Astronomy 121 (3) – Flashcards
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In what sense are there only two important objects in our solar system?
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Because Jupiter is so massive our solar system is a two object system in the broadest sense (with the Sun)
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What is differential rotation, and how is it observed on Jupiter?
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Differential rotation: rotation of a planet is not constant from one location to the other. (Equatorial zones rotate faster on Jupiter, the interior rotates at the same rate as the polar regions).
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What does Jupiter's degree of flattening (oblateness) tell us about its interior?
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Jupiter would be more flat if the core was solely hydrogen and helium, it must have a dense compact core, probably rocky in composition.
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What is the Great Red Spot and what is known about its source of energy?
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A storm of circulating winds--an atmospheric storm--powered by zonal motion, north of the storm moves westward, motion southward moves east.
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What is the cause of colors in the atmosphere of Jupiter?
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It depends on the layer of cloud we are viewing, there are three major ones. White regions are the tops (ammonia), yellows reds and browns are the second layer (ammonium hydrosulfide ice), while the lowest levels are blue (water ice)--we don't see this layer from space.
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Why does Jupiter have most of its original atmosphere?
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Massive size=greater surface gravity--which means higher levels of lighter elements (H, He).
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Explain the theory which accounts for Jupiter's internal heat source.
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It emits more heat than it receives from the Sun so it must have an internal source of heat. As the planet took shape, some of the gravitational energy was converted into heat in the interior. The heat is slowly leaking out.
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What is Jupiter thought to be like beneath its clouds, and why do we think this?
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Density and temperature increase with depth, atmosphere gradually liquefies. Towards the center hydrogen behaves like a liquid metal, at the center there is a rocky core. No surface exists, its atmosphere just becomes denser because of increasing pressure.
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In what senses are Jupiter and its moons like a miniature solar system?
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Orbits are in the same direction as Jupiter's orbit, roughly circular, lie close to the equatorial line, densities of the moons decrease with distance from the planet. Formation of the satellites may have mimicked the formation of the Sun and inner planets.
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What is the cause of Io's volcanic activity?
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Gravity--its close orbit with Jupiter tidal forces are present; it is also tugged by Europa. To prevent a synchronous orbit Io "wobbles" which squeeze and flex Io's interior.
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What evidence is there for liquid water below Europa's surface?
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Equivalent of lava flows on Earth--water erupted through the surface and flowed before solidifying. Weak magnetic field that changes strength and direction.
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What is the evidence that Ganymede's interior was heated as recently as one billion years ago?
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Internal differentiation indicates it was largely molten; its magnetic field and possible subsurface water suggest the interior may still be warm.
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How does cratering vary among the Galilean moons? Does it depend on location, and if so, why?
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Less to do with location and more to do with age; outer moons have more cratering because their surfaces are older, the inner moons have undergone volcanic activity which covers their craters.
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Why does Saturn have a less varied appearance than Jupiter?
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Chemical composition is similar, but atmospheric layers on Saturn is thicker because of its weak gravity (less mass). Because the clouds are thicker there are few holes and gaps in the top layer.
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What does Saturn's shape tell us about its deep interior?
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It is the "flattest" planet; but it still must have a rocky core
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Compare and contrast the atmospheres and weather systems of Saturn and Jupiter, and tell how the differences affect each planet's appearance.
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Atmospheres: similar composition (hydrogen and helium) amount of helium on Saturn is higher. Clouds arranged in three layers on both--but layers are thicker on Saturn because of lower gravity (causes the relatively uniform appearance). Weather systems: less distinct on Saturn but still seen. They both have bands, ovals, and flow patterns powered by convection in the middle.
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Compare the thicknesses of Saturn's various layers (clouds, molecular hydrogen, metallic hydrogen, and core) with the equivalent layers in Jupiter. Why do the thicknesses differ?
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Atmospheres are similar (mostly hydrogen and helium), arranged in three layers on both planets, the major difference is that on Saturn the layers are thicker because of its weaker gravity. Like Jupiter, the planet also has bands, ovals, and flow patterns powered by convection.
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What is the mechanism responsible for the relative absence of helium in Saturn's atmosphere, compared with Jupiter's atmosphere?
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The low abundance of helium is the result of it being rained down to lower levels. This happened because helium condensed out of surrounding hydrogen and has been causing a light shower through its interior ever since.
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What would happen to a satellite if it came too close to Saturn?
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Tidal forces would increase as it got closer, it would then reach a point where tidal forces stretch if more than the internal forces can hold the satellite together. It would be torn apart by the gravity and spread around the planet, eventually to form a ring.
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What evidence supports the idea that a relatively recent catastrophic event was responsible for Saturn's rings?
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Rings must be young because there is too much going on within them for it to remain a constant. A small moon may have been hit by a large comet or even another moon.
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What effect does Mimas have on Saturn's rings?
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Ring particles in the Cassini division are locked in a 2:1 resonance with Mimas. Particles in the division receive a gravitational tug from Mimas at exactly the same location in their orbit every other time around. Successive tugs reinforce on another, initially circular orbits become elliptical, and in their new orbits particles collide eventually forcing them into new circular orbits at different radii. The net effect is the number of particles in the Cassini division is reduced.
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What are shepherd satellites?
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Moons that orbit rings; their gravitational influence keeps the ring tightly confined in its orbit. Particles that stray are guided back.
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Compare and contrast Titan with Jupiter's Galilean moons.
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Titan has a dense atmosphere and favorable surface conditions. Jupiter's Galilean satellites are large, like Titan.
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Why does Titan have a dense atmosphere, whereas other large moons in the solar system do not?
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It is a result of being further from the Sun. Water ice was able to absorb methane and ammonia which were abundant in early times. As internal temperatures warmed the moon, ice released the trapped gases, forming a thick atmosphere. Sunlight split the ammonia into hydrogen which escaped, but nitrogen, methane and argon remained behind.
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What is the evidence for geological activity on Enceladus?
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Devoid of impact craters which were erased by lava flows (actually water), and plate tectonics found near the moon's South Pole.
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What mystery is associated with Iapetus?
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It is a two-faced moon--the dark, leading face reflects little sunlight whereas the icy trailing side reflects much more.
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Why does Uranus spin 'on its side'?
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A collision between another planet-sized object.
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What is responsible for the color of Uranus?
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A large amount of methane (outer jovian planets have little ammonia because it freezes at 70 K which is hotter than cloud-top temperatures on Uranus and Neptune).
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How is the interior of Uranus thought to differ from those of Jupiter and Saturn?
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Uranus and Neptune have high-density "slushy" interiors containing thick layers of water clouds because pressure outside the core is too low to force hydrogen into a metallic state.
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How does the magnetic field of Uranus compare with that of Earth?
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The strength are comparable, but on Uranus the field is tilted 60 degrees and the field lines are not centered.
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Why are the rings of Uranus so narrow and sharply defined?
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They require shepherd satellites to keep from diffusing. The inner satellites also shape the rings.
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What causes Triton's geysers?
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They form when liquid nitrogen is heated and vaporizes by internal energy sources. This produces high pressure and forces the gas through fissures in the crust.
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What is the predicted fate of Triton?
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It has a retrograde motion and is sinking towards the planet, it will be destroyed by the gravitational field and turn into a new ring around the planet.
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Will Pluto and Neptune ever collide?
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No, they are locked in a 3:2 resonance, even though their orbits cross they are in no danger of colliding.
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In what respect is Pluto more like a moon than a Jovian or terrestrial planet?
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It is not massive enough to "clear the neighborhood" of objects in the congested Kuiper belt (part 3 of the IAU definition of a planet). It is also resonantly tied to Neptune's orbital motion.
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What are the Trojan, Apollo, and Amor asteroids?
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Trojan: orbit at the distance of Jupiter in a 1:1 resonance with Jupiter. Apollo: Earth-crossing asteroids Amor: Asteroids whose orbits cross only the orbit of Mars.
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How are asteroid masses measured?
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Estimate size by the amount of sunlight they reflect and the heat they radiate.
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What are the Kirkwood gaps? How did they form?
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Resonant gravitational tugs from Jupiter leave "holes" in distribution of asteroid periods (just like the interaction between moons and ring particle resulting in gaps in Saturn's rings.
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How do the C-type and S-type asteroids differ?
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C-type: darker and contain large amounts of carbon, (outer regions of asteroid belt). S-type: contain silicate or rocky materials (more reflective, mostly found in the inner portions of the asteroid belt)
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Are all asteroids found in the asteroid belt? Explain.
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No, Earth-crossing asteroids (influenced by nearby Mars and Jupiter) intersect with Earth's orbit.
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Where in the solar system do most comets reside?
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The Oort cloud, a very small number have highly elliptical orbits that bring them into the inner solar system. Some come from the Kuiper belt beyond the orbit of Neptune.
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Describe the various parts of a comet while it is near the Sun.
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Nucleus of a comet(a few kilometers in diameter) surrounded by a coma of dust and gas, and a hydrogen envelope. Behind the comet is a long tale (the result of cometary material and solar wind.
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What are the typical ingredients of a comet nucleus?
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Cold mixture of gas and dust loosely packed--dust particles within a mixture of methane, ammonia, carbon dioxide, and ordinary ice water.
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Describe two ways in which a comet's orbit may change.
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Close encounters with other comets, or gravitational influence of outer planets may "kick" a Kuiper belt comet bringing into the inner solar system.
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What are some possible fates of comets?
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Mass decreases with time as it passes by the Sun (evaporation), comets that survive encounter with the Sun continue their journey to the edge of the solar system where they spend much of their time.
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In what ways is the Kuiper belt similar to the asteroid belt and in what ways do they differ?
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They both move in roughly circular orbits between about 30 and 50 AU from the Sun, never venturing inside the orbits of the jovian planets.
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What causes a meteor shower?
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Occur when Earth's orbit insect the orbit of a young cluster of meteoroids.
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Explain the difference between a meteor, a meteoroid, and a meteorite.
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Meteors: "shooting stars" are bright streaks of light that flash across the sky as meteoroids. Meteoroids: pieces of interplanetary debris. Meteorite: a meteoroid that reaches the ground.
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Why do meteorites contain information about the early solar system, yet the Earth does not?
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They represent ancient material with very little change, Earth has undergone substantial change since formation.
