Transcript Integrative Studies 410 Our Place in the Universe

Studying for Exam II
• Same type of exam as first one
• Chapters covered: parts of Ch.1, Ch. 4-8.
– Very little from Chapters 7&8
Mars
• Northern Hemisphere
basically huge volcanic
plains
– Similar to lunar maria
• Valles Marineris –
Martian “Grand Canyon”
– 4000 km long, up to 120
km across and 7 km deep
– So large that it can be seen
from Earth
Martian Volcanoes
• Olympus Mons
– Largest known volcano in the solar system
– 700 km across at base
– Peak ~25 km high (almost 3 times as tall as Mt. Everest!)
Martian Surface
Iron gives the characteristic Mars color: rusty red!
View of Viking 1
1 m rock
Sojourner
Water on Mars?
Mars
Louisiana
Runoff channels
Outflow Channels
Life on Mars?
• Giovanni Schiaparelli (1877) – observed “canali”
(channels) on Martian surface
• Interpreted by Percival Lowell (and others) as
irrigation canals – a sign of intelligent life
• Lowell built a large observatory near Flagstaff, AZ
(Incidentally, this enabled C. Tombaugh to find Pluto in 1930)
• Speculation became more and more fanciful
– A desert world with a planet-wide irrigation system to carry
water from the polar ice caps?
– Lots of sci-fi, including H.G. Wells, Bradbury, …
• All an illusion! There are no canals…
Viking Lander Experiments
(1976)
• Search for bacterialike forms of life
• Results inconclusive
at best
Atmospheric Histories
• Primary atmosphere: hydrogen, helium,
methane, ammonia
– Too light to “stick” to a planet unless it’s very
big  Jovian Planets
• Secondary atmosphere: water, CO2, SO2, …
– Outgassed from planet interiors, a result of
volcanic activity
Atmospheric Histories - Venus
• Venus is closer to Sun than Earth hotter
surface
• Not a lot of liquid water on surface initially
• CO2 could not be absorbed by water, rocks
because of higher temperatures
•  run-away Greenhouse effect: it’s hot, the
greenhouse gases can’t be be stored away, it
gets hotter …
Earth’s Atmospheric History
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•
•
•
•
Volcanic activity spews out water steam
Temperature range allowed water to liquify
CO2 dissolves in oceans, damping greenhouse effect
More water condenses, more CO2 is absorbed
If too cold, ice forms  less cloud cover  more
energy
• No oxygen at this point, since it would have been
used up producing “rust”
• Tertiary atmosphere: early life contributes oxygen
– 1% 800 Myrs ago, 10% 400 Myrs ago
Mars – Freezing over
• Mars once had a denser atmosphere with liquid
water on the surface
• As on Earth, CO2 dissolves in liquid water
• But: Mars is further away from the Sun
 temperature drops below freezing point 
inverse greenhouse effect
• permafrost forms with CO2 locked away
• Mars probably lost its atmosphere because its
magnetic field collapsed, because Mars’ molten
core cooled down
Greenhouse Effect
• Earth absorbs energy
from the Sun and
heats up
• Earth re-radiates the
absorbed energy in
the form of infrared
radiation
• The infrared radiation
is absorbed by carbon
dioxide and water
vapor in the
atmosphere
Global Warming
• Excessively
“politicized” topic
• Very complex
problem scientifically
• Slow changes over
long periods of time
• Sources of heating,
sources of cooling
themselves are
temperature dependent
Man-made CO2 in the Atmosphere goes up
Correlation: Temperatures rise when
Carbon Dioxide levels rise
• This is true since prehistoric times
The Jovian Planets
Saturn
Jupiter
Uranus
Neptune
Comparison
• Terrestrial
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–
–
–
–
–
–
–
–
close to the Sun
closely spaced orbits
small radii
small masses
predominantly rocky
high density
solid surface
few moons
no rings
• Jovian
–
–
–
–
–
–
–
–
–
far from the Sun
widely spaced orbits
large radii
large masses
predominantly gaseous
low density
no solid surface
many moons
many rings
History
• Jupiter and Saturn known to the ancients
– Galileo observed 4 moons of Jupiter and Saturn’s
rings
• Uranus
– Discovered telescopically by William Herschel in
1781 (actually barely visible to naked eye)
• Neptune
– Predicted from observed perturbations of Uranus’
orbit: Adams (1845) and Leverrier (1846)
– Observed by Galle (1846)
– Discovery great triumph for computational
astronomy/physics
Grand Tour of Voyager 1 & 2
• Used
gravitational
slingshot to
get from
planet to
planet
Rotation
• About 10 hours for Jupiter and Saturn; about 17 hours
for Uranus and Neptune
• Differential rotation: rotation speed varies from point
to point on the “surfaces”
– Gaseous bodies with no solid surfaces!
– On Jupiter, the equatorial regions rotate 6 minutes slower
than polar regions
– On Saturn the equatorial region is about 26 minutes slower
• Tilt of rotation axes:
– Jupiter: almost none – no seasons!
– Saturn, Neptune: about like Earth
– Uranus: weird
Uranus’ Strange Seasons
Jupiter’s Atmosphere
• Cloud bands parallel
to equator
• Great Red Spot
– First observed in
1664 by Robert
Hooke
Jupiter’s Atmosphere
• 86% Hydrogen, 14%
Helium; some methane,
water, ammonia
• Several layers of clouds:
ammonia, ammonium
hydrosulfide, water
• Colors mostly due to
compounds of sulfur
and phosphorus
Jupiters’ Bands: Zones and Belts
• Belts: cool, dark, sinking
• Zones: warm, bright, rising
• Jovian weather mostly
circles the planet due to
high rotation rate
• Bands exhibit east–west
flow Great Red Spot lies
between regions of opposite
wind flow
Great Red Spot
• About twice
the diameter
of the Earth
• A hurricane
that is
hundreds of
years old!
Saturn’s Atmosphere
• 92% Hydrogen
7% Helium;
some methane,
water, ammonia
• Belt structure
similar to
Jupiter’s, but
fainter
• Storms are rarer
• White spot seen,
1990 (Voyager)
Uranus’ and Neptune’s Atmospheres
Neptune’s Dark Spot
• Ammonia frozen out; more methane
– Methane absorbs red light, leads to bluish color
• Almost no band structure on Uranus
Magnetospheres
• Very strong – Jupiter's
extends past the orbit of
Saturn!
• Indicate the presence of
conducting cores
Rings
Saturn
Uranus
Jupiter
Neptune
Saturn
• Rings composed of
small, icy fragments,
orbiting in concentric
circles
• Orbits obey Kepler’s
laws (of course!)
– Inner rings move faster
than outer ones
Visibility of Saturn’s Rings
2009
How Do They Form?
• Miscellaneous debris
• Moons or other small
bodies torn apart by
tidal forces
• Roche limit – distance
inside of which an
object held together by
gravity will be pulled
apart
Ring Formation
• Rings may be short lived (on the time scale
of solar system)
• Means that they must form fairly frequently
• A moon may pass too close to a planet
(within the Roche limit) and be destroyed
by tidal forces
– This will probably happen to Triton (a moon of
Neptune) within 100 million years!