Mercury - Overview
Distance
36 million miles (0.39 AU)
Orbital Period
88 days
CLOSEST Planet to Sun
FASTEST Planet
Rotation Period
59 days
SLOW rotation**
Radius
2440 km (0.38 R⊕)
SMALLEST Planet (no Pluto)
Mass
3.3 x 1023 kg (0.055 M⊕)
LEAST MASSIVE
Density
Atmosphere
Surface T
5.4 g/cm3
Essentially none
800 F (day), -290 F (night)
DENSEST (exc Earth)
LARGEST TEMP DIFF.
**Nearly Synchronous!
Mercury - Overview
Distance
36 million miles (0.39 AU)
CLOSEST Planet to Sun
Orbital Period
88 days
FASTEST Planet
Rotation Period
59 days
SLOW rotation
Radius
2440 km (0.38 R⊕)
SMALLEST Planet (no Pluto)
Mass
3.3 x 1023 kg (0.055 M⊕)
LEAST MASSIVE
Density
5.4 g/cm3
DENSEST (exc Earth)
Atmosphere
Essentially none
Surface T
Obliquity
800 F (day), -290 F (night)
0 degrees
LARGEST TEMP DIFF.
seasons?
Observing Mercury
• Hardest Naked Eye Planet
WHY?
Mariner 10: Venus/Mercury flyby (1974)
1974: no
evidence for
recent geologic
activity
Mercury cooled off?
Mercury - Spacecraft data
Mariner 10: Venus/Mercury flyby (1974)
Measured Mass
Calculated HIGH
density (5.4g/cm3)
WHY??
LARGE iron core!
Mercury - Spacecraft data
Mariner 10: Venus/Mercury flyby (1974)
Small Magnetic
Field (1% Earth)!
WHY??
Mercury - Spacecraft data
Messenger: Mercury Orbiter (2004-)
Flybys: 2/1/08, 10/6/08, 9/29/09
Mercury Orbit: March 18, 2011
Inner Core Molten!
Surface Features
Messenger
Terrain
Craters/Rayed Craters
Impact Basins
Planitiae (Plains)
South Pole
Current Geologic Activity?
Surface Features
Rays & Bright Craters
Different Rock
Composition?
Surface Features
Rupes & Lobate Scarps
• Compression Folds/Cliffs
• Large (>100 km!)
• Mercury contracted quickly
from cooling (R<20km) Why?
• Closed off volcanic vents
Surface Features
NEW! Double Ring Basin!
Caloris Basin
Largest feature on Mercury
HUGE (960 km) Impact Basin with
WEIRD TERRAIN opposite
3.8-3.9 bil. yrs old
WEIRD TERRAIN
Mercury - A History
➡Formation close to Sun
•sunlight/wind 6.25x more intense...
no atmosphere
•tidal forces/slow rotation...
small magnetic field
•HOT
➡Heavy Bombardment
➡Volcanism
➡Planet Cooled (Small!)
Venus - Overview
“Planet from Hell!”
Distance
Orbital Period
Rotation Period
Radius
Mass
Density
Surface T
Atmosphere
Obliquity
67 million miles (0.72 AU)
2nd planet from Sun
225 days
243 days
Orbits slow & retrograde**
6052 km (0.95 Earth)
EARTHLIKE
4.9 x 1024 kg (0.81 Earth)
EARTHLIKE
5.2 g/cm3
860 F
HOT HOT HOT
96.5 % Carbon Dioxide
Densest of ALL
177 degrees
seasons?
**No Strong Magnetic Field
Venus - Early Observations
•Galileo - 1610/1611
•Phases of Venus
Venus from Earth
•Brightest object besides Sun & Moon
•why?
What time of day
is Venus
observable?
Venus - Radar Mapping
RAdio Detection And Ranging
Use RADAR to Map surface of Venus!
Venus - Earth’s Evil Twin
Atmosphere of sulfuric
acid & carbon dioxide
(96.5% CO2!)
Venus - Spacecraft data
Magellan (1990-1994) - Orbiter, radar mapping
Smooth Surface &
Few Craters:
Evidence for recent
geologic activity
INFER core/mantle/Crust
(similar to Earth)
THICK Lithosphere
(HOT)
Venusian Surface Features
Mountains & Terrae
•2 “Continents”
•Afrodite Terra
•Ishtar Terra
Venusian Surface Features
Impact Craters Golubkina Crater
•not many (~1000)
•NO small craters (<3 km)
•thick atmosphere
•young surface
Why Not?
30 km
Mead Crater
Alcott Crater
63 km
280 km
Venusian Surface Features
Volcanoes
>1600 major volcanoes!
167 larger than 100km!
Why so big?
Maat Mons
Sif Mons
Venusian Surface Features
Rampant Volcanism
- Pancake domes
- Coronae
- Lava Channels
Effect??
30 km
Mead Crater
Volcanic Outgassing & Atmosphere
Formation - ON VENUS
a) Trapped gases released during volcanic activity:
– H2O, CO2 , N2 , H2S, SO2
b) Solar UV breaks up some molecules,
-light elements escape
- O/O2 forms ozone layer, protects from UV
X
TOO
c) H2O condenses to form liquid water - rain!
HOT!
d) Water combines with CO2 to create carbonate rocks
(e.g. limestone)
Venus: RUNAWAY Greenhouse Effect
•H2O/CO2 are greenhouse gases
(absorb IR radiation)
T ↑ → water boils, vapor absorbs IR
→ T ↑ → no water to absorb CO2, CO2 absorbs IR
→ T ↑ etc. (until insanely hot!)