Asteroid Belt Facts

Asteroids are mostly really big rocks that follow the same general orbit around the Sun. Scientists say there are more than a million asteroids in our solar system, and asteroids sometimes impact the Earth. One impact caused most of the dinosaurs to go away forever and a very long time ago.

Asteroid Belt Facts for Kids

• Asteroids are large chunks of rocks leftover from when the solar system formed 4.6 billion years ago.
• Asteroids do not have air or any living things on them.
• The smallest asteroid is about 30 feet in diameter and the biggest more than 300 miles across.
• Scientists count and track 1,055,437 asteroids in the asteroid belt.
• The asteroid belt has far more space than asteroids, so a collision with the Earth is impossible most time.
• The combined size of all asteroids in the asteroid belt is less than the size of Earth’s moon.

An asteroid is something that scientists only became aware of about 200 years ago when telescopes finally became strong enough to see them. Compared to other objects in the nighttime sky, like stars and the moon, an asteroid is really hard to see. Most people only see an asteroid when a very small one enters the Earth’s atmosphere and burns up without ever reaching the ground.

Those really small meteors are like really tiny asteroids but manage to show up a lot more often. Some even make it all the way to the ground and can cause a lot of commotion. But most just die out when they burn up and leave a trail of light in the nighttime sky. Those are the shooting stars that many people enjoy watching when a meteor shower makes its way through our part of the solar system.

Asteroids and comets are not the same things. A comet generally is made up of ice, dust, and rock. An asteroid mostly is rock and metal, which makes it much denser than a comet. Both objects orbit the Sun, but a comet gets smaller whenever it passes near the Sun as it loses some of its ice. An asteroid stays the same size – unless it impacts the Earth or another planet, moon, or similarly massive object.

Comets also never are confused with planets, but asteroids actually qualify as planets in many instances. Some have an internal core with a mantle, just like Earth. The largest known asteroid even has telltale signs of volcanic activity that went dormant long ago. But the similarities between asteroids and the planets near them suggest the asteroids are much more closely related to nearby planets than the comets that make regularly scheduled passes through the solar system.

What is the asteroid belt?

The asteroid belt sounds really scary and big, but it really is not either one. Instead, the asteroid belt is an area in our solar system where just about all asteroids that scientists at NASA and other places like it have located. The asteroid belt is a grouping of more than a million very large rocks that continually orbit the Sun. Those rocks often are made of the very same materials as the planets located nearby. That has many scientists convinces that asteroids are the leftovers from when our solar system first came into existence.

Some of the bigger asteroids even have names, like Vesta, which is the biggest one of them all, with a diameter measuring 329 miles. Vesta is a big rock in space that is very much a part of our solar system. It also is just like the more than 1 million other asteroids in the asteroid belt in that it comes from the same event that created our planet, the Sun, and all the other great objects in our solar system.

NASA says Vesta shows signs that lava once flowed on its surface. That means it used to have volcanos, just like the Earth does now. Maybe it even was part of the Earth or one of the other eight planets in our solar system but separated before things cooled enough to keep it all together.

Vesta is not round. Instead, it has a kind of a smashed shape to it, with its surface covered with lots of pockmarks. Those are the scars from smaller asteroids striking its surface and creating smaller craters. It is kind of like acne for asteroids.

Nothing lives on Vesta, at least not like we know living things to be. That is because Vesta, like all other asteroids, does not have an atmosphere. An atmosphere is a thing that keeps everything on Earth alive with breathable air and a stable environment. Without an atmosphere, the Earth would be a mostly barren rock, just like Vesta or the moon.

Vesta undergoes extreme temperature changes, with sunlit areas being extremely hot and those facing away from the Sun is extremely cold. Those extreme temperature changes make it impossible for life to exist on Vesta, which some scientists say is more of a tiny planet than an asteroid. It even has its own smaller asteroids that stay with Vesta as the moon stays with the Earth.

What is the asteroid belt made of?

The asteroid belt still is a bit of a mystery to scientists in that they are not sure what exactly made it. They know it is as old as the planets and includes many large objects, like the Vesta asteroid, that many scientists say is a tiny planet. More than 1 million of these large rocks and tiny planets ranging in size from about 30 feet in diameter to more than 300 miles across make up the asteroid belt.

The asteroid belt has two general sources that created all of the objects within it. Those are the planets located closer to the Sun, like the Earth, that are dense and generally rocky. The other source is the outer planets in the solar system that are less rocky and more gaseous in nature. That means their outer surfaces lack the rocky firmness of Earth or Mars and are more like a soupy substance – that either is exceptionally hot or frozen over.

The asteroids that are closer to the Earth and Mars are made up of silicate and other things more like it. Those asteroids are called “S-type” because of the silicate that they contain. The asteroids that are located closer to large and gassy planets like Jupiter are called C-type asteroids because they have a lot more carbon than the S-type asteroids. Another type, called “M-type,” is generally metallic.

The S-type asteroids are more common in the inner part of the asteroid belt, which is closer to the Earth and Marts. The C-type asteroids more commonly are found on the outer edges of the asteroid belt. The two types of asteroids and their nearness to the planets that are more like them raise a new theory on how the asteroid belt came about. There are other types of asteroids, but the S-, C- and M-types are the most common.

A new theory suggests the material in the asteroid belt is discarded from the planets and their moons in fixed orbits and makes its way into the asteroid belt. Once the loose material enters the asteroid belt, they wind up staying for as long as the solar system remains intact. The total mass of all the objects inside the asteroid belt is much less than what the moon has inside of it.

Where is the asteroid belt?

The asteroid belt is located in orbit around the Sun and positioned between Mars and Jupiter. The largest portion is located just beyond Mars, which is the planet located fourth-closest to the Sun. The Earth is the third-closest planet to the Sun. The asteroid belt has a very larger inner ring that has the majority of the more than 1 million known asteroids located within it. Those asteroids generally are rocky in nature and likely come from the rocky planets in the solar system. Those planets are Mars, Earth, Venus, and Mercury.

Although that thick inner ring has many hundreds of thousands of asteroids inside it, those asteroids have a lot of space separating them. The belt itself is mostly empty, which makes it far less likely that an asteroid will strike out the planet anytime soon.

The outer edges of the asteroid belt are located roughly along the same orbit as Jupiter and contain mostly gaseous and icy asteroids. They are less in number and follow an even longer orbit around the Sun than the Earth, which virtually nullifies any threat they might pose to our planet.

How was the asteroid belt created?

The source of the asteroid belt generally is known, but exactly how it was made is unknown. The general theory is that the asteroids are parts of the planets themselves but became separated over time. The outer planets are mostly bigger and less dense than rocky planets like Earth. So are the asteroids that are located near those planets.

The asteroids located near rocky planets like Earth mostly have a similar structure. The common nature of asteroids and the planets that are closest to them tells some researchers that those asteroids are part of the same material and events that created the solar system and maybe even the universe. Scientists say the debris left from the creation of the planets in our solar system now makes up the asteroid belt.

Others say the asteroid belt is a work in progress and continues to get larger as more debris makes its way into the belt from the nearby planets and their moons. Whether growing or staying the same size, the asteroid belt always will hold our attention.

Does Earth pass through the asteroid belt?

The Earth does not pass through the belt itself but does cross its orbital path once every year. More often than not, the Earth and the asteroids that make up the belt are located very far apart and are not a threat to one another. NASA maintains a watch on every known asteroid and uses math to see if any might become a threat to Earth. So far, nothing has proven threatening.

The total mass of the asteroids contained inside the belt is much smaller than the Earth’s entire mass. Mass refers to the amount of matter that something has inside it, and the Earth has a lot of it. Asteroids, thankfully, do not. That makes it highly unlikely a massive asteroid strike will cause a significant change in the Earth’s atmosphere and have a bad effect on all things living here.

With Jupiter and Mars located much closer to the asteroid belt, odds are both have taken many more asteroid strikes than Earth. Yet, both planets remain intact, although with no life on them. If an asteroid were to become a threat, scientists on Earth would have lots of warning and a better idea of potential damage, if any, that might happen

Can an asteroid hit Earth?

Yes, an asteroid can hit the Earth. Meteorites are very small asteroids that make their way into the atmosphere and survive the entry until impacting the Earth. More than one already has struck the Earth, but it has been a very, very long time since that happened. NASA scientists say an asteroid hits the Earth about once every 100,000 years, which makes it unlikely it will happen again anytime soon.

For an asteroid to strike the Earth, the asteroid belt and Earth would have to occupy the same space at the same time. Most times during the year, that just cannot happen. That is because the Earth and the asteroid belt almost never are in the same place at the same time. Instead, they often are located at opposite ends of the solar system, with the Sun being the one common thing that keeps them close to each other.

Saying something is close in the solar system is not like saying something is close to where you are sitting. The solar system is an incredibly large place made up of mostly empty space. The asteroid belt also has mostly empty space separating the more than 1 million asteroids found inside the belt.

What happens if asteroids hit Earth?

An asteroid strike could cause mass destruction, but only if it is about a kilometer or larger in size. The best-known example of a very large asteroid hitting the Earth happened about 66 million years ago. Scientists say an asteroid strike near Mexico’s Yucatan Peninsula likely caused about 75 percent of life on Earth to die out – including those dinosaurs that so many of us love to watch in movies like Jurassic World. That asteroid hit the Earth with such force that it created a huge crate and virtually destroyed the asteroid.

The impact from that asteroid strike likely created a global layer of dust and soot that reduce the amount of sunlight reaching Earth. The impact also likely created deadly gases that killed many of the plants and animals on the planet. The combination of reduced sunlight for an unknown number of years and deadly gases in the atmosphere made sure the big dinosaurs living on Earth could not survive.

When large asteroids impact the planet, they leave telltale signs. The one that killed off the dinosaurs left a crater that measures more than 93 miles across. The largest known asteroid crater is twice as big and comes from an asteroid impact that happened about 2 billion years ago in South Africa. Scientists say the asteroid that made the largest known crater measures about 6 miles across, which is just a tiny fraction of the size of the largest known asteroid.

How far away is the asteroid belt?

The asteroid belt is more of empty space than a location occupied by actual asteroids. The belt refers to their general path of orbit around the Sun. That path is mostly empty, which is why not only the Earth but Mars and other planets regularly pass through the asteroid belt’s orbit with no impacts.

The actual distance from the Earth to the asteroid belt varies but generally ranges from between about 100 million miles and 200 million miles. That is about the same distance between the Earth and the Sun, but that distance varies based on how the objects are orbiting. The asteroids within the belt at times are located on the opposite side of the Sun as the Earth, which makes it virtually impossible for an asteroid to strike during such periods.

The Earth does cross paths with the asteroid belt once each year. The asteroid belt has a longer orbit and generally crosses the Earth’s path or orbit about every three years or so. That means the Earth is not going to come into contact with an asteroid anytime soon. It also means our scientists can keep an eye on the asteroid belt and have lots of warning if another major asteroid strike might repeat the damage done 66 million years ago when the dinosaurs died out due to a likely asteroid strike near Mexico.