Mercury, Venus, Mars

1
Mercury, Venus, Mars

• Basic Properties
• Rotation Rates
• Mercury
• Radar signals
• tidally locked to sun, but with a very eccentric
  orbit
• 11.5 synchronicity
• Venus
• sluggish retrograde
• Mars
• very similar to Earth

2

• Atmospheres
• Mercury
• temporarily trapped solar wind
• high temp low mass gt no atm
• 600 K temperature range
• Venus
• upper atmospheric temp stratosphere
• more massive, greater height, greater pressures
• CO2 nitrogen
• clouds of sulfuric acid droplets
• composed of haze and fast moving clouds
• runaway greenhouse effect
• Mars
• thin, low pressure
• mostly CO2
• CO2,nitrogen,argon,oxygen,CO,H2O
• 50K cooler than Earth

3

• Runaway Greenhouse Effect
• Earth
• primary atmosphere
• secondary atmosphere
• volcanic outgassing
• oceans form
• life develops
• ozone layer develops
• Venus
• primary atmosphere
• secondary atmosphere, at higher temperatures
• either no oceans or runaway effect
• evaporation of water less CO2 retained
• increased atmospheric concentrations lead to
  higher temperatures
• surface temp twice as high in past
• H2O rises, dissolves, is lost
• current atm absorbs 99 of IR radiation emitted
  at surface gt 730K

4

• Greenhouse Effect
• Mars
• primary atmosphere
• secondary atmosphere
• dense atm 4 billion yrs ago surface temp above
  0o C
• lost due to impacts reverse runaway greenhouse
  effect
• CO2 dissolves in oceans
• water freezes out of atmosphere
• temperatures drop
• level of H2O in atm is maximum possible for
  current temp density
• water in permafrost polar caps could cover
  surface several meters deep

5
Surface of Mercury

• Like lunar highlands
• greater surface gravity gt lower walls and
  tighter ejecta blanket
• no extensive maria
• intercrater plains
• scarps (cliffs)
• after intense bombardment ended
• formed when crust cooled and shrank

6
Surface of Venus

• Mostly smooth - rolling plains
• 2 continents
• 8 of total surface area
• mountains up to 14 km
• crust is buckled and fractured
• no tectonic activity
• volcanism
• periods of extensive lava flows
• lava domes
• shield volcanoes
• coronae
• active today SO2 in atm and bursts of radio
  energy
• basaltic granite rocks
• some cratering

7
Surface of Mars

• Visual Mars
• Seasonal changes occur
• polar caps of CO2, H2O
• dark regions
• planetwide dust storms
• Northern hemisphere
• volcanic plains
• 3 billion yrs old
• 4 km lower
• Southern hemisphere
• heavily cratered highlands
• 4 billion yrs old
• original crust

8

• Tharsis bulge
• 10 km higher than surface
• 2-3 billion yrs old (youngest on planet)
• no plate tectonics
• red color
• rocks high iron content
• oxygen in atm gt iron oxide rust
• Volcanism
• largest known volcanoes in solar system
• large height due to low surface gravity
• Olympus Mons 25 km high, 700 km in diameter
• shield volcanoes
• active as recently as 100 million yrs ago

9

• Martian Grand Canyon
• Valles Marineris
• formed when surface split and cracked
• at least 2 billion yrs old
• 4000 km long ( 1/5 planet's equator)
• Liquid Water on Mars
• runoff channels
• dried up bed of rivers
• channels run from mountains to valleys
• outflow channels
• due to past catastrophic flooding
• only in equatorial regions
• formed same time as Northern plains
• 100s of times more water than Amazon
• rounded pebbles rocks in outflow channels
  consistent with theory
• today permafrost? polar caps?
• Crater Yuty

10

• Water on Mars
• 4 billion years ago, water froze out
• 3 billion years ago, flash flooding as
  permafrost melted
• water re-freezes
• Mars is dry today!

11
Internal Structure

• Mercury
• magnetic field 1/100 Earth's
• possibly a fossil remnant?
• High density
• large, iron-rich core (radius 1800 km)
• solid crust prevents volcanism and tectonic
  activity
• hot inner region gt dense, largely metallic
  composition
• cooled more slowly than moon
• formation of core gt planet shrinks and surface
  contracts
• dead longer than moon

12

• Interior of Venus
• probably a partially molten, iron-rich core
• no magnetic field
• young Earth
• volcanic activity but no tectonic activity
• slow cooling rate?
• Soft crust?
• Too much volcanism?
• Interior of Mars
• weak field
• core is nonmetallic or nonliquid
• core of iron sulfide 2500 km
• cooled quickly
• stifled tectonic activity
• rigid mantle thick crust
• dead about 2 billion yrs