16. Planetary Geology

PLANETARY GEOLOGY (Comparative Planetology) J.T. II Olivar, MAEd Faculty of Arts and Letters University of Santo Tomas

The planets: An overview  The solar system includes:

 Sun  Nine planets and their satellites  Asteroids  Comets  Meteoroids

The planets: An overview  A planet's orbit lies in an orbital plane

 Similar to a flat sheet of paper  The orbital planes of the planets are inclined  Orbital planes of seven planets lie within 3 degrees of the Sun's equator

Orbits of the planets

The planets: An overview  Two groups of planets occur in the solar

system:  Terrestrial (Earthlike) planets – Small, dense, rocky planets of Mercury, Venus, Earth, and Mars  Jovian (Jupiter-like) planets – Large, low density, gaseous planets of Jupiter, Saturn, Uranus, and Neptune  Pluto is not included in either group

The planets: An overview  Planets are composed of:

 Gases – mainly hydrogen and helium  Rocks – silicate minerals and metallic iron  Ices – ammonia, methane, carbon dioxide, and water

Origin and evolution of the planets  Nebular hypothesis

 Planets formed about 5 billion years ago  Solar system condensed from a gaseous nebula  As the planets formed, the material that compose them separated in a process called chemical differentiation

Origin and evolution of the planets  Due to their surface gravitations, Venus

and Earth retained atmospheric gases  Due to frigid temperatures, the Jovian planets contain a high percentage of ices

Earth’s moon  General characteristics

 Diameter of 2150 miles is unusually large compared to its parent planet  Density – about three times that of water  Gravity – one-sixth of Earth’s

Earth’s moon  Lunar surface

 Maria – darker lowlands covered by basaltic lava flows  Highlands – brighter more densely cratered regions  Craters are produced by meteoroid impacts

Major topographic features on the lunar surface

Formation of lunar maria

Earth’s moon  Lunar History

 Most widely accepted hypothesis suggests that a giant asteroid collided with Earth to produce the moon  One method used to work out lunar history is to observe crater density – Older areas have a higher density – Younger areas are still smooth

Earth’s moon  Lunar History

 Moon evolved in three phases – Original crust (highlands) around 4.5 billion years old (same age as Earth) – Formation of maria basins between 3.2 and 3.8 billion years ago – Formation of rayed craters (ejected material from craters is still visible)

The planets: a brief tour  Mercury:

the innermost planet  Second smallest  No atmosphere  Cratered highlands  Vast, smooth terrains that resemble maria  Very dense  Revolves quickly and rotates slowly

The planets: a brief tour  Venus:

the veiled planet  Second to the moon in brilliance  Similar to Earth in size, density, mass, and location in the solar system  Shrouded in thick clouds of carbon dioxide  Surface mapped by radar is mainly subdued plains covered by volcanic flows

Mons Olympus – a large, inactive shield volcano on Mars

The planets: a brief tour  Mars:

the red planet  Atmosphere of carbon dioxide is only 1 percent as dense as Earth’s  Surface of numerous large volcanoes and canyons  Tectonically dead  “Stream drainage” pattern found in some areas

The planets: a brief tour  Jupiter:

lord of the heavens  Largest planet  Rapid rotation – less than 10 hours  Banded appearance due to winds  Great Red Spot is a cyclonic storm  Surface is thought to be a vast ocean of liquid hydrogen  At least 16 moons

The planets: a brief tour  Saturn:

the elegant planet  Similar to Jupiter in atmosphere, composition, and internal structure  Most prominent feature are an extensive system of rings  Multiple moons – Titan is second largest in the solar system  Dynamic atmosphere with cyclonic storms

The ring system of Saturn

The planets: a brief tour  Uranus

 Uranus and Neptune are considered “twin” planets  Rotates “on its side”  System of rings  Large moons with quite varied terrains

The planets: a brief tour  Neptune

 Dynamic atmosphere – one of the windiest places in the solar system  Eight satellites  Triton, the largest of Neptune’s moons, exhibits retrograde motion, lowest surface temperatures in the solar system, and volcanic-like activity

The planets: a brief tour  Pluto

 Too dim to be visible with the unaided eye  Discovered in 1930  Highly elongated orbit causes it to occasionally travel inside the orbit of Neptune

Minor members of the solar system  Asteroids:

microplanets  Most lie between Mars and Jupiter  Small bodies – largest (Ceres) is about 620 miles in diameter  Some have very eccentric orbits  Many of the recent impacts on the Earth and Moon were asteroids  Origin is uncertain

The asteroid belt

Minor members of the solar system  Comets: dirty snowballs

 Composition of frozen gases with some rocky and metallic materials  Frozen gases vaporize to produce a glowing head when the comet is near the Sun  Origin is not well known  Most famous short-period comet is Halley’s comet

Minor members of the solar system  Meteoroids

 Called meteors when they enter Earth’s atmosphere  Referred to meteorites when they are found on Earth  Classified by composition – irons, stony, stony-irons, and carbonaceous chondrites  Give an idea as to the age of the solar system

Reference  Tarbuck

and Lutgens. 2001. Earth Science (9th edition). New Jersey: Prentice-Hall, Inc.