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2232 EARTH, SUN, PLANETS Midterm Notes

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Western University
Astronomy 2022A/B
Livio Tornabene

CHAPTER 1 A TOUR OF THE SOLAR SYSTEM PlutNeptune Uranus Saturn Jupiter Mars Earth Venus Mercury Giant planets Terrestrial planets Characteristics of a planet: In orbit around the Sun Large enough for its own gravity to make it round Has cleared its neighborhood of smaller objects Moons = satellites Planetary bodies: Planets, their satellites, and other small bodies such as asteroids. The planets orbit counterclockwise in ~same plane. Sun and most planets rotate counterclockwise on their own orbits. Length of a day ranges from 244 Earth days (Venus) to ~10 hours for Jupiter and Saturn. Terrestrial Planets THE SUN The sun is a star composed mostly of hydrogen and helium 5770K at surface, 15,000,000K at center 11 Mean distance from centers of Sun to Earth is 1.5x10 meters (150 million kilometers) MERCURY Smallest terrestrial planet, no atmosphere (very tenuous) Temperature range 80K 740K Many impact craters left from asteroids and comets Volcanism is the most prevalent method for resurfacing 10 times less dense than Earth (creates an extreme vacuum) Mean density = almost as high as Earth, each day lasts 1.5 years Missions: Mariner 10 (1974-75), Messenger (2011) VENUS You have likely seen it before, looks like an extremely bright star Earths twin in size & density, and has a significant atmosphere o BUT, very different atmospheres and surfaces Complicated surface, fewer impact craters but many volcanoes and lava plains Like a high-pressure oven, 670K 97% CO , 2ntensegreenhouse gas effect Retrograde rotation (each day lasts longer than one year) 1 Missions: Venus Express (2010) EARTH Mean surface temperature is 288K (15 degrees Celcius) 78% nitrogen, 21% oxygen Diameter = 12,756 km Moon rotates the Earth 13 times/year o Rotation period and orbit period match (~27 days) o Always presents the same face, meaning its rotation period matches its orbital period o Called synchronous rotation o Craters and smooth less-cratered dark areas called maria o Diameter = 3,476 km, distance fro Earth = 384,300 km Basaltic lavas cover 70% of the Earths surface MARS The red planet, most Earth-like (even has seasons!) Huge canyon system called Valles Marineris o Represents a fracture in the planets surface, extends 4000km Largest volcano in the solar system is called Olympus Mons 95% CO o2,y 0.006 atmospheric pressure of Earth, 223K surface temperature Desert-like and dry, can go from reasonably warm to very cold Formidable winds, large dust storms Two very small satellites, Phobos and Deimos, thought to be captured asteroids Missions: 3 orbiters and 2 active rovers (Curiosity and Opportunity) Evidence of ancient running water o Small valley networks (dendritic channels), sinuous valleys, gullies, pitted materials in martian craters, etc. ASTEROIDS Leftover from the formation of the solar system, they didnt get the chance to form planets but were too large to get blown away by the Suns radiation Between Mars and Jupiter is asteroid belt Extends all the way around the sun and each asteroid orbits the sun Vesta and Ceres are two largest asteroids Missions: Dawn (2011) Jovian Planets The outer planets are gas giants and contain mostly hydrogen and helium, but have solid cores. Jovian means like Jupiter. Although their density is lower than the terrestrial planets, they are much more massive. Saturn has very obvious rings, but all of the Jovian planets have rings. None of the terrestrial planets have rings. JUPITER The largest planet, radius is over 10 times that of Earth 2 Density is only a quarter of Earths, made up mostly of gas o Other giant planets share this feature, sometimes known as gas giants Rotates in 9.9 hours, winds Great Red Spot is a huge storm that has been observed for the last few hundred years 90% hydrogen, 10% helium, temperature from 120K 6000K 66 satellites o Io: pizza-like surface from volcanic activity, input of energy comes from tidal heating o Europa: has an icy cracked surface with few impact craters, indicating its youth Possible global ocean of melted ice beneath icy surface! Cryovolcanism: When cold slurries of ice and liquid erupt and flow across the surface like cool volcanoes. o Ganymede: largest satellite in solar system, bigger than Mercury but mostly icy o Callisto: another very large satellite of Jupiter Missions: Pioneer 10 (1973), 5 since then including Galileo probe SATURN Slightly smaller than Jupiter, rotates in 10.7 hours giving rise to an atmosphere that bulges at the equator Rings are made of small icy particles and boulders o Probably come from a break-up of moon 62 satellites: o Mimas: cratered with one massive crater o Titan: half Earths size, similar in atmosp
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