Astronomy Semester Exam-Things to know:
Exam will consist of Chapters 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 and 13.
What to know for Chapters 9, 10 & 11 (Venus, Mars & Jupiter):
Venus
Mars
Jupiter
Planet order
2
4
5
Orbital period
0.62 years
1.88 years
11.9 years
Semi-major axis
0.72 AU
1.52 AU
5.2 AU
Mass
0.82 x Earth
0.11 x Earth
318 x Earth
Radius
0.95 x Earth
0.53 x Earth
11.2 x Earth
3
3
Density
5240 kg/m
3930 kg/m
1300 kg/m3
Surface Gravity
0.91 x Earth
0.38 x Earth
2.5 x Earth
Escape speed
10.4 km/s
5.0 km/s
59.5 km/s
Rotational Period
-243 days
1.026 days
0.41 days
Inclination (axis tilt) 177.4°
23.98°
3°
Surface Magnetic Field less than 0.001 x Earth 1/800 x Earth
14 x Earth
Surface Temperature 730 K
about 150-310 K 125 K
Number of Moons
0
2
63 and counting
Venus
Earth's Sister Planet
Observing Venus from Earth
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Venus never separates from the Sun by more than 47o, as viewed
from the Earth
o appears above the horizon
 before sunrise and after sunset.
Extremely bright
o (10 x brightest star) (reflectivity = 70%)
o 3rd brightest object in the sky, next to the Sun and the Moon
Venus - General Properties
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2nd Planet from the Sun
semi-major axis ("radius") = 0.72 AU
o period = 225 days
Radius = 6052 km = 0.95 REarth
Mass = 4.9 x 1024 kg = 0.82 MEarth
Density = 5240 kg/m3
o Radius, mass, & density are Earth-like or "sister planet"
Rotational Period = 243 days ( retrograde)
o Solar day on Venus = 117 Earth days
o Why retrograde -> collision?
Atmosphere
o very dense => high altitude clouds of sulfuric acid block
surface
90x as massive as the Earth's atmosphere
o 96.5% CO2 (by volume)
o few % Nitrogen (very little water)
surface temperature = 730K (TEarth=300K, TMercury=100-700K)
Greenhouse Effect
o temperature uniformity - poles, equator, day, night
Exploration of Venus
More than 20 spacecraft have visited, more than any other planet
o
o
o
visits began in the early 1960's
first soft landing on surface by Soviet Venera 7 in 1970
Magellan - August 1990
 produced spectacularly detailed surface images
 resolution of about 120 m
Venus' atmosphere is different from Earth's?

On Earth, CO2 is absorbed in the oceans and rocks.
Summary of Atmospheric Components
(percentages by volume)
CO2
Nitrogen
Water
Oxygen
Earth
absorbed in rock
free in atmosphere (78%)
mostly condensed on surface
product of life (21%)
Venus
free in atmosphere (96.5%)
free in atmosphere (3.5%)
decomposed long ago, and hydrogen escaped
no life to produce it
Evolution of Venus' Atmosphere

During secondary atmosphere formation temperature of Venus
high
o no oceans form (Water is broken down and H escapes) and
gases are not absorbed
o gases in atmosphere trap heat (greenhouse effect)
o temperature rises even more
o runaway greenhouse effect
Venus' Surface
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A couple of continental sized features
o Ishtar Terra (southern high latitudes)
o Aphrodite Terra (near the equator),
o with Earth-like mountains
No oceans
o rolling plains (65%)
o lowlands (27%)
o modest highlands (8%) (continents)
No plate tectonic activity
Lava flows -> volcanic origin
Craters - mostly of volcanic origin
The surface of Venus is rather young (less than 1 billion years) due
to volcanic activity
Volcanism today?
Probably (SO levels above the thick cloud cover and suggestive radio
emissions)
2
Venus' Magnetic Field and Internal Structure
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Magnetic field - none detectable
o this is consistent with slow rotation period of 243 days
Model of internal structure is based on little hard data
o Surface resembles surface of young Earth (at an age of about
1 billion years)
 thin crust, volcanic activity,
 internal convective processes not yet established
 not yet developed plate tectonics
o Why no development of plates?
 Cooling slowly due to high surface temperature
 crust remains too soft for Earth-style plates to
develop
 absence of water may also be important
 no lubricating mechanism
Mars
A Near Miss for Life?
General Properties of Mars
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Mars is the 4th Planet from the Sun
semi-major axis ("radius") = 1.52 AU
closest opposition roughly every 15 years (in August/September) > brightest
orbital period = 687 days (1.88 years)
Radius = 0.53 Rearth
Mass = 0.11 Mearth
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=> Density = 3900 kg/m3
Rotational Period = 24.6 hours
Inclination of 24.0° (23.5° for Earth)
o tilt causes seasons
History of Observations from Earth
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1877 - Mars is unusually close to Earth
o Italy: Giovanni Schiaparelli
 Observed network of linear markings (canali)
o Percival Lowell, in US
 Motivated by report of "canals", gives up successful
Boston business to build observatory in Flagstaff,
Arizona
 devoted life to studying "canals" and Martian intelligent
society
Space Probes to Mars
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Mariner 4 (1965)
o First spacecraft to reach Mars
Viking 1 and Viking 2 (1976)
o landed on Mars and conducted biological experiments to
search for evidence of life
Pathfinder (& Sojouner, landed July 4, 1997)
o landed at mouth of outflow channel
o rocks deposited by flood water
Mars Global Surveyer
o launched November, 1996
o start mapping, March, 1999
Mars Exploration Rover Mission
o Spirit landed on January 3, 2004, in a rocky landscape
o Opportunity landed halfway around Mars from Spirit
found rocks that had been very wet in the past, after landing
on January 23, 2004.
o The rovers were expected to last 3-6 months, but each
continued to explore over a few kilometers and send data
back for several years.
 Spirit stopped communicating in 2010 after traveling
over 7 kilometers
 Opportunity goes on, having traveled over 27
kilometers
Phoenix Mission
o landed in North polar region in 2008
o dug trenches and discovered white material that is almost
surely ice
Major results of these missions
1. the surface of Mars contains much more iron that the surface
of the Earth
 less differentiation on Mars
2. so far, no evidence of life, now or in the past
o
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Mars' Atmosphere
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Mars has a very thin atmosphere
o (1/150 of Earth's atmosphere)
o 95.3% CO2 (by volume)
o surface temperature:
 noon, summertime 300K
 night-time - 200K (much colder than on Earth)
 (Tearth=300K)
=> dust storms (occasionally months-long)
Composition of Mars' atmosphere similar to Venus, yet 10,000
times thinner
o -> reverse greenhouse effect
Mars' Surface
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Huge shield volcanoes:
o Olympus Mons
 About 700 kilometers in diameter
 would cover all of Washington and half of Oregon
 Rises 25 kilometers above the surrounding plains
 (82,000 feet)
 (largest volcano in the Solar System)
o Mariner Valley
 crack in the surface of the planet
 huge canyon running along the equator for about 4000
km -about 1/5 the circumference
Vast dune fields:
North-south asymmetry:
o Northern Hemisphere: lava plains -> younger surface
o Southern Hemisphere: heavily cratered highlands -> older
surface
THE MAJOR FEATURE:
o Tharsis bulge
 size of North America, near equator
 rises 10 km above rest of surface
Impact cratering:
o wide spread cratering,
o eroded by the atmosphere
o appearance of craters (liquid splash) suggest permafrost
(water ice) just below the surface
 compare this to typical craters on the Moon, such as
Copernicus, shown here on the left
Running water in the past:
o the best evidence that water once existed in great quantities
on the surface is the channels
 runnoff channels:
 southern highlands
 4 billions years ago
 - thick atmosphere & surface water
 outflow channels:(another view)
near equator
 from south to north
 enormous flow rates> 100xAmazon
 about 3 billion years ago
o No water today on the surface
 a large amount of this water may now be locked in the
polar caps and under the surface (permafrost)
Polar Caps
o north and south
o primarily dry ice (CO2)
o seasonal variation
o temperature remains below 150K
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Mars' Magnetic Field and Internal Structure
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Mars' has a weak magnetic field
o => about 1/800 of Earth
o (but rotation period is similar to Earth 24.6 hours)
 so -> core is non-magnetic, or has no liquid, or both
planet probably never differentiated much
o - large abundance of surface iron
Moons of Mars
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Two very small moons:
o Phobos (fear) & Deimos (panic)
 Irregularly shaped and cratered
 Orbits at about 3 and 7 planetary radii
 (Earth's Moon orbits at about 60 radii)
 Both orbit synchronously
 tidally locked, like the Moon
 Both orbit prograde direction
 Large (Stickney) Crater on Phobos
Captured asteroids?
o
low density like typical asteroid
Martian Asteroids and the Evidence for Life on Mars
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About a dozen meteorites from the surface of Mars have been
found on Earth
o (identified by gases trapped in rocks)
1984 - scientists discovered a rock ( ALH84001) on Antarctic ice
field
1992 - detailed study of the rock - found (within a small region of
the rock)
1. organic molecules that might be associated with life
2. several minerals characteristic of biological activity
3. tiny tubular and egg-shaped structures resembling ancient
single-celled bacteria found on Earth
These observations were announced August 7, 1996
This evidence cannot be established as due to life forms
o The features could all have been produced by chemical
reactions without any involvement of life
o Could ALH84001 have been contaminated? (it sat on ice in
Antarctica for 13,000 years)
o More evidence is need to resolve this
NASA plans future visits to Mars to attempt to understand whether
life did or did not exist on Mars in the past
Jupiter
Giant of the Solar System
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Jupiter is the third brightest object in the night sky (after the Moon and
Venus)
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Differential rotation
o period of rotation at equator shorter than at higher latitudes
Equatorial bulge
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due to rapid rotation
Prominent visual features
o Bands: belts and zones
o Great Red Spot
o four prominent moons
 Discovered by Galileo in 1609
It takes over half an hour for light (or radio signals from a spacecraft) to get
from Jupiter to the Earth
Jupiter as a "failed star"
o If Jupiter's mass were 80 times larger, the gravitational collapse would
have ignited its hydrogen into thermonuclear fusion, creating a second
star in the Solar System
o
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Discovery of Jupiter
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Jupiter has been known of since ancient time since it is bright in the night
sky
Space Probes to Jupiter
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Pioneer 10 - (launched by USA, March 3, 1972)
o flew by Jupiter on December 1, 1973
o Carrying a gold, anodized plaque intended to communicate with
extraterrestrials
Pioneer 11 - (launched by USA, April 6, 1973)
o flew by Jupiter on December 1, 1974
o flew by Saturn in 1979
Voyager 1 - (launched by USA, September 5, 1977)
o Voyager 1 flew by Jupiter on March 5, 1979
o flew by Saturn on Nov 13, 1980
Voyager 2 - (launched by USA, August 20, 1977)
Voyager 2 flew by Jupiter on July 9, 1979
flew by Saturn on Aug 27, 1981
o flew by Uranus on Jan 30, 1986
o flew by Neptune on Aug 15, 1989
Galileo - (launched by USA and Europe, October 18, 1989)
o
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Galileo was designed to study Jupiter's atmosphere, satellites and
surrounding magnetosphere for 2 years.
o
o
o
o
During the journey, Galileo made encounters with asteroids
 Gaspra on October 29, 1991
 Ida and moon Dactyl on August 28, 1993.
During voyage, had direct view of the Comet ShoemakerLevy impacts on Jupiter (July, 1994)
Arrived at Jupiter, December, 1995
Significantly advanced our knowledge of the Galilean moons
Atmosphere of Jupiter
Elemental Makeup of Jupiter's Atmosphere
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86.1% molecular hydrogen (by number)
13.8% helium (by number)
traces of methane (CH4), ammonia (NH3), and water vapor (H2O)
little of the early atmosphere escaped due to the strong gravity (large
escape velocity)
Clouds: Bands and Spots caused by different chemistry vs. altitude
Zones and belts appear as we see different depths of the atmosphere
o
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Zones (light warm, rising regions)
Belts (dark ; cool, falling regions)
Zonal Flow
Great Red Spot
o
Large hurricane in the south
about 2 times the size of Earth
 at least 300 years old
revolves with inner region of Jupiter
rotates counterclockwise
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Other storm related features
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gigantic lightning flashes and Auroral activity
White ovals and Brown ovals
 persist for many years or decades
Rings of Jupiter
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Faint ring discovered by Voyager I
Main ring lies above cloud layer and inside orbit of innermost moon
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Galileo spacecraft has explored the ring, and concluded that the ring system
( main ring + gossamer rings) has been formed by the dust kicked up when
interplanetary meteoroids smash into the inner moons
Internal Structure and
Magnetosphere of Jupiter
Jupiter's Internal Structure
Emits twice as much energy as it receives from the Sun
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---> internal heat built up during Jupiter's formation is slowly
leaking out
 gravitational energy
Atmosphere gets denser and denser towards its interior
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gaseous hydrogen
liquid hydrogen
liquid metallic hydrogen (generates large magnetic field)
rocky core (about 5 times Earth's mass)
Jupiter's Magnetosphere
Intrinsic strength of magnetic field nearly 20,000 times Earth
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surface magnetic field 14 times Earth's surface field
field oriented opposite to Earth's
Very large magnetosphere
----> larger than size of the sun
Large sea of trapped, charged particles
----> like Van Allen Belts
Plasma torus (moon Io)
Moons of Jupiter
63 known moons
16 major moons of greater than 10 km diameter
Four sets of four or five moons each
Tidally locked
1.) Inner moons (inside Galilean) = 4 small moons
2.) Galilean moons ( 4 moons)
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discovered by Galileo in 1609
largest, similar in size to Earth's Moon
3., 4.) Outer moons ----> 2 sets of 4 known major moons
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Each set appears to have been a single body,
captured by Jupiter, then broken into 4 major sections each.
Orbital motion
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inner 3 sets are prograde
outer set is retrograde
Galilean Moons of Jupiter
orbits are prograde, circular, and lie in Jupiter's equatorial plane
all rotate synchronously (tidal lock)
Galileo spacecraft has been on a tour of discovery around the
Galilean moons
Io:
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Most geologically active object in Solar System
Voyager's observed erupting volcanoes
plasma torus produced by Io in Jupiter's magnetosphere
volcanoes caused by Jupiter's tidal forces + Europa's
influence
Europa:
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surface network of lines :
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cracks in ice cover?
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Ocean?
Ganymede:
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largest moon in Solar System (larger than Earth's Moon,
Mercury or Pluto)
---> largely ice
Callisto:
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cratering and concentric rings