Asteroids and comets are two of the most common flying bodies in space. The objects have destroyed countless worlds and collided with Earth numerous times. Some scientists also credit them for bringing water to our planet.
However, this doesn’t mean they’re the same. So, what is the difference between asteroids and comets? You’ll find out in this article.
What Is the Difference Between Asteroids and Comets? Key Characteristics of Both
Images make it hard to tell the difference between an asteroid and a comet. You need to understand the features of both celestial bodies.
On the one hand, asteroids are rocks that have been inhabiting our solar system since its formation more than 4.5 billion years ago. On the other hand, they’re remnants from this primordial period orbiting the sun. Most of them can be found in the Asteroid Belt, a part of the system between Jupiter and Mars that contains countless rocks.
The term “asteroid” derives from Ancient Greek for “starlike” because scientists initially thought the objects resembled stars. They come in different shapes and sizes, with diameters of some units eclipsing the 300-mile mark. To put this into perspective, the asteroid that wiped out dinosaurs more than 60 million years ago was just 7.5 miles across. Some units are even smaller, with diameters of approximately 30 feet.
On the other hand, comets are made up of ice, gas, and rocks. Like asteroids, they’ve been traveling the solar system since its formation and revolve around the sun. As a comet approaches the sun, its dust, and ice melt, creating a gorgeous trail. The trails can span more than a million miles, and you can sometimes spot them from Earth.
So far, astronomers have discovered nearly 4,000 comets, but the number is likely much higher. There are probably billions in our solar system. Most reside in the so-called Kuiper Belt, an area near Neptune. They’re also located in the Oort Cloud, surrounding the system’s outer edges.
Considering all these features, you can already answer the titular question: What is the difference between asteroids and comets? Of course, the most significant difference is the composition. Comets mainly comprise rocks, dust, and ice, whereas rocky materials and metals make up asteroids.
Another significant difference is the place of their formation. Although both asteroids and comets formed in the solar system’s earliest days, comets were created far from the sun. As a result, their ice couldn’t melt. Conversely, asteroids were developed relatively near our central star, where ice couldn’t remain solid. This is how the rocky, solid surface of these objects was formed.
We’ve also mentioned their primary locations. You can commonly find asteroids in the belt between Jupiter and Mars, while comets typically orbit our central star in two areas. Most are in the Kuiper Belt, but some have settled in the Oort Cloud.
On top of that, asteroids typically don’t produce meteor showers, while this is one of the most famous properties of comets. In fact, comets are the typical source of meteors that shower the Earth once a year. The reason is simple – comets are relatively flimsy and leave trails of ice when coming close to the central star.
As our planet plows through these trails, the debris enters the atmosphere, and we experience captivating meteor showers. For instance, the Eta Aquariids and Orionids are showers brought about by debris from Halley’s Comet. The Leonid Shower originates from Tempel-Tuttle.
The last difference has to do with their trajectory when approaching the sun. When passing near the star, comets develop tails, and their orbit isn’t uniform. In contrast, asteroids don’t have tails when traveling near the sun, and the trajectory is constant.
Exceptions to the Rule
If someone were to ask you now, “What is the difference between asteroids and comets?” you’d probably list the above characteristics. But unfortunately, not all asteroids and comets fall into those categories. As with any other generalization, there are exceptions to the rule.
For instance, not all comets come from the Kuiper Belt and Oort Cloud. There’s also a small group whose orbits are close to the central star. These comets have orbital periods shorter than two centuries and the same trajectories as planets. The only exception is Halley’s Comet, which moves in a unique direction.
We’ve also discussed that meteor showers generally stem from a comet. However, that’s not always the case. For example, the Geminid shower, which takes place every December, springs from 3200 Phaethon, a mysterious celestial object. It’s often referred to as a rock-comet because it combines the characteristics of asteroids and comets. It has a rocky surface, but unlike other asteroids, it grows a tail when approaching the sun.
This isn’t the only body that blurs the distinction between comets and asteroids. For example, 311P/PANSTARRS is an asteroid that doesn’t have just one tail – it creates six trails when it starts melting. This object is one of the so-called main-belt comets, a group of comets that contain buried ice dating from the creation of our solar system.
What Are the Different Types of Asteroids?
Asteroids come in various sizes, but that’s not the only way they’re classified. Astronomers use two main categories to distinguish between different types of asteroids:
Composition
Here’s how asteroids are categorized according to their composition:
C-Type Asteroids
C-Type asteroids got their name from high contents of carbon. Nearly three quarters of all asteroids fall into this group, especially in the belt between Jupiter and Mars.
Besides carbon, they’re also rich in other metals and silicates. That’s why they’re dark and haven’t been detected in large groups at the edges of the solar system. Another thing that prevents astronomers from discovering them is that they absorb virtually 100% of the sunlight directed at the surface. Consequently, they reflect little-to-no light, which searches much harder.
The C-Type is the oldest type of asteroid in the system. Plus, they’re far away from our central star (3.5 astronomical units), reducing the effects of physical or chemical solar deformation. This makes them perfect artifacts for examination.
The largest C-Type asteroid is Hygiea, with 270 miles across. The title belonged to Ceres, but the rock was eventually classified as a dwarf planet.
S-Type Asteroids
S-Type asteroids are iron-nickel and silicate, making them the second most abundant rock group in the system. They’re usually found on the inner edges of the Jupiter asteroid belt, contributing to about 17% of the total number of asteroids.
They’re brighter than C-Type rocks, allowing scientists to discover them more easily. The biggest S-Type asteroid is 15 Eunomia, with a surface of 205 miles across.
M-Type Asteroids
The last composition category is the M-Type. They’re the least common group, so little is known about the formation. Most contain iron and nickel, but specific characteristics depend on the distance from the dun. The closer they are to the central star, the larger portion of their surface has been melted. Conversely, those at a safe distance retain their structure and composition.
The biggest M-Type asteroid is 16 Psyche, that’s 120 miles in diameter.
Location
Asteroids are also classified according to their location:
Main-Belt Asteroids
Most known asteroids are located in the belt between Jupiter and Mars. The rocks typically have circular orbits, and the belt contains approximately 1.5 million asteroids that are 0.6 miles or longer in diameter. The number of smaller rocks is much larger.
Gravity is the main culprit for the formation of this belt. Early in the system’s history, Jupiter’s gravity terminated the region’s creation and caused smaller bodies to slam against one another. In turn, the objects were fragmented into asteroids.
Near-Earth Asteroids
Near-Earth asteroids have orbits close to Earth. Some rocks even trespass our planet’s orbit and are called Earth-crossers.
Trojan Asteroids
Trojan asteroids are a unique group that shares the same orbit as a nearby planet. Astronomers also call them co-orbital objects, and they’re located near the areas of gravitational equilibriums of larger moons or planets (Lagrange points). These regions are convenient because they help prevent the planets and asteroids from colliding.
There are two massive Trojan groups near Jupiter – the Greek and Trojan Camp. This group is in a never-ending astronomical dance. The gravity of Jupiter pulls the rocks toward the planet. The dun does the same (larger but far away), resulting in a swarm in Lagrange points that never leave the area.
Surprising as it may sound, there are Trojan asteroids near Earth too. One of them is named 2010 TK7. Its width is about 200 miles, but it doesn’t threaten the planet because the orbit is stable.
What Are the Different Types of Comets?
Comets don’t have official classifications. Instead, they fall into various categories based on their trajectory, location, and many other characteristics.
Periodic Comets
These comets orbit the dun and are divided into two groups:
- Short-period Comets – These are comets that complete their orbits in under 200 years.
- Long-period Comets – Their orbit takes more than two centuries to complete.
Periodic comets are generally named after the people who discovered the objects. For example, the Shoemaker-Levy rocks are named after David Levy, Carolyn Shoemaker, and Eugene Shoemaker. Other comets are named after scientists who calculated the orbit, like 27P/Crommelin and 2P/Encke.
Non-Periodic Comets
Comets that people have observed just once or whose trajectory takes millennia to complete are non-periodic comets. Even though some have orbits, the chances of noticing them are minimal.
Comets Without a Meaningful Orbit
These comets originate from our solar system but don’t have a fixed trajectory. The dun only serves as a powerful slingshot that sends them flying to other parts of the universe. They’re also known as parabolic comets.
The most famous parabolic comet is the Great Comet of 1106. It was observed by scientists worldwide, from Continental Europe, England, and Wales to Japan, China, and Korea. The rock split into various pieces and formed several other comets.
Sungrazing Comets
Sungrazing comets generally belong to the so-called Kreutz Sungrazers. This group originated from the Great Comet of 1106 and a comet that approached the Earth in 371 BC.
Dead Comets and Exocomets
The gasses of these dead comets are consumed, which is why they lack tails.
Finally, exocomets exist outside the solar system. Most of these have been located orbiting Beta Pictoris, the second-brightest star in the constellation Pictor.
What’s the Largest Comet Ever Recorded?
Astronomers have recorded many gigantic comets, but none larger than Bernardinelli-Bernstein (C/2014 UN271). Captured in 2022, the image of this comet shows an 80-mile object hurling 22,000 miles per hour. The core is about 50 times bigger than average cores, and the body is more massive than Rhode Island.
The temperature of the comet is approximately -350° Fahrenheit. But despite the icy surface, it has enough warmth to expel carbon monoxide, forming a cloud of gas and dust around the center.
The Hubble Space Telescope photographed this behemoth, which is expected to pass the sun in the next 10 years or so. Still, it should be more than one billion miles away from our central star and nowhere near close enough to threaten Earth.
What About Shooting Stars?
Another term frequently appearing when discussing asteroids and comets is “shooting stars.” However, a shooting star isn’t actually a star. On the contrary, it’s a small celestial body that enters our atmosphere and heats up so intensely that it produces a bright light. If it’s large enough, it’ll have enough minerals to survive the air and reach the ground.
Astronomers don’t like the term “shooting star.” So instead, they use meteors and meteorites. Meteors are parts of comets that burn up before reaching Earth’s surface, while meteorites make it to their destination. Also, meteorites shouldn’t be mistaken for asteroids because they’re much smaller.
Simple Distinctions
Without advanced equipment, experts would still be puzzled: what is the difference between asteroids and comets? Cutting-edge technology has provided the answer – comets have tails and ice, whereas asteroids are mostly rocky objects without tails.
Regardless of the differences, both celestial bodies will remain fascinating research subjects for years to come.