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Mercury – Craters

Mercury – Craters. Mercury – Craters. Craters are shallower More gravity Craters are separated by smooth areas. Caloris Impact Basin. Giant crater Very old Subsequent lava flows inside it Shock waves created “chaotic terrain” on other side of Mercury. Volcanism on Mercury.

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Mercury – Craters

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  1. Mercury – Craters

  2. Mercury – Craters • Craters are shallower • More gravity • Craters are separated by smooth areas

  3. Caloris Impact Basin • Giant crater • Very old • Subsequent lava flows inside it • Shock waves created “chaoticterrain” onother sideof Mercury

  4. Volcanism on Mercury • Extinct Volcanoes Discovered on Mercury • Many “plains” look like they were caused by volcanism Volcanic Vent Crater Flat plains Flat crater floor

  5. Scarps on Mercury • Giant cliffs ~ few km tall • Hundreds of km wide

  6. Scarps – Cracks in the Crust • Large metal core • Hot initially • Metal expands when hot • Core cooled • Metal shrinks • Portions of the surface “fell” • Cracks on the surface rock metal

  7. Venus Images visible ultraviolet

  8. How We Know What We Know Magellan • Many early spacecraft – limited success • Venera – Soviet Landers – 60’s and 70’s • Magellan – ’89 – Radar Mapping • Venus Express (ESA) –2006 to 2014 • Akatsuki (Japan) – Since 2015 Akatsuki Venus Express Venera 9

  9. Venus – Basic Facts • Size – Slightly smaller than Earth • Mass – Slightly less massive than Earth • Comparable density to Earth • Orbit: • 0.723 AU, nearly circular • Venus year = 225 Earth Days • Rotation: • Backwards every 243 Earth Days • 2 Venus Days ~ 1 Venus Year • Atmosphere – Thick – 93  Earth pressure • Mostly Carbon Dioxide (CO2) Q. 35: Temperature of Venus

  10. Venera – Surface Images of Venus • Rocks similar to Earth rocks

  11. Venus – Temperature and Climate • Surface temperature: 720-750 K – hotter than hell • Hottest planet – strong greenhouse effect (CO2) • Uniform temperature – thick atmosphere • No water • Surface – too hot for water or ice • Atmosphere – no water • Clouds – cover planet entirely in visible light • Clouds are sulfuric acid (H2SO4) • “Rain” of acid, but evaporates before it hits the ground • Lightning – cause unknown – more than Earth

  12. Venus in Radar • Clouds block views of surface • Magellan mapped 98% in radar • Continents and “seas” • Craters – rare, like Earth • Mountains • Volcanoes

  13. Venus Surface Features and Composition • Continents are madeof light rocks • No water in “seas” • Craters are uniformlydistributed (?) • Suggests entireplanet was resurfaced< 1 billion years ago • No evidence of plate tectonics – all one plate • Probably thicker crust? • Composition similar to Earth

  14. Mountains and Craters on Venus • Comparable in number and size to Earth • No small craters (thicker atmosphere) Q. 36: Volcanism on Venus

  15. Volcanoes on Venus • Several objects that look like volcanoes

  16. Volcanoes on Venus • At present, no actual volcanoes have been seen erupting, but . . . • Comparable in size to Earth • Sulfur compounds in the atmosphere indicate recent activity • Lots of evidence of recent eruptions • Lava makes pancake-like lava outflows • Generally agreed – Venus is still geologically active, like Earth

  17. Venus vs. Earth • Why is Venus’s atmosphere so different from Earth? Early Venus: • H2O oceans, CO2 atmosphere • Lots of water evaporates • Water is greenhouse gas • Water dissociated by UV • Hydrogen and Oxygen lost • CO2 continues greenhouse Early Earth: • H2O oceans, CO2 atmosphere • Little water evaporates • Some CO2 dissolves in ocean • CO2 combines with rocks • Plants convert CO2 to O2 • Runaway greenhouse effect

  18. Mars Images Q. 37: Mars’s Appearance

  19. How We Know What We Know • Many early missions (before 2000) • Mars Odyssey (’01-present) • Mars Express (’03-present) • Mars Exploration Rovers (’04-’18) • Mars Reconnaissance Orbiter (’06-present) • Mars Phoenix Lander (’08) • Mars Science Laboratory (’12-present) • MAVEN (’14-present) • Mars Orbiter Mission (’14-present) • ExoMars Trace Gas Orbiter (’16-present) • InSight (’18-present) • More missions planned (’20 and beyond)

  20. CurrentSpacecraft at Mars Mars Orbiter Mission Mars Odyssey ExoMars TGO InSight Mars Reconn-aissance Orbiter Mars Science Laboratory MAVEN Mars Express

  21. Mars – Basic Facts • Size – Half the size of Earth • Twice the size of Mercury • Mass – 1/10 of Earth’s • Slightly less dense than Earth • Orbit: • 1.38 AU, fairly eccentric • Mars year = 1.9 Earth years • Rotation: • Once every 24 hours 40 minutes • Atmosphere – Thin – < 1% Earth pressure • Mostly Carbon Dioxide (CO2) • Too thin for appreciable greenhouse effect

  22. Mars – Pictures from the Surface

  23. Mars – Pictures from the Surface • Rocks and sand • Reddish color due to iron oxide – aka rust

  24. Mars – Climate Sun Mars Mars Mild summer north Severe winter south Mild winter north Severe summer south Q. 37: Climate on Mars

  25. Mars – Climate Sun Mars Mars • Colder than Earth (far from Sun) • 130 K – 290 K • Pressure fluctuates seasonally • Southern hemisphere is more extreme

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