Earth Space Science : 08 Our Solar System : 08.00 Our Solar System Pretest Our Solar System Pretest Our solar system is our neighborhood within a vast universe. And just as in any city, we're not the only neighborhood around. The Milky Way galaxy has many solar systems, just as the universe has many galaxies. Let's look at how our solar system got its start. The solar system was formed about four and a half billion years ago when a cloud of gases and dust became compacted. At the center a star was born, the sun, which contains more than 99 percent of the solar system's mass. The dust that orbited the sun agglomerated to form planets, including Earth, as well as millions of other celestial bodies such as asteroids and comets. The solar system has a total diameter of twelve billion kilometers. Every solar system was brought together by the same force—gravity. Gravity plays a tremendous role in the universe. Whether it is involved in forming suns and planets or influencing the structure and stability of solar systems, there is much to learn about the effects of gravity. With gravity and millions of years, particles of matter can come together in space. As gas molecules and dust particles move closer to one another, the gravitational pull between them increases. Little by little, the mass adds up and increases the rate at which matter assembles. It eventually groups into large gas and dust clouds called nebulas, which are birthplace for stars and their solar systems. Consider the anchoring phenomenon for this module: Gravity is a pivotal force in the birth, development, motion, and interactions of objects within our solar system. It is also this same force of gravity that caused a lot of chaotic bombardment in the early formation of the objects in the solar system. This module will focus on these driving questions: • What models, theories, and tools have scientists used to understand our solar system and its formation? • How have forces played a role in the development of our solar system, and how do they allow us to represent and predict planetary motion? • What are the properties of the objects in our solar system, and how do those properties help us understand the age and formation of objects in the solar system? • How do Earth, the sun, and the moon interact to form a system that creates observable phenomena? Earth Space Science : 08 Our Solar System : 08.01 Formation of Our Solar System Objectives How have ideas about our solar system changed over time? At the end of this lesson, you will be able to: • explain the formation of the planetary system in our solar system • explain how the work of scientists has shaped our views of the solar system • compare models of our solar system over time • identify different methods of measuring astronomical distances and apply them in various scenarios Gazing into the night sky, ancient people explained astronomical events in terms of religion and philosophy. With the European Renaissance, scientific and religious explanations for astronomical events diverged. As the distinctions between science and religion became clearer, scientists increasingly used scientific instruments to make astronomical observations. Imagine you could travel backward in time and talk to scientists from the past. The scientists would tell you about two different models of the solar system. Use the activity below to place a “call” to two important scientists from the past: Call between Ptolemy and Copernicus Sound of dialing followed by ringing followed by a phone being answered Ptolemy: Hello, this is Claudius Ptolemy. Student: Hello. I’m a student in an Earth space science class in the 21st century. Can you tell me what you think about astronomy and our solar system? Ptolemy: Oh, yes, I have lots of ideas about the solar system. I even wrote books about the topic. Student: Really? Where does Earth fit into the solar system? Ptolemy: Why, that’s an easy one! Earth is the center. When you look at the sky at night, you can see all the stars moving around Earth. Therefore, Earth is at the center. Student: Thank you. I have another call to make. It was nice talking to you. Sound of phone being hung up, followed by new dialing, ringing, and another phone being answered Student: Hello, may I speak to Nicolaus Copernicus? Copernicus: This is he. What can I do for you? Student: I understand you lived during the scientific revolution that happened during Europe’s Renaissance. Can you tell me anything about the location of Earth within the solar system? Copernicus: Indeed, I can. I have taken many observations and I have concluded that the sun is the center of the solar system. Student: Really? I heard differently? Copernicus: Well, sometimes science builds on both the accomplishments and mistakes of the past. I am convinced my model is the correct view of the solar system. Student: Thank you. I appreciate your time. Sound of phone being hung up Our Solar System In 1977, NASA launched two unmanned space probes, Voyager 1 and Voyager 2, to explore our solar system and beyond. Answer: The probes have been travelling for more than 30 years, and they still have not reached the very outer limits of the solar system, as most scientists define it. However, the probes did pass the outermost planets in 1989. Solar System: The Sun: The sun is the star in our solar system that provides warmth and light to the planets. The Planets: Planets are objects that orbit a star. A planet is massive enough to have gravity of its own but not massive enough to ignite. Moon: Moons are objects that orbit planets. Comet: One of the small objects in our solar system that orbit the sun. Small Bodies: Many objects not big enough to be planets orbit the sun. These objects include comets, asteroids, and meteorites. Each will be described in more detail in a subsequent lesson in this module. The Universe: The universe includes all galaxies, stars, dust, gases, planets, and space. Our solar system is a very tiny fraction of the size of the universe. Distances In Space: Distances in space can be measured using a variety of units. For large distances, a light year is often used. For distances within the solar system, the astronomical unit is often used. One AU equals 150 million kilometers, Earth's average distance from the sun. (Because the distance between Earth and the sun changes throughout the year, it is more appropriate to speak of Earth's average distance from the sun, which is approximately 149,597,871 kilometers. For simplicity's sake, this number is rounded up to 150 million kilometers, or 93 million miles). The solar system does not simply stop at a certain point. It's a bit like a city, where the edges are hard to define. Because the outer boundary of the solar system is not clearly defined, it's difficult to say how big the solar system is. Its size can be measured from a region beyond Pluto's orbit where the sun's influence greatly decreases and interstellar space begins. The region encompassed from the sun to this boundary is called the heliosphere, as shown in the image below: As you can see, the heliosphere is very large. The solar system occupies only a small part of the heliosphere. Let's estimate the size of the solar system by imagining the sun on a scale you can easily visualize. The sun is approximately 1.4 million kilometers in diameter. To create our scale model of the solar system, think about the sun as being the size of a basketball (78 centimeters in diameter). Using this scale, Earth's diameter would be only 7 millimeters. Using this same scale, the distance to Pluto would be about 3,300 meters. If a basketball on your desk represented the sun, then by the same scale you would have to walk more than 2 miles to reach Pluto! Calculating of AU: How many kilometers are represented by 155 AU? To calculate the answer, complete the following activity: Calculation of AU Step 1 1 AU = 150,000,000 km This is the conversion factor used to determine the answer. This is a known value. Calculation of AU Step 2 155 AU = x km To calculate the number of kilometers in 155 AU, set up the following equation. The unknown portion of the equation is the number of kilometers. Calculation of AU Step 3 155 AU 150,000,000 km /1AU = x km Now use the conversion factor to convert AU to kilometers. Because 1 AU is equal to 150 million kilometers, that ratio can be substituted into the equation. Calculation of AU Step 4 155 AU 150,000,000 km /1AU = 23,250,000,000 km Multiplying the number of AU by the conversion factor gives the correct answer. Practice This One On Your Own: How many AU are represented by 480 million kilometers? The History of Solar System Models Claudius Ptolemy: Ptolemy wrote a book that contained the key astronomical ideas of the time. From about 150 AD, his model dominated scientific thought. He thought the solar system was geocentric—the planets and sun travel around Earth in “epicycles,” or large perfectly circular orbits. His model is also known as the Ptolemaic view of the solar system. Prior to Ptolemy, other ancient philosophers, such as Aristotle, also suggested the universe was geocentric, but Ptolemy was the first to explain this model in detail. Nicolaus Copernicus: Copernicus is considered the father of modern astronomy.