Earth Science: Beyond Earth PDF

Earth Science / Beyond Earth Beyond Earth © 2023 PF High School, LLC Page: 1 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth Overview While everyone is familiar with gravity, it may not be obvious that this force is intimately responsible for the formation of the solar system and the structure of the universe. As gravity acts over huge distances, it influences the life cycles of stars, galaxies, and the universe as a whole. Today, the idea of gravity may seem obvious since people are familiar with its effects. However, this idea once challenged the beliefs surrounding Earth's place in the galaxy. This lesson will explore how gravity played a role in the early formation and behavior of the solar system. It also will explore how gravity helps explain the nature of the universe. © 2023 PF High School, LLC Page: 2 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth Objectives Analyze the relationships among the sun, the moon, the earth, and other planets Describe the formation and interaction of the main solar system components Examine the life cycles of stars, and identify the features of the sun Recognize characteristics of the Milky Way galaxy and other known galaxies © 2023 PF High School, LLC Page: 3 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth Analyze the Relationships Among the Sun, the Moon, the Earth, and Other Planets © 2023 PF High School, LLC Page: 4 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth The Sun-Earth-Moon System Relative Positions of the Earth, Moon, and Sun Humanity's view on the structure of the solar system has developed throughout history. The Roman mathematician Claudius Ptolemy (ca. 170–100 CE) developed a cosmological model (a mathematical model of the universe) that placed a stationary Earth at the center of the universe, with all other celestial objects or satellites (objects such as planets and stars) moving around it. The Greek philosopher Aristotle developed the same model, albeit 400 years earlier. This model for the solar system is called a geocentric model. The model is intuitive, in that from our point of view, it does seem that the sun, moon, and stars seem to revolve around us. And, Roman cultural dominance over a long period of time instilled faith in the geocentric idea. However, a closer look at the motions of the moon and planets reveals that they don't quite fit this model. Consequently, the geocentric model didn't correctly describe the moon's apparent backward, or retrograde, motion. The model postulated that this was the moon reversing in its orbit. However, that isn't accurate. The moon doesn't reverse in motion when in retrograde but only appears to do so. is image shows a side-by-side comparison of the heliocentric and geocentric models. In contrast, the Polish astronomer Copernicus (1473–1543) held a view of the solar system that placed the sun at the center, with all other celestial bodies of the solar system orbiting around it. Furthermore, Copernicus stated that all planets orbit the sun in circular orbits. As a result, Copernicus's model of the solar system is called the heliocentric model. One important figure who provided data that helped validate Copernicus's model was Galileo Galilei (1564–1642), an Italian astronomer and mathematician. Galileo dispelled many incorrect suppositions regarding the structure of the planets, the moon, and the sun. After publishing his findings in support of the heliocentric model, the Catholic Church twice put Galileo on trial for heresy. Even after being warned in 1616 to abandon the heliocentric © 2023 PF High School, LLC Page: 5 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth model, he continued publishing manuscripts supporting it. Galileo was eventually convicted of heresy in 1633 and spent the rest of his life under house arrest. To learn more about the scientific contributions of Galileo, read Galileo Galilei's Solar Planet Model(https://sciencing.com/galileo-galileis-solar- planet-model-3747.html). Introduction to Gravity and the Earth-Moon-Sun System To understand the earth-moon-sun system, you must understand the concept of gravity. Gravity is defined as a force that pulls objects toward each other. Specifically, the sun's gravity keeps planets in our solar system in orbit around the sun. Theories of gravity, prompted by observations of planetary motion, date as far back as the mid-sixteenth century. Over the next 150 years, astronomical science flourished, culminating in 1687 with the publication of Isaac Newton's Principia. This work expounded on the laws of gravity and would form the foundation of physics for the next 200 years. Newton's principles enabled humanity to begin exploring the solar system, taking our first tentative steps into space. They continue to help us understand our place in the universe, its formation, and even important aspects of life on Earth. (You'll learn more about Newton later in this section.) Kepler's Laws of Planetary Motion While Copernicus correctly deduced that the planets in the solar system orbit the sun, his assertion that these orbits were circular wasn't entirely correct. This became clearer once the German astronomer Johann Kepler (1571–1631) devised what became known as the laws of planetary motion. Kepler's work was built on an exhaustive analysis of astronomical data that had been collected by a Danish astronomer named Tycho Brahe (1546–1601). Brahe's observations were precise and careful enough for Kepler to build upon. The Orbit Law Kepler's first law, published in 1609, is sometimes called the orbit law. It states that all orbits are specific types of conic sections. Conic sections describe curves that can be created by slicing through a cone. There are four types of conic sections: the circle, the ellipse, the parabola, and the hyperbola. The parabola and hyperbola are both open curves, which simply means—in this context—that they represent orbits in which the object will not come back to the same position repeatedly. Comets are examples of bodies that have open orbits. © 2023 PF High School, LLC Page: 6 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth Circles and ellipses are examples of closed orbits, meaning that the orbiting object will repeat the same path over and over. It's important to note that, from a geometric perspective, a circle is just a special type of ellipse, resulting from slicing a cone in a plane that's perpendicular to its base. The orbits of all the planets in the solar system are slightly elliptical. (Pluto, which is classified as a dwarf planet, completes a very elongated elliptical orbit.) Using Tycho Brahe's careful measurements of Mars's orbit, Kepler found that Mars moves in a very slightly elliptical orbit. The fact that Mars's orbit isn't perfectly circular contradicts Copernicus's model of the solar system. "Perfection," based on assumptions about how a divine creator would work, was a persistent idea throughout history that would influence many fields yet was contradicted by careful observation. All ellipses have a few important geometric characteristics that relate to orbits. They all have two lengths, called the minor and major axes. The minor axis is drawn through the center of the ellipse at its narrowest point. The major axis is drawn through the center across its longest width, and travels through the two foci. It is related to the amount of time required for a planet to orbit completely around its star. An ellipse has a focus at two points that lie along the major axis, called foci (foci is just the plural of focus). When a planet orbits a star, one focus point is within the star, and is what we think of as the point that the planet orbits around. The other focus is at a mirror-image location on the other side of the ellipse. Technically, a planet doesn't orbit a star—instead, both orbit a shared point that lies between them, at the center of their two masses. However (in the case of our solar system), since the sun is more than 99.9 percent of the combined mass of planet and star, the focus point is within the sun, near it's center, and it appears that planet simply orbits the sun. The planet orbits along the edge of the ellipse. The consequences of this type of motion and the location of the sun in its orbit led to Kepler's second law. The Area Law Kepler's second law, sometimes called the area law, states, "A line that connects a planet to the sun sweeps out equal areas in equal times." While this may seem complex, the law makes a statement about the amount of time required for a planet to move through a portion of its orbit. Consider, as an example, a planet moving in an elliptical orbit around a star. The planet moves faster when it's closer to the star but slower when it's farther away. Yet in the case of a circular orbit, the planet is always the same distance from the star. Thus, such a planet always moves in its orbit at the same velocity. © 2023 PF High School, LLC Page: 7 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth is diagram shows how a planet orbits a star. e star is located at a focus of the ellipse, and the planet moves around the edge of the ellipse. Four important points are located on the ellipse. So, what does this have to do areas? Take a look at the following diagram of the elliptical orbit of the earth around the sun. The shaded areas are portions of the ellipse that show the areas covered by the orbit over specified points in time—from point A to point B and then from point C to point D. As the planet moves from point A to point B, it covers a portion of the ellipse equal to Area 1. The amount of time this takes is T1. Now, as the planet moves from point C to point D, it covers a portion of the ellipse equal to Area 2. The amount of time this takes is T2. Kepler's second law states that Area 1 and Area 2 are equal; it also states that T1 and T2 are equal. This argument can be extended to two more points, E and F, which enclose Area 3. The amount of time required to travel between E and F is T3. According to Kepler's second law, T3 will be equal to T1 and T2 when Area 3 is equal to Area 1 and Area 2. To learn more about Kepler's laws in application, watch Basic Orbit Shapes(https://www.youtube.com/embed/pRvVK2m_wGE? rel=0&showinfo=0). The Period Law Kepler's third law was published in 1619 and is sometimes called the law of periods. It states that the period of a planet's orbit squared is proportional to the cube of its semi- major axis. A planet's period, or revolution, is the amount of time it takes to make one complete orbit around the sun. For Earth, this time amount is 365.25 days, or one Earth year. © 2023 PF High School, LLC Page: 8 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth As you learned earlier, each ellipse has two axes. The minor axis is drawn through the center of the ellipse at its narrowest point. The major axis is the longest width of the ellipse and travels through the center as well as the two foci. Increasing the size of the ellipse by increasing the major axis will increase the period of the orbiting body. Kepler figured out how to calculate the period based on the size of the major axis and semi-major axis. The semi-major axis is a section of the major axis that's half its total distance, or the distance from its center to its outer point. Kepler found that the square of the orbital period is proportional to the cube of the semi-major axis of the orbit. In other words, if you were to graph all of the planets' orbits with the squares of their orbital periods on the horizontal axis and the cube of the semi-major axis on the vertical axis, you could draw a straight line to connect them. This law holds for every planet in the solar system. It means that if you know the period of an orbit, you can calculate the distance of its axes and vice versa. The important point to remember when examining Kepler's laws is that they describe how objects move through space, based on real astronomical observations. However, the laws don't describe why objects move in this way, nor do they describe why these observations pertain to systems involving two astronomical bodies. Understanding those points requires Newton's laws. Kepler's ideas were widely debated and examined throughout the seventeenth century, and his ideas were widely accepted by the time Isaac Newton published his groundbreaking Principia. Newtonian Gravity It wasn't until nearly the end of the seventeenth century that the English physicist, astronomer, and mathematician Isaac Newton developed his theory of gravitation. Finally, there was an underlying mathematical theory that could be used to reproduce Kepler's laws. To craft his theory, Newton needed to invent an entirely new field of mathematics, called calculus. He also formulated his three laws based on observations and clever deductions. According to Newton's theory, the strength of gravity must be proportional to the mass of the two bodies in the orbit. The strength of gravity also decreases with the square of the distance between the two bodies. This means that if the distance between the two bodies quadruples, gravity is 1⁄16 as strong. One important consequence of Newton's theory is that Kepler's laws become something of an approximation when the planet is much less massive than the star it orbits. As you learned earlier, a star and a planet orbit the shared point that lies between them, at the center of their two masses. This explains the motion of binary stars. A binary star system is a pair of stars with similar masses orbiting a shared point in space that's at the center of their combined masses. In our solar system, each of the planets exerts its own influence on the position of the sun, and the effects from all eight major planets partially cancel each other. To learn more about the earth-moon-sun system, view this simulator(http://phet.colorado.edu/sims/html/gravity-and- © 2023 PF High School, LLC Page: 9 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth orbits/latest/gravity-and-orbits_en.html), which uses a model to track the paths of the moon and Earth around the sun. You can modify the masses of the sun and Earth to see how this would affect motion in this system. © 2023 PF High School, LLC Page: 10 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth Equinoxes, Solstices, and Eclipses Earth's elliptical orbit and its tilt along its rotation axis determine solstices and equinoxes throughout the year. The following figure shows a diagram of the solstices and equinoxes that occur throughout the course of a year. is image identi es the position and orientation of Earth during solstices and equinoxes. Seasons are labeled for the Northern Hemisphere. Solstices occur when earth’s axis is tilted directly toward and away from the sun. One hemisphere is having a summer solstice, the day of the year with the longest amount of sunlight and first day of summer. The other hemisphere is having their winter solstice, the day of the year with the shortest amount of sunlight, and first day of winter, at the same time. The seasons noted on the diagram apply to the Northern Hemisphere. Halfway between the solstices are equinoxes, days that have approximately equal daylight and night. One equinox occurs in September, and in the Northern Hemisphere, this autumnal equinox marks the end of summer and the beginning of autumn. At this point, the © 2023 PF High School, LLC Page: 11 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth days start getting shorter and the nights, longer. The opposite occurs on March 21, which is the spring equinox in the Northern Hemisphere: The days start getting longer, and the nights start getting shorter. Earth's tilt is also what causes the sun to follow a path through the sky that isn't perfectly aligned with the equator. The path of the sun as it appears from the vantage point of the earth is called the ecliptic. If you trace this path along the edge of the earth, you'll see that the ecliptic crosses the equator at two points. Equinoxes occur when the sun passes through the point where the equator and the ecliptic intersect. Eclipses As the earth-moon system moves around the sun, the three bodies periodically align to produce eclipses. Two types of eclipses can occur. The first, called a solar eclipse, occurs when the moon passes between the sun and the earth, momentarily blocking the sun's rays from reaching certain areas of the earth. A diagram showing the positions of the sun, moon, and earth during a solar eclipse is shown in the figure that follows. Here you see the positions of the moon, sun, and earth during a solar eclipse. e moon blocks sunlight from reaching the earth. As the moon moves between the earth and the sun, it casts a shadow on certain areas of the earth. This shadow is composed of two regions, called the umbra and penumbra. The umbra is a darker shadow that lies directly behind the moon, while the penumbra is a lighter shadow that surrounds the umbra. If you view the eclipse from the earth while standing inside the umbra, the moon appears to completely obscure the sun for a brief moment. If you're standing in the penumbra while viewing the eclipse, the moon will appear to obscure only a portion of the sun. © 2023 PF High School, LLC Page: 12 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth Shown here are the positions of the moon, sun, and earth during a lunar eclipse. e earth blocks sunlight from reaching the moon. The second type of eclipse, called a lunar eclipse, occurs when the moon moves behind the earth. As in a solar eclipse, the earth can block sunlight from reaching the moon, creating an umbra and a penumbra. During a lunar eclipse, the moon briefly passes through the penumbra, where it receives much less sunlight. This causes the moon to appear dim. As the moon passes through the umbra, it appears deep orange or red. Even though the earth is blocking direct sunlight, red light passes through the atmosphere and refracts towards the moon, while the atmosphere scatters away blue light from the sun. This is why only red light can reach the moon during a lunar eclipse. A diagram showing the positions of the sun, moon, and earth during a lunar eclipse is shown in the following figure. Tides Tidal activity, or the periodic rise and fall in sea level, is a result of gravity. It's important to note that tides aren't the same thing as ocean waves. Waves are caused by convection within water and drag from winds, causing water to exhibit a back-and-forth, horizontal motion. Think of the oceans collectively as a large, connected body of water that isn't directly connected to the seafloor. It has a large mass and experiences gravitational pull from the moon and the sun. Gravity pulls on the water, causing it to bulge toward the large, external masses of the moon and sun. As the moon rotates around the earth, and as the earth rotates around the sun, the moon and sun pull water toward or away from shorelines, causing high and low tides. When the earth, moon, and sun are all in a straight line—with the moon between the earth and the sun—the gravitational pull of both the moon and the sun are combined. This alignment is regular and coincides with the new moon phase (not to be confused with eclipses, which are precise alignments that are relatively rarer). During © 2023 PF High School, LLC Page: 13 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth a new moon phase, the sun's gravity and the moon's gravity combine to produce a spring tide. During the first and third quarters of the moon's revolution around the earth, the sun's gravity and the moon's gravity point along different directions, perpendicular to one another, producing the neap tide. Spring tides produce the greatest difference between high and low tides, while neap tides produce the smallest difference between high and low tides. If you look at the following figure with an understanding that gravity is an attraction of objects based on their masses and distances from each other, you can see why spring tides are strongest. is diagram shows where the moon and sun are in various positions around the earth during each of the moon's phases and how this a ects spring and neap tides. © 2023 PF High School, LLC Page: 14 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth Lunar Surface Features Throughout human history, people have tried to understand the moon by observing it with the naked eye. It wasn't until the time of Galileo that humans could get a closer view of the moon's surface. Later, the Soviet Luna 2 and American Apollo missions would give us a close-up view of the moon and reveal more about its composition and origins. To learn more about the moon, you can use Google Maps(http://www.google.com/maps/space/moon) to get a close-up view of its surface. Lunar Exploration Newton's gravitational theory formed the basis of nearly all aspects of physics until the time of James Clerk Maxwell (1831–1879). Maxwell stated that light, magnetism, and electricity were manifestations of the same phenomena. This paved the way for Einstein's revolution of Newtonian physics in the early twentieth century. Even after Einstein, without Newton's theory, many modern advances that humans take for granted wouldn't have been possible. Newton's theory also provides humans with a path to explore the solar system using satellites and orbital probes. The first unmanned mission to reach the moon (or any other extraterrestrial body) was the Soviet Union's Luna 2 program. The most significant lunar exploration missions were the Apollo missions. In 1969, two of the three-man crew of the Apollo 11 mission were the first humans to walk on the surface of the moon. Five additional Apollo missions would follow, with the program ending in 1973. More recently, Japan, India, and the European Space Agency have revisited the moon with pilotless craft. During the Apollo missions, lunar rovers and astronauts collected many rock samples. Scientists evaluated these to determine the chemical composition of the moon and inform explanations about the moon's formation. The Moon's Origin Uranium-lead dating of zircon fragments gathered during the Apollo 14 mission yielded an age of 4.5 billion years old, which is very close to the age of Earth. Other samples gathered from the Apollo missions have an isotopic composition that's nearly identical to the isotopic composition of rocks on Earth. This supports the idea that the moon and the earth formed from the same starting materials, or that the moon was even part of the earth at one time. © 2023 PF High School, LLC Page: 15 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth Giant Impact Hypothesis The giant impact hypothesis, which currently enjoys favor among scientists, states that a large, Mars-sized object collided with the newly formed earth. (This hypothetical, colliding body is named Theia, after the moon goddess from Greek mythology.) That direct impact completely merged the contents of the two colliding bodies, with debris from the collision coalescing into the current earth and moon.The heat from this collision turned both bodies to a molten state. In addition, the moon's orbit would have slowed over time from tidal friction—a kind of drag resulting from the masses of molten liquid pulling on each other. As the new moon's orbit slowed, it moved away from the earth but still remained in orbit due to gravity. The moon then settled into a more stable orbit around the earth once its surface completely solidified. Other Ideas There are other notable ideas that attempted to explain the presence of Earth's moon. One was the fission hypothesis. This idea states that a rapidly spinning, molten Earth spun off a large piece of mass shortly after it formed, and this piece of mass later cooled and formed the moon. George Darwin, son of the famous biologist Charles Darwin, suggested that the earth's moon spun away from the earth early in its formation. Originally (and at a time preceding our understanding of plate tectonics), it was thought that the Pacific Ocean basin was the void left behind after the moon spun off of the earth. Another idea, called the accretion hypothesis, states that the moon and the earth originally formed close to each other from the same material, cooling and solidifying separately. These hypotheses are consistent with evidence that shows rock from the moon and the earth have nearly the same age and composition. (However, the composition of the moon is dissimilar to that of the Pacific seabed.) One idea that isn't compatible with the available evidence is the capture hypothesis. This hypothesis states that the moon initially formed far from the earth and later became captured in the earth's gravity, eventually settling into a stable orbit around it. The problem with this idea is that the chances of the moon having an identical chemical composition to the earth is very small. In addition, for the moon in this scenario to be nearly the same age as the earth would be a great coincidence. Some have postulated that the moon became captured in the earth's orbit as a result of aerobraking. This is a spaceflight maneuver that uses drag in the atmosphere to decrease the velocity of an orbiting object and change its trajectory. However, if this were the case, the moon would have settled into an orbit much closer to the earth. Aerobraking might properly explain why gas giants like Saturn and Jupiter have so many moons. Surface of the Moon The moon is tidally locked, meaning that the same side of the moon always faces the earth. Yet the side of the moon facing away from us, often called the "dark" side, isn't perpetually dark. During a new moon, the sun's light illuminates that side of the moon that we never see. The "dark" side of the moon can be explored only with orbiting satellites. © 2023 PF High School, LLC Page: 16 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth Over time, a number of missions have explored and photographed the entirety of the moon's surface. Recently, a Chinese rover began exploring the surface of the "dark" side (which again, is only dark from a vantage point of Earth). When Galileo began examining the moon with a telescope, it was widely believed that the moon was flat and featureless. The dark stretches on the moon's surface were thought to be oceans. Galileo found that the moon's surface contains mountains and valleys, just like the surface of the earth. In fact, the moon's surface preserves a great deal of evidence from the early solar system and gives us clues to events that happened during the earth's formation. For one thing, the moon's surface shows evidence of asteroid impacts. All of the planets and moons experienced a period of repeated impacts from asteroids during the formation of the solar system. This period of heavy bombardment for the earth and the moon ended about 3.8 billion years ago. Scientists believe that the early solar system was filled with many more smaller objects than exist in it today, and as they collided to form larger bodies, impacts became less frequent. Since that time, plate tectonic activity and erosion on Earth have erased much of this early activity. In contrast, the moon lacks plate tectonic activity, an atmosphere, and erosion, so evidence of the early solar system is preserved on its surface. We now know that the moon was molten during its early formation. Its surface was hot enough to cause volcanism, and many of the moon's ridges and craters are the remains of dead volcanoes. Volcanoes also erupted whenever asteroids struck the molten surface. The interior of the moon has a structure similar to that of Earth, with a somewhat molten core, a solid mantle, and a solid crust. Despite the similarities in geology between the earth and the moon, the two bodies are quite different. The moon is much smaller than the earth, and its surface cooled too quickly for tectonic plates to form. As a result, the moon's surface is continuous and, as stated previously, devoid of plate tectonic activity. Like its ridges and craters, the moon's mountains formed from volcanic activity and asteroid impacts as well. The moon's mass also is too small to hold an atmosphere. On Earth, an atmosphere helps trap heat and keeps the planet warm. The fact that the moon doesn't have an atmosphere is another reason that its surface became cool enough to solidify. This absence of atmosphere also allows even small asteroids to strike the moon and deform its surface. Although a hot core supplies heat throughout its interior, the moon is still too cool for tectonics and volcanism. All volcanism ended after the moon had completely solidified. Exploring Space with Telescopes Due to limitations in propulsion technologies—which could potentially get humans to Mars, but not return them—manned missions to space have only progressed as far as the moon. Unmanned missions have extended to the edge of the solar system and beyond, and these probes have captured breathtaking images of the solar system along the way. Unfortunately, exploring the nearest stars or any other part of the universe with spacecraft is currently impossible. The only way to explore the rest of the universe is with telescopes. © 2023 PF High School, LLC Page: 17 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth A telescope is any device that gathers light from a distant object and focuses it into an image. Telescopes can work with visible and invisible light. As you learned earlier, James Maxwell showed in the late nineteenth century that light is an electromagnetic wave, and all light falls into some portion of the electromagnetic spectrum. Visible light only corresponds to a small portion of the electromagnetic spectrum. Most light isn't visible to the human eye and must be detected with sophisticated instruments. Light is classified according to wavelength, and visible light spans wavelengths from 400 to 700 nanometers. Visible wavelengths on the electromagnetic spectrum range from 400 to 700 nanometers (nm). The use of ground-based telescopes on Earth is limited because the atmosphere distorts and filters electromagnetic radiation. Specialized optical systems can be used to reduce the atmospheric effects on images gathered with these telescopes. For this reason, many terrestrial telescopes are placed high on mountaintops. Placing them in remote areas helps these telescopes avoid light pollution from nearby cities. The most precise telescopes are placed in orbit around the earth as this allows them to avoid atmospheric effects completely. Telescopes placed in space can be used to easily capture images at wavelengths outside the visible range. The universe looks quite different when examined using light outside the visible range. Measurements of light emitted outside the visible range are useful for understanding the structures of galaxies as well as the chemical composition and life cycles of stars. One example of an orbiting telescope that operates in the microwave range is the Wilkinson Microwave Anisotropy Probe. This telescope measures temperature differences throughout the universe and was used to map the background radiant heat left over from the Big Bang. This provided direct evidence that the Big Bang essentially created the universe. Perhaps the most famous orbiting telescope is the Hubble Space Telescope. The Hubble orbits Earth and has captured some of the most interesting and meaningful images of any telescope. It operates by capturing light ranging from infrared to ultraviolet and can capture images of extremely distant objects. The Hubble Telescope's many discoveries include previously unknown moons around Pluto and some of the farthest galaxies ever seen. Hubble's pictures, along with images from the Wilkinson probe, have allowed scientists to extrapolate the age of the universe to nearly 14 billion years. © 2023 PF High School, LLC Page: 18 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth As a successor to the Hubble, the James Webb Space Telescope was launched in 2021. This telescope will focus on infrared wavelengths and must be kept extremely cold. To maintain this cold temperature, the telescope will be placed at a specific point in the earth- sun system, called a Lagrange point. Anything placed at this particular point will remain fixed at the same relative location within the earth-sun system. This will allow the James Webb Telescope to continuously shield itself from the sun's radiation so that it can capture more accurate images than Hubble. Placing this telescope at a Lagrange point also will allow it to remain stationary and won't require course correction. Scientists recently began searching for planets that orbit other stars and that might provide conditions suitable for life. These planets are called extrasolar planets, or exoplanets. Locating these potentially life-bearing planets requires measuring a specific event that occurs around distant stars, called a transit. If a planet is orbiting a star, there's a chance that the planet will pass between the telescope and the star, as occurs during an eclipse. This momentarily blocks some light from the star, and the reduction in light can be measured with a telescope. While experts previously believed exoplanets to be rare, recent surveys have found that they're quite common. More than 300 extrasolar planets were discovered in 2018 alone. It remains to be seen whether any of these planets can support complex life. © 2023 PF High School, LLC Page: 19 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth Key Points and Links Kepler's laws and Newton's theory of gravitation explain the orbits of planets around stars as well as the orbits of moons around planets. e orientation and relative positions of the sun, moon, and earth—and the earth's tilt on its axis—cause solstices, equinoxes, tides, seasons, and eclipses. Although the moon's surface bears many of the same characteristics as the surface of the earth, the moon doesn't have plate tectonic activity or active volcanoes. Exploring beyond the solar system requires powerful telescopes that collect light ranges throughout the electromagnetic spectrum. Links Galileo Galilei's Solar Planet Model(https://sciencing.com/galileo-galileis-solar-planet-model-3747.html) Basic Orbit Shapes(https://www.youtube.com/embed/pRvVK2m_wGE?rel=0&showinfo=0) Google Maps(https://www.google.com/maps/space/moon/@0,-75.6500048,22963938m/data=!3m1!1e3) © 2023 PF High School, LLC Page: 20 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth Self Assessment: Analyze the Relationships Among the Sun, the Moon, the Earth, and Other Planets Open Link © 2023 PF High School, LLC Page: 21 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth Describe the Formation and Interaction of the Main Solar System Components © 2023 PF High School, LLC Page: 22 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth Our Solar System Gravity is the fundamental force in the formation of the solar system and stars. If it weren't for gravity, the solar system, galaxies, and various stars throughout the universe never would have formed. Before proceeding, you should lean an important term that's used to quantify distances within the solar system—the astronomical unit, or AU. This unit refers to the average distance between the earth and the sun (93 million miles). Therefore, the distance between these two bodies is written as 1 AU. Remember, the earth's orbit is elliptical, so 1 AU is an average value. For perspective, Mars is 1.524 AU from the sun, while Saturn is 9.5 AU from it. The astronomical unit provides a convenient way to communicate large distances throughout space. Formation of the Solar System Solar systems form from dust clouds that contain elements heavier than hydrogen. Our solar system began forming 4.6 billion years ago following the gravitational collapse of a large cloud of gas and dust. This type of cloud is called a nebula. Many nebulae exist throughout the universe; two examples are the Orion Nebula and the Crab Nebula. © 2023 PF High School, LLC Page: 23 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth is is a photograph of the Orion Nebula captured with the Hubble telescope. Colors in images from the Hubble telescope are added from a lter that measures speci c wavelengths. Since objects are attracted to one another as a result of gravity, the gas and dust of our origin nebula pulled together to form what's called a solar nebula. Compression from gravity caused this solar nebula to become hotter and denser near the center, similar to what occurs in the cores of stars and planets. This solar nebula was extremely hot near the center and cooler at the edges. Just like ice skaters who spin more quickly as they pull in their arms, the nebula began to spin as it collapsed inward. Within this spinning disk, particles began to clump together under the influence of gravity. Pieces of material that are the same distance from the center of a spinning disc orbit at nearly the same velocity. (If you were standing within the solar nebula, nearby material would appear to be stationary.) Gravity between pieces of material that neighbor each other causes them to accumulate additional material easily because they're moving at nearly the same velocity within the solar nebula. Because larger chunks of material exert stronger gravity on nearby dust and gas, these initial chunks of material grew faster, eventually forming planets or moons. Denser elements such as iron settled closer to the center of the solar nebula since the gravitational © 2023 PF High School, LLC Page: 24 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth force is stronger on them. This led to the formation of rocky planets closer to the center of the solar system. Meanwhile, less massive elements such as hydrogen and helium tended to accumulate farther from the center of the disk, leading to the formation of gaseous, giant planets such as Jupiter, Saturn, Uranus, and Neptune. Gravity near the center of the solar nebula was so strong that gases near the center of the cloud formed into the sun. As the sun formed, solar wind pushed remaining gases farther away from the center of the solar nebula, where they accumulated as part of gas giants or were blown away from the new solar system completely. Smaller chunks of mass, namely meteorites and asteroids, are thought to be left over from this early phase of the solar system. As was mentioned earlier, samples from meteorites were used to place the age of the solar system at 4.6 billion years old. The Kuiper Belt and Dwarf Planets Outside the newly formed solar system lies the Kuiper Belt. This region is similar to an asteroid belt and contains frozen water, methane, ammonia, dust, and other rocky objects that didn't accumulate within the inner planets. The Kuiper Belt is a ring that extends 50 AU beyond the edge of the solar system. Many comets, meteorites, and other large bodies called dwarf planets can be found in the Kuiper Belt. According to the International Astronomical Union (IAU), a celestial object must have the following characteristics to be classified as a planet: 1. It must follow a closed orbit around a star. 2. It must be in hydrostatic equilibrium, meaning it must be spherical. 3. Aside from its own moons, its gravity must be strong enough to have cleared its neighborhood of other objects. Although Pluto originally was categorized as one of the "regular" planets in our solar system, the IAU demoted it to dwarf planet in 2006. Though it orbits the sun and is spherical, it does not have enough gravity to have cleared the neighborhood near its orbit. Pluto is just one of many Kuiper Belt objects of similar size that are classified as dwarf planets because they don't meet the third point listed above. Currently, the IAU recognizes five dwarf planets in or near the solar system: Pluto, Haumea, Makemake, and Eris are all found in the Kuiper Belt, while Ceres is classified as a dwarf planet in the asteroid belt. Orbit and Rotation of Planets in the Solar System The eight major planets within our solar system orbit the sun almost completely within the same plane, called the plane of the ecliptic. This direction of motion also matches that of the original solar nebula. When a planet's direction of motion matches the direction of the sun's rotation, the motion is said to be prograde. Similarly, the motion is said to be retrograde if the direction of motion is opposite the sun's motion. All planets have prograde orbits, meaning the orbital direction matches the direction in which the sun spins; however, not all planets have prograde rotation. © 2023 PF High School, LLC Page: 25 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth Of the eight planets in the solar system, Venus and Uranus exhibit retrograde rotation, meaning they rotate on their axes in a direction opposite to that of the sun. When viewed from the sun's North Pole, all planets except Venus and Uranus rotate counterclockwise, matching the rotation of the Sun. In the case of Uranus, its rotation axis is nearly parallel to the plane of the ecliptic. This is thought to have been caused by a collision between an Earth-size object and Uranus as the solar system was forming. The rotation of Venus is more complicated because its rotation axis is nearly vertical to the plane of the ecliptic. This opposite rotation is thought to be caused by tidal forces exerted by the sun's gravity against Venus's thick atmosphere. Although Venus may have rotated in the same direction as Earth, Mercury, Mars, Neptune, Jupiter, and Saturn early in its formation, tidal forces within its thick atmosphere may have become large enough to force Venus to spin in the opposite direction, leading to retrograde rotation. Gravity and Moons in the Solar System Most moons have prograde orbits about their planets, meaning that they orbit in the same directions as their planets spin. The moons of Uranus orbit in the direction that Uranus rotates, which is retrograde to the sun. (This observation supports the giant impact hypothesis for the formation of Earth's moon.) A moon that exhibits retrograde motion compared to its planets is thought to have been captured by the planet's gravity. This doesn't mean that such capture only produces retrograde motion. The direction of the moon's orbit depends on the direction in which it approached the planet. It's also possible that a giant impact could produce retrograde motion, depending on the direction of the impact. All known moons in the solar system are tidally locked. This means it takes a moon the same amount of time to make a rotation (one complete spin on its axis) as it does a revolution (one complete spin around the host planet or star). Because of this, the same side of the moon is always facing its planet. The exceptions to tidal locking are Hyperion, which orbits Saturn, and small moons of Pluto. One interesting case of tidal locking occurs in Pluto, which is tidally locked with its largest moon, Charon. These two bodies are of similar size and mass, and they exert a strong gravitational force on each other. As a result, Pluto and Charon constantly face each other as they orbit. Pluto's other moons aren't tidally locked, possibly because the tidal force between Pluto and Charon overwhelms the tidal forces among the other moons. © 2023 PF High School, LLC Page: 26 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth The Inner and Outer Planets The Inner Planets Listed in order from closest to the sun to farthest, the inner planets are Mercury, Venus, Earth, and Mars. Closer to the center of the solar nebula, these rocky, or terrestrial, planets formed from heavier elements. These elements made up only about 0.6 percent of the material in the solar nebula. Therefore, the terrestrial planets didn't grow very large, and they couldn't exert a strong gravitational pull on hydrogen and helium gas within the nebula. This explains why hydrogen and helium don't exist in Earth's atmosphere, nor can they be found naturally in the atmospheres of the other three inner planets. Instead, all of Earth's hydrogen is locked up in water and other molecules. Hydrogen and helium are extracted from mines and from wells that produce natural gas. Earth is the largest of the inner planets, and its gravitational pull is sufficient to keep a thin atmosphere of other gases around its surface. Mercury An Image of Mercury Produced with Color Mapping In contrast to Earth, Mercury, the innermost planet, has almost no atmosphere, and what little atmosphere exists is constantly getting blown away by solar wind. This solar wind carries some hydrogen and helium that accumulates in Mercury's atmosphere, while © 2023 PF High School, LLC Page: 27 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth oxygen is thought to come from the surface. Sodium, potassium, and calcium also are present in Mercury's atmosphere and are likely produced from the surface of the planet. The atmosphere on Mercury is too thin and doesn't contain enough greenhouse gases to keep the planet at a stable temperature. Every time the planet's surface heats, more of these latter three elements are released into the atmosphere. The surface of Mercury is solid with evidence of volcanism. The surface also contains numerous craters from asteroid impacts. In the past, volcanoes were active on Mercury, and lava flows can be seen from images its surface. Much like the moon, Mercury is quite small, and its surface eventually cooled to the point that it solidified. Thus, there's currently no plate tectonic activity on Mercury. Venus is image of Venus shows lava ow on the planet. Venus is just slightly smaller than Earth. Unlike Mercury, the atmosphere of Venus is very hot and dense. Venus's atmosphere is approximately 95 percent carbon dioxide, which keeps the surface temperature hot enough to melt most metals. This atmosphere arises because, like Earth, Venus is large enough to hold an atmosphere due to gravity. However, unlike Earth, Venus is caught in a positive feedback loop of increasing carbon dioxide: the more carbon dioxide in its atmosphere, the hotter it became. This then released more carbon dioxide from rocks, which wasn't absorbed by either plant life or plate tectonics. The atmosphere also contains small amounts of gaseous sulfuric acid, carbon monoxide, © 2023 PF High School, LLC Page: 28 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth argon, and water vapor. Much of the surface of Venus is composed of molten bedrock, with some impact craters. Craters are much less common on Venus than on Mercury due to Venus's thick atmosphere, which causes many small meteorites to break apart before they reach the surface. Volcanism is very common on Venus and appears to the dominant cause of geological changes. Mars is image shows the seasonal polar ice caps of Mars, which are composed of carbon dioxide. Mars is about half the size of Earth and Venus, thus its gravitational pull can only maintain a very thin atmosphere composed almost entirely of carbon dioxide. Its north and south poles get no sunlight during winter, and the surface becomes so cold that carbon dioxide condenses into polar ice caps. The surface of Mars is pocked with craters since asteroids and meteorites easily pass through the thin atmosphere. Mars also appears to have exhibited volcanic activity in the past, though an active volcano has never been observed on the planet's surface. The Outer Planets An asteroid belt lies between the first four planets closest to the sun—the rocky, inner planets—and the last four, gaseous, giant planets. Jupiter, Saturn, Uranus, and Neptune are collectively known as the Jovian planets, and they have different structures than the © 2023 PF High School, LLC Page: 29 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth inner planets. For one thing, the Jovian planets have relatively small, dense cores surrounded by huge layers of gas. In addition, these planets don't have solid surfaces and are made almost entirely of hydrogen and helium. As you venture below the surfaces of the Jovian planets, their interiors become denser just as in the terrestrial planets. In fact, their interiors becomes dense enough to contain hydrogen as a liquid and eventually as a solid. The inner cores of the Jovian planets are solid and consist of mixtures of hydrogen compounds, solid rock, and metals. is image shows a comparison of the sizes of planets in the solar system. e planets' sizes are shown to scale. One might wonder why such massive collections of hydrogen gas haven't collapsed into stars under gravity. After all, the sun formed from a similar process of coalescing gas that then ignited under great pressure. And, the Jovian planets contain large amounts of hydrogen, similar to the sun. The reason lies in the fact that these planets spin extremely quickly on their axes. These fast rotations originated because these planets formed farther from the center of the solar nebula. Jupiter and Saturn both complete a full rotation in approximately 10 hours, and Uranus and Neptune complete a full rotation in approximately 17 hours. As the original solar nebula was spinning during the formation of the solar system, the rotation rates of the gas giants grew to a very fast rate. This fast rotation rate creates a strong centrifugal force that prevents gases in these planets from collapsing into a small volume. In turn, this allows the gas giants to accumulate extremely large masses without collapsing into stars. The fact that the Jovian planets formed beyond a certain distance from the sun is no accident. Hydrogen that was located beyond a certain point in the solar nebula, called the frost line, was low enough in temperature to condense and freeze. In contrast, the temperature of hydrogen inside the frost line was too high for the gas to freeze. This © 2023 PF High School, LLC Page: 30 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth hydrogen was slowly pushed toward the edge of the solar nebula by solar wind and centrifugal force. That, in turn, allowed the hydrogen to start building up, in time forming the outer planets under gravity. Rings and Moons around the Jovian Planets In addition to their larger sizes, the Jovian planets contain many more moons than the terrestrial planets. Their large masses and high levels of gravity enable them to capture nearby objects much more easily, trapping them in orbit. Gravity from the Jovian planets even prevents their smaller moons from accumulating into larger moons. In this way, each of the Jovian planets can be viewed as a miniature solar system. The four largest moons that orbit Jupiter are rather famous since they led to the rejection of a geocentric solar system. When Galileo first examined Jupiter with a telescope, he discovered four moons that appeared to be moving back and forth near the planet. A geocentric model states that all celestial objects orbit Earth, so this observed back-and- forth motion seemed illogical. A more accurate model found that these moons simply orbited Jupiter. Such an idea was important, even crucial, in confirming the validity of the heliocentric model. Today, we know that Jupiter has more than 60 moons, Saturn has more than 30, Uranus has more than 20, and Neptune has more than 10. The Jovian planets also contain rings, though only Saturn's rings are prominent enough to be seen from Earth. Jovian rings, composed of small rocks, dust, and ice, orbit their respective planets like tiny moons. Yet the rings orbit their planets at a closer distance than any of the planets' actual moons. © 2023 PF High School, LLC Page: 31 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth is image shows Uranus tilted 98 degrees on its axis, with rings that aren't visible to the naked eye. Jovian rings likely formed through the capture of nearby particles. Another theory supposes they could have formed as larger objects broke up under tidal forces from the nearby planets. If a massive object passes too close to a planet, the tidal forces from gravity are strong enough to break up the object. If the planet is very dense, then tidal force strength is even more powerful and can break up objects at a farther distance from the planet. The limit to which an object can approach a planet without being destroyed by tidal forces is called the Roche limit, and this limit depends on the density of the object, the density of the planet, and the size of the planet. The rings of Saturn are located inside Saturn's Roche limit, so it's possible that the rings formed from the breakup of more massive objects such as meteors or asteroids. © 2023 PF High School, LLC Page: 32 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth Asteroids, Meteors, and Comets The terms asteroid, meteoroid, and comet refer to different objects in the solar system. Asteroids are large rock bodies that never accumulate enough mass to grow into planets. (When an object is massive enough, gravity tends to transform it into a sphere, which is one of the defining characteristics of a planet). Some asteroids are composed of large amounts of iron and nickel. Asteroids are primarily found in the asteroid belt between Mars and Jupiter and found in places in Jupiter's orbit. Astronomers believe that asteroids may be found in the Kuiper Belt as well. The motion of other planets can alter the orbit of an asteroid, causing its position to change and even come closer to Earth. In general, an asteroid doesn't have an atmosphere because atmosphere is the product of gravity, and asteroids aren't massive enough to keep gases at their surface. However, some asteroids are large enough to have their own moons. Small rocks and other debris smaller than asteroids are called meteoroids. Most meteoroids that enter Earth's atmosphere vaporize before they ever reach the surface. They create trails of light as they burn, known as meteors or shooting stars. Most meteors are harmless, but some explode in the atmosphere and create massive shockwaves. For example, a meteoroid hundreds of feet in size entered the atmosphere above Yeniseysk Governorate, Russia in 1908. This meteoroid exploded in the atmosphere, producing a shockwave that knocked down trees for hundreds of square miles. Unlike asteroids and meteoroids, comets are clumps of rock, dust, frozen gases, and ice that fly through the solar system at high speed. Many comets originate in the Kuiper belt and become trapped in a large orbit around the sun. As these bodies travel around the sun, they release gas and dust in their wake as a long tail. Solar wind causes the tail of a comet to trail away from the sun at all times, rather than always trailing behind the comet. To learn more about the differences among asteroids, comets, and meteoroids, watch this video(https://www.youtube.com/embed/dvd47rMYia0?rel=0&showinfo=0) by Less Than Five. Using Space Probes for Exploration Over the past six decades, NASA has launched 142 probes into space to explore the solar system. Other countries, such as the Soviet Union, Japan, India, China, and member states of the European Space Agency have launched their own probes to explore the solar system. The use of these probes allows scientists to gather accurate measurements on the © 2023 PF High School, LLC Page: 33 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth composition, motion, and layout of the planets throughout the solar system. Many probes have landed on the moon, orbited the inner planets, and even explored the asteroid belt and the dwarf planet, Ceres. As of 2019, there are 20 active probes throughout the solar system. Probably the simplest missions are fly-by missions, in which a probe passes near a planet and captures images along the way. The most famous probe that completed this type of mission is Voyager 2. Launched on August 20, 1977, Voyager 2 passed by all the Jovian planets, eventually leaving the solar system. Along the way, it captured close-up, first images of the outer two gas giants: Jupiter and its moons and Saturn's rings. Other notable probes that explored the terrestrial planets were the Mariner probes. These probes explored Mars, Venus, and Mercury, and they were responsible for accumulating much of our knowledge on the composition of these planets. They also captured the first close-up images of these planets. Other probes are designed to orbit other planets, allowing the probes to continually observe the planets' surfaces, atmospheres, and magnetic fields. Some of these probes have gone offline (ceased communicating with Earth) over the passage of time. Eventually, their orbits will decay, and the probes will crash into the planets they're orbiting. The sun also is being actively explored with space probes. The Parker Solar Probe was launched on August 12, 2018 and will orbit the sun within its corona, which is the layer of gases surrounding the sun. The goal is to take measurements of the corona, the sun's magnetic field, and the solar wind. Because space probes are too small to carry large amounts of fuel to power propulsion systems, they're launched on very specific trajectories to reach their destinations. Probes don't travel along straight lines. Instead, they travel along curved trajectories and take advantage of the gravity of other planets in the process. The most common type of maneuver used to steer probes is called a gravity-assist maneuver. In this maneuver, the probe uses the gravity of a nearby planet to accelerate or decelerate. This alters the trajectory of the probe toward the next point along its journey. Scientific Knowledge Gained from Space Exploration The total amount of scientific knowledge gained from space exploration, both near Earth and farther out in the solar system, is too broad to cover in full detail. In short, knowledge gained from studying other planets has provided insight into all of the fundamental sciences, including physics, biology, geology, and chemistry. By comparing Earth with different worlds, scientists have learned more about Earth's geological history and why it can support life. This has also aided our search for Earth-like, extrasolar planets. Space probes and telescopes have been instrumental in yielding knowledge on the composition of planets, stars, galaxies, and the universe as a whole. In addition, the knowledge gained from examining background radio waves has helped us understand how the universe began. Such activity has driven important advances in engineering new materials, instrumentation, and communications technology. Manned missions have provided useful knowledge on the human body. For example, studies of the human body's response to extended periods in low Earth orbit on the International Space Station have helped us better understand the aging process. © 2023 PF High School, LLC Page: 34 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth In addition to the scientific knowledge gained from space exploration, NASA's space program has produced a number of inventions that are used in our daily lives. Read more to learn about the practical benefits of space exploration(https://www.jpl.nasa.gov/infographics/20-inventions-we-wouldnt- have-without-space-travel) from the NASA Jet Propulsion Laboratory. To learn more about the formation of the solar system, read Section 22.3(https://opentextbc.ca/geology/chapter/22-3-how-to-build-a-solar- system/) in Physical Geology. © 2023 PF High School, LLC Page: 35 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth Key Points and Links Key Points e solar system formed from a solar nebula of dust and gas. Gravity pulled nearby dust and gas into clumps, causing them to grow over time into planet-sized objects. Heavier elements accumulated in the inner portion of the solar nebula; thus, the four terrestrial planets are composed primarily of heavier elements. e Jovian planets contain dozens of moons that became captured as a result of gravity. ese planets also contain rings that may have formed as massive objects broke up after passing the Roche limit of a particular planet. Space exploration yields scienti c and practical bene ts for humankind. e knowledge gained from space exploration helps us understand Earth and has produced many useful inventions commonly used in modern life. Links What's the Di erence between Comets, Asteroids, Meteoroids, Meteors, and Meteorites? (https://www.youtube.com/embed/dvd47rMYia0?rel=0&showinfo=0) 20 Inventions We Wouldn't Have without Space Travel(https://www.jpl.nasa.gov/infographics/20-inventions-we- wouldnt-have-without-space-travel) Physical Geology, Section 22.3: How to Build a Solar System(https://opentextbc.ca/geology/chapter/22-3-how-to- build-a-solar-system/) © 2023 PF High School, LLC Page: 36 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth Self Assessment: Describe the Formation and Interaction of the Main Solar System Components Open Link © 2023 PF High School, LLC Page: 37 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth Examine the Life Cycles of Stars, and Identify the Features of the Sun © 2023 PF High School, LLC Page: 38 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth Stars Life Cycle of Stars Stars form from nebulae, which as you'll recall, are clouds of dust and gas. In the previous section, you learned how crucial nebulae were to the formation of the solar system. The term nebula once referred to almost any astronomical object that extended over a large area. Before astronomers knew that galaxies were distant collections of stars, galaxies were called "nebulae" because they appeared fuzzy in telescopes. Today, the word is reserved for clouds of gas and dust. Stars form in nebulae due to gravity, much in the same way that planets form. Gravity will cause a clump of hydrogen gas to gather and compress. As this mass of hydrogen gas increases, its gravity increases, and it pulls in more hydrogen gas. This causes a situation in which large clumps of hydrogen grow progressively larger. Eventually, nearby hydrogen has gathered into a single region. This cloud of hydrogen begins to collapse in on itself due to gravity. Nuclear fusion occurs in the interior region of this new star if its mass is large enough, forming a core that emits a large amount of energy. (You'll learn more about nuclear fusion shortly.) This heats up the entire cloud of gas to an extremely high temperature, and a specific structure begins to form in the interior of the new star. As the new star begins emitting light, it and others like it cause the nebula they occupy also to start shining. Stars aren't static. Their structures, their light emission, and their sizes change over time as they burn fuel. The life cycle of a star depends primarily on its mass. Massive stars burn their fuel more quickly than smaller stars. As a result, these massive stars may only live a few million years. Smaller stars burn their fuel much more slowly and can last for billions of years. Energy Production in Stars Stars produce energy through nuclear fusion. This process refers to the creation—or fusion —of heavier elements from lighter elements. The process emits subatomic particles and light, and the fused elements reach very high temperatures. For nuclear fusion to begin, elements must undergo extremely high temperatures and pressures. These conditions can be found only in the interiors of stars and planets or inside particle accelerators. One reason that fusion can't be used in nuclear power plants is that the intense pressure and temperature required would destroy the reactor. © 2023 PF High School, LLC Page: 39 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth e temperature and pressure are high enough in the core of a star to force hydrogen to fuse into helium. Stars form from hydrogen gas, and the temperature and pressure in the core of a star are high enough to force hydrogen to fuse into helium. The high temperature and pressure result from gravity, which compresses the interior of the star so that it's very dense. This figure shows the chain of reactions required to produce helium from hydrogen. The products of each of these reactions are extremely hot, and these hot products radiate their heat throughout the interior of the star. This warms the entire star to a very high temperature. Eventually, the star converts a large portion of its initial hydrogen to helium. That causes the star to enter a new phase of its life cycle. As the star's hydrogen fuel is depleted and converted to helium, the star begins to cool and expand, forming a red giant. Red Giants and Beyond Eventually, the hydrogen fuel that powers nuclear fusion in the core will begin to run out and become completely converted to helium. At this point, the star will enter the next phase © 2023 PF High School, LLC Page: 40 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth of its lifetime and become a red giant. As star stops burning hydrogen fuel, it starts to cool and expand. This causes the color of the star to change to a deeper red color. What happens next depends on the initial mass of the star. If the mass of the star was initially small, similar to the mass of our sun, the star will burn its fuel slowly and can last billions of years before entering the next phase of its life. Yet if the star was initially very massive, it will burn through its hydrogen fuel very quickly. A more massive star will form a red supergiant. Less massive stars still form red giants, but they're smaller and hotter than supergiants. During the red giant phase of a star's life cycle, gravity causes the core to collapse on itself, and the internal pressure and temperature are high enough that helium can begin fusing into carbon. This can actually cause two shells to form in the interior of a star, where helium fuses into carbon in the core, and any remaining hydrogen fuses into helium in the outer shell. The End of a Red Supergiant Once helium is depleted from the core of a red supergiant, the core begins collapsing again. The mass of a red supergiant is large enough that gravity continues to compress carbon atoms together. The temperature and pressure in the core continue increasing, causing the fusion of hydrogen, helium, and carbon into heavier elements. All heavier elements that are found throughout the universe, including the heavier elements that make up Earth, were formed through this process. The process of continued compression and fusion eventually causes the temperature and pressure of the star to become so hot that it explodes. This scatters its chemical constituents away from the star at extremely high velocity. The explosion is called a supernova, and it expels heavier elements and radioactive isotopes. The leftover core of the exploded star produces x-rays and gamma rays that can be detected with telescopes. Again, the next step in the star's life cycle depends on the mass of the star. After the supernova explosion, the remnants of the star primarily contain neutrons. The mass of the star is already large enough for gravity to compress neutrons to a minuscule volume. Thus, this supernova remnant is called a neutron star. Stars that were originally 10 to 29 times the mass of the sun will end their life cycles as neutron stars. As mass is expelled in the supernova explosion, the rotation of the neutron star increases to a very high rate. Neutron stars that happen to be magnetized or binary can emit intense bursts of x-rays, which are detectable with telescopes. If the mass of the star was originally greater than 29 times the mass of our sun, it's large enough for the supernova remnant to form a black hole. In this process, the density of the matter left over from a supernova explosion is so great that the remaining matter is compacted by gravity into a very small volume. The force of gravity produced by these objects is so strong that even light can't escape. As a result, scientists aren't able to observe black holes directly. The Death of Smaller Stars © 2023 PF High School, LLC Page: 41 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth Smaller stars don't die in as spectacular a fashion as very massive stars. During the red dwarf phase, the outer portion of the star expands away from the core, while helium continues fusing into carbon and continues collapsing. This forms a planetary nebula in the outer layers. Note that the term planetary nebula has nothing to do with the formation of planets. Rather, these objects were originally mistaken for planets when viewed through small telescopes, and the term has remained. The hot gases in the outer layers move away, leaving behind a compact core called a white dwarf. This core eventually cools and dims. is image shows the life cycle of stars. Light Emitted from Stars Stars emit light via two mechanisms: blackbody radiation (also called thermal radiation) and line spectra. Both of these types of light are used to determine the temperature and composition of a star. Line spectra are related to the chemical composition of stars, while blackbody radiation is related to the temperature of a star. Any object with a degree of temperature emits blackbody radiation. The blackbody spectrum is a broad band of many colors that spans into the infrared and ultraviolet regions of the electromagnetic spectrum. A very hot object can emit blue light as well as light that's deeper within the ultraviolet spectrum. In contrast, objects with temperatures that are commonly found on Earth emit light in the infrared region and don't generate visible light. As the temperature of an object increases, the light it emits changes from infrared to visible red light. At extremely high temperatures, the light moves into the blue and ultraviolet regions. © 2023 PF High School, LLC Page: 42 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth Although the sun appears yellow, it emits blackbody radiation across a wide range of colors. These colors combine to give the sun its particular shade of yellow as seen with the human eye. However, if you use a device called a spectrometer to collect light from the sun, you'll see a broad band that spans throughout the visible region of the electromagnetic spectrum. Some of the light emitted from the sun is infrared, and a small amount is ultraviolet. The blackbody spectrum has a peak wavelength, and this wavelength depends on the temperature of the object. A star's peak wavelength corresponds to a specific color of light and largely determines the star's overall appearance. As the temperature of a star increases, the peak wavelength decreases, corresponding to a transition from red to blue. To learn more about the blackbody spectrum, view a simulator(https://phet.colorado.edu/en/simulation/blackbody-spectrum) that shows the spectrum produced by stars with different temperatures. You can adjust the temperature of the "star" to get an idea of how peak wavelength changes with temperature. Line spectra are much different from the blackbody spectrum. As you read previously, line spectra tell us about a star's chemical composition. This information also can be used to estimate the progress of the star's life cycle. Each element in the periodic table is composed of protons, neutrons, and electrons. The electrons occupy certain regions around the nucleus of an atom, called orbitals. An electron must have a certain amount of energy to occupy a specific orbital. If an electron moves to a higher-energy orbital, it will eventually return to its original orbital and emit a photon of light in the process. Each photon has a very specific wavelength, and each wavelength depends on the transition an electron takes within the atom. These photons can be collected with a spectrometer, producing a specific series of lines. The line spectrum for hydrogen is shown in the following figure. Different elements produce different line spectra, and these line spectra act like fingerprints for various atoms. © 2023 PF High School, LLC Page: 43 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth is horizontal graph shows the line spectrum of hydrogen compared to the ultraviolet, visible, and infrared spectra. Inside a star, the situation is more complicated. An atom that emits photons as part of the line spectrum also absorbs light at those same wavelengths. Light that's emitted as part of the blackbody spectrum can be reabsorbed by atoms in the star as blackbody light travels away from the star. When light from the star is examined with a spectrometer, lines called absorption lines appear in the blackbody spectrum that matches the line spectra from the atoms that make up the star. It's these lines in the blackbody spectrum that can be used to determine the elemental composition in a star and the density of each element. To learn more about the line spectra of stars, visit the Sloan Digital Sky Survey(http://cas.sdss.org/dr6/en/proj/basic/spectraltypes/stellarspectra.asp). When multiple elements such as hydrogen and helium are present in a star, they both create absorption lines. The strength of each absorption line in the blackbody spectrum will depend on the relative amount of each element in the star. For example, if more hydrogen is present, then the absorption line from hydrogen will be brighter than the absorption line from helium. © 2023 PF High School, LLC Page: 44 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth The Sun's Structure The sun is composed of many layers of hot gas. The central region is the core, which has the highest temperature and pressure. In the sun's core, gravity compresses hydrogen to the point where it fuses into helium and releases energy through nuclear fusion. All energy that leaves the sun and reaches the earth originates from the core. The temperature of the core is approximately 15,000,000 °C. The layer surrounding the core is called the radiative zone, so named because energy travels through it as radiation. The radiative zone isn't as dense as the core, although it's still extremely dense. The light, released from the core as gamma rays, travels only a few millimeters in the radiative zone before it's reabsorbed by another atom. Then it's re- released, and this process repeats thousands of times before it can break free of the zone. With each absorption and release, the gamma rays lose some of their energy and eventually convert to x-rays and UV radiation. It takes a significant amount of time for light to reach the next layer, called the convection zone, so named because energy is carried through the movement of matter. As photons enter the convection zone—after already having traveled for thousands of years since they were first emitted from the core—the zone heats the gas surrounding it. The matter in the convection zone is still very hot but not hot enough to re-radiate energy, as occurred in the radiative zone. Instead, the heat rises, just as a boiling pot brings heat to the surface, and then sinks again in a convection cell. These convection cells carry heat to the outer layers of the sun. The outer layers of the sun make up its atmosphere. The interior portion of the sun's atmosphere, called the photosphere, is responsible for producing the majority of blackbody radiation observed from the sun. The temperature of the photosphere is about 5,800°C. This layer isn't solid, even though, because it's opaque, it's commonly referred to as the "surface" of the sun. The outer portion of the sun's atmosphere is called the chromosphere. The chromosphere is an irregular layer above the photosphere where the temperature increases from 6,000 °C to about 20,000 °C. At these higher temperatures, hydrogen emits light with a reddish color, called H-alpha emission. Emission from this region is seen easily during a total solar eclipse. © 2023 PF High School, LLC Page: 45 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth is image illustrates the structure of the sun. With a coronagraph, one can observe the sun's corona, which is the outermost layer. The final layer of the Sun is the corona. This layer consists of superheated gases at over 1,000,000 °C and very low density, and this cloud of gases extends millions of kilometers beyond the chromosphere. The corona is very dim and not visible to the naked eye due to the sun's intensity. However, you can view the corona from Earth during a total solar eclipse with a special instrument called a coronagraph. Chemical Composition The same elements that are present on Earth are also present in the sun, although at substantially different concentrations. The sun is mostly hydrogen, which accounts for 73 percent of its mass. Helium produced by nuclear fission accounts for another 25 percent of the sun's mass. The remaining two percent consists of oxygen, nitrogen, carbon, and other heavier elements. The sun is so hot that matter doesn't exist there in any of the three phases—solid, liquid, or gas—that are found on Earth. Instead, matter exists in a state known as plasma. The temperature inside the sun is hot enough that electrons can escape from atoms as ions. A particular spectral line from ionized iron provided the first evidence that the temperature of the sun's upper atmosphere was over 1,000,000 °C. Features on the Sun The sun exhibits some peculiar features on its photosphere. When viewed with a telescope, the photosphere appears to have a grainy surface. These granules exist as the © 2023 PF High School, LLC Page: 46 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth tops of convection cells. They're immense, spanning hundreds or thousands of miles. Their central areas are hotter and brighter, while their boundaries are cooler, and thus darker. The granules (convection cells) move across the photosphere and can last for minutes at a time before dissipating or being absorbed by larger granules. is is an image of sunspots on the photosphere captured with a small telescope. Like Earth, the sun generates a magnetic field. Its magnetic field, however, arises as a result of plasma convection. The movement of plasma near the sun's equator is much faster than near its poles. This causes magnetic field lines to curve near the equator, which causes sunspots to form in the photosphere. That immobilizes small areas of the photosphere that are unable to acquire heat by convection. As a result, these areas are much cooler than the surrounding areas of the photosphere, and they appear dark against the bright background of the photosphere. Unlike Earth, where the magnetic field reverses after approximately 2 million years, the sun's magnetic field reverses every 11 years. The ultimate cause of this flip in the sun's magnetic field is unknown, although some astronomers suspect that it occurs as a result of periodic gravitational effects of the alignment of the sun, Venus, Earth, and Jupiter. © 2023 PF High School, LLC Page: 47 of 78 © 2023 Career Step, LLC © 2023 Education Holdings 1, LLC © 2023 Sokanu Interactive Earth Science / Beyond Earth To read more about research on changes in the sun's magnetic field, visit Science Alert(https://www.sciencealert.com/a-strange-force-is-messing- with-our-sun-s-activity-and-scientists-might-finally-know-what-it-is). The sun also ejects charged particles at nearly one million miles per hour. This solar wind originates from ions in the corona. Solar wind primarily originates from the portion of the corona near the poles of the sun, creating regions called coronal holes. Closer to the sun's equator, the magnetic field traps the corona closer to the sun. Coronal holes can be observed from ultraviolet and x-ray images of the sun. The electrical force between ionized atoms is much stronger than the force of gravity, and this allows them to acquire their high speeds as they radiate outward from the sun. Astronomers estimate that the Sun is losing approximately 10 million tons of material each year through the solar wind. While this loss of mass may seem large, it is insignificant compared to the mass of the sun. When the solar wind reaches Earth, our magnetic field deflects it near the equator. Near the poles, Earth's magnetic field turns inward, and some solar wind strikes the atmosphere, causing it to glow. This produces auroras in the upper atmosphere that span over very large areas. The previous description of the sun applies to many stars in the early phases of their life cycles. Absorption lines and blackbody radiation are the two primary tools used to determine the ages, composition, and density of stars throughout the universe. Classifying Stars

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