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Objectives Explain the nebular hypothesis of the origin of the solar system and describe how the planets formed Distinguish between inner and outer planet characteristics Describe unique features of all the planets
The Nebular Hypothesis solar system-the sun and all of the planets and other bodies that travel around it Scientists have long debated the origins of the solar system In the 1600s and 1700s, many scientists thought that the sun formed first and threw off the materials that later formed the planets This was incorrect.
Nebular Hypothesis solar nebula -a rotating cloud of gas and dust from which the sun and planets formed; also any nebular from which stars and planets may form In 1796, French mathematician Pierre Simon, advanced a hypothesis now known as the nebular hypothesis. States: a large cloud of gas and dust (nebula) collapses because of gravitational forces and begins to spin Scientific calculations support this hypothesis The sun is composed of about 99% of all of the matter that was contained in the solar nebula.
Solar System Formation 1.) Solar nebula begins to collapse because of gravity 2.) Solar nebula rotates, flattens, and becomes warmer in the center 3.) Planetesimals begin to form within the swirling disk 4.) As planetesimals grow, their gravitational pull increases. The largest planetesimals begin to collect more of the gas and dust of the nebula
Formation continued 5.) Small planetesimals collide with larger ones and the planets begin to grow. 6.) the excess dust and gas is gradually removed from the solar nebula, which leaves planets around the sun and thus creates a new solar system
Formation of the Planets planetesimal -a small body from which a planet originated in the early stages of development of the solar system While the sun was forming in the center of the solar nebula, planets were forming in the outer regions. Some planetesimals joined together through collisions and through the force of gravity to form larger bodies called protoplanets. Protoplanets gravity attracted other planetesimals, which collided, and added to the protoplanet s mass. Eventually, they became very large and condensed to form planets and moons.
Formation of the Planets, continued The diagram below shows the formation of the Solar System..
Formation of Inner Planets The four protoplanets closest to the sun became Mercury, Venus, Earth, and Mars. The features of a newly formed planet depended on the distance between the protoplanet and developing sun. The inner planets are smaller, rockier, and denser than the outer planets. They contain large percentages of heavy elements, such as iron and nickel. Lighter elements may have been blow or boiled away by radiation from the sun, and because at the temperature of the gases, gravity was not strong enough to hold their gases.
The Inner Planets terrestrial planets- one of the highly dense planets nearest to the sun; Mercury, Venus, Mars, and Earth These planets consist mostly of solid rock and metallic cores. The number of moons per planet varies from zero to two. The surfaces of inner planets have bowl-shaped depressions called impact craters, that were caused by collisions of the planets with other objects in space.
Unique Features of inner planets Mercery surface is heavily cratered, has daily temperature range between 427 C and -173 C Orbital period: 88 days; axis rotation: 59 days Venus- similar to Earth in size, mass, and density, but atmospheric pressure is 90x Earth s has a runaway greenhouse effect, 96% CO2- keeps temperatures high average being 464 C Surface has many volcanoes and lava plains Orbital period: 225 days; axis rotation 243 days Earth Mars has seasons, has volcanoes and marsquakes, has frozen water in ice caps, is red in color Orbital period: 687 days; axis rotation 24hours and 37 minutes
Mars Why is Mars red? The iron-rich rock oxidizes (rusts) and turns red Could there be life on Mars? Could have been at some point when the water was liquid, some plants or microbials https://www.youtube.com/watch?v=iwpo- VViwx4
Water on Mars The pressure and temperature of Mars s atmosphere are too low for water to exist as a liquid on Mars s surface. Several NASA spacecrafts have found evidence that liquid water did exist on Mars s surface in the past. Surface features on Mars are characteristic of erosion by water. Although most of the water on Mars is trapped in polar icecaps, it may also exist as permanent frost or as a liquid just below the surface.
Formation of the Outer Planets The next four protoplanets became Jupiter, Saturn, Uranus, and Neptune. These outer planets formed far from the sun and therefore were cold. They did not lose their lighter elements, such as helium and hydrogen, or their ices, such as water ice, methane ice, and ammonia ice. The intense heat and pressure in the planet's interiors melted the ice to form layers of liquids and gases. These planets are referred to as gas giants because they are composed mostly of gases, have low density, and are huge planets.
The Outer Planets gas giant -a planet that has a deep massive atmosphere, such as Jupiter, Saturn, Uranus, and Neptune. The planets furthest from the sun are separated from the inner planets by a ring of debris called the asteroid belt.
Gas Giants Gas giants are larger and more massive than terrestrial planets, but much less dense. Each planet probably has a core made of rock and metals. Each gas giant has a thick atmosphere made mostly of hydrogen and helium gases. Unlike terrestrial planets, gas giants did not lose their original gases during formation. All gas giants have ring systems that are made of dust and icy debris that orbit the planets.
Features of the Outer Planets Jupiter- largest planet, has 60 moons, several thin rings made of particles, atmosphere is 92% Hydrogen and Helium (no nuclear fusion), has lightning and thunderstorms, temperatures reach 30,000 C Jupiter s Great Red Spot is an ongoing, massive, hurricanelike storm that is about twice the diameter of Earth. Orbital period: 12years, axis rotation: 9hours and 50minutes Saturn least dense planet, cold, average temperature of - 176 C, has at least 60 moons, also made mostly of Hydrogen and Helium, rings of dust and ice that are 2x planets diameter Orbital period: 29.5years, axis rotation:10hours and 30minutes
Features of the Outer Planets Uranus- 3 rd largest planet, has 24 moons, at least 11 rings, axis is almost parallel to the plane of its orbit, atmosphere mostly hydrogen and Helium with large amount of methane Orbital period: 84years, axis rotation: 17hours, 14minutes Neptuen- similar in size and mass to Uranus, has at least 8 moons and possibly 4 rings, atmosphere mostly hydrogen, helium, and methane, strong winds exceed 1,000km/hr Orbital period:164years, axis rotation:16hours The Great Dark Spot on Neptune was a giant storm the size of Earth that appeared and disappeared on Neptune s surface.
Objective Describe the formation of the land, the atmosphere, and the oceans of Earth. Summarize the features that allow Earth to sustain life.
Remember Early Earth Earth formed 4.6 billion years ago. Scientists think that Earth began as a ball of dust, rock and ice. Gravity pulled this mass together. As Earth grew larger, gravity increased. Pulled in nearby dust, ice and rock. As objects hit Earth at high speeds, their energy changed into thermal energy. Energy from collisions caused Earth s temp to rise until planet was very hot. Scientist believe Earth may have become so hot it melted. Denser materials sank toward the center formed Earth s dense iron core. At same time, Earth continuously lost heat to cold of space. Less dense molten material hardened to form Earth s outer layers. Oceans form.
Earth Earth is the third planet from the sun. The orbital period of Earth is 365 1/4 days. Earth completes one rotation on its axis every day. Earth has one large moon. Geologic records indicate that over the last 250 million years, Earth s surface has undergone many changes.
Water on Earth Earth s unique atmosphere and distance from the sun allow water to exist in a liquid state. Other planets are too close or far away from the sun to have liquid water Life on Earth Earth is the only known planet that has the proper combination of water, temperature, and oxygen to support life.
Formation of Solid Earth Early Solid Earth When Earth first formed, it was very hot, Earth cooled to form three distinct layers. In a process called differentiation, denser materials sank to the center, and less dense materials were forced to the outer layers. The center is a dense core composed mostly of iron and nickel. Around the core is a thick layer of iron- and magnesiumrich rock called the mantle. The outermost layer of Earth is a thin crust of less dense, silica-rich rock.
Present Solid Earth Eventually, Earth s surface cooled enough for solid rock to form from less dense elements that were pushed toward the surface during differentiation Interactions with the newly forming atmosphere and the heat in Earth s interior continues to change Earth s surface
Differentiation of Earth and Formations of Earth's Atmosphere The diagram below shows the differentiation of Earth.
Formation of Earth s Atmosphere Earth s Early Atmosphere The atmosphere formed because of differentiation. Earth s gravity is too weak to hold high concentrations of hydrogen and helium gases and is blown away by solar winds. Outgassing Outgassing formed a new atmosphere as volcanic eruptions released large amounts of gases, mainly water vapor, carbon dioxide, nitrogen, methane, sulfur dioxide, and ammonia. The ozone formed from remaining oxygen molecules after solar radiation caused ammonia and some water vapor to break down.
Earth s Present Atmosphere The ozone collected in a high atmospheric layer around Earth and shielded Earth s surface from the harmful ultraviolet radiation of the sun. Organisms, such as cyanobacteria and early green plants, could survive in Earth s early atmosphere by using carbon dioxide during photosynthesis. These organisms produced oxygen as a byproduct of photosynthesis and helped slowly increase the amount of oxygen in the atmosphere.
Formation of Earth s Oceans The first ocean was probably made of fresh water. Over millions of years, rainwater fell to Earth and dissolved some of the rocks on land, carrying those dissolved solids into the oceans. As the water cycled back into the atmosphere through evaporation, some of these chemicals combined to form salts. Through this process, the oceans have become increasingly salty.
Objective Explain why Earth has seasons
Earth Rotates Earth rotates spin of a body on its axis Earth s axis is an imaginary line that goes through the center of Earth from pole to pole Earth s axis is tilted at 23.5 Each complete rotation takes about one day. The Earth rotates from west to east. Earth s rotation gives us day and night. Part of Earth facing Sun has daylight and part facing away from sun has nighttime.
Earth Revolves Earth revolves when one object moves around another object One revolution takes 365 1/4 days Orbit path an object follows as it revolves around another object
Why do we have seasons? Take a look at our globe. It s not tilted like that because it looks nice. No way. That s the way the Earth is tilted in space s because the Earth s axis is tilted.
Look at this diagram. Notice how the Earth is always tilted in the same direction. As the Earth revolves the part of Earth tilted toward the sun changes.
During part of the year the North Pole tilts towards the sun. This season is summer.
During another part of the year, the North Pole points away from the sun. This season is winter.
The number of daylight hours is greater for the hemisphere, or half of Earth, that is tilted toward the Sun. Summer is warmer than winter (in each hemisphere) because the Sun's rays hit the Earth at a more direct angle during summer than during winter
When the North Pole is tilted toward the Sun, the Sun travels higher overhead in the sky. The Sun s rays shine straighter down on that part of the Earth. It is summer in that part of the Earth. It s like pointing a flashlight at a piece of paper. When you hold the flashlight straight above the paper, the rays from the flashlight shine down straighter.
When the North Pole is tilted away from the Sun, the Sun stays lower in the sky. It is then winter in that part of the Earth. If you point your flashlight at a piece of paper at an angle, the rays from the flashlight spread out.
Objective Explain what a solstices and equinox is.
What are they? Solstice When tilt of Earth s axis is oriented directly towards or away form the Sun when the sun is at its greatest distance from the equator Makes Sun appear to reach its northern and southern most extremes Happens twice a year Marks the start of a season Winter: Dec. 21 Summer: June 21 Equinox A day lasts 12 hours and a night lasts 12 hours Equinox literally means equal night one of two opposite points on the celestial sphere where the celestial equator and ecliptic intersect. Sunlight strikes the Earth most directly at the equator Occurs twice a year Vernal (spring): March 21 Autumnal (fall): Sept. 21
Approximate Dates The dates of the equinoxes and solstices are only approximate dates. The actual length of a year is about 365 ¼ days (365 days, 5 hours, 49 minutes), not exactly 365 days. We have to add an extra day to a year every four years to keep the seasons synchronized with the seasons (leap year). Over a longer period of time, we need to skip a leap year to compensate the extra minutes we add in every leap year to keep the calendar in sync.
Objective Explain why is Pluto no longer a planet.
New Definition of a planet Object that orbits the sun Object is large enough to have become round due to the force of its own gravity Has to dominate the neighborhood around its orbit To dominate a neighborhood a plant needs to sweep up asteroids, comets, and other debris in its orbit making a clear path
Pluto Demoted Pluto is no longer a planet. Pluto does orbit the sun in an unusually elongated and tilted ellipse. Not the same plane as the other planets It is round in shape It HAS NOT cleared its neighborhood of debris
Not a Planet Pluto Characteristics Odd Planet farthest from the sun It was the smallest known planet (smaller than Earth s moon) Scientists think Pluto is made up of frozen methane, rock, and ice. The average temperature on Pluto is 235 C. Recently, astronomers have discovered hundreds of objects similar to Pluto that exist beyond Neptune s orbit. None of these objects are larger than Pluto, but Pluto is probably one of these objects.
What is Pluto? Pluto is a Dwarf Planet According to the International Astronomical Union, which sets definitions for planetary science, a dwarf planet is a celestial body that: Orbits the sun. Has enough mass to assume a nearly round shape. Has not cleared the neighborhood around its orbit. Is not a moon.
Objects Beyond Pluto Kuiper belt a region of the solar system that is just beyond the orbit of Neptune and that contains small bodies made mostly of ice This is where many comets come from In recent years, scientists have discovered hundreds of objects in our solar system beyond Neptune s orbit. Some objects are more than half of Pluto s size. Scientists think that if other objects larger than Pluto are found on the Kuiper belt, then Pluto should no longer be classified as a planet. Sedna, one of the most distant objects in the solar system, was found beyond the Kuiper belt, is threefourths the size of Pluto.
Exoplanets Exoplanets- are planets that circle stars other than Earth s sun. Exoplanets cannot be directly observed with telescopes. Most exoplanets can be detected only because their gravity tugs on stars that they orbit. All of the exoplanets that have been identified are larger than Saturn because current technology can only detect large planets.