Transcript Solar System Formation, Earth, Mercury, and the Moon (Professor

The orbits of the planets - A clue to the formation of our Solar System
All planets orbit the sun in the same direction.
Most rotate in this direction too.
Characteristics of the Solar System
• Disk shape of solar system comes from the disk
shape of the nebula
• Revolution and rotation of sun and planets are in
pretty much the same direction because they all
formed from the same rotating gas cloud.
• Orbits of planets lie in a plane because the solar
nebula collapsed in a disk and the planets formed
in that disk.
• Strange orbits/rotations of Venus, and Uranus
were probably caused by a large collision of
planetesimals late in their formation.
Formation of Solar System
•The solar system is
believed to have
formed from a cloud of
gas and dust in a
process know as
accretion.
1. As it
collapses its
slight
rotation
increases,
due to
conservation
of angular
momentum.
As
thefaster
collapsing
cloud of dustforce
Spins
faster,
Spins
as it contracts.Centrifugal
pushes
matterit
outward, andand
a disk
forms.
contracts,
Centrifugal
force pushes matter
outward, and a disk forms.
2. Collapsing gas and dust heats through collisions
to around 3000 K, so everything is in gaseous
form. Hydrogen (about 89%) and Helium
(about 10%) make up most of nebula, silicates
and iron compounds about 1% .
Nebula cools
The Sun forms in center, and planets form in
outer disk. Outer parts cool off more than
the inner parts , since the temperature, and
density depends
upon the
distance from
proto-sun.
In the inner solar system, temperatures are hot (1600 K
near the central core). Only metal (iron, nickel) and rocks
(silicates) can survive in solid form.
Thus inner planets
and asteroids are
rocky.
In the outer solar system (beyond the asteroid belt),
it is cold enough for gases to condense into solid
ices (ammonia, methane, water, etc).
3.Gas molecules and dust grains are in circular
orbits. Those in noncircular orbits collide with
particles and eventually dampen noncircular
motion. Gravity tends to divide nebula into ringshaped zones and, later planets form.
•Planets will also differentiate later on: heavy metals
in core - lighter near surface
Forming Planetesimals by Accretion
• Materials moving in
the same rotating
orbit “rub shoulders”
with other materials.
• These materials
collide and stick
together forming
planetesimals,
which continue to
grow.
Growth of Protoplanets
•Terrestrial planets have very little H &
He because their low masses can’t keep
these gases from leaking into space.
•Jovian planets began as bits of rock and ice
that reached 15 Earth masses, and being so
massive allows them to capture hydrogen
and helium gas directly.
Clearing the Nebula
• (1) The solar wind, streaming particles from the
sun, pushes the small dust, and gas out of the
nebula.
• (2) The moons and planets are constantly getting
bombarded by meteorites. Heavy bombardment—
took place roughly 4 billion years ago.
• (3) Ejection of material from the solar system by
close encounters with planets
Icy planetesimals near Jupiter and Saturn were flung
just outside of out of solar system, while those near
Uranus and Neptune were flung to large orbits,
becoming the Oort Cloud .
Characteristics of the Solar System
• A planet did not form between Mars and
Jupiter in the asteroid belt area, due to the
planet Jupiter.
•Jupiter’s gravitational influence kept
disturbing the motions of the planetesimals,
breaking them up, and ejecting some from
the solar system , or toward the sun.
•Jovian worlds all have ring systems. Their
large mass makes it easy for them to hold
onto orbiting ring particles.
Characteristics of the Solar System
• The comets are just remains of the
icy planetesimals that Jupiter threw
out far into the solar system.
The Terrestrial Planets
Name
Dist (AU)
Radius
Earth =1
Mass
Earth =1
# of
Moons
Density
G/cm^3
Mercury
0.39
0.38
0.05
0
5.43
Venus
0.72
0.95
0.89
0
5.25
Earth
1.00
1.00
1.00
1
5.52
Mars
1.5
.53
0.11
2
3.95
Terrestrial Planets: Have few moons
Small and close to the Sun
Not very massive , but dense
They have rocky outer parts, and iron cores.
Planetary Configurations
All planets in the Solar System revolve around the Sun
in a counterclockwise direction when viewed from the
north pole of the celestial sphere.
As viewed from Earth, Mercury and Venus never get
very far from the Sun.
•The maximum elongation angle for Mercury is 28
degrees, and the maximum elongation angle for Venus is
45 degrees.
•Therefore Mercury and Venus are visible only either
shortly after sunset, evening star, or shortly before
sunrise, morning star.
Inferior Planets
Because they lie closer to the Sun than the Earth, Mercury
and Venus are called inferior planets.
•When the Mercury or
Venus is directly
between the Earth and
the Sun, we say it is at
inferior conjunction.
•When the Mercury or
Venus is directly
behind the Sun as
viewed from Earth, we
say it is at superior
conjunction.
Superior Planets
The planets lying outside the Earth's orbit and are called
superior planets. All of the superior planets can be visible
at any time of night.
When a superior
planet lies directly
behind the Sun, we
say it is at
conjunction.
When a superior
planet lies directly
opposite the Sun as
viewed from the
Earth, we say it is at
opposition.
The Earth
93 million miles (149,600,00 km)
from the sun.
Diameter - 7,926 miles ( 12,756 km).
Mass - 5.98 x 10^24 kg
Velocity of escape - 24,840 mi/hr.
Period of rotation - 23.93 hours
Year- 365.26 days to revolve around the Sun.
Axis tilt - 23.45 deg, causing the seasons.
Rotation speed - 1040 mi/hr (1670 km/hr)
at the equator
Temperature range - from -127 to 136 deg F.
Composition of the Atmosphere
The atmosphere is primarily
composed of Nitrogen (N2, 78%),
Oxygen (O2, 21%).
Other components present include, water (H2O,
"greenhouse" gases), Ozone , and Carbon Dioxide.
There is so much oxygen due to life and
photosynthesis. Atmosphere very thin < 100 km
The Earth’s atmosphere was formed by planetary
degassing, from the interior of the Earth by way of
volcanoes, and other life processes.
Layers of the Atmosphere
The atmosphere of the Earth may be divided into several
distinct layers, as the following figure indicates.
Reflection of radio waves
Weather takes place here
The Troposphere : Lowest level where
our weather takes place.
The Stratosphere and Ozone Layer
The thin ozone layer in the upper
stratosphere has a high concentration of
ozone.
This layer is primarily responsible for
absorbing the ultraviolet radiation from the
Sun, and prevents an intense ultraviolet
radiation from reaching the surface, where it
is quite hazardous to the evolution of life.
The Ionosphere
The ionosphere is very thin, but it is where
aurora take place, and is also responsible
for absorbing the most energetic photons
from the Sun, and for reflecting radio waves,
thereby making long-distance radio
communication possible.
The greenhouse effect traps heat in our
atmosphere.The atmosphere lets some infrared
radiation escape into space; some is reflected
back to the planet.
Differentiation



When the entire earth was molten, the heavy
elements (iron, nickel) sank to the interior.
The lighter materials (granite-type rocks) rose to
the surface.
The medium density rocks (basalt-type) wound
up in the middle.
Plate Tectonics
The Earth’s crust is composed of huge moving
plates of rock, that float on a soft churning layer.
Earthquakes, mountains, volcanoes, occur at
plate boundaries.
•The Appalachian Mountains were formed from wrinkling of the Earth's surface
produced by the collision of the North American and African plates.
Solid Inner Core Interior
2400 km diameter
Iron & Nickel
Mantle
2900 km thick
Basaltic rocks
Structure
Liquid Outer Core
2270 km thick
Iron & Nickel
Crust
20-100 km thick
Granitic rocks
Inner Core (kept solid by the immense pressure of all the
material on top of it.)
Outer Core (less pressure allows it to be a liquid.)
The Earth's magnetic field and Van Allen radiation belts
The Earth has a magnet in the center, much like a bar
magnet.(dipole) The molten interior, and rotation sustains the
field. The poles reverse about every 300,000 years.
The inner and outer Van Allen belts.The primary source of
charged particles is the stream of particles emanating from
the Sun that we call the solar wind.
The belts surrounding the Earth are called the
magnetosphere, and they largely prevents the solar wind
from entering.
The Planet Mercury
MASS: 0.055 (Earth=1)
•DENSITY: 5.43 (g/cm^3)
•GRAVITY: 0.376 (Earth=1)
•ORBIT PERIOD: 87.97 (Earth days)
• solar ROTATION PERIOD: 176 (Earth days )
88 consecutive days each of sunshine, and darkness.
Mantle – basalt, but
not as thick as
moon.
Crust – anorthosite,
like the moon
Most iron-rich
planet in the
solar system.

Very elliptical orbit – more than any other planet except
Pluto 46 to 70 million km distances from sun
Temps: +800oF to –280oF. More variation than any other
planet ! Some water in deep polar craters that are always in
shadow. Detected by Arecibo RT

Difficult to study, because it is always near the sun. Sets
or rises within 1 to 2 hours of the sun.
Transits occur about twelve times a century when the sun, Earth
and Mercury are aligned
Maria are concentrated on the near side of the
Moon.
•Heavily cratered surface Less dense cratering than moon
•Gently rolling plains, Scarps & no evidence of tectonics
Mercury’s
Surface
LOTS of craters
•Smoother regions
are likely ancient
lava flows
Features much
like the Moon
Basic Moon Facts
Property
Value
Diameter
3,470 km (2,160 mi)
Surface Gravity
0.17 (1/6 of Earth’s)
Density
3.34 gm/cm3 (0.6 of Earth)
Sidereal Rotation 27.3 days Phases 29.5 days
Orbital Eccentricity 0.055
Orbital Inclination
5.15o
Distance from Earth 3.84 x 105 km (240,000 mi)
Temperature Range 120-390 K (-240 to +240 oF)
Atmosphere
Almost a Vacuum (Ar gas)
No global magnetic field
Only world visited by humans
The Moon’s surface was shaped by heavy
bombardment followed by lava floods
4.5-3.8 billion years ago: Heavy
bombardment by planetesimals, cratering
of highlands.
3.8-3.1 billion years ago: Lava flows up
through cracks, flooding low-lying maria
with basalt.
3.1 billion years ago-NOW: No more lava
flows, decreasing bombardment.
The Structure of the Moon’s Interior
A crust about 65 km thick,
A mantle about 1000 km thick, and
A core that is about 500 km in radius.
The outer core may be molten.
It has no magnetic field to speak of due
to little iron and slow rotation.
Composition of the Moon similar
to the Earth’s Mantle, very little
metal (iron, nickel), mainly rock
Thicker crust on the far side explains why
there are almost no maria on the far side
Lunar surface features
 Craters
 Highlands
 Maria
 Wrinkle
ridges
 Rilles
 Weathering
& Erosion Processes
It’s the expanding vapor, not the impact,
that forms the crater. That’s why craters
are round, even if the meteorite impacts
from a low angle.
Older craters have poorly defined walls with lots of
slumping.
Recent craters have sharp walls with little slumping
inside.
Some craters have rays, or a blanket of
material thrown out by the impact.
The impact digs through to a deeper, lightercolored layer.
Over time, ultraviolet light from the sun darkens the
rays. So, craters with bight rays must be very
young.
Maria: Old lava fields
created by large
meteorite impacts
•Appear:
–charcoal black
Highlands:
•Surface of the Moon elevated
several kilometers above the
Maria
•Appear:
–smooth
–relatively light-colored
–few craters
–cratered
Craters:
•Bowl shaped depression
created from impacts with
interplanetary debris
Crater rims are raised above the
surroundings.
Rebound of the rock under the impact can
form a central peak in larger craters. Over
time, the crater walls can slump, creating
terraces.
Lunar Highlands

The highlands are more heavily cratered
than the other lower regions of the moon.
This indicate, according to the “law of
cratering”, that the highlands are older than
the lower, smoother regions. They were
formed 4.6 – 3.8 billion years ago.
Rocks of the highlands are made of Anorthosite, a
close relative of granite
The lunar maria are just bigger craters,
formed like any other, but they have one
important difference.
The impacts that formed them were large
enough to punch cracks all the way to the
moon’s still-molten core.
Over
time, runny, dark, molten lava moved up
through the cracks to fill in the floors of the
crater basins, giving a smooth, dark surface.
Mare – singular
Maria - plural
No plate tectonics,but mountains form at the edges
of the Maria.
As the basalt cooled in the maria basins, it becomes skinned
over and then contracted, forming Wrinkle Ridges.
Rilles look remarkably like dry river beds. They are found
on the maria, by a flowing material, but it wasn’t water – it
was lava.
Erosion on the moon
Erosion does occur on the moon, but
there’s no running water.
Two things contribute to erosion
on the Moon:
(1) The drastic changes in temperature,
and meteorite impacts.
(2) The hot – cold cycle causes rocks
to break into smaller pieces, and
can even cause slopes (crater walls)
to slowly slump downhill.
Main lunar materials
• Highlands
– Anorthosite )
• Dark maria
– Basalt (Lava rocks)
• Others
– impact breccia -made from
smashed/melted remains of other rocks
– Regolith -pulverized lunar dirt
Impacts are still continuing today, but most are
micro-meteorites.
Meteorite impacts fracture rocks into lunar
soil, a fine powder that builds up at the rate
of about 1 meter depth / billion years.
The Moon’s Regolith, or
surface layer of powdered
and fractured rock, was
formed by meteoritic
action.
Impacts also melted larger rock fragments
together, forming very rough rocks called
“Breccias”
Lunar Rocks - Highlands
The light colored rock in the lunar highlands
are called anorthosite; rich in aluminum
and calcium. (similar to Granite)
Lunar Rocks
The maria were formed from molten rock,
mostly of the same minerals that are found in
volcanic rocks in Hawaii. This rock is called
basalt.
Basalt has more of the
heavier elements like iron,
manganese, and titanium.
Basalt
Timing of Activity on the Moon
•
•
•
•
Formation: 4.5 billion years
Heavy Cratering: 4.5 – 4.0 billion years
Mare Volcanism: 3.7 – 3.0 billion years
Later small craters:continually decreasing
Origin of the Moon
The most probable :
A planetary body about the size of Mars collided
with the young Earth, and the ejected matter
coalesced into the Moon.
Apparent motion: The Moon’s orbit:
• The Moon takes about 27 days to go once
around the Earth.
• Because of the Earth’s movement in its
orbit, the Moon takes 29.5 days to get back
to the same place relative to the Sun.
Apollo Missions to the Moon (1969-1972)
Brought back 382 kg of rocks for chemical
analysis, radioactive dating.
Tidal Effects
Tidal effects are an important aspect of gravity, the
Moon pulls on the Earth - The Earth pulls on the Moon.
The Moon’s pull causes tides (bulging of the ocean).
The Earth’s pull slows
the rotation of the
Moon (Tidally locked)
and the Moon’s pull
slows the rotation of the
Earth (by about 0.7 seconds/year).
The Earth’s pull is also slowing down the Moon.
Spring Tides:
Sun, Moon in
same alignment
magnify effect
The greatest tides
occur at New and
Full Moons
Neap Tides:
Sun, Moon in
opposite
alignment
diminish effect
The lesser tides
occur at First and
Last Quarter
Spring Tides
Neap Tides