Mercury Craters Mercury Craters Craters are shallower More

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 • Extinct Volcanoes Discovered on Mercury • Many “plains” look like they were caused by volcanism Crater Flat crater floor Volcanic Vent 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 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 • 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 Q. 35: Temperature of Venus • Atmosphere – Thick – 93 Earth pressure – Mostly Carbon Dioxide (CO 2)

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 (CO 2) – 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 (H 2 SO 4) – “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: • H 2 O oceans, CO 2 atmosphere • Lots of water evaporates • Water is greenhouse gas • Water dissociated by UV • Hydrogen and Oxygen lost • CO 2 continues greenhouse Early Earth: • H 2 O oceans, CO 2 atmosphere • Little water evaporates • Some CO 2 dissolves in ocean • CO 2 combines with rocks • Plants convert CO 2 to O 2 • 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) Exo. Mars Trace Gas Orbiter (’ 16 -present) In. Sight (’ 18 -present) • More missions planned (’ 20 and beyond)

Current Spacecraft at Mars Orbiter Mission Mars Odyssey Exo. Mars TGO Mars Reconnaissance Orbiter Mars Express In. Sight Mars Science Laboratory MAVEN

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 (CO 2) – 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 Mild summer north Severe winter south Mild winter north Severe summer south Q. 37: Climate on Mars

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