1. The Formation of the Solar System.pdf
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Lesson 1 The Solar System Copyright © 2020 by W. W. Norton & Company, Inc. What Makes Up the Solar System? ▪ Our Solar System is made up of many different types of objects, held together by gravity as they orbit the sun. ▪ Planets ▪ Dwarf planets ▪ Moons ▪ Comets ▪ Asteroids ▪ Kuiper Belt ▪ Oort...
Lesson 1 The Solar System Copyright © 2020 by W. W. Norton & Company, Inc. What Makes Up the Solar System? ▪ Our Solar System is made up of many different types of objects, held together by gravity as they orbit the sun. ▪ Planets ▪ Dwarf planets ▪ Moons ▪ Comets ▪ Asteroids ▪ Kuiper Belt ▪ Oort Cloud ▪ Sun Planets of the Solar System ▪ The Solar System contains eight planets. ▪ An object is defined as a planet if 1. it orbits the Sun; 2. it is spherical; and 3. it has cleared its orbit of other objects either by incorporating them through collisions or absorbing them as moons. ▪ Key here is the IAU definition of 2006 applies ONLY to our own Solar System. Figure 22.1a Objects in the Solar System Table 22.1 The Solar System ▪ Terrestrial planets: Mercury, Venus, Earth, and Mars ▪ Giant planets: Jupiter, Saturn, Uranus, and Neptune Figure 1.4 Pluto: A Dwarf Planet ▪ A dwarf planet meets only the first two conditions; it hasn’t met the third of clearing its orbit. ▪ Other dwarf planets include Ceres, Eris, Haumea, Makemake. Figure 22.2 Arrangement of the Solar System ▪ The planets all orbit on or very near the same flat surface or plane around the Sun’s equator. Oblique view of all eight planetary orbits. NOT to Scale. Figure 22.3a Orientation of the Planetary Orbits ▪ From the Earth we observe the planets as following on or very near the line of the ecliptic . The orientation of the planetary orbits (top) and of the Moon’s orbit (bottom) relative to the ecliptic plane. Figure 22.3b Comparing the Planets ▪ Various characteristics of the planets as compared to Earth ▪ Many display prograde motion, meaning they move counterclockwise around the sun as viewed from the Sun’s North Pole ▪ Nearly all have orbital planes that lie within 3o of the Earth’s orbit (Ecliptic plane) ▪ Mercury’s orbit is 7o even greater than the moon’s which is 5o ▪ Most objects orbit the sun in prograde direction, some comets move in retrograde direction, even satellites orbit planets in prograde motion, except for some small distant satellites and Neptune’s moon Triton which is large. Planets: Axis of Rotation Tilts ▪ The tilt of a planet’s rotation is specified relative to its orbit. ▪ An axis perpendicular to its orbital plane would have a 0° tilt whereas an axis parallel to its orbital plane would have a 90° tilt. ▪ A comparison of the planets displays a range of tilts. ▪ Note Venus is flipped almost 180 degrees. Figure 22.4 Formation of the Earth and Other Solar System Objects ▪ First generation stars were massive and short lived, massive so that they could collapse for fusion to begin ▪ Stars like our sun burn cooler and can burn for billions of years ▪ Sun like stars can only form if nebulae that contain tiny (0.01 mm) dust and ice particles which formed from the condensation of matter into solids which could only occur in nebulae containing large atoms (silicon, oxygen, iron), ones produced by stellar nucleosynthesis and supernova nucleosynthesis ▪ Ice and dust are important because they disperse heat and decrease thermal pressure in protostars and permit smaller protostars to collapse enough to ignite and become true stars ▪ When such stars form, gas, dust and ice remain in the disk surrounding the protostar and this disk provides the material from which planets are formed ▪ Condensation theory is the theory that ice and dust containing nebulae evolves into a star surrounded by planets Figure 1.9a Formation of the Earth and Other Solar System Objects ▪ An accretion disk forms within an nebulae in the arms of the Milky Way ▪ The disk contains hydrogen, helium and larger atoms ▪ The central ball of the disk collapsed to become the sun around 4.57 Ga ▪ The outer part of the accretion disk- the matter that did not drawn into the sun by gravity-remained in orbit around it ▪ This region is known as the protoplanetary disk because it provided the matter that would be incorporated into planets ▪ As soon as the sun become a nuclear furnace the solar wind began to blow carrying volatile material from the inner part of the protoplanetary disk into the outer part where some froze into ice specks, creating a boundary known as the frost line ▪ Inside the frost line, nearer to the sun, the terrestrial planets formed, outside the frost line the volatile materials formed the Jovian planets Figure 1.9a Planetary Growth ▪ Specks of dust acted as “seeds” to which other atoms could attach growing into soot-sized particles and under the influence of gravity grew into grains which drifted together to form boulders which combined into larger building blocks pulling in more materials forming planetesimals, solid bodies with diameters greater than 1 km ▪ Some planetesimals attracted other objects into their orbit becoming protoplanets, bodies approaching the size of the planets today ▪ The Solar System may have had up to 80 protoplanets, as some grew their gravitational pulls caused some to fall into the sun, some to escape the solar system and some to collide eventually leaving only 8 planets including the Earth and moon ▪ The Condensation Theory explains how all planets lie on the same plane as they all formed from the same protoplanetary disk ▪ The terrestrial planets consisted mostly of dust and consist of rock and metal ▪ The Jovian planets formed from volatile materials and consist more of gas and ice surround small cores of rock and metal ▪ Large numbers of planetesimals and their fragments lie in the asteroid belt between Mars and Jupiter and are called asteroids and contain rock and metal and are fragments that never become planets or planetoids that broke apart Figure 1.9a Formation of the Earth and Other Solar System Objects Figure 1.9a Nasa’s Osiris Rex ▪ NASA’s OSIRIS-REx, the first U.S. mission to collect a sample from an asteroid, will return to Earth on Sept. 24, 2023, with material from asteroid Bennu. ▪ When it arrives, the OSIRIS-REx spacecraft will release the sample capsule for a safe landing in the Utah desert. The pristine material from Bennu – rocks and dust collected from the asteroid’s surface in 2020 – will offer generations of scientists a window into the time when the Sun and planets were forming about 4.5 billion years ago. Formation of the Earth and Other Solar System Objects ▪ Condensation theory (summary): • Rotating protoplanetary disk (proplyd) • Dust and ice accumulate into planetesimals. • Due to gravity, accumulate into larger protoplanets The protoplanetary disk consisted of gas, ice, and dust. Figure 1.9a Internal Differentiation of the Earth ▪ Internal temperatures of planetesimals increase as their sizes increase as gravity pulls matter together and compression occurs causing it to warm up. Collision of planetesimals creates heat and radioactive atoms break down and create heat ▪ Melting occurs internally, forming a metallic core and rocky mantle. Early on, the Earth was fairly homogeneous inside. When the temperature got hot enough, iron began to melt. Figure 1.10 The iron accumulated at the center of the planet to form a metallic core. This occurred when the universe was 9 billion years old between 4.56 to 4.54 Ga ago, the age of the Earth Making the Earth Round ▪ Small planetesimals are cool and rigid and stay irregular in shape. ▪ Large planetesimals (~ 400–800 km) become warm internally. ▪ Gravity will eventually pull in matter to a sphere if the mass is sufficient. Figure 1.11 Class Questions Class Question 1 Our Solar System is part of which galaxy? a. Renaissance b. Milky Way c. Ford d. Andromeda e. Neptune Class Question 1 Answer Our Solar System is part of which galaxy? a. Renaissance b. Milky Way (answer) c. Ford d. Andromeda e. Neptune Class Question 2 The four planets closest to the Sun are referred to as the _____ planets. a. inner sanctum b. central orbit c. giant d. terrestrial e. solarian Class Question 2 Answer The four planets closest to the Sun are referred to as the _____ planets. a. inner sanctum b. central orbit c. giant d. terrestrial (answer) e. solarian Class Question 3 Condensation theory addresses a. how the universe formed. b. how early stars formed. c. how the solar system formed. d. how Earth differentiated. Class Question 3 Answer Condensation theory addresses a. how the universe formed. b. how early stars formed. c. how the solar system formed. (answer) d. how Earth differentiated. Class Question 4 What year did the IAU officially define what a planet in our Solar System is? a. 2006 b. 1992 c. 1976 d. 1957 Class Question 4 Answer What year did the IAU officially define what a planet in our Solar System is? a. 2006 (answer) b. 1992 c. 1976 d. 1957 Class Question 5 Most planets in the Solar System have a. orbital planes that lie within 3 degrees of the ecliptic plane. b. orbital planes that lie within 3 degrees of the Earth’s orbital plane. c. prograde motion. d. all of the above e. a and c Class Question 5 Answer Most planets in the Solar System have a. orbital planes that lie within 3 degrees of the ecliptic plane. b. orbital planes that lie within 3 degrees of the Earth’s orbital plane. c. prograde motion. d. all of the above (answer) e. a and c Think-Pair-Share Question 1 Study the diagram and using page 36 explain why the Earth and planets are round Textbook Questions Page 47 #6-9, 20-21
