Download Four Unexplained Features of our Solar System

Four Unexplained Features
of our Solar System
√ Why do large bodies in our solar system have
orderly motions?
--> 2) Why are there two types of planets?
3) Where did the comets and asteroids come
from?
4) How can we explain the exceptions the the ‘rules’
above?
Why are there two types of planet, when all
planets formed from the same nebula?
As gravity causes
cloud to contract,
it heats up
(Conservation of
energy)
Inner parts of
disk are hotter
than outer parts.
Rock can be
solid at much
higher
temperatures
than ice.
Fig 9.5
Inside the frost line: too hot for hydrogen compounds to form ices.
Outside the frost line: cold enough for ices to form.
Tiny solid
particles stick to
form
planetesimals.
Gravity draws
planetesimals
together to form
planets
This process of
assembly
is called
accretion
Gravity of rock
and ice in jovian
planets draws in
H and He gases
Moons of jovian planets form in miniature disks
Why are there two types of
planets?
1.
2.
Outer planets get bigger because abundant
hydrogen compounds condense to form
ICES.
Outer planets accrete and keep H & He in
the gaseous phase.
Four Unexplained Features
of our Solar System
√ Why do large bodies in our solar system have
orderly motions?
√ Why are there two types of planets?
--> 3) Where did the comets and asteroids
come from?
4) How can we explain the exceptions the the ‘rules’
above?
Comets and asteroids are
leftover planetesimals.
• Asteroids are rocky because
they formed inside the frostline.
• Comets are icy because they
formed outside the frostline
Four Unexplained Features
of our Solar System
√ Why do large bodies in our solar system have
orderly motions?
√ Why are there two types of planets?
√ Where did the comets and asteroids come
from?
--> 4) How do we explain the existence of our
Moon and other “exceptions to the rules”?
Earth’s moon was
probably created when
a big planetesimal
slammed into the newly
forming Earth.
Other large impacts
may be responsible for
other exceptions like
rotation of Venus and
Uranus
luna320x240s.mpg
Review of
nebular theory
The Inner Planets
Terrestrial Planet Surfaces
How do they compare to one another?
Comparison of Planetary Surfaces
•
Mercury (& the Moon)
•
•
•
Venus
•
•
volcanoes and bizarre bulges
Mars
•
•
•
heavily cratered {scars from the heavy bombardment}
some volcanic plains
volcanoes and canyons
apparently dry riverbeds {evidence for running water?}
Earth
•
all of the above plus liquid water and life
Inside the Terrestrial Worlds
•
After they have formed, the molten planets
differentiate into three zones:
core - made of metals
• mantle - made of dense rock
• crust - made of less dense rock
Lithosphere - the rigid, outer layer of crust & part
of the mantle which does not deform easily
•
•
Inside the Terrestrial Worlds
Magnetic Fields
•
Electric charges moving via convection in a
molten iron core and spinning acts like an
electromagnet
magnetic field
•
•
•
Earth has a magnetic field
Venus, Mars, & the Moon do not
Mercury surprisingly has a weak magnetic field ??
Mercury’s temperature range is the most
extreme in the solar system
•
•
•
•
Daytime with the Sun overhead reaches 700K (or
800°F)
Midnight with the Sun completely obscured is 100K (or
-280°F)
Earth typically has temperature differences between
day and night of about 11K (or 20°F)
Mercury’s slow 176 day rotation and the lack of an
appreciable atmosphere means temperatures vary
enormously from one side of the planet to the other.
Why is there no atmosphere on Mercury?
Homework #5
What is the average speed of hydrogen atoms
(m=1.67x10-27 kg) in the Sun’s photosphere (T = 5800
K)?
8kT
8(1.38 10−23 )(5800)
v=
[m/s] =
π m
(3.14159)(1.67 10−27 )
11, 000 [m/s]
What is the escape velocity from Mercury?
vesc
2GM Mercury
RMercury
4,300 [m/s]
[m/s]
2(6.67 10 11[m 3 /kg s 2 ])(3.30 10 23 [kg])
2.4 10 6 [m]
Average speed of particles in a gas on Mercury:
8(1.38 10 23 )(700)
3.14159(1.67 10 27 )
4300
Number of
particles
v
8kT
[m/s]
m
Speed of
particles
3,840 [m/s]
The surface of
Venus is
completely
hidden beneath
permanent
cloud cover
Venus
•
•
Atmosphere is 96% CO2
Temperature is 750K
–
–
–
much higher than Mercury
daytime AND nightime
caused by the greenhouse effect
The greenhouse effect heats Venus’s
surface
Venus is covered with gently rolling hills,
two “continents,” and numerous volcanoes
Venus
Searing heat, heavy pressure, clouds of sulfuric acid,
frequent volcanic eruptions; as Carl Sagan said:
Venus is the planet most like hell!
Mars as viewed
from Earth
Canals on Mars!
October 30th, 1938:is known as "mischief
night." Thirty-two million people were
relaxing that evening listening to their
favorite shows.
Suddenly the broadcast was interrupted
by a series of news bulletins: A large
meteor had impacted in New Jersey near
Grover's Mill. The object turned out not to
be a meteor, but a metal cylinder. The
cylinder opened and Martians, driving
huge fighting machines, emerged. They
were advancing upon New York City.
Within thirty minutes the voice of a radio
reporter, supposedly covering the event
from a window in Manhattan, told of a gas
attack on the city.
Then the reporter stopped talking. There
was silence for a few seconds. Then the
plaintive cry of a ham radio operator:
Isn't there anyone on the air? Isn't there
anyone?
Many people panicked.
Like Earth,
Mars has
polar ice caps
that grow
and shrink
with the
changing
seasons.
They are
water ice and
solid CO2
Enormous
shield
volcanoes
Valles Marineris is many times larger than the Grand Canyon
Olympus Mons - the largest volcano in the solar
system has a base larger than the state of Colorado
Early space probes to Mars
found no canals but did find
some controversial features
Surface features indicate that
water once flowed on Mars
Ohio
River
valley
on
Earth
River
channels
on Mars
The Martian meteorite
found in Antarctica has not
provided conclusive
evidence about life on
Mars
Mars’ two moons, Phobos and Deimos,
look more like potatoes than spheres
Earth
•
•
most active geology
volcanoes & tectonics
•
•
moderate atmosphere
N2 O2 H2O
H2O exists in liquid state
• rampant erosion
• few craters
life
•
•
•
ongoing plate tectonics
What have we learned?
•
What four characteristics of our Solar System must be
explained by a formation theory?
•
•
What is the basic idea behind the nebular theory?
•
•
Patterns of motion, why there are terrestrial and Jovian planets,
why there are asteroids and comets, and why there are
exceptions to the rules.
Our Solar System formed from a giant, swirling cloud of gas
and dust.
What are the exceptions to the nebular theory?
•
•
•
•
The large size of Earth’s Moon
The extreme tilt of Uranus
Backward orbit of Triton
Venus goes the wrong way
What have we learned?
•
How did gravitational collapse affect the Solar
nebula?
•
•
•
•
The nebula heated up, spun faster, and flattened into a disk.
Know the general characteristics of the inner
planets.
Make sure you can calculate an escape velocity.
What key fact explains why there are two types of planet?
•
Differences in condensation at different distances from the Sun:
only metal and rock condensed inside the frost line, while
hydrogen compounds could also condense outside the frost line.
Which is the biggest? Smallest? Oldest? Newest?
UH 0.6-m Telescope
0.6 m
Optical
UH
1968
UH 2.2-m Telescope
2.2 m
Optical/Infrare
d
UH
1970
NASA Infrared Telescope
Facility (IRTF)
3.0 m
Infrared
NASA
1979
Canada-France-Hawaiÿi
Telescope (CFHT)
3.6 m
Optical/Infrare
d
Canada/France/UH
1979
United Kingdom Infrared
Telescope (UKIRT)
3.8 m
Infrared
United Kingdom
1979
W. M. Keck Observatory
(Keck I)
10 m
Optical/Infrare
d
Caltech/ Univ. of
California/NASA
1992
W.M. Keck Observatory
(Keck II)
10 m
Optical/Infrare
d
Caltech/ Univ. of
California/NASA
1996
Subaru
8.1 m
Optical/Infrare
d
Japan
1999
Optical/Infrare
d
Millimeter/
Canada/Chile/Argentina/Brazil
1999
Caltech/NSF
1987
Millimeter/
Submillimeter
United Kingdom/
Canada/Netherlands
1987
Smithsonian Astro-physical
Observ./ Taiwan
2001
National Radio Astronomy
Observatory
1992
Millimeter/Submillimeter Telescopes
Gemini Northern 8-m
Telescope
Caltech Submillimeter
8m
James Clerk Maxwell
Telescope (JCMT)
15 m
Observatory (CSO)
Submillimeter Array
10.4 m
Submillimeter
Eight 6- Submillimeter
m
antenn
Other Facilities
ae
Very Long Baseline Array
25 m
Centimeter
What have we learned?
•
What is the origin of asteroids and comets and
where are they?
•
•
Asteroids are leftover planetesimals of the inner Solar
System typically between Mars and Jupiter and comets
are leftovers of the outer Solar System.
How do we explain the exceptions to the rules?
•
Collisions or close encounters with leftover
planetesimals can explain the exceptions.
What have we learned?
•
How do we think that our Moon formed?
•
•
A Mars-sized “leftover” slammed into Earth, blasting rock from
Earth’s outer layers into orbit, where it re-accreted to form the
Moon.
Why are Jovian planets so different from terrestrial
planets?
•
Formed in cold, outer Solar System at the centers of “miniature
Solar nebulas”.
What did you think?
•
Is the temperature on Mercury, the closest planet to the
Sun, higher than the temperature on Earth?
The temperature on the daytime side of Mercury is much higher than on
Earth, but the temperature on the nighttime side of Mercury is much
lower than on Earth because Mercury rotates so slowly and has little
atmosphere to retain heat.
•
What is the composition of the clouds surrounding Venus?
The clouds are composed primarily of sulfuric acid.
•
Does Mars have surface liquid water today?
No, but there are strong indications that it had liquid water in the distant
past.
•
Is life known to exist on Mars today?
No life has yet been discovered on Mars.
What have we learned?
• What does the solar
system look like?
•
Our solar system
consists of the Sun,
eight planets and
their moons, and
vast numbers of
asteroids and
comets. Each world
has its own unique
character, but there
are many clear
patterns among the
worlds. The sun
accounts for 99.98%
of the mass.
What have we learned?
• Where did the solar
system come from?
•
The cloud of gas that
gave birth to our solar
system was the product
of recycling of gas
through many
generations of stars
within our galaxy. This
gas consisted of 98%
hydrogen and helium
and 2% everything else
combined.
What have we
learned?
• What caused the orderly
patterns of motion in our solar
system?
•
A collapsing gas cloud
naturally tends to heat up,
spin faster, and flatten out as
it shrinks in size. Thus, our
solar system began as a
spinning disk of gas. The
orderly motions we observe
today all came from the
orderly motion of this
spinning disk of gas.