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Unformatted text preview: Chloe List ASTR 100 Final Review Lecture 29-PLANETS There are 8 planets 4 terrestrial planets Mercury, Venus, Earth, Mars 4 Jovian planets Jupiter, Saturn, Uranus, Neptune 1930-2006 Pluto was listed as a planet planet comes from the Greek word for wanderer in 2006 IAU adopted the first official planet definition o Pluto was demoted to a dwarf planet A planet must be massive enough to have had self-gravity shape into a sphere, and to have cleared out its local neighborhood of smaller debris Pluto (and a few other objects) satisfy the first requirement, but not the second dwarf planets Inner solar system is populated by 4 rocky worlds called terrestrial (Earth-like) planets They are composed of heavy elements, primarily iron and nickel Mercury, the closest planet to the sun, is the smallest of the inner planets o Its small size and proximity to the sun has stripped it of any atmosphere it may have had in the past o Recent observations have shown it was volcanic in the past, but it has cooled to the point that it has a solidified interior Venus is slightly smaller than the Earth and is shrouded by a thick atmosphere of carbon dioxide o Venus is a hellish environment with surface temperature reaching nearly 900 F Earth is the largest of the inner planets o Mostly nitrogen atmosphere o Moderate temperatures and abundant water o Both Venus and Earth have molten iron-nickel cores that drive volcanic activity o This hear is produced by radioactive decay Mars is the most studied planet besides Earth o Surface studied through robotic missions o Evidence for past liquid water and current stores of water ice (small amounts) o Thin carbon dioxide atmosphere o Core once molten like Earth and Venus, has cooled, ended volcanic activity Beyond asteroid belt lies the outer planets, the Jovians (Jupiter-like) planets Jupiter is the largest planet in the solar system Jupiter is a gas giant with a thick atmosphere of H, He, methane, and other substances o After sun, Jupiter has greatest gravitational influence in solar system o Its upper atmosphere has visible bands of clouds that show convection and storms o Average density of Jupiter is same as sun (that of water) Saturn is the jewel of the solar system o Surrounded by ring system o Rings are believed to have formed from failed moons, torn apart by gravity of Saturn o Like Jupiter, Saturn is mostly gas like H and molecules Outside of Saturn lies Uranus o Smallest outer planet o Atmosphere=H and He o Rotations axis lies perpendicular to orbital axis Neptune is the last planet in the solar system o A gas giant with lots of methane in its atmosphere Each of the outer planets were observed by the Voyager Deep space probes launched in the 1970s Lecture 29-HISTORY OF ASTRONOMY Constellations are a special case of Asterisms o Asterisms are any group of stars Thales of Miletus regarded as founder of greek Philosophy...
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- Spring '11