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 “chaotic terrain” on other side of Mercury

4. 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

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 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

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

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

11. Venus – Temperature and Climate
Surface temperature: 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 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

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. Current Spacecraft 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