Asteroids, Comets, and Meteors: 10 Questions Kids Ask

1. What's the difference between an asteroid, a comet, and a meteor?

Think of it like this: Asteroids are mostly made of rock and metal. They usually live in the inner part of our solar system, especially in a big belt between Mars and Jupiter. They're like big, lumpy potatoes of rock.

Comets are more like dirty snowballs. They're made of ice, dust, and rock. They usually come from the outer, colder parts of our solar system. When they get close to the Sun, the ice melts and forms a beautiful tail.

A meteor is what we call a small piece of an asteroid or comet that enters Earth's atmosphere. It burns up from the friction with the air, creating a bright streak of light we call a 'shooting star.' If a piece of that rock survives and lands on Earth, it's then called a meteorite.

2. Are asteroids dangerous, and could one hit Earth?

It's a good question to ask! Scientists keep a close watch on asteroids that could come near Earth. While very large asteroids could cause big problems if they hit our planet, most asteroids are quite small and would burn up harmlessly in our atmosphere.

Scientists use powerful telescopes to track thousands of asteroids. They know the paths of almost all the really big ones. So far, no large asteroid is known to be on a path to hit Earth anytime soon. It's something we monitor carefully, but it's not something to worry about every day.

3. Where do asteroids and comets come from?

Most asteroids come from the 'Asteroid Belt,' a huge doughnut-shaped region between the orbits of Mars and Jupiter. This belt is filled with millions of asteroids, from tiny pebbles to objects hundreds of kilometers wide. They are leftover building blocks from when our solar system first formed, about 4.6 billion years ago.

Comets come from much farther away. Many come from the 'Kuiper Belt,' which is beyond Neptune and Pluto. It's like a second, much bigger asteroid belt, but filled with icy objects. Even farther out is the 'Oort Cloud,' a vast, spherical cloud of icy bodies that surrounds our entire solar system. Comets are also ancient leftovers from the solar system's birth.

4. What are comets made of, and why do they have tails?

Comets are often called 'dirty snowballs' or 'cosmic icebergs.' They are made of frozen gases (like water, carbon dioxide, and methane), mixed with dust and rocky particles. At their heart is a solid, icy core called the nucleus.

When a comet gets closer to the Sun, the Sun's heat makes the ice turn directly into gas – a process called sublimation. This gas, along with dust particles, streams away from the comet, pushed by solar wind and sunlight. This creates the beautiful, glowing tail (or sometimes two tails!) that we see. The tail always points away from the Sun, no matter which way the comet is moving.

5. Have we ever sent a spaceship to an asteroid or comet?

Yes, absolutely! Scientists have sent several amazing missions to visit these space rocks. For example, NASA's OSIRIS-REx mission collected a sample from an asteroid called Bennu and brought it back to Earth in 2023. Japan's Hayabusa2 mission also brought samples back from asteroid Ryugu.

For comets, the European Space Agency's Rosetta mission famously orbited Comet 67P/Churyumov-Gerasimenko for over two years and even landed a small probe, Philae, on its surface! These missions teach us so much about the early days of our solar system.

6. What is a 'shooting star,' and is it really a star?

A 'shooting star' is not actually a star at all! It's a small piece of rock or dust – usually from a comet or asteroid – that enters Earth's atmosphere at very high speed. As it zips through the air, friction causes it to heat up and glow brightly. This burning trail of light is what we see as a 'shooting star.'

The scientific name for a 'shooting star' is a meteor. Most meteors are tiny, often no bigger than a grain of sand, and they burn up completely long before they reach the ground. Sometimes, Earth passes through trails of dust left behind by comets, causing many meteors to light up the sky in what we call a 'meteor shower.'

7. How big are asteroids and comets usually?

Asteroids come in a huge range of sizes. The biggest asteroid, Ceres, is so large (about 940 kilometers across) that it's also classified as a dwarf planet! But most asteroids are much smaller, from just a few meters to a few hundred kilometers across. Many are like boulders or even pebbles.

Comet nuclei (their solid, icy cores) are usually much smaller than asteroids, typically ranging from a few hundred meters to tens of kilometers across. However, when a comet gets close to the Sun and grows its tail, the tail itself can stretch for millions of kilometers, making it one of the largest structures in the solar system!

8. Could we mine asteroids for valuable materials?

This is a fascinating idea that scientists and engineers are thinking about for the future! Asteroids are rich in metals like iron, nickel, and even precious metals like platinum. Some also contain water ice, which could be used for drinking water, or even broken down into hydrogen and oxygen to make rocket fuel.

Mining asteroids is very challenging because they are so far away and moving so fast. We don't have the technology yet to do it easily or cheaply. But it's an exciting possibility that could one day provide resources for space exploration or even for use back on Earth.

9. Why do some comets visit us often, and others only once?

It all depends on their orbit! Comets are grouped into 'short-period' and 'long-period' comets. Short-period comets, like the famous Halley's Comet, have orbits that bring them close to the Sun (and visible from Earth) relatively often, usually less than 200 years. Halley's Comet visits every 75-76 years, which means some people get to see it twice in their lifetime!

Long-period comets, on the other hand, come from the very distant Oort Cloud. They have extremely stretched-out orbits that can take thousands or even millions of years to complete. When one of these comets swings into the inner solar system, it might be the first and only time humans will ever see it. After that, it heads back out into the deep, cold reaches of space for a very, very long time.

10. Are there still undiscovered asteroids or comets out there, and how many?

Yes, definitely! Space is vast, and there are still countless asteroids and comets waiting to be found. Scientists are constantly discovering new ones with powerful telescopes. We know the locations of most of the very large objects, but smaller ones are still being found all the time.

For asteroids, we've discovered hundreds of thousands, but there are likely millions more, especially the smaller ones. For comets, many of the long-period comets from the Oort Cloud are still unknown because they spend most of their time so far away from the Sun and Earth. Every year, new discoveries are made, adding to our understanding of our solar system's population!