Astronomy Chapter 6: Formation of the Solar System – Flashcards
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What does the solar system look like?
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Planets are very tiny compared to distances between them
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Sun
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-Over 99.8% of solar system's mass -Made mostly of H/He gas (plasma) -Converts 4 million tons of mass into energy each second
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Mercury
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-Made of metal and rock; large iron core -Desolate, cratered; long, tall, steep cliffs -Very hot and very cold: 425°C (day), -170°C (night)
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Venus
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-Nearly identical in size to Earth; surface hidden by clouds -Hellish conditions due to an extreme greenhouse effect -Even hotter than Mercury: 470°C, day and night
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Earth
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-An oasis of life -The only surface liquid water in the solar system -A surprisingly large moon
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Mars
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-Looks almost Earth-like, but don't go without a spacesuit! -Giant volcanoes, a huge canyon, polar caps, and more -Water flowed in the distant past; could there have been life?
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Jupiter
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-Much farther from Sun than inner planets -Mostly H/He; no solid surface • -300 times more massive than Earth -Many moons, rings -Jupiter's moons can be as interesting as planets themselves, especially Jupiter's four Galilean moons -Io: Active volcanoes all over -Europa: Possible subsurface ocean -Ganymede: Largest moon in solar system -Callisto: A large, cratered "ice ball"
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Saturn
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-Giant and gaseous like Jupiter -Spectacular rings -Many moons, including cloudy Titan -Cassini spacecraft currently studying it -Rings are NOT solid; they are made of countless small chunks of ice and rock, each orbiting like a tiny moon.
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Uranus
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-Smaller than Jupiter/Saturn; much larger than Earth -Made of H/He gas and hydrogen compounds (H2O, NH3, CH4) -Extreme axis tilt -Moons and rings
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Neptune
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-Similar to Uranus (except for axis tilt) -Many moons (including Triton)
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Pluto and Other Dwarf Planets
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-Much smaller than other planets -Icy, comet-like composition -Pluto's moon Charon is similar in size to Pluto
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QUESTION: Which planet has the largest tilt to its rotation axis?
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Uranus
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QUESTION: Most of the solar system's planets: A - Are made of rocks and minerals B - Are made of gas C - Revolve (orbit) around the Sun in the same direction D - Rotate in the same direction as they orbit the Sun
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C - Revolve (orbit) around the Sun in the same direction D - Rotate in the same direction as they orbit the Sun
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Motion of Large Bodies
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-All large bodies in the solar system orbit in the same direction and in nearly the same planet -Most also rotate in that direction
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Two Major Planet Types
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-Terrestrial planets are rocky, relatively small, and close to the Sun. -Jovian planets are gaseous, larger, and farther from the Sun
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Swarms of Smaller Bodies
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-Many rocky asteroids and icy comets populate the solar system
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Notable Exceptions
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-Several exceptions to normal patterns need to be explained
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What is the nebular theory?
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-According to the nebular theory, our solar system formed from a giant cloud of interstellar gas
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Origin of the Nebula
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-Elements that formed planets were made in stars and then recycled through interstellar space
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Evidence from Other Gas Clouds
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-We can see stars forming in other interstellar gas clouds, lending support to the nebular theory
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QUESTION: Which planets have a rocky, relatively dense composition?
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-Mercury, Venus, Earth, and Mars
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Conservation of Angular Momentum
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-The rotation speed of the cloud from which our solar system formed must have increased as the cloud contracted -Rotation of a contracting cloud speeds up for the same reason a skater speeds up as she pulls in her arms
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Flattening
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-Collisions between particles in the cloud caused it to flatten into a disk -Collisions between gas particles in a cloud gradually reduce random motions -Collisions between gas particles also reduce up and down motions -The spinning cloud flattens as it shrinks
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QUESTION: Why did the solar nebula flatten into a disk?
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-It flattened as a natural consequence of collisions between particles in the nebula, changing random motions into more orderly ones
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Disks Around Other Stars
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-Observations of disks around other stars support the nebular hypothesis
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QUESTION: Why did the nebula making the solar system heat up as it collapsed during its formation?
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-As the cloud shrank, its gravitational potential energy was converted to thermal energy
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Conservation of Energy
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-As gravity causes the cloud to contract, it heats up -Inner parts of the disk are hotter than outer parts. -Rock can be solid at much higher temperatures than ice. -Inside the frost line: Too hot for hydrogen compounds to form ices -Outside the frost line: Cold enough for ices to form
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Formation of Terrestrial Planets
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-Small particles of rock and metal were present inside the frost line. -Planetesimals of rock and metal built up as these particles collided. -Gravity eventually assembled these planetesimals into terrestrial planets -Tiny solid particles stick to form planetesimals -Gravity draws planetesimals together to form planets. -This process of assembly is called accretion
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Accretion of Planetesimals
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-Many smaller objects collected into just a few large ones
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Formation of Jovian Planets
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-Ice could also form small particles outside the frost line. -Larger planetesimals and planets were able to form. -The gravity of these larger planets was able to draw in surrounding H and He gases -The gravity of rock and ice in jovian planets draws in H and He gases - Moons of jovian planets form in miniature disks -Radiation and outflowing matter from the Sun—the solar wind— blew away the leftover gases
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QUESTION: How would the solar system be different if the solar nebula had cooled with a temperature half its current value?
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-Jovian planets would have formed closer to the Sun
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Asteroids and Comets
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-Leftovers from the accretion process -Rocky asteroids inside frost line -Icy comets outside frost line
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Heavy Bombardment
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-Leftover planetesimals bombarded other objects in the late stages of solar system formation
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Origin of Earth's Water
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-Water may have come to Earth by way of icy planetesimals from the outer solar system
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Captured Moons
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-The unusual moons of some planets may be captured planetesimals
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Odd Rotation
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-Giant impacts might also explain the different rotation axes of some planets
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QUESTION: Which of these facts is NOT explained by the nebular theory? A. There are two main types of planets: terrestrial and jovian. B. Planets orbit in the same direction and plane. C. Asteroids and comets exist. D. There are four terrestrial and four jovian planets.
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-There are four terrestrial and four jovian planets
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How do we know the age of the solar system?
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-We cannot find the age of a planet, but we can find the ages of the rocks that make it up. -We can determine the age of a rock through careful analysis of the proportions of various atoms and isotopes within it
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Radioactive Decay
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-Some isotopes decay into other nuclei. -A half-life is the time for half the nuclei in a substance to decay
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Dating the Solar System
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-Age dating of meteorites that are unchanged since they condensed and accreted tells us that the solar system is about 4.6 billion years old
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QUESTION: Suppose you find a rock originally made of potassium-40, half of which decays into argon-40 every 1.25 billion years. You open the rock and find 15 atoms of argon-40 for every atom of potassium-40. How long ago did the rock form?
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-5 billion years ago
