Download Chapter 6 - Formation of the Solar System

This Week in Astronomy
HUGE NEWS – Discovery of Gravitational Waves!
Washington site
Louisiana site
Laser Interferometer
Gravitational-Wave
Observatory (LIGO)
This Week in Astronomy
HUGE NEWS – Discovery of Gravitational Waves!
E = mc2
Washington site
Louisiana site
Energy released as
gravitational waves
equal to mass-energy
of 3 solar masses
(about 1031 kg)
Recall: Converting
0.1 kg to energy
gives you this:
Exam #1
Average: 68.2%
Scores available on Blackboard
High: 100%
Exam #1 likely
to be most
difficult exam.
You can see
your exam by
visiting office
hours.
Exam #1
A hot solid (like a piece of metal or rock) gives off a light
spectrum like… – see images below – A, B, C from top
to bottom:
Blackbody (thermal)
radiation
Moon Myths
The Moon does not rotate.
- Wrong! The Moon rotates once every month (29.5 days).
The unseen far side of the Moon is always dark.
- Wrong! Far side of the Moon gets as much sunlight as the
side facing us over the course of a month.
You can’t see the Moon during the day.
- Wrong! The Moon is often up during the day.
The Moon phases are caused by the Earth’s shadow.
- Wrong! No phase is caused by Earth’s shadow. The phases
are caused by different illuminations of the side of the Moon
facing Earth.
Phases of the Moon
 Half of Moon is
illuminated by Sun and
half is dark at all
times.
 The phase of the Moon
depends on what
fraction of the lit half is
visible from Earth.
 There is no “dark side
of the Moon” – this is a
misnomer
 There is a “back side of
the Moon” which never
faces Earth
Earth’s shadow does not cause Moon phases!
Movement of Sun
It takes the Sun ~30 days to move through one zodiac
constellation. But all stars plus Sun rise and set each day
because of Earth’s rotation. STARS ARE NOT “FIXED” IN
THE NIGHT SKY!
The angular momentum of a planet around the Sun
A) is greatest when the planet is nearest the Sun.
B) is greatest when the planet is farthest from the Sun.
C) is always the same regardless of where the
planet is in its orbit.
D) is proportional to the square of the period of the
planet around the Sun.
Angular momentum (m *v *r) is conserved
 it is always a constant value
Chapter 6
Formation of the Solar System
Comparative Planetology
•
We can learn more about a world like our
Earth by studying it in context with other
worlds in the solar system.
•
Stay focused on processes common to
multiple worlds instead of individual facts or
trivia specific to a particular world.
•
In general, we want to answer the question
“why” rather than “how many” or “how far”.
There currently are eight major planets (sorry,
Pluto, Planet 9) with nearly circular orbits
orbiting the Sun in the same direction.
Pluto and Eris and other “dwarf planets” are
smaller than the major planets and have more
elliptical orbits.
What are the major features
of the Sun and planets?
Sun and planet sizes to scale, but distances are not
Planets are very
tiny compared to
distances between
them.
Again, the Sun is
the size of a
grapefruit.
Jupiter is the size of a marble, Earth is the tip of a ball-point pen
Sun
• Over 99.9% of solar system’s mass
• Made mostly of hydrogen/helium gas + 1% heavier elements
• Converts 4 million tons of mass into energy each second via
E = mc2 by the fusion process
Radius of Sun = 109 REarth = ~2 Earth-Moon
The Terrestrial (Rocky/Metal) Planets
Mercury
Venus
Earth
Mars
Mercury
• Made of metal and rock; large iron core
• Desolate, cratered; long, tall, steep cliffs
• Extremely tenuous, almost non-existent atmosphere
Largest day/night swing in temperature in the Solar System : 520 K
Surface
similar in
appearance
to Earth’s
Moon.
Venus
• Nearly identical in size to Earth; surface hidden by clouds
• Hellish conditions due to an extreme greenhouse effect
• Even hotter than Mercury: 733 K, day and night
A Venusian day lasts longer than a Venusian year!
Rotation speed only 6.5 km/hr – a moderate walking pace
Actual view of Venus’s surface by Soviet lander Venera 13
before it was crushed after 127 minutes by the 89 Earth
atmosphere pressure.
Thunder and lightning was detected.
Earth
• An oasis of life
Earth and Moon with
sizes shown to scale
(Moon about ¼
diameter of Earth)
• The only surface liquid water in the solar system
• A surprisingly large moon
Mars
• Looks almost Earth-like on surface, but thinner atmosphere.
• Giant volcanoes, a huge canyon, polar caps, more
• Water flowed in distant past; could there have been life?
More comfortable than Tuscaloosa in summer, not so nice in
Mount Olympus – 3 times higher than Mt. Everest, 600 km across.
The largest volcano known in the Solar System.
Viking - 1977
Mars Global Surveyor - 2001
Viking - 1977
Galle crater on Mars
Moons of Mars gravitationally locked in a 1:1 resonance
Densities 1.76 g/cm3 and 1.9 g/cm3, like asteroids – captured?
A view from Viking 1
A view from Pathfinder
Sunset on Mars
Which of the following is not a common
characteristic of the terrestrial planets?
A) they have few/no Moons
B) they have similar composition as the Sun
C) they all orbit in the same direction around
the Sun
D) they all have nearly circular orbits
Which of the following is not a common
characteristic of the terrestrial planets?
A) they have few/no Moons
B) they have similar composition as the Sun
C) they all orbit in the same direction around
the Sun
D) they all have nearly circular orbits
Sun is 99% hydrogen/helium, planets made nearly all of heavier
elements (C, O, Si, Fe, etc.)
The Gas Giant (Jovian) Planets
Jupiter
Saturn
Uranus
Neptune
Jupiter
• Much farther
from Sun than
inner planets
• Mostly
hydrogen/heli
um; no solid
surface
• 300 times
more massive
than Earth
• Many moons,
rings
Much less dense than inner rocky planets (because it is mostly gas).
Jupiter harbors many moons, including four large
“Galilean” moons shown here.
Saturn
• Giant and gaseous like Jupiter
• Spectacular rings
• Many moons, including cloudy Titan
Only 2/3 as dense as water!
Rings are
NOT solid;
they are
made of
countless
small chunks
of ice and
rock, each
orbiting like a
tiny moon.
Artist’s conception
Uranus
• Smaller than
Jupiter/Saturn; much
larger than Earth
• Made of H/He gas
and hydrogen
compounds
(molecules - H2O,
NH3, CH4)
• Extreme axis tilt
• Many moons and a
faint ring system
• Excess methane
gives bluish color
Uranus spins on its side – rotational axis points toward Sun
~42 years of continuous daylight followed by
~42 years of continuous night at the poles.
Neptune
• Similar to
Uranus (except
for axis tilt)
• Many moons
(including
Triton) and a
faint ring system
How do gas giant (Jovian) planets differ
from the terrestrial (rocky/metal) planets?
A) gas giants have many moons
B) gas giants are made mostly of H/He
and hydrogen compounds
C) gas giants have rings
D) all of the above
How do gas giant (Jovian) planets differ
from the terrestrial (rocky/metal) planets?
A) gas giants have many moons
B) gas giants are made mostly of H/He
and hydrogen compounds
C) gas giants have rings
D) all of the above