The Kuiper Belt orbits around the sun just beyond the orbit of Neptune. It covers a vast region of space starting about 2.7 billion miles (4.4 billion kilometers) from the sun. It stretches to about 9.3 billion miles (14.9 billion kilometers) away from the sun.
Here’s another way of thinking about it. The distance from the sun to the Earth is described as 1 atomic unit (AU). The Kuiper Belt stretches from 30 AU to 100 AU from the sun. That means the distance from the inside edge of the Kuiper Belt to its outside edge is much wider than the region inside the Kuiper Belt, the region from the sun to Neptune! (Compare that to the Asteroid Belt, which is only 140 million miles wide.)
If you have ever seen a model of the solar system, you know the eight planets all travel in the same plane around the sun. Their orbits–the paths they take–look like a disc (or flat plate) of rings around the sun. The Main Asteroid Belt also orbits around the sun, between the orbits of Mars and Jupiter, along this same plane. The Main Asteroid Belt is flat.
Unlike the Main Asteroid Belt, the Kuiper Belt is not flat. It is donut-shaped with icy bodies orbiting the sun above and below the plane or disc formed by the orbits of the planets.
The largest object in the Kuiper Belt is the dwarf planet Pluto. Astronomers once called Pluto a planet, but in 2006 it was reclassified as a dwarf planet. Like other planets, it orbits the sun and it has enough mass to have formed a round shape, instead of the bumpy, irregular shape of an asteroid. But Pluto’s gravity has not cleared a path through Pluto’s orbit of asteroids and other bodies.
Most of the objects floating in the Kuiper Belt are small clumps of rock and ice. These are ancient remnants left over from the formation of our Solar System.
The solar system is made of giant, orbiting bodies: planets
Eight planets orbit the sun, forming our solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Asteroids also orbit the sun in the Main Asteroid Belt and the Kuiper Belt. The planets and the Main Asteroid Belt orbit the sun in a flat plane, like an invisible plate in space where the planets pass mainly through the plate. Sometimes they rise higher than the plate, sometimes they travel a little lower, but not by much.
The planets are very large objects. The sun, at the center, is the largest object in our solar system.
Tiny atoms are made of microscopic bodies that orbit each other
Next, let’s look at some of the very smallest objects in our universe: atoms. According to physicist and author Brian Greene, in his book The Elegant Universe, the ancient Greeks believed that “the stuff of the universe was made up of tiny ‘uncuttable’ ingredients that they called atoms.” The ancient Greeks thought the atom was the smallest building block of all matter. They said the atom was not made of anything smaller and could not be divided.
In the nineteenth century, scientists found that oxygen and carbon were made of the smallest pieces that could be recognized. “[F]ollowing the tradition laid down by the Greeks, they called them atoms. The name stuck,” Greene writes.
But it was later learned that oxygen and carbon atoms, and atoms of all the other elements, were made up of even smaller pieces. “Far from being the most elementary material constituent, atoms consist of a nucleus, containing protons and neutrons, that is surrounded by a swarm of orbiting electrons,” Greene writes.
Writers create new ideas by converting large to small or small to large
Today, let’s do the reverse. Let’s take something very, very large–our solar system–and imagine it as small as an atom. If a sun were the nucleus of an atom, and if each electron orbiting around that nucleus were a planet, what kind of solar system can you imagine?
Build your mini-system!
Imagine your miniature solar system.
Would your planets be inhabited? Would the third planet–like Earth–support life?
Would travelers cross the vast distances between atoms to visit?
Where would your atom-sized solar system be floating? Would it be safe?
Today is Wednesday, so it’s time for our regular feature What is that? Here’s today’s term:
Comet – an object orbiting the sun made of rock and ice that grows a “tail” of vapor and dust when it approaches the sun
Comets are sometimes described as “dirty snowballs” because they are made of a mixture of both ice and rock and dust. They orbit the sun in an elongated, oval path that can take hundreds or even millions of years to complete. They may spend much of their time traveling through the Kuiper Belt, a region of space beyond Neptune, the furthest planet from our sun.
Comets are different from asteroids, which tend to be composed of rock and/or metals, because they contain large amounts of ice–frozen water and other frozen gases.
This image of Comet Ison, published in 2013, was made from combined photos taken through blue and red filters. Source: NASA/ESA/Hubble Heritage Team (STScI/AURA).
“When frozen, they are the size of a small town. When a comet’s orbit brings it close to the Sun, it heats up and spews dust and gases into a giant glowing head larger than most planets,” according to NASA.
When a comet’s orbit brings it near to the Sun, the Sun’s warmth heats up the comet’s ice. The melted ice boils off and the comet’s ice, dust, and rock surface make a cloud around the comet. As the cloud trails behind the comet it leaves a wide path of particles millions of miles long. The sun lights up this tail, sometimes making it visible on Earth.
Parts of a comet
Nucleus–the main body of the comet, which is made of frozen gases, rock and dust
Coma–the cloud of particles and gases that form around the comet nucleus when it is heated by the Sun
Head–when a comet is traveling near the sun, and a coma forms, the head is the nucleus and coma, which may be 600,000 miles (1 million kilometers) across. The head is a bright cloud of particles and gases lit by the sun.
Tail–when the comet is near the sun and the coma forms, the tail is the long trail of particles and gases left behind the head as it hurtles through space. Tails can stretch for millions of miles.
How many comets are there in our solar system?
Scientists estimate there are billions of comets orbiting the Sun in paths that pass far outside Neptune’s orbit. They travel in the far distant portions of our solar system called the Kuiper Belt and the Oort Cloud.
Although scientists think there are billions of comets, we have only discovered and named less than 4,000 comets.
How are comets named?
A comet is usually named after the person that discovered it. Halley’s Comet, perhaps the most famous comet, is named after Edmond Halley, an English astronomer. He studied historical reports of other astronomers and suggested that reports of a comet appearing every 75 years might be the same comet. He predicted it would appear again in 1758. He was right and the comet was named after him. But he did not live long enough to see its return and his theory proven.
Halley’s comet will not appear to us on Earth again until 2061.
Many comets now have the names of spacecraft in their names–names like Linea, Soho and Wise–because spacecraft (and their operators) are very good at finding comets.
Design your own comet!
Imagine you discovered a comet flying through space and it was named after you. What would it look like? What types of ices and rock would it be made of? How long would it take to orbit the Sun? What year would we see it next in Earth’s nighttime sky?
Asteroid – lump of rock or metal that orbits the sun
An asteroid, a word also meaning “like a star,” is a lump of rock or metal–and sometimes ice–that orbits the sun. Some orbit the sun directly, some orbit other planets, and some orbit our entire solar system.
What is the Asteroid Belt and where is it located?
Millions of asteroids orbit the sun just like the Earth and the planets do. Most of the asteroids scientists have found are located in the Main Asteroid Belt, which is a band of asteroids 140 million miles wide. The Main Asteroid Belt starts just outside the orbit of Mars and is well inside the orbit of Jupiter, which is the next planet out from Mars.
See an amazing image of the Main Asteroid Belt here at Space.com. (The Main Asteroid Belt is shown in green.)
If you have ever seen a model of the solar system, you know the eight planets all travel in the same plane around the sun. Their orbits–the paths they take–look like a disc (or flat plate) of rings around the sun. The Main Asteroid Belt creates a thick ring on this same plane, like its part of the same disc or plate. The asteroids in the Main Asteroid Belt also travel in the same direction around the sun as all the planets of our solar system.
What are asteroids made of?
Most asteroids in the Asteroid Belt are made of rock. Some asteroids are made of metal–mostly iron and nickel. These metal asteroids are shiny and reflect the sun’s light. Some asteroids are made of a mix of rock and metal. And some more distant asteroids are made of ice. Some asteroids may even contain ice made from water, which could be useful to support astronauts if we colonize the Asteroid Belt.
Some asteroids are solid. Some asteroids are just “piles of rubble held together by gravity,” according to an article by Nola Taylor Redd on Space.com. “Most asteroids aren’t quite massive enough to have achieved a spherical shape and instead are irregular, often resembling a lumpy potato.”
How big are asteroids?
Asteroids range from the size of specks of dust to moonsize. The largest asteroid in the Asteroid Belt is the dwarf planet Ceres. It is almost 590 miles across (diameter). That is small compared to Earth’s moon, which has a diameter of 2,158 miles. But it’s much bigger than one of Mars’s moons, Deimos, which is only seven miles across.
Ceres comprises 25 percent of the mass in the Main Asteroid Belt.
There are a number of other asteroids that are 100 and 200 miles long.
What about other asteroids?
Beyond Neptune is an even wider ring of asteroids called the Kuiper Belt. The Kuiper Belt includes the dwarf planet Pluto, which astronomers once used to count among the nine planets in our solar system. There is even a snowman-shaped asteroid in the Kuiper Belt named Arrokoth.
The asteroid Eros has made history both in astronomy and science fiction.
Discovery of Eros
Two astronomers discovered Eros independently on the same day, August 13, 1898–Gustav Witt in Berlin, Germany and Auguste H.P. Charlois in Nice, France. It was the first near-Earth asteroid ever discovered.
NASA’s visit to Eros
Eros was also the first asteroid on which we have landed a spacecraft. Eros, named after the Greek god of love, was first orbited by a spacecraft, the NEAR spacecraft, on Valentine’s Day, February 14, 2000. After nearly a year orbiting and studying Eros, the NEAR spacecraft landed on Eros on February 12, 2001.
Astronomers have also used Eros to determine the distance between the sun and the Earth and to determine the combined mass of Earth and the Moon.
Eros also entered the annals of Science Fiction in the novel Ender’s Game, which won both the Hugo and Nebula awards.
In Ender’s Game, the hero Ender Wiggin travels to the asteroid Eros, which has been turned into I.F. Command, a military base and training center, to finish his military training.
“The tug reached Eros before they could see it. The captain showed them the visual scan, then superimposed the heat scan on the same screen. They were practically on top of it–only four thousand kilometers out–but Eros, only twenty-four kilometers long, was invisible if it didn’t shine with reflected sunlight.”
“The captain docked the ship on one of the three landing platforms that circled Eros. It could not land directly because Eros had enhanced gravity, and the tug, designed for towing cargoes, could never escape the gravity well.”
. . . .
“Ender hated Eros from the moment he shuttled down from the tug. He had been uncomfortable enough on Earth, where floors were flat; Eros was hopeless. It was a roughly spindle-shaped rock only six and a half kilometers thick at its narrowest point. Since the surface of the planetoid was entirely devoted to absorbing sunlight and converting it to energy, everyone lived in the smooth-walled rooms linked by tunnels that laced the interior of the asteroid. The closed-in space was no problem for Ender–what bothered him was that all the tunnel floors noticeably sloped downward. From the start, Ender was plagued by vertigo as he walked through the tunnels, especially the ones that girdled Eros’s narrow circumference. It did not help that gravity was only half of Earth-normal–the illusion of being on the verge of falling was almost complete.
[E]veryone lived in the smooth-walled rooms linked by tunnels that laced the interior of the asteroid.
“There was also something disturbing about the proportions of the rooms–the ceilings were too low for the width, the tunnels too narrow. It was not a comfortable place.”
By the end of Ender’s Game, we learn the secret of the unusual construction of the base inside Eros. But I won’t spoil author Orson Scott Card’s surprise. So read Ender’s Game and find out for yourself.
Design your own asteroid!
As we’ve seen, asteroids can be any shape you want. What shape would you make your asteroid? Would you create a military base or a shopping mall inside it? Or would you make a theme park or a factory on the outside?
Would you add your own gravity–like I.F. Command did in Ender’s Game? Or would you let visitors enjoy the fun of zero-grav?
Today is Wednesday, so it’s time for our regular feature What is that? Here’s today’s term:
Light Year – a unit of length used to measure great distances in space
Light Year is a confusing term. We all know what a year is. A year is the length of time from your birthday to your next birthday. It is also the length of time it takes the Earth to travel around the sun one time. That idea may help us.
A year measures time. It is how long the Earth takes to travel around the sun. We could make up a term called an Earth Year. It would mean how far the Earth travels in one year — or how far that trip around the sun is. By the way, that is about 584,000,000 miles. (If you live anywhere besides the United States, then that is about 940,000,000 kilometers.)
If an “Earth Year” (my made up term) is how far the Earth travels in one year, then a Light Year is how far a beam of light travels in one year. Light travels very, very fast. It can travel from the sun to the Earth in about 8 minutes. That is about 92,960,000 miles (149,600,000 kilometers). It takes me more than 8 minutes just to run one mile.
Light also travels at a constant speed in the vacuum of space. (It does slow down when it passes through air, a window, or water. But even then, it travels super fast. Michael Phelps is fast in water, but light is still faster.) In the vacuum of space, light does not get tired and stop flying along.
Because light travels so fast, it travels very far in one year. That makes a Light Year–a measure of distance–very useful for measuring the vast distances between stars. For example, the nearest star to our sun is Proxima Centauri. It is about 25,000,000,000,000 miles away (40,000,000,000,000 kilometers). It’s much easier to say (and to write) 4.25 light years.
So, when someone says “That is light years away,” they mean it is very far. They are not talking about time or how quickly a human could travel that distance. They are just talking about how large the distance is.
Invent your own measurement!
Let’s invent our own measurement of distance.
First, decide what you will use to set your measurement length. Will it be the length of an object? (To measure small distances, we could use the length of a twig we found.) Will it be the distance that something travels? (Like how far you can ride your bike in five minutes?)
What will you use your new measurement length to measure? The length of your hand? Then length of a car? The length of your neighborhood?
Finally, what will you name your measurement length? An “twig unit”? A “bike in 5”? Will you name it after yourself? (A “Matthew Mile”?) Or create a shiny, brand-new name you made up yourself? (A “plenth”?)