Ast111

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1. What impact did the telescope have on our knowledge of the Solar System? Approximately when were the outer planets discovered? The first asteroid?

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The telescope helped us discover the moons of Jupiter, Saturn’s moon Titan, the moons of Mars, the planet Uranus (1758), the planet Neptune (1846), Pluto (1930), and the first asteroid (Ceres, 1801).

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2. What is the currently accepted definition of "planet"? How does Pluto fail to be a planet? What is Eris?

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A planet is a celestial body that:
• Is in orbit around the Sun
• Has sufficient mass for its self gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape
• Has cleared the neighborhood around its orbit (Pluto failed this one so its now a “dwarf planet”)
Eris is an object bigger than Pluto that helped decide that Pluto was also a “dwarf planet”. Pluto’s and Eris’ orbits are much more tilted then the other planet’s orbits.

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How are the various properties (masses, distances, radii, densities, temperature, etc.) of the planets determined?

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Various planet properties:
• Masses determined from Kepler’s 3rd Law and Newton’s Law of Gravitation
• Density can be calculated knowing the radius and mass (D=M/V)
• Distance from the Earth can be detected using radars or light travel times
• Radius is found from angular size and distance
• Temperature…

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3. What are the two types of planets in our Solar System? What properties distinguish these types from each other? How many planets fall into each catagory? Which ones?

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Jovian Planets: gas giants, or “Jupiters”. These are large, massive, spread widely far from the Sun, gassy, low density and they have lots of moons, ring systems, strong magnetic fields, and fast rotations. The four J/P include: Jupiter, Saturn, Uranus, and Neptune.
Terrestrial Planets: rocky, or “Earths”. These are smaller, less mass, grouped tightly close to the Sun, rocky, high density and have few or no moons, no rings, weak magnetic fields, and slow rotation. The four T/P include: Mercury, Venus, Earth, and Mars.

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4. Stars form from giant clouds of gas. What are the conditions inside such a cloud? What is the cloud made of? What forces shape the cloud as it forms a star and planets?

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The gas in the cloud is initially very cold and very low density. A star forms from the process of gravitational collapse. As it collapses it becomes hotter and denser and begins to spin faster. Then nuclear fusion begins and the object turns into a star.

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5. The star forms a disk. What happens in the disk to lead to planets? How does this process lead to the types of planets we see today?

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As the gas and dust cools, the gases condense into solid particles. The first particles to form are small, as more form they stick together and larger objects grow by accretion. The planetesimals collide frequently at low velocities and some bind together from gravity. Gravity pulls in more particles and planet grows.

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6. What is the primary chemical that causes gas giants to form differently than rocky worlds? Why do gas giants have so many moons?

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Water. Atmospheres of gas planets are mostly hydrogen and helium. The gas giants form disks around themselves and the process repeats itself on a smaller scale and forms moons. Gas planets have more moons b/c they have stronger gravity.

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7. What happens to the interiors of the young rocky worlds after they form? What happened to their surfaces? What evidence do we see today that these two events occurred?

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The planet completely melts and the heavier elements sink and the lighter elements float. This process, differentiation, produces metal rich cores and silicate rock outer layers. The melting releases volatile elements that form an atmosphere. Some surfaces are heavily cratered from the heavy bombardment period during the first billion years of the Solar System.

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8. How do we know the ages of rocks? What is a "half-life"?

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Daughter/Parent= (2^N)-1 gives “N” or the rocks half life. The half life is the time it takes for half of the sample to decay.

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9. Approximately how many planets are known to orbit other stars? Do all stars have planets? What methods are used to detect these planets? How do these methods work?

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• 200 planets
• 5% of stars have planets
• Transit Method- measure the brightness of a crowded patch of starry sky regularly. Any stars that periodically dim by 1-2% probably harbor a planet.
• Doppler Wobble Method- requires large telescopes. It detects the Doppler shift of the dark lines in the absorption spectrum of the star. Measure the wobble of the star to find the effect of a planet.

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10. What type of planets have been found so far? What was shocking about the discovery of the "hot Jupiters"? How are "brown dwarfs" different from planets?

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Terrestrial worlds and Jovian worlds. Terrestrial worlds are small and close to the Sun and are made of metal and silicate rock. Jovian worlds are large orbit widely from the Sun and are made of abundant ices, hydrogen, and helium.
A hot Jupiter is a Jovian planet that is unusually close to a star because of planet migration.
The difference between a brown dwarf and a planet is based on how the object was formed. Brown dwarfs form from gravitation collapse of a cloud (like a star). Planets form in a disk around a star. Their size is b/t a large planet and a small star.

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11. How is most of the exploration of the Solar System achieved? Human missions or robotic missions? Where have humans left footprints?

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Robotic missions explore the Solar System for us. Only 12 people have left footprints on the Moon.

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12. What can you tell about Earth just by visiting? What processes shape Earth's surface? Why doesn't Earth exhibit a heavily cratered surface like the Moon?

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• Lots of liquid water
• Frozen water at North and South poles
• Water vapor in the atmosphere
• Liquid water precipitation out of the atmosphere, running across continents
• Wide range of land forms: mountains, deserts, plains, canyons
• Lots of lights at night in interesting patterns
Tectonics and volcanism causes the land to rise. Erosion by wind, water, and life causes lowering and rearranging of the land.
Earth isn’t heavily cratered because during Earth’s formation it completely melted (process called differentiation).

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13. What are the distinct parts of Earth's interior? Which contains the most mass? Which part are we standing on directly? How do we know the properties of Earth's mantle? It's core?

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• Crust (we stand on)
• Mantle (most mass, made of silicate rock, we know this from chemical analysis of lava from volcanoes)
• Inner and Outer Core (90% iron, we know this from laboratory experiments of rock and metal under extreme pressure and temp combined with detailed calculations).

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14. What is Earth's core made of? What are conditions like in the core? What information do we have that the outer core is liquid? That the inner core is solid?

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The Earth’s core is 90% iron with some oxygen, sulfur, and nickel. At lower pressures of the outer core, high pressures lead to low viscosity so metal flows like water. The inner core is at such high pressure that the metal is frozen solid.