Transcript Powerpoint for today

General Features
Mass: MEarth = 6 x 1027 g
Radius: REarth = 6378 km
Density:  = 5.5 g/cm3
Age: 4.6 billion years
Orbital period = 365 days
Rotation period = 1 day
Clicker Question:
A moon covered with numerous and very old
craters created by meteorite impacts likely
A: has no ocean to cover the craters
B: orbits a large Jupiter sized planet
C: a cold, solid interior
D: has no protective magnetic field
Clicker Question:
Volcanoes are usually found in places where
A: the low pressure of the aptmosphere pulls the lava/magma
to the surface
B: earthquakes occur from oceanic plates colliding with continental
plates
C: deep-rooted mountains have cracked the Earth’s crust
D: the Earth’s rotation has caused weak spots in its crust
Clicker Question:
The change in position of the continents over time
is primarily caused by
A: the continental plates floating on the ocean
B: mantle material circulating inside the Earth
C: the Earth’s slow shrinking as it cools
D: global wind patterns and sustained ocean currents
Terrestrial Planets' Spin, Habitability
Mercury
Mass = 3.3 x 1026 g
= 0.055 MEarth
Radius = 2439 km
= 0.38 REarth
Density = 5.4 g/cm3
(Earth 5.5 g/cm3)
Gravity = 0.38 that of Earth
Semimajor axis = 0.39 AU
Discovery of Water Ice on
Mercury
Goldstone 70m radar received by
the VLA
Polar regions could be 125 K and
never warmed by the Sun
Orbit of Mercury
3:2 resonance with the sun
Orbital period of 88 days
Sidereal rotation of 59 days
1 “day” on mercury = 176 earth
days
Daytime temp = 500 K
Nighttime temp = 100 K
Structure of Mercury
(from Mariner 10 and theoretical arguments)
1.Crust 100-200
km thick
2. Mantle 600 km
thick
3. Core, 1800 km
in radius
And no atmosphere, so no wind or erosion.
Surface reflects geologic history well.
Messenger at Mercury in 2011
Venus
Mass = 0.82 MEarth
Radius = 0.95 REarth
Density = 5.2 g/cm3
Average distance from Sun = 0.72 AU
Orbital period = 225 days
Rotation period = 243 days (longer
than orbital period, and retrograde!)
Venus' Atmosphere
- Pressure at surface is 90 x that of Earth's => much more gas in
atmosphere. No oceans.
- Consequence - meteoroids burn up easily. No impact craters less
than ~3 km.
- 96.5% CO2
- Yellowish color from sulfuric acid clouds and haze.
- Hot at surface - 730 K! Almost hot enough to melt rock
- Why so hot? Huge amount of CO2 leads to strong greenhouse
effect.
Early on, T may have been much lower (but still warmer than Earth).
Oceans?
But if warm enough, T would start to rise because of...
Runaway Greenhouse Effect
1) Water and CO2 evaporate from oceans into atmosphere.
2) Greenhouse effect more efficient.
3) Temperature rises.
4) More evaporation (back to #1).
=> complete evaporation of oceans. Thick atmosphere.
Missions to Venus
Soviet Venera 4 -18 (1967 - 1983)
Mariner 2, 5 and 10 (1962, 1967 and 1974)
Pioneer Venus
(1978)
Magellan (1989)
Venera 13 photo of
surface. Rocks are
basalt and granite.
Color is due to
atmosphere.
Color corrected
for atmosphere.
"Radar Echo" technique measures altitude
Magellan probe
time for signal to return tells you the
altitude of surface feature.
Planet Surface
Radar data (Pioneer Venus mission) reveal altitude
variations on surface. Flatter than Earth, no evidence for
plate boundaries => no large scale plate tectonics.
1 km
But plenty of evidence of stresses and
fractures on smaller scales => much
small-scale shifting of crust
Impact Craters
Unlike Moon, larger impact craters distributed randomly over surface =>
all parts of surface have about same age.
Paucity of large impact craters => surface is young, 200-500 million years?
Volcanism
Shield volcano elevation map from Magellan radar data. About 100 km across.
Volcanism may be ongoing, based on sulfur dioxide variations in atmosphere.
But very little resurfacing in past 200-500 million years.
Volcanism
Shield volcano elevation map from Magellan radar data. About 100 km across.
Volcanism may be ongoing, based on sulfur dioxide variations in atmosphere.
But very little resurfacing in past 200-500 million years.
Venus surface flyover
Clicker Question:
Venus and the Earth are very similar (within
10%) in their:
A: Amount of carbon dioxide in their atmospheres.
B: Distance from the Sun.
C: Surface gravity.
D: Length of a day.
E: All of the above.
Clicker Question:
It takes 8 minutes for light to travel 1 AU,
how long does it take for a radar signal to
travel from Earth to Mercury and back at its
closest point to Earth in its orbit?
A: 1 minute
B: 10 minutes
C: 2 hours
D: 2 days
E: 1 year
Mars
Mass = 0.11 MEarth
Radius = 0.53 REarth
Density = 3.9 g/cm3
Average distance from Sun = 1.52 AU
eccentricity = 0.093
Range in distance from Sun = 1.38 1.66 AU
Rotation Period = 24.6 hours
Orbital Period = 687 days
Mars' History
Smaller than Earth, Mars cooled faster.
Most volcanic activity ended two billion years ago.
Differentiation less complete than on Earth.
No evidence for plate tectonics.
Atmosphere mostly froze out into subsurface ice, polar ice
caps and surface rocks.
Mars' History
Smaller than Earth, Mars cooled faster.
Most volcanic activity ended two billion years ago.
Differentiation less complete than on Earth.
No evidence for plate tectonics.
Atmosphere mostly froze out into subsurface ice, polar ice
caps and surface rocks.
Valles Marineris flyover movie
The Martian Atmosphere
- 95% CO2
- Surface Pressure 0.006 that of Earth's atmosphere (thin air!)
- Surface Temperature 250 K.
- Dust storms sometimes envelop most of Mars, can last months.
A "Reverse Runaway Greenhouse Effect" may have happened:
during volcanic phase (first two billion years), thicker
atmosphere, warmer surface, possibly oceans. But gradually
most CO2 dissolved into surface water and combined with rocks,
then atmospheric and surface water froze (creating ice caps and
possible permafrost layer).
Or: most atmosphere lost due to low gravity
Or: most atmosphere lost due to heating by early impacts
The Martian Surface
Olympus Mons
Tharsis Bulge
Valles Marineris
Hellas Basin
Southern Hemisphere ~5 km higher
elevation than Northern, and more
heavily cratered.
South is like lunar highlands, surface ~4
billion years old, North like maria, ~3
billion years old.
Valles Marineris - 4000 km long, up to
7 km deep. Ancient crack in crust.
Reasons not clear.
(Mars Global Surveyor radar data)
Tharsis Bulge - highest (10 km) and
youngest (2-3 billion years) region.
Olympus Mons - shield volcano,
highest in Solar System, 3x Everest in
height. 100 km across.
Hellas Basin - large impact crater, ~4
billion years old.
The View From the Surface
Dry, desert-like. Red => high iron content. Mars didn't differentiate as
completely as Earth. Sky has butterscotch hue due to dust.
Viking 1 site (1976)
Sojourner robot from Pathfinder (1997)
“Endurance” crater from Opportunity rover (2004)
Pathfinder site was an outflow channel
Red arrows: rounded boulders indicating water erosion?
White arrows: "conglomerate" rock, like in Earth's riverbeds?
Blue arrows: sharp-edged boulders, volcanic rock?
Spirit and Opportunity Rovers
Scenes from “Roving Mars” (start at 20:27)
Opportunity’s first pictures from Victoria Crater
Deepest crater explored by far (230 feet, 10 times deeper than
Endurance Crater) => more layers of geologic history. Will it go in?
Will it ever get out?
Mars Reconnaissance Orbiter view of Victoria Crater
QuickTime™ and a
H.264 decompressor
are needed to see this picture.
Evidence for Past Surface Water
"runoff channels" or
dry rivers
"outflow channels"
standing water erosion in craters?
teardrop "islands" in
outflow channels
Did Mars once have a huge ocean?
Long stretches along border are very
even in elevation, like a coastline
Ocean fed by outflow channels from
higher elevation southern hemisphere?
Clicker Question:
Large scale motions of the crust (plate
tectonics) are seen on which planets:
A: Mercury and Venus
B: Earth, Venus and Mars
C: Only the Earth
D: Mars and Venus
E: All terrestrial planets - Mercury, Venus, Earth and Mars.
Clicker Question:
From Mars, Deimos has an angular diameter
of 140 arcseconds. Would colonists on Mars
ever see Deimos produce a total solar
eclipse?
A: Yes, every day on Mars
B: Yes, every new moon
C: Yes, but rarely
D: Never
Clicker Question:
The largest mountain in our solar system is:
A: Caloris Basin range on Mercury
B: Gula Mons on Venus
C: Mt. Everest on Earth
D: Olympus Mons on Mars
.
Clicker Question:
Where is the water that once flowed on the
surface of Mars?
A: In the atmosphere
B: In the polar caps only
C: In a layer of permafrost below the surface and in the
polar caps
D: It was diverted to Los Angeles
Evidence for "Permafrost" layer beneath surface
"Splosh" craters suggesting liquefied ejecta.
Valles Marinaris flyover movie
QuickTime™ and a
YUV420 codec decompressor
are needed to see this picture.
Mars' Moons Phobos and Deimos
Phobos: 28 x 20 km
Deimos: 16 x 10 km
Properties similar to asteroids. They are probably asteroids captured
into orbit by Mars' gravity.
Next mission – Mars Science Laboratory – fall 2009 launch