AST101H Chapter 7 Our Planetary System Notes

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Astronomy & Astrophysics
Michael Reid

October 15, 2011 Chapter 7: Our Planetary System 7.1 Studying the Solar System - Comparative planetology = compare the worlds (planet) to one another, seeking to understand their similarities and differences - Our solar system exhibits many clear patterns Sun - Composition: 98% hydrogen and helium, 2% other elements - The brightest and largest object in our solar system - Contains more than 99.8% of the solar system’s total mass - The surface is speckled with sunspots that appear dark in photographs only because they are slightly cooler than their surroundings - The source of the sun’s energy lies deep in its core, where the temperatures and pressures are so high that the sun is a nuclear fusion power plant - Sun’s gravity governs the orbits of the planets - It is the source of virtually all the visible light in our solar system - Charged particles flowing outward from the sun (the solar wind) help shape planetary magnetic fields and can influence planetary atmospheres Mercury The innermost planet of our solar system, and the smallest of the eight official planets - A desolate, cratered world with no active volcanoes, no wind, no rain, and no life - It is a world of both hot and cold extremes: daytime temperatures reach 425 degree celsius, night time temperatures fall below -150 degree celsius - 58.6-day rotation period; rotates exactly three times for every two of its 87.9-day orbits of the sun - Very large iron core Venus - Nearly identical in size to Earth - Rotates on its axis very slowly and in the opposite direction of Earth, so days and nights are very long and the Sun rises in the west and sets in the east - Surface = 470 degree Celsius - Day and night, Venus is hotter than a pizza oven, and the thick atmosphere bears down on the surface with a pressure equivalent to that nearly a kilometer (0.6 mile) beneath the ocean’s surface on Earth - Venus has mountains, valleys, and craters, and shows many signs of past or present volcanic activity Mars - 2 small moons: Phobos and Deimos - The last of the four inner planets of our solar system - Mass is about 10% that of Earth October 15, 2011 - Ancient volcanoes that dwarf the largest mountains on Earth, a great canyon that runs nearly one-fifth of the way around the planet, and polar caps made of frozen carbon dioxide and water - Mars is frozen today, but the presence of dried-up riverbeds, rock-strewn floodplains, and minerals that form in water offers clear evidence that Mars had at least some warm and wet periods in the past - The air pressure in Mars is far less than that on top of Mount Everest, the temperature is usually well below freezing, the trace amounts of oxygen would not be nearly enough to breathe, and a lack of atmospheric ozone Jupiter - At least 63 moons - Its mass is more than 300 times that of Earth, and its volume is more than 1000 times that of Earth - Its long-lived storm called the Great Red Spot is itself large enough to swallow two or three Earths - Jupiter is made primarily of hydrogen and helium and has no solid surface - Four large moons: Io, Europa, Ganymede, and Callisto - Io is the most volcanically active world in the solar system - Europa has an icy crust that may hide a subsurface ocean of liquid water Saturn - At least 60 moons - Saturn orbits nearly twice as far from the Sun as Jupiter - The second-largest planet in our solar system, only slightly smaller than Jupiter in diameter - Made mostly of hydrogen and helium and has no slid surface - Saturn’s rings are made of countless small particles, each of which orbits Saturn like a tiny moon - At least two of Saturn’s moons are geologically active today: Enceladus, which has ice fountains spraying out from its southern hemisphere, and Titan, the only moon in the solar system with a thick atmosphere - Saturn has an erosion-carved landscape that looked Earth-like, except that it has been shaped by extremely cold liquid methane or ethane rather than liquid water - Vast lakes of liquid methane or ethane on Titan’s surface Uranus - At least 27 moons - Uranus lies twice as far from the sun as Saturn - Much smaller than either Jupiter or Saturn but much larger than Earth - Made largely of hydrogen, helium, and hydrogen compounds such as water, ammonia, methane - Methane gas gives Uranus its pale blue-green color - Lacks a solid surface - The entire Uranus system – planet, rings, and moon orbits – is tipped on its side compared to the rest of the planets. This extreme axis tilt may be the result of a October 15, 2011 cataclysmic collision that Uranus suffered as it was forming, and it gives Uranus the most extreme seasonal variations of any planet in our solar system Neptune - At least 13 moons - Looks nearly like a twin of Uranus, although it is more strikingly blue - Slightly smaller than Uranus in size, but a higher density - Largest moon, Triton, is larger than Pluto and is one of the most fascinating moons - Triton’s icy surface has features that appear to be somewhat like geysers - Triton is the only large moon in the solar system that orbits its planet “backward”, in a direction opposite to the direction in which Neptune rotates (which makes it certain that Triton once orbited the Sun independently before being captured into Neptune’s orbit) Pluto (and other Dwarf planets) - At least 3 moons - Cold and dark - Pluto’s largest moon, Charon, is locked together with it in synchronous rotation, so Charon would dominate the sky on one side of Pluto but never be seen from the other side - Pluto is much smaller and less massive than any of the other planets, and its orbit is much more eccentric and inclined to the ecliptic plane - Dwarf planets located in the Kuiper belt are of great distances and have small sizes; Pluto, Eris, Ceres are examples - Comparative study has revealed similarities and differences among the planets that have helped guide the development of ou
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