Inner Planets (Part I) 1)Science 2)Intro to Inner Planets 3)Four Main Processes 4)Planetary...
-
Upload
abraham-morton -
Category
Documents
-
view
215 -
download
0
Transcript of Inner Planets (Part I) 1)Science 2)Intro to Inner Planets 3)Four Main Processes 4)Planetary...
Inner Planets (Part I)
1) Science2) Intro to Inner Planets3) Four Main Processes4) Planetary Comparisons5) Intro to Atmospheres
Sept. 16, 2002
Announcements
If you are not here today due to Yom Kippur, there will be an opportunity to make up today’s quiz after class on Weds.
An extra credit problem will be available on the course web site tonight or tomorrow morning. It is due Thurs. Sep 19 at 5pm
Review
Pieces of the Solar System Sun (in a few weeks) inner planets (this week) outer planets (next week) other stuff (following week)
Angular momentum angular momentum is conserved
Solar System formation accretion disk, rotation, protostar planetesimals solar wind
Fact vs. Theory Facts are data which has been measured
e.g. the Sun rose this morning Theory is a model which describes/explains
data or predicts future events e.g. the Sun will set tonight a thrown baseball will follow an arc because of gravity and Newton’s Laws the Earth
revolves around the Sun and will continue to do so
It is impossible to prove a theory even Newton’s Laws are a theory
It IS possible to disprove a theory when facts do not agree with the model
Examples Fact: All major (currently observed)
planets/moons/asteroids are revolving around the Earth in the same direction and in a similar plane Theory: The Solar System was created from
a revolving sphere of gas and dust Facts: The inner planets are composed
primarily from refractory materials while the outer planets are mostly volatile materials Theory: The inner region was hotter and the
volatile materials did not survive there, but did in the outer region, this contributed to the planets’ formations
NASA Solar System Missions Flyby missions - satellite to pass by another object
quick look, but cheap examples: Voyager, Mariner, Pioneer, …
Orbiters - satellite in orbit around a planet or moon more detailed studies, but not “hands-on” examples: Galileo, Clementine, Magellan, …
Landers - lander on the surface of a planet or moon get rock samples and direct data, limited area can be
covered examples: Viking, Mars Surveyor, Mars Odyssey, …
Manned missions - humans on the surface of a planet or moon
can do advanced, complicated studies/experiments, but very expensive
examples: Apollo 11 through Apollo 17
Differentiation During planetary formation, the rocks
and planetesimals compress together due to gravity energy is converted into heat material melts and becomes fluid
Differentiation is the process of the heavier materials sinking towards the center of the planet while lighter materials rise to the outer edges materials become separated by type
Outer surface of planet cools fastest and hardens
Planet Interiors Layered
solid inner core liquid outer core solid outer mantle/crust
Hotter inside, cooler outside planet radiates heat into space outer crust cooled and hardened center is hottest and has highest pressure
Melting point depends on temperature and pressure in the center, pressure wins and material is solid farther out, temperature wins and material is
liquid outer edge, both lose and material is solid
Planet Interiors (cont)
The inner planets have similar structure although we don’t have a lot of data on
other planets Data on Earth’s interior comes from
seismic readings of earthquakes
Four Main Processes These processes shape the surfaces of
planets1) Tectonism
movement of pieces of the planet’s crust (plates)
2) Volcanism flow of material (lava) from beneath the
planet’s crust
3) Impact Cratering meteors hitting a planet’s surface
4) Gradation erosion of the surface
The first 3 processes build up structure on the surface (mountains, valleys, etc)
The last process wears the surface down
Tectonics
Major movements of the planets crust create mountain ranges, deep valleys on Earth: tectonic plates rub against each
other other planets: not plates, but major
cracking/shifting (fractures)
Interior Heating Radiative cooling alone should have cooled
the Earth’s interior more than observed Friction adds some of the heat
tidal forces due to the gravitational pull of the Moon and Sun cause pieces of the interior to rub together
this rubbing generates heat (just like rubbing your hands together)
Radioactive decays add most of the heat The interior temperature is a balance
between original heat, radiative cooling and additional heat
As the radioactive material disappears, the Earth’s interior will cool
Volcanism
Fissures in the planet’s crust can allow hot mantle to flow to the top (lava)
the mantle is solid, but after relieving the pressure from the crust, it can turn liquid
Long fissures cause shield volcanoes (large, long mounds of cooled lava) to form over long time periods
Local “holes” can form mounds on Earth, plate movement limits the size and can result
in a chain of islands Large flows of more fluid lava can create great
plains of lava e.g. Lunar mares (seas)
Amount of volcanic activity indicates how active a planet is
Comparative Volcanism Moon
mares are volcanic in nature and indicate the Moon once had a lot of lava flow
Mercury some visual indications of lava flow, not
enough known Mars
largest mountains in the Solar System (up to 25 km high) caused by volcanism
Venus evidence of a lot of complex volcanic activity
Earth lots of current and previous volcanic activity
(Pompeii, Hawaiian Islands, Mt. St. Helen’s)
Impact Cratering The number of collisions between objects
depends on how many objects there are Early in the Solar System there were many more
small planetesimals: more collisions Number of craters can be used to “date” a planet
Craters can be erased by tectonism, volcanism and gradation
occurs on “active” planets (e.g. Earth)
on “dead” planets, craters remain (e.g. Moon)
Formation: heats and compresses material thrown outward surface rebounds
Comparative Cratering Moon
lots of craters in all sizes Mars
craters with impact craters which indicate there might have been water on Mars once
Venus dense atmosphere protects Venus
Earth protected by atmosphere (many meteors
burn up) large oceans leave no impact crater most craters erased by gradation
Moon from the Earth
Theory: the Moon comes from the Earth Mars size protoplanet hit Earth early in its
history this impact showered large amounts of
material into Earth orbit volatile materials were lost remaining materials condensed to form the
Moon Facts which are explained:
Moon composed of same materials as Earth (moon rocks)
Moon has no significant volatile materials (water, air)
Moon is large fraction of Earth’s size
Surface leveling caused by blowing wind, flowing water and
water/ice freezing/melting Moon & Mercury
no atmosphere, possible ice, little gradation Mars
large dust storms observed, evidence of water flow
Venus evidence of blowing wind, no evidence of water
Earth all processes present e.g. dust/wind storms, rain, tides, glacier flow
Gradation
Magnetic field Inner planets all have some magnetic field This magnetic field is not caused only by
magnetized materials At least partially caused by rotation of Earth
spinning electric charges in core create magnetic field
Facts: Earth has a strong magnetic field Earth’s magnetic field moves with time (magnetic
north pole not the same as celestial north pole) the Moon has no or very small magnetic field Mercury has strong magnetic field Venus and Mars have small magnetic field
Gases – Some Basics Lighter gases rise
This is really because heavier gases sink and push the lighter gases upward
Temperature of a gas is really the speed of the molecules Faster gases are hotter
Sunlight and heat from a planet’s interior provide energy to heat atmospheres Sunlight can also break up molecules
Fast atoms/molecules in the outer atmosphere can escape the planet’s gravitational pull
Planets have a hard time hanging onto hydrogen and helium
Primary Atmosphere
A planet’s original atmosphere comes from the gas of the accretion disk It is composed mainly of hydrogen and helium
same stuff the Sun is made of
If a planet’s gravity isn’t strong enough, it can’t hold onto these light gases They escape and leave the planet without an
atmosphere Heating and solar wind help these processes
This happened to the inner planets We will see later it did not happen to the gas
giants