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Module 4 Notes.docx

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Wilfrid Laurier University
Shohini Ghose

Module 4 Notes a) Mercury - moderately high orbital eccentricity (0.206) meaning its orbit is observably elliptic - orbital inclination is also high (7 degrees), greater than all others except Pluto - rotational axis tilt is 0 degrees; no seasons on Mercury - orbital period: 88 days, synodic period of 116 days (time between successive conjunctions with Earth) - solar day of 176 Earth days The two elongations, eastern and western, are the greatest angular positions the inner planet ever has with respect to Earth. The two conjunctions, superior and inferior, refer to when Mercury is lined up with the Earth and the Sun. When the order is Earth-Sun-Mercury, we have a superior conjunction and when Mercury is between the Sun and Earth, we have an inferior conjunction. We might see a solar transit during an inferior conjunction. - not tidally locked to the Sun; rotates one and a half times during each orbit - a solar day on Mercury (sun rise to sun rise) is 176 Earth days long (rotates very slowly) - about 61% iron and has an iron core about 75% of the radius of the planet - surface has craters everywhere - very thin atmosphere, too small to retain any gas - the iron core makes up about 42% of its volume, magnetic field is similar to Earth’s in shape but only about 1% as strong - Mariner 10 visited Mercury in the 70s, but it is very difficult to explore due to high temperatures b) Venus - orbital eccentricity of 0.0068, almost a perfect circle; greatest elongation is 47 degrees away from Sun - brightest object in sky other than Sun and Moon; 16x brighter than any star because it is close to the Sun, close to Earth, relatively large (about same as Earth), and its albedo is 0.59 - during an inferior conjunction, it is possible to have a solar transit of Venus - Venus’ rotation is retrograde; it rotates backwards very slowly - sidereal day that is 243 Earth days, orbital period 224.7 days, and solar day of 117 Earth days - axial tilt is 177.4 degrees; north pole points downward; rotational axis of 2.6 degrees (no seasons) - 740 K - dry, hot, uninhabitable desert, two large highland features: Ishtar Terra and Aphrodite Terra - no tectonic activity, evidence of volcanic activity, erosion, no current bombardment - atmosphere is 90 times as dense as Earths, lots of CO a2d water vapour in atmosphere - greenhouse effect causes there to be no water - no magnetic field due to slow rotation; no protection from solar wind generates thick atmosphere c) Earth - orbit is almost circular (e = 0.017) - average distance from Sun is 1 AU, takes 365.25 days to orbit the Sun - rotational axis inclined at 23.5 degrees causing seasons - slightly bigger than Venus, radius of almost 6400km - average surface temperature is 9 degrees Celsius; range is 60 to -90 degrees Celsius - one natural satellite, the Moon, which orbits Earth in 29.5 days (solar period) - atmosphere of nitrogen and has a magnetic field - core is surrounded by a molten shell, thick mantle, and a thin crust - lithosphere is about 100km thick, covered with liquid water (75%) and solid land mass (25%) - two main seismic waves are p-waves (primary) which are pressure waves and s-waves (secondary) which are shear waves; solid inner core of radius 1300km surrounded by 3500km molten outer core - centre is around 6,000K, rich in nickel and iron - crust consists of granite and rocks, upper mantle largely iron-magnesium-silicate mixture - changing surface due to volcanic activity, plate tectonics and erosion - melting point within the mantle is well above the actual temperature, so mantle is solid - continental drifts causes plates to move slowly forming mountains, ocean ridges, new land - atmosphere is unique, 77% nitrogen, 21% oxygen, 1% argon, some water and carbon dioxide - temperature is cool enough to allow water vapour to condense as rain - CO 2issolves in water so oceans hold some of it and rainfall carries minerals from rocks/land into the ocean which react with dissolved CO to 2orm carbonate minerals which fall to ocean floor - oxygen originally built up in atmosphere when only planets existed and few animals used it up - very strong magnetic field resulting “magnetosphere” extending beyond the atmosphere - at 3000 and 20,000km above Earth’s surface are two zones of trapped, charged, high-energy particles called the Van Allen belts surrounding the Earth centred on the magnetic equator; particles are from solar wind and these belts protect life on Earth from the harmful effects of the solar wind particles - aurora borealis in the North and aurora australis in the South are caused by these particles d) The Moon - average distance from Earth to Moon is 384,400 km - sidereal period is 27.3 days, but takes 29.53 days to move through phases due to Earth’s orbit - tipped at 6.7 degrees, size is 0.27 of Earth - large dark areas on the surface are called maria, and lighter-coloured regions are called highlands - the lunar highlands are covered with hundreds of craters - large water ice deposits near both poles have been detected, which likely came from meteoroids - largest crater in Solar System discovered on far side of the moon, 2500km wide, Aitken Basin - Neil Armstrong set foot on the Moon on July 20, 1969 - virtually no atmosphere, low escape speed so any gas molecules eventually leave - no erosion and no tectonic action so surface changes very, very slowly - no global magnetic field - large impact hypothesis theory imagines a collision between a very young, molten Earth and a large, Mars-like object where debris particles in a ring began to accelerate into larger bodies - plans exist to establish human colonies on the Moon for further exploration, mining, and scientific research e) Mars - average orbital radius of about 1.5 AU with a relatively large eccentricity - fairly bright but less than Venus due to smaller size, distance from Sun and lower albedo of 0.15 - rotation is similar to Earth’s, around 24.6 hours, and tipped at about 24 degrees resulting in seasons - radius about 50% of Earth and mass about 10% but with a density 70% of Earth - polar ice caps made of CO 2r dry ice, NOT water, although water ice below surface of poles - huge volcanoes (largest in solar system), deep canyons, huge dune fields - lava flows in the north, Tharsis bulge contains volcanoes, Valles Marinis canyon rises 10km high than any other part of planet, Olympus Mons (largest volcanoe) is 600km in diameter and rises 21km - no tectonic activity, volcanoes are inactive - the Vallex Marineris canyon was formed when the planet’s surface bulged out under the forces of crustal formation, is about 4000 km long, 120km across at widest point, 7km deep in some areas - the canyon was NOT created by water flow or tectonics but rather by heat conduction forces - two Mars rovers called Spirit and Opportunity (which is still functioning) - significant evidence of previous presence of water on Mars - very thin atmosphere with a pressure of about 1/150 that of Earth consisting of mostly carbon dioxide (95.3%) and other gases - "Mars apparently was once a world with pleasant temperatures and streams, rain, glaciers, lakes and possibly oceans. It had all the necessities for life as we know it. But the once hospitable planet turned into a frozen and barren desert at least 3 billion years ago, and it is unlikely that Mars will ever be warm enough for its frozen water to flow again. If life once existed on Mars, it is either extinct or hidden away in a few choice locations, such as hot springs around not-quite-dormant volcanoes. As we think about the possibility of future climate change on Earth, Mars presents us
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