million miles wide and also have a tail as long as 160 million miles long. To give you an idea of how long these comet tails can be, Earth itself is at a average distance of about 93 million miles so a comet’s tail can sometimes be calculated 60 million miles longer than this distance. As you can see, comets leave a vast debris field behind them that will stay in that orbit until something crosses paths and cleans it up. Now because comets can easily be predicted and their orbital paths be tracked, therefore so can meteor showers. When Earth later crosses one of these old comet paths, the night skies light up with many meteors, hence the name meteor shower. Sometimes these meteors can be seen every couple of minutes and can last for weeks at a time.
Halley’s Comet and the Orionid meteor shower
Halley’s comet is perhaps the most famous comet that was first discovered in 1758 by Edmond Halley who was an English Astronomer from the United Kingdom. It is a short-period comet that can be seen from Earth by the naked eye every 75-76 years. It will next pass by Earth around July 28th, 2061 for all the world to witness yet once again. Some lucky people will even live long enough to see this event happen twice in their lifetime. While its radius is only 3.4 miles, this tiny ice-ball in the sky leaves an orbital debris path behind it that makes for an amazing show in the night sky during an event we call the Orionid meteor shower. The Orionids name came from the point they appear to centrally radiate from, called the radiant, lies in the constellation Orion as seen from the northern hemisphere. This shower usually produces about 20 meteors per hour and can be seen every year from around October 2 through November 7th with peak viewing around October 20th. Although this comet itself passes by only every 75 years or so, keep in mind it’s the dust and debris remnants that can be seen annually as Earth sweeps through this leftover path year after year. The radiant (or center-point) of the Orionids is actually located between the constellations Orion and Gemini (in the south-eastern sky before dawn, as viewed from mid-northern hemispheres. Hence the name Orionid meteor shower. This is just one example of a meteor shower, but the International Astronomical Union (IAU) actually lists nearly 900 of them with 100 well understood. Remember, that’s the same Union who demoted Pluto as a Dwarf planet? Yeah, they are a very busy group over there.
Doomsday Meteors
From movies like Armageddon to Deep Impact, Hollywood certainly knows how to scare and entertain us while leaving doomsday images in our minds for many years. Just this week, there are articles upon articles cascading out around the web about how NASA is supposedly reporting that Earth will be slammed by a 4.4 kilometer asteroid when in fact they created a “hypothetical simulation” video to demonstrate how NASA could potentially try to deflect an asteroid and what would happen if a chunk broke loose and hit Manhattan as an example. The video can be seen here and is for demonstration purposes only and was actually released in 2019, but getting mixed up with recent reports of a 4.4 km object to pass by Earth in April 2020. That is, if you consider 3.9 million miles away as actually passing by Earth.
https://www.youtube.com/watch?v=BWri_KBV_-I
This simulation video combined with an actual real report of an asteroid to “pass by” Earth on April 29 at a distance of 3.9 million miles away. Our moon is about 240,000 miles away so if this is actually considered close to Earth, then at least it gives science fiction writers a lot to mis-articulate online.
What size meteorite killed the dinosaurs?
Speaking of doomsday meteorites, what are the requirements and probability of a meteor like the one to have caused the dinosaurs to go extinct? The Chicxulub asteroid as it is called was estimated to be around 50 miles wide in orbit and 6 to 9 miles wide at impact. This meteorite was an asteroid or comet that blasted into Earth 66 million years ago, devastating the entire globe from immediate impact shock waves that likely circled Earth several times over and left the skies dark for many years thereafter, blocking the sun from reaching the ground long enough to cause an ice-age. How likely is this to ever happen again? Experts speculate that the dinosaur killer event is a 1 every 100 million year event.
In comparison, the Tunguska event was a 1908 meteor that exploded in mid air before making contact with the ground and flattened an estimated 80 million trees over an 830 square mile forested area. Then there’s the largest and oldest known impact crater, Vredefort Crater, located in South Africa. It is approximately 250 kilometers in diameter and is thought to to be about two billion years old. Then there’s the Barringer Crater in Arizona that although it’s not the biggest of impact craters here on Earth, it is one of the most well preserved and measures just under a mile wide. The Barringer Crater object hit about 50,000 years ago and was estimated to be just 50 meters wide.
So what does all this mean?
Although it’s not completely impossible, the chances of a doomsday impact from outer space is actually so low that it can’t accurately be calculated in a realistic statistic, but it’s safe to say this has indeed happened at least once since life formed on Earth. Meteors happen daily and even during the day. Just because you can’t see them streak across the sky most of the time during the day doesn’t mean these same events happen less often when the sun shines down as opposed to night, because they certainly do. In fact, Earth plows through so much dust and debris on a daily basis that it’s estimated to collect between 5 and 300 metric tones of material in a 24 hour period. Most of these meteors however, never make contact with the ground and never cause damage or often hit underpopulated areas and are often never even witnessed. Although Hollywood wants you to believe that big impacts only take place over large populated areas, it’s simply not true and not even a common event to happen in anyone’s lifetime.
The next time you gaze upon the contrasting dark and glimmer of the night sky and suddenly see a streak of light across the backdrop of the night sky, know that somewhere at sometime, a comet, asteroid or meteoroid went rogue to travel a personal unfortunate journey that included a fate with a mightier object we call Earth. This is when these fast traveling rogue objects physically transform into a meteor whether it be a sporadic event or a predictable yet fantastic meteor shower. Oh and not to forget, if one of these meteors has enough material to survive its fiery descent upon Earth and actually make impact with the ground, it is then known as a meteorite.
So whether you call them meteors or falling stars, don’t forget to listen to Shooting Star by Bad Company during the next meteor shower and listen closely to the lyrics, “Don’t you know that you are a shooting star” because no matter what we call them, “all the world will love you just as long, As long as you are“.
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