Transcript Today`s Powerpoint

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Clicker Question:
Why is Venus the hottest planet in the Solar
System?
A: It is the closest planet to the Sun.
B: There is a lot of radioactive material in the crust.
C: There is a large concentration of carbon dioxide in the
atmosphere.
D: The Russians left the lights on in the Venera 5 landing
vehicle.
E. Paris Hilton lives there.
Mars
Mass = 0.11 MEarth
eccentricity = 0.093
Radius = 0.53 REarth
Range in distance from Sun = 1.38 1.66 AU
Density = 3.9 g/cm3
Average distance from Sun = 1.52 AU
Rotation Period = 24.6 hours
Orbital Period = 687 days
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”? During volcanic
phase (first two billion years), thicker atmosphere, warmer
surface, possibly oceans. Gradually most CO2 dissolved into
surface water and combined with rocks, then atmospheric and
surface water froze (creating ice caps and probable permafrost
layer).
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.
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
The Martian Surface
Olympus Mons
Tharsis Bulge
Valles Marineris
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.
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)
Opportunity panorama: inside Victoria Crater
Deepest crater explored by far (230 feet) => apparently it was the top
of an underground water table.
Evidence for Past Surface Water
"runoff channels" or
dry rivers
"outflow
channels"
South
standing water erosion in craters?
North
teardrop "islands" in
outflow channels
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?
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?
Evidence for "Permafrost" layer beneath surface
"Splosh" craters suggesting liquefied ejecta.
Evidence for Water on Mars Now
subsurface ice
Phoenix Lander (2008) Deployable arm
Phoenix mission – icy soil at the poles!
Phoenix analyzing scooped up
dirt – was Mars ever favorable
for microbial life? Organic
compounds?
Mars' History
Smaller than Earth, Mars cooled faster.
Atmosphere and surface water in first 1.5 billion years. Life?
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.
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
Martian ‘Snick’ meteorite ALH84001 shows odd shaped features that are
reminiscent of bacteria. General consensus is no life.
Evidence for "Permafrost" layer beneath surface
"Splosh" craters suggesting liquefied ejecta.
Valles Marinaris flyover movie
The Face on Mars
Viking orbiter photos showed this:
Newer, high resolution photo – Mars Global Surveyor
1998
Isn’t this more disturbing???
Spirit and Opportunity Rovers
Scenes from “Roving Mars” (start at 15:10, skip to 20:27, skip to 26:16)
The Jovian Planets
Saturn (from Cassini probe)
Jupiter
Uranus
Neptune
(roughly to scale)
Discoveries
Jupiter and Saturn known to
ancient astronomers.
Uranus discovered in 1781 by
William Herschel.
Neptune discovered in 1845 by
Johann Galle. Predicted to exist by
John Adams and Urbain Leverrier
because of irregularities in Uranus'
orbit.
Basic Properties
Mass
(MEarth)
Jupiter
Radius
(REarth)
Orbit semi-major axis Orbital Period
(AU)
(years)
318
11
5.2
11.9
Saturn
95
9.5
9.5
29.4
Uranus
15
4
19.2
84
Neptune
17
3.9
30.1
164
(0.001 MSun)
Major Missions
Launch
Voyager 1
1977
Planets visited
Jupiter, Saturn
Voyager 2
1979
Jupiter, Saturn, Uranus, Neptune
Galileo
1989
Jupiter
Cassini
1997
Jupiter, Saturn
Jupiter's Atmosphere and Bands
Whiteish "zones" and brownish "belts".
Optical – colors dictated by how
molecules reflect sunlight
Infrared - traces heat in
atmosphere, therefore depth
So white colors from cooler, higher clouds, brown from warmer, lower
clouds. Great Red Spot – highest.
Composition: mostly H, some He, traces of other elements
(true for all Jovians). Gravity strong enough to retain even
light elements. Mostly molecular. Spectroscopy of
reflected sunlight reveals which molecules present.
Altitude 0 km defined as
top of troposphere (cloud
layer)
NH4SH
(NH3)
These molecules
should all give white
clouds. Molecules
responsible for colors
actually not clear!
Other Jovian planets: banded structure and colors
More uniform haze layer makes
bands less visible. Reason:
weaker gravity allows clouds to
rise higher and spread out to
create more uniform layer
Blue/green of Uranus and blue
of Neptune due to methane.
Colder than Jupiter and Saturn,
their ammonia has frozen and
sunk lower. Methane still in
gas form. It absorbs red light
and reflects blue.
- Zones and belts mark a convection cycle. Zones higher up than belts.
- Zones were thought to be where warm gas rises, belts where cooled gas sinks.
Now less clear after Cassini, which found numerous upwelling white clouds in
the dark belts.
-
- Jupiter's rapid rotation stretches them horizontally around the entire planet.
- Winds flow in opposite
directions in zones vs.
belts. Differences are
hundreds of km/hr.
Storms on Jovian Planets
Jupiter's Great Red Spot: A hurricane
twice the size of Earth. Has persisted for at
least 340 years. Reaches highest altitudes.
New storm “Oval BA”
"white ovals" - may last decades
"brown ovals" - only seen near 20°
N latitude. Not known why. May
last years or decades
Neptune's Great Dark Spot: Discovered by
Voyager 2 in 1989. But had disappeared by
1994 Hubble observations. About Earthsized.
Why do these storms last so long?
Jupiter's Internal Structure
Can't observe directly. No seismic information. Must rely on physical
reasoning and connection to observable phenomena.
(acts like a liquid metal,
conducts electricity)
Core thought to be molten or partially molten rock,
maybe 25 g/cm3, and of mass about 10-15 MEarth .
Other Jovians similar. Interior temperatures, pressures and densities less
extreme.
Rapid rotation causes Jupiter and Saturn to bulge:
Gravity
Gravity
without rotation
with rotation
Jupiter and Saturn rotate every ~10 hours.
Radius at equator several % larger due to bulge.
Differential Rotation
Rotation period is shorter closer to the equator:
Near poles
At equator
Jupiter
9h 56m
9h 50m
Saturn
10h 40m
10h 14m
Uranus
16h 30m
14h 12m
How do we know?
Differential Rotation
Rotation period is shorter closer to the equator:
Near poles
At equator
Jupiter
9h 56m
9h 50m
Saturn
10h 40m
10h 14m
Uranus
16h 30m
14h 12m
How do we know? Tracking storms at various
latitudes, or using Spectroscopy and Doppler shift.
Uranus' rotation axis is tilted by 98o
Why? Unknown. Perhaps an early, grazing collision
with another large body.