Modeling the Structure of the Solar System

Students research and learn about the structure of the solar system and our solar neighborhood. Then, they identify major solar system structures using a kitchen-sink model.

• If replicating the kitchen-sink model in the classroom, be sure to use a sink that has a flat bottom and a faucet that can swing away from the drain. Consider using a camera connected to a classroom projector for greater visibility.
• Download videos prior to showing in class.
• Read the Teachable Moment "Then There Were Two: Voyager 2 Enters Interstellar Space" to gain an understanding of the boundary between the heliosphere and interstellar space.

A solar system is made up of a star and all of the objects that orbit it—planets, moons, asteroids, comets and meteoroids. Most stars host their own planets, so there are likely tens of billions of other solar systems in the Milky Way galaxy alone. Solar systems can also have more than one star. These are called binary-star systems, if there are two stars, or multi-star systems, if there are three or more stars.The solar system we call home is located in an outer spiral arm of the vast Milky Way galaxy. It consists of the Sun (our star) and everything that orbits around it. This includes the eight planets and their natural satellites (such as our moon), dwarf planets and their satellites, as well as asteroids, comets and countless particles of smaller debris.

Our solar system formed about 4.5 billion years ago from a dense cloud of interstellar gas and dust. The cloud collapsed, possibly due to the shockwave of a nearby exploding star, called a supernova. When this dust cloud collapsed, it formed a solar nebula – a spinning, swirling disk of material. At the center, gravity pulled more and more material in. Eventually the pressure in the core was so great that hydrogen atoms began to combine and form helium, releasing a tremendous amount of energy. With that, our Sun was born, and it eventually amassed more than 99 percent of the available matter.

Matter farther out in the disk was also clumping together. These clumps smashed into one another, forming larger and larger objects. Some of them grew big enough for their gravity to shape them into spheres, becoming planets, dwarf planets and large moons. In other cases, planets did not form: the asteroid belt is made of bits and pieces of the early solar system that could never quite come together into a planet. Other smaller leftover pieces became asteroids, comets, meteoroids and small, irregular moons.

The order and arrangement of the planets and other bodies in our solar system is a result of the way the solar system formed. Nearest the Sun, only rocky material could withstand the heat when the solar system was young. For this reason, the first four planets – Mercury, Venus, Earth and Mars – are terrestrial planets. They're small with solid, rocky surfaces. Meanwhile, materials we are used to seeing as ice, liquid or gas settled in the outer regions of the young solar system. Gravity pulled these materials together, and that is where we find the gas giants, Jupiter and Saturn, and ice giants, Uranus and Neptune.

Our solar system extends much farther than the eight planets that orbit the Sun. The solar system also includes the Kuiper Belt that lies past Neptune's orbit. This is a sparsely occupied ring of icy bodies, almost all smaller than the most well-known Kuiper Belt object, dwarf planet Pluto. Far beyond the fringes of the Kuiper belt is the Oort Cloud. This giant spherical shell surrounds our solar system. It has never been directly observed, but its existence is predicted based on mathematical models and observations of comets that likely originate there. The Oort Cloud is made of icy pieces of space debris the size of mountains and sometimes larger, orbiting our Sun as far as 1.6 light years away. This shell of material is thick, extending from 5,000 astronomical units to 100,000 astronomical units. One astronomical unit (or AU) is the distance from the Sun to Earth, or about 93 million miles (150 million kilometers). The Oort Cloud is the boundary of the Sun's gravitational influence, where orbiting objects can turn around and return closer to our Sun.

The solar wind – a stream of electrically charged gas blowing outward from the Sun in all directions – creates a bubble around the Sun called the heliosphere. The Sun’s heliosphere doesn’t extend as far as the Oort Cloud. The boundary where the solar wind is abruptly slowed by pressure from interstellar gases is called the termination shock. This edge occurs between 80 and 100 astronomical units. The region beyond the termination shock but before interstellar space is called the heliosheath, and the outer boundary of the heliosphere is called the heliopause. Beyond the heliopause lies interstellar space, the place where the Sun's constant flow of material and magnetic field stop affecting its surroundings.

Two NASA spacecraft, launched in 1977, have crossed into interstellar space: Voyager 1 in 2012 and Voyager 2 in 2018. Both are still returning data about this mysterious region. But it will be many thousands of years before the two Voyagers exit the Oort Cloud and move out of our solar system, at which time the probes will have long fallen silent, their waning power source having decayed beyond use.

Examine pre and post drawings to evaluate learning. Students should be able to identify the major parts of the solar system.

• Have students predict solar system scale using this activity.
• Have students make a scale model of the solar system using string and beads.
• Have students investigate planetary features using art.
• Engage students in writing poetry about the solar system.
• Engage students in learning how we communicate with spacecraft like Voyager at such far distances.
• Have students learn more about dwarf planets.