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1 Lecture 12 Surface and Atmosphere of the Inner Planets January 7a, 2014 2 Terrestrial Planets We’ll examine each planet starting from the atmospheres and working inward to the surfaces and then the inner geology. 3 Basic Information Distance (AU) Mercury Venus Earth Mars 0.4 0.7 1 1.5 243 days 24 hours 24.6 hours (retrograde) Spin Period 59 days Orbital Period 88 days 225 days 1 year 1.9 years Radius (R) 0.4 0.95 1 0.5 Mass (M) 0.055 0.8 1 0.1 Eccentricity 0.21 0.007 0.017 0.093 no no 1 2 Moons 4 Atmosphere of the Earth • Clouds of water vapor • Seasonal variations (23º tilt) • Protects us from – harmful radiation – meteoroids falling from space • Keeps surface of planet warm – Greenhouse effect Nitrogen(78%) Oxygen (21%) + trace compounds 184 to 330 K (−123°F to 134°F) 1 atm 5 None Atmosphere of Mercury • No true atmosphere – Temperature too high – thermal velocity exceeds escape velocity • Extreme temperature variations – No insulating atmosphere – One solar day on Mercury = 176 Earth days! • No tilt http://www.nasa.gov/mission_pages/messenger /multimedia/messenger_gallery.html 100 K (night) to 700 K (day) (−279°F to 800°F) 0 atm 6 Atmosphere of Venus • Permanent cloud cover keeps surface hidden. • Tilt = 177º (i.e. retrograde spin) • Little daily or seasonal temperature variation. • High temperatures due to Greenhouse effect Mostly CO2; clouds = sulfuric acid 750 K (890°F) 90 atm 7 Greenhouse Effect • Sunlight hits surface of planet warming the ground. • Planet radiates heat in the form of infrared radiation 8 Greenhouse Effect • Greenhouse gases (CO2, H2O) trap infrared radiation, keeping the planet warm. • Planet eventually comes to equilibrium and temperature stops increasing 9 Greenhouse Effect • Greenhouse effect elevates average temperature of Earth by ~23C (~41 F). • Too much CO2 or other greenhouse gas in atmosphere could elevate temperature even more, changing climate on the Earth 10 Moons of Mars Deimos (MRO) Size ~ 15 × 12 × 11 km • • • • Phobos and Deimos Irregular shape Heavily cratered Rotate synchronously (like Earth’s Moon) Phobos (Viking 1) 10/19/1978 Phobos (MRO) Size ~ 27 × 22 × 19 km 11 Atmosphere of Mars CO2 100 to 300 K (−279°F to 80°F) 0.007 atm http://antwrp.gsfc.nasa.gov/apod/ap030602.html • Thin water vapor clouds and fog but no rain. • Strong winds cause dust storms • Tilt = 24º gives seasonal variation similar to Earth. 12 Wind Features on Mars Global Dust-storm Sand dunes in Hellas Region Image area ~ 2.3 x 3.6 km Sand Dunes in Endurance Crater (Opportunity) 13 Why is Venus’ surface hotter than Mercury’s? A. Carbon dioxide in Venus’ atmosphere traps heat that radiates from its surface. B. Sulfuric acid in Venus’ atmosphere produces thermochemical energy. C. Venus is closer to the Sun than Mercury. D. Venus rotates more slowly, so it “bakes” more in the Sun’s heat. E. Clouds in Mercury’s atmosphere reflect sunlight back into space, keeping its surface cool. 14 Why is Venus’ surface hotter than Mercury’s? A. Carbon dioxide in Venus’ atmosphere traps heat that radiates from its surface. B. Sulfuric acid in Venus’ atmosphere produces thermochemical energy. C. Venus is closer to the Sun than Mercury. D. Venus rotates more slowly, so it “bakes” more in the Sun’s heat. E. Clouds in Mercury’s atmosphere reflect sunlight back into space, keeping its surface cool. 15 Origin of Earth’s Atmosphere • Original atmosphere was H and He leftover from formation of SS. – Too hot near the Sun – H and He are very light elements. • vgas > vescape – Gravity of Earth could not hold them. 16 • Second atmosphere was possibly out-gassed from volcanoes. – water vapor, methane, carbon dioxide (CO2), nitrogen (N) compounds. – N2 freed by UV light – Earth cooled, water vapor condensed into oceans. – CO2 dissolved in oceans or became locked up in rocks. 17 • Current atmosphere is mainly N2 and O2 – 3.8 – 3.5 billion years ago life became established, releasing O2 into atmosphere via photosynthesis. – Free oxygen does not build up until ~ 2 billion years ago – Ozone layer formed after free oxygen increases. 18 Continuing Questions • Was atmosphere created gradually or were most gases released early when surface was still molten? • Could comet impacts have added some carbon dioxide and water? How much? 19 Why are Venus and Mars Different from the Earth? • Venus -- too close to Sun – Too hot for water to condense. – CO2 was not trapped in the oceans. – Increased the greenhouse effect “Runaway Greenhouse Effect” • Mars -- too far from the Sun – Initially warm after formation, water condensed. – Water froze, trapping CO2 – Less greenhouse effect 20 Mercury Messenger http://www.nasa.gov/mission_pages/messenger/main/index.html http://en.wikipedia.org/wiki/MESSENGER • Launched August 2004 • Arrived 2011 • Found water and water ice • Obtained visual evidence of past volcanic activity • Determined the planetary core is partially liquid http://messenger.jhuapl.edu/the_mission/artistimpression/atmercury_br.html 21 Messenger Fly-by August 2, 2005 http://en.wikipedia.org/wiki/File:Mdis_depart_anot.ogv 22 Surface of Mercury • Appears similar to Moon • Heavily cratered due to bombardment by debris in space early in history. • No weather or geologic activity Any crater that is formed remains. 23 Craters on Mercury Mercury Moon 24 Surface Features • Heavily cratered areas (similar to lunar highlands) – Surface likely 3.8 byrs or older • Inter-crater plains (similar to lunar maria) – Likely formed in same manner as on Moon. – More craters than on lunar maria, so they likely formed earlier than lunar maria. 25 Inter-crater Plains 26 Scarps • Cliffs in crust of planet which cut across craters. – Formed when interior cooled and core shrunk more than the crust. – Crust developed “wrinkles.” before after 27 Caloris Basin • Enormous crater - possibly due to large impact Mare Orientale (Moon) Caloris Basin (Mercury) 28 Caloris Basin (NASA Messenger 2008) 29 Weird Terrain Caloris Basin “weird terrain” 30 Which surface feature is unique to Mercury? A. B. C. D. E. Maria Impact craters Mountains Scarps Plains. 31 Which surface feature is unique to Mercury? A. B. C. D. E. Maria Impact craters Mountains Scarps Plains. 32 Synchronous Orbit of Mercury 3Pspin 2Porb • Pspin=59 days • Porb=88 days • Mercury’s orbit is eccentric (0.21) • Mercury is slightly elongated • Tidal forces of Sun try to align Mercury 34 Surface of Venus • Mapped by Magellan (radar) probe • Some craters • Many volcanoes • No water 35 Venus - Magellan • Radar maps of Venus – (Left image – bright = rougher terrain) – (Right image – colored to resemble Earth globe) 36 Venus – Magellan 37 Craters • Impacts occur • Fewer craters – thicker atmosphere – geologic activity 38 Venera • Venera probes (Russian) landed on Venus. – Hot and dry 39 Slow Retrograde Spin of Venus • What would cause Venus to spin so slowly, and in the opposite direction (clockwise when viewed from above north pole) from most of the other planets? – A collision with some large object? – Tidal forces from the Sun? – Atmospheric friction? 40 Surface of Mars • Red colored -- iron oxide (rust) in surface rocks. • Canali – Dark lines observed by Sciaparelli (1877) – Believed to be irrigation channels. – Natural surface features. • No liquid water (too cold) 41 General Surface Features • Northern Hemisphere = “lowlands” – Few craters = younger surface – Lower average elevation – Evidence for geologic activity • Southern Hemisphere = “highlands” – Many craters = much older surface – Age ~3-4 byrs Google Mars Map 42 Surface -- Pathfinder Mission 43 Pathfinder 44 Martian Landscape near Gusev Crater – Spirit Rover http://photojournal.jpl.nasa.gov/jpeg/PIA06770.jpg 45 Mars Landscape in Gusev Crater – Spirit Rover marsrovers.jpl.nasa.gov/gallery/press/spirit/20040106c.html 46 Martian Landscape in Meridiani Planum – Opportunity Rover marsrovers.jpl.nasa.gov/gallery/press/opportunity/20040125a.html 47 Curiosity Rover • Landed in Gale crater August 6, 2012 • Twice as long and 5 times heavier than Spirit and Opportunity • Found more evidence for large amounts of surface water in the past http://www.nasa.gov/mission_pages/msl/multimedia/gallery-indexEvents.html 48 Water on Mars • Dry riverbeds seen • Channels are ~4 billion years old. Mars was warmer earlier in its history. – Thicker atmosphere. – Cooled slowly 49 Spherules on Mars appear to have condensed out of water http://antwrp.gsfc.nasa.gov/apod/ap040405.html Opportunity Rover in Meridian Planum http://antwrp.gsfc.nasa.gov/apod/ap040210.htm 50 Dry Riverbeds on Mars Nirgal Vallis http://barsoom.msss.com/http/ps/channels/channels.html 51 Martian Gullies 52 Where is the Water Now? • Polar caps. – water polar caps -- permanent – CO2 caps grow during winter and shrink during summer. • Frozen under surface as permafrost. • Occasional melting – Volcanic activity – Meteor impacts 53 Polar Caps 54 Water Distribution on Mars – Mars Odyssey 55 Water Distribution on Mars – Mars Odyssey 56 Life on Mars? • Martian meteorite – – – – – Found at South Pole May have been blasted off of Mars by an impact. Much debate over validity of results. Possible contamination by Earth life. Need sample from Mars. • Viking -- tested soil samples, no clear evidence for current life. • Mars Pathfinder -- no clear evidence for current life. 57 We now know that water exists on Mars. This water is in the form of A. B. C. D. liquid in rivers only. atmospheric water vapor only. ice in polar icecaps only. permafrost, polar icecaps, and atmospheric vapor 58 We now know that water exists on Mars. This water is in the form of A. B. C. D. liquid in rivers only. atmospheric water vapor only. ice in polar icecaps only. permafrost, polar icecaps, and atmospheric vapor