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Astronomy Study GuideChapter 6. Jovian Planets. Rings, and Moons- Jupiter and Saturn similar to each other, different from Uranus and Neptune- J and S made almost entirely of hydrogen and helium- Overall composition much more similar to sun than terrestrial planets- Uranus and Neptune are made primary of hydrogen compounds such as water methane and ammonia- Formed where it was cold enough for hydrogen compounds to condense into ices- Grown from ice rich planetesimals of about the same mass- Uranus and Neptune did not pull in as much gas because of distance from sun- On Jupiter: you would never encounter a solid surface but find higher temperature and pressures as you descend- Jupiter changes from gaseous to liquid to metallic hydrogen as you descend- Strong magnetic field is in the metallic hydrogen layer- Core contains a mix of hydrogen compounds, rock, and metal compressed to a very high density- Pressures within Uranus and Neptune are not high enough to form liquid or metallic hydrogen, and only have a thick layer of gaseous hydrogen surrounding the core- Core may be liquid so life may even exist- Weather: dynamic winds and weather with colorful clouds and enormous storms- Driven by energy from sun and heat generated by planets themselves- All but Uranus generate a great amount of internal heat- Probably comes from conversion of gravitational potential energy into thermal energy- Several gases that can condense to form clouds, distinct cloud layers at different atmospheres- Jupiter’s striped appearance occurs because atmospheric flow patterns create cloudy and clear zones at different latitudes- Saturn has same clouds but occur deeper in its cooler atmosphere, making colors more subdued- Uranus and Neptune contain more methane gas and are so cold that it condenses into methane clouds. Methane gas absorbs red light from thee sunand gives them their distinct blue colors. - Jupiter’s Red Spot: more than twice as wide as Earth. Winds circulate around a high-pressure region and is extremely long lived. - Rings: only Saturn’s rings are easily visible. Rings are made of countless icy particles. Photographs show a huge number of rings, gaps, and ripples.- Rings and gaps are formed by particles bunching up at some orbital distancesand being forced out of others when gravity nudges the orbits of ring particles in some ways.- Another source of nudging comes from small moons located within the gaps in the rings themselves called gap moons.- Orbital resonance: reinforcement due to repeated gravity, when they resonate with one another and amplify their effects. - New ring particles must be continually replacing those that are destroyed from moonlets that formed in the disks of material orbiting the young Jovian planets which are constantly grinded away by tiny impacts.- Planets are orbited by more than 150 known moons, Jupiter has more than 60.- Vast majority of the moons are small and no more than a few kilometers in diameter. - Have solid surfaces and are shaped by the same geological processes as the terrestrial planets- Formed in the cold outer solar system and have substantial amounts of ice with also metal and rock so much less heated is necessary - Interactions between orbiting moons create tidal heating that is not present in the inner planets- Galilean moons of Jupiter are the four discovered by Galileo: 1. Io- by far the most volcanically active world in the solar system. May be quite hot inside. Must have other source of heating because of its small size and source is tidal heating which comes from tidal forces exerted by Jupiter. Tidal heating strongest because its closest to Jupiter. 2. Europa- probably has a deep ocean of liquid water beneath icy crust. Tidal heating makes it one of most interesting places in solar system. Europa has a metallic core and rocky mantle, surrounded by a layer of water that is frozen near the surface but tidal heating keeps water liquid a few kilometers below surface. Contains more than twice as much liquid water as found on Earth. 3. Ganymede and 4. Callisto have more impact craters but may also contain subsurface oceans. Ganymede has some dark and densely cratered regions suggesting it looks much the same today and Callisto looks like a heavily cratered ice ball due to lack of tidal heating. - Jupiter’s tidal force on the moons is so strong that it has caused all four moons to keep the same face towards Jupiter all teams. - Varying tidal force due to elliptical orbits flexes interior and is generating friction and heat. - Ganymede, Europa, and Io are exactly lined up periodically and over time these alignments have stretched the orbits from circles into ellipses- Saturn’s active moons: Titan and Enceladus1. Titan: Second largest moon in the solar system and has a thick atmosphere that hides its surface from view except at a few specific wavelengths of light. Methane and ethane in atmosphere are greenhouse gases that make it warmer than it otherwise would be. Its complex atmosphere probably produces numerous organic chemicals, which are the basis of life. Cassini spacecraft that orbits Saturn to parachute a soft landing on Titan. There is a presence of liquid methane or ethane lakes onTitan. We can attribute its geological activity to the combination of large size and icy composition. 2. Enceladus shows evidence of ongoing geo activity even thou its only 500 kilometers across. Grooves near its south pole vent huge clouds of water vapor and ice crystals, driven by internal heat. May have an underground reservoir of liquid water. - Uranus and Neptune’s moons have surprising geological activity. - Of Uranus’s five medium size moons, at least three have past volcanism or tectonics. - Neptune’s moon Triton is large but does not follow orbital patterns of all other large moons and orbits Neptune backwards at a high inclination to Neptune’s equator- This shows that it was captured rather than formed. Regions show evidence of past volcanism and regions that appear tectonic in nature. Likely source is heating. - Most of these moons contain ices that can melt or deform at lower temperatures than rock, and can experience geological activity even when interior temperatures have cooled. - Ice geology is possible at far lower temperature than rock geology. This and extra heating by tidal heating explain how they have geological activity despite small sizes.Asteroids, Comets, and the Impact threat- Asteroids come in a wide range of sizes-

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UMD ASTR 101 - Astronomy Study Guide

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