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

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

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

Venus Images visible ultraviolet

How We Know What We Know Magellan Akatsuki Venus Express Venera 9 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

Venus – Basic Facts Q. 35: Temperature of Venus 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

Venera – Surface Images of Venus Rocks similar to Earth rocks

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

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

Venus Surface Features and Composition Continents are made of light rocks No water in “seas” Craters are uniformly distributed (?) Suggests entire planet was resurfaced < 1 billion years ago No evidence of plate tectonics – all one plate Probably thicker crust? Composition similar to Earth

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

Volcanoes on Venus Several objects that look like volcanoes

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

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

Mars Images Q. 37: Mars’s Appearance

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)

Current Spacecraft at Mars Mars Orbiter Mission Mars Odyssey ExoMars TGO InSight Mars Reconn-aissance Orbiter Mars Science Laboratory MAVEN Mars Express

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

Mars – Pictures from the Surface

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

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

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