Topic 25:  Evolution of the Solar System

Space Missions:

Apollo  -  Man to the Earth's Moon (six landings from 
1969 to 1972).  The last mission, Apollo 17, included geologist 
Harrison Schmitt as part of the two-man crew to land at 
Taurus Littrow.

Magellan  -  Radar mapping of the surface of Venus 
(launched 1989)

Mariner  -  Photographing of the surface of Mars (orbits 1971).  
Includes photographic missions to Venus and Mercury.

Pioneer  -  Geophysical measurements of Jupiter and Saturn  
(1973-1979)

Venera (USSR)  -  Landing of unmanned missions on Venus 
(1961 to 1983)

Viking  -  Landing of an unmanned mission on Mars (1976).

Voyager  -  Photographs the outer solar system;  discovers 
27 new satellites around the four planets of the outer solar 
system (1979 to 1989).


Rocky Planets  -  Diverse atmospheres cover terrestrial planets. 
 Shells of silicates overlay inner metallic cores.

Mercury - The surface of Mercury and the Earth's Moon have 
very similar, old crusts displaying a nearly complete record 
of impacts over more than 4 billion years.  Caloris Basin is a 
ringed impact of an asteroid 4 billion years ago.  No satellites. 

Venus - An atmosphere so thick that its surface can only be mapped 
by radar.  The surface contains abundant evidence for volcanoes 
such as Fula Mons which is 1.8 miles high.

Earth - To be described in the next 28 lectures of GSC 20.

Moon - Same age as the earth (4.6 billion years). The moon's crust, 
a vast panorama of craters, fractures, and lava flows, is four times 
thicker than earth's. Vast mare areas, composed of dark basalts, 
smudge the familiar near side of the moon.  Brighter highlands 
dominate the far wide, where a suspected thicker crust may have 
checked the flow of mare material to the surface.  Interior heat 
from radioactivity causes partial melting, and basaltic material 
rises along fractures, filling the basin layer by layer to form a mare.

Mars - Shows polar ice caps, large volcanoes (Olympus Mons sours 
15 miles above its plane, has a base 335 miles across, and a 45 
mile wide caldera), rift canyons extending the length of the United 
States (Valles Marineris is 150 miles wide and 4 miles deep), 
shifting sand dunes and other indications of wind erosion, and river 
canyons cut by torrential rains which occur when vast amounts of 
water are not tied up in polar ice caps.

Giant Planets - Emitting more energy than they receive from the 
sun, the gas giants are actually composed of much the same material 
as the sun.  Together they account for more than 90% of the mass 
of the solar system.

Jupiter - Cloudy with high-pressure storms lasting years to centuries.  
Internal heat drives the turbulence.  Jupiter's cloud cover consists 
of three layers: ammonia crystals over ammonium hydrosulfide over 
ice crystals.  Below the atmosphere is a sea of liquid hydrogen and 
helium.

Io - Youngest surface in the solar system.  Erupts continually heated
 by gravitational tugs from Jupiter and Europa.  Displays three types 
of plumes based on interactions between its molten silicate interior, 
sulfurous mantle, and hard sulfur crust.

Europa -  Has one of the smoothest surfaces in the solar system - most 
likely a thin ice crust over a global ocean of water kept warmer 
by the insulating effect of the icy crust.  Streaks that paint the 
surface were probably fissures in the surface ice that were filled 
by upwelling water or soft ice.  Their patterns suggest that at one 
time Europa's ice crust was expanding and cracking on a grand scale.  
Only a few impact craters mar the moon's surface, indicating it is 
relatively young.

Ganymede - Largest moon of solar system. Fresh white ice was 
ejected by most recent meteorite impacts.  Sinuous strips of 
alternating parallel grooves and ridges indicate crustal movement 
millions of years ago.  Crustal faulting and movement reworked the 
surface to leave only the most recent impact craters.

Callisto - Concentric ridges were heaved up by the collision of a huge 
meteorite.  The impact basin has been filled in by ice, and, though later
 battered by smaller meteorites, is nearly level.  Callisto shows a 
nearly complete record of impacts.

Saturn -  Saturn's atmosphere is like Jupiter's but less dynamic 
because it is further from the sun and, hence, colder.  The rings of 
Saturn are 65,000 miles across and as few as ten meters thick

Mimas - Ammonia condenses with water.  The ice of Mimas is nearly 
as rigid as granite and reacts similarly when struck.

Enceladus - Ices oozed through fissures.

Titan - Main gases are nitrogen and methane with methane in three 
phases.

Icy Planets  -  Have cores equal to the closer-in giants but have 
much smaller accretions of gas.  Huge mantles of water, methane, 
and ammonia probably underlay their dense atmospheres.

Uranus -  Hides its atmospheric features beneath a deep layer of 
hydrogen.  Very bland surface.  Unlike Jupiter, Saturn, and Nepture, 
it has no severe turbulence beyond local thrunderheads.

Miranda - A complex terrain which may have been repeatedly shattered 
by collisions and reassembled by gravity.  Ammonia and water ices, 
erupting as lava does on Earth, could have partly smoothed the surface.  
Has ice cliffs higher than the Earth's Grand Canyon.

Neptune - Orbiting in a deep freeze within 60¡C of absolute zero, 
Nepture unleashes winds that may be the fastest in the solar 
system.  Storms form as convection shoots hydrocarbon gases up 
into colder regions where they condense into bright ices.  

Triton - Largest moon of Neptune