The Components of the Solar System
Are you teaching your middle school science students about the components of the solar system? The solar system is a fascinating topic. It is a part of both ancient history and the future. Ancient Greeks looked at the night sky and named the constellations. Scientists and businesses are working together to send people to Mars as soon as possible. There is something for everyone in the story of our solar system.
Gravity is the beginning of the story of the solar system. It holds us on Earth, and it keeps the Earth orbiting around the Sun. We see the effects of gravity every day. Gravity is the force of attraction between objects. It is one of the four fundamental forces of the universe.
Orbits of the Components of the Solar System
If gravity pulls objects toward each other, why don’t planets fall into the Sun the way an apple falls to Earth? To answer this question, it is helpful to think about the satellites we send into space to orbit the Earth. The Earth’s gravity pulls on these satellites, and they are falling toward the Earth. However, they are moving so fast that they are traveling around the curvature of the Earth as they fall. Because the Earth is a sphere, as the satellite falls closer to the Earth, the Earth curves away from it, so it remains the same distance about the surface. The satellite falls in a circle over and over again, and that is its orbit.
It is hard to imagine this happening from the Earth’s surface because we can’t throw anything fast enough to be affected by the curvature of the Earth. Even the fastest bullet shot out of a gun falls to the ground in less than half a second. We also have something on Earth that doesn’t exist in space. Friction. Anything flying through the air within the Earth’s atmosphere will run into trillions of air molecules. Each time it hits an air molecule, it will slow down. However, space is a vacuum. That means it doesn’t have air molecules, or any other molecules, for an object to hit. As a result, objects in space follow Isaac Newton’s first law of motion, objects in motion stay in motion unless acted upon by an outside force.
The components of the solar system including satellites, planets, moons, asteroids, meteoroids, comets, and dwarf planets have stayed in orbit around the Sun for 4.5 billion years because their speed keeps them falling around the Sun instead of into the Sun. When an object isn’t moving fast enough to fall around the Sun, it does fall into the Sun. It happened a lot as the solar system was forming, and it happens to some comets today. However, without the introduction of an outside force, the planets will keep falling around the Sun for billions of more years.
The Formation of the Solar System
No humans were around to see the solar system form 4.6 billion years ago, but scientists can guess how it formed based on what they observe about solar systems forming around other stars and what our solar system looks like today.
Scientists believe that our solar system started as a nebula. A nebula is a giant cloud of gas, ice, and dust. Nebulae are huge. They can stretch from hundreds to millions of light-years across.
The nebula that became our solar system was rotating slowly in space until something made it start spinning faster. Scientists suspect a shockwave from a nearby exploding star caused the change.
As the nebula spun, it flattened into a disk, and most of the matter was pulled to the center of the disk. The intense pressure at the center of the disk meant the temperature soared to over 15 million degrees Celsius, and nuclear fusion began. During nuclear fusion, two smaller atoms combine to form one larger atom, and immense energy is released. The center of the disk became our Sun, and hydrogen atoms are still fusing to form helium. We see the energy released as sunlight.
How the Components of the Solar System Formed
While over 99.8% of the matter from the nebula that formed our solar system ended up in the Sun, bits of dust, gas, and ice were left revolving around the center of the disk. Over millions of years, these particles came together to form the other components of the solar system, including planets, moons, asteroids, comets, and planetesimals.
Temperatures close to the Sun were so hot that most of the gas and ice vaporized and were blown away by solar wind. As a result, the four planets closest to the Sun are small, rocky planets. We also call them the terrestrial planets because terrestrial means related to land or Earth.
Farther away from the Sun, the ice and gas combined to form the four outer planets. These are called the Jovian planets. Jovian means like Jupiter. Jupiter is the largest planet in the solar system. These planets are much bigger than the inner four planets and are primarily made up of gases like hydrogen and helium and ice from water, methane, and ammonia.
There is no precise definition of a planet. Some moons are larger than planets, and some objects, like Pluto, orbit the Sun like a planet. Scientists believe there are thousands of dwarf planets in our solar system.
The Asteroid Belt
In 1766, the German astronomer, Johann Daniel Titius, examined the orbits of the six known planets and discovered a pattern in their distances from the Sun. Using his pattern, he accurately predicted the approximate distance of Uranus, a planet that wouldn’t be discovered for another 15 years. The pattern also showed that a planet should exist between Mars and Jupiter. However, it appears that Jupiter’s massive gravity prevented a planet from forming there.
In 1801, while studying the space between Mars and Jupiter, the Italian astronomer, Giuseppe Piazzi, discovered something strange. At first, he thought it was a comet, but he didn’t see a coma around the nucleus. Then, he thought it might be a planet. He had discovered a new component of the solar system. He named it Ceres after the Roman goddess of corn and harvests.
A year later, another object was found in the same orbit. It was named 2 Pallas. Over the next fifty years, nearly 100 more objects were found. They were given the name asteroids meaning starlike.
Most of the asteroids in the solar system occupy the space between Mars and Jupiter. Scientists have named it the asteroid belt. The asteroid belt is 1 AU wide, or about the same distance as between the Sun and the Earth. Despite how it is shown, the asteroid belt is mostly empty space. Scientists estimate there are millions of asteroids in the asteroid belt, but their total mass is just 4% of the mass of the Moon. Ceres makes up about a third of the total mass.
The Kuiper Belt
In 1951, Gerard Kuiper published a paper predicting the existence of icy, rocky objects outside Neptune’s orbit around the Sun. Pluto had already been discovered in 1930, but it was considered another planet, not a part of a larger system of objects.
Dave Jewitt and Jane Luu had been looking for Gerard Kuiper’s icy, rocky objects for five years when they discovered the first one in 1992. Astronomers went on to find more and more KBOs (Kuiper Belt objects), proving the existence of the Kuiper Belt. After Eris, an object similar in mass to Pluto, was discovered in 2005, astronomers demoted Pluto to one of many dwarf planets in the Kuiper Belt. Today, over 2,000 KBOS have been cataloged, and astronomers believe there are millions orbiting the Sun four billion miles away from the Earth.
Similar to the way Jupiter prevented a planet from forming within the asteroid belt, astronomers believe Neptune’s gravity stopped a planet from forming in the Kuiper Belt. Instead, millions of objects ranging in size from dwarf planets like Pluto and Eris to grains of dust swirl around space. When two of these objects collide, they break into smaller pieces and can even form comets. Comets and the Kuiper Belt are both components of the solar system.
The Scattered Disc
Some scientists consider the scattered disc an extension of the Kuiper Belt, while others claim it is a different region of the solar system. The Kuiper Belt and the scattered disk are both full of icy, rocky objects called KBOs (Kuiper Belt objects), SDOs (scattered disc objects), or TNOs (trans-Neptunian objects).
The largest object in the scattered disc is the dwarf planet Eris. While many astronomers consider Eris a member of the Kuiper Belt, others point out that most objects in the Kuiper Belt orbit around the Sun at about the same plane as the planets in the solar system. Eris, however, has an orbit that is tilted at 44 degrees. As a result, it travels above and below the plane of the planets as it orbits around the Sun.
Many other objects in the scattered disc also have titled orbits. Their orbits are also more elliptical and wild than objects within the Kuiper Belt. As a result, they can travel as much as 100,000 AUs away from the Sun before returning closer to Neptune’s orbit.
Astronomers think the scattered disc formed when Neptune pushed farther away from the Sun when Jupiter and Saturn’s orbits changed. Neptune ran into objects in the Kuiper Belt, creating their crazy orbits around the Sun.
The Oort Cloud
The Oort Cloud is the most distant region of our solar system. It starts between 2,000 and 5,000 AUs away from the Sun. An AU is an astronomical unit that represents the distance between the Sun and the Earth. The Oort Cloud is also huge. It extends to between 10,000 and 100,000 AUs from the Sun. That is about one-fourth of the distance to the next star.
Right now, the Oort Cloud is still theoretical. While Jan Oort, a Dutch astronomer, hypothesized about the Oort Cloud in the 1950s, we have yet to find any object to prove its existence. However, astronomers are confident that we will find it someday because it is the likely source of long-period comets. Long-period comets take over 200 years to orbit around the Sun. For example, comet C/2013 A1 Siding Spring passed close to Mars in 2014 and won’t return to the inner solar system for 740,000 years.
The Oort Cloud is different from the other components of the solar system. While astronomers believe it is filled with icy, rocky objects similar to those found in the scattered disc and Kuiper Belt, it does not sit on the same plane as the rest of the objects in the solar system. Instead, it forms a spherical shell around the Sun, like a bubble protecting the rest of the solar system.
Components of the Solar System Digital Science Unit
Want your students to know all of this and more about the components of the solar system? Grab my digital science unit on the solar system! You can get it right now at Teachers Pay Teachers. Click the link to see all of the information pages and review activities to help your students learn about the solar system.
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