Download solar system form

Neil F. Comins • William J. Kaufmann III
Discovering the Universe
Eighth Edition
CHAPTER 5
Formation of the Solar System
Essay Questions for this Lecture

What are the major similarities and differences
between inner and outer planets?

How did the solar system form? How does the
condensation sequence theory explain the
similarities and differences between Jovian and
Terrestrial planets?

How do we detect other planetary systems
around distant stars? What are the strengths
and limitations of each method?
WHAT DO YOU THINK?
1.
2.
3.
How old is the Earth? How do we
know???
How old are the Sun and other planets?
Were they created during the “Big
Bang”? How do we know?
Have any Earthlike planets been
discovered orbiting Sunlike stars? How
can we tell?
In this chapter you will discover…
how the solar system formed
 why the early solar system was much
more violent than it is today
 how astronomers define various types of
objects in the solar system
 how the planets are “grouped”

In this chapter you will discover…
how moons formed throughout the solar
system
 the “debris” in the solar system
 that disks of gas and dust, as well as
planets, have been observed around a
growing number of stars
 that newly forming stars & planetary
systems are being observed

The solar system exhibits clear patterns of composition and
motion.
These patterns are far more important and interesting than
numbers, names, and other trivia.
Planets are very
tiny compared to
distances
between them.
Sun
• Over 99.9% of solar system’s mass
• Made mostly of H/He gas (plasma)
• Converts 4 million tons of mass into energy each second
Mercury
• Made of metal and rock; large iron core
• Desolate, cratered; long, tall, steep cliffs
• Very hot and very cold: 425°C (day), –170°C (night)
Venus
• Nearly identical in size to Earth; surface hidden by clouds
• Hellish conditions due to an extreme greenhouse effect
• Even hotter than Mercury: 470°C, day and night
Earth
Earth and
Moon to scale
• An oasis of life
• The only surface liquid water in the solar system
• A surprisingly large moon
Mars
• Looks almost Earth-like, but don’t go without a spacesuit!
• Giant volcanoes, a huge canyon, polar caps, and more
• Water flowed in the distant past; could there have been
life?
Jupiter




Much farther
from Sun than
inner planets
Mostly H/He;
no solid
surface
300 times
more massive
than Earth
Many moons,
rings
Jupiter’s moons
can be as
interesting as
planets
themselves,
especially
Jupiter’s four
Galilean moons
• Io (shown here): Active volcanoes all over
• Europa: Possible subsurface ocean
• Ganymede: Largest moon in solar system
• Callisto: A large, cratered “ice ball”
Saturn




Giant and gaseous like Jupiter
Spectacular rings
Many moons, including cloudy Titan
Cassini spacecraft currently studying it
Rings are
NOT solid;
they are made
of countless
small chunks
of ice and
rock, each
orbiting like a
tiny moon.
Artist’s conception
The Rings of Saturn
Cassini probe
arrived July
2004.
(Launched in
1997)
Uranus




Smaller than
Jupiter/Saturn;
much larger than
Earth
Made of H/He
gas and
hydrogen
compounds
(H2O, NH3, CH4)
Extreme axis tilt
Moons and rings
Neptune

Similar to
Uranus (except
for axis tilt)

Many moons
(including
Triton)
Pluto and Eris



Much smaller than other planets
Icy, comet-like composition
Pluto’s moon Charon is similar in size to
Pluto
Space isn’t empty…
We know space is filled with gas and dust – the
raw materials from which planetary systems
form!
…and its composition changes
Spectra of exploding and old stars shows
heavier elements being ejected, too
Clues to Formation of our
Solar System?
Clue #1: Motion of Large Bodies

All large bodies in
solar system orbit
in same direction
& in nearly same
plane.

Most also rotate in
that direction.
Clue #2: Two Major Planet Types

Terrestrial planets
are rocky,
relatively small, &
close to Sun.

Jovian planets
are gaseous,
larger, & farther
from Sun.
Clue #3: Swarms of Smaller
Bodies

Many icy
comets, small
“dwarf planets”,
& rocky
asteroids
populate solar
system in 3
areas
Notable Exceptions

Several
exceptions to
normal
patterns need
to be
explained.
What theory best explains the
features of our solar system?
According to the
nebular theory, our
solar system formed
from a giant cloud of
interstellar gas.
(nebula = cloud)
Why are there two major types of
planets?
The Laws of Physics
1. As gravity causes the cloud to contract, it
heats up. (Conservation of Energy!)
2. As it contracts, it spins faster.
(Conservation of Angular Momentum!)
3. As it spins and contracts, it flattens.
4. The temperature varies by distance
Inner parts of
the disk are
hotter than
outer parts.
Rock can be
solid at much
higher
temperatures
than ice.
Temperature Distribution of the Disk and the Frost Line
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
Formation of Terrestrial
Planets
•
Small particles of rock and metal were
present inside the frost line.
•
Planetesimals of rock and metal built up
as these particles collided.
•
Gravity eventually assembled these
planetesimals into terrestrial planets.
Tiny solid
particles stick to
form
planetesimals.
Summary of the Condensates in the Protoplanetary Disk
Gravity draws
planetesimals
together to form
planets.
This process of
assembly
is called
accretion.
Summary of the Condensates in the Protoplanetary Disk
Accretion of Planetesimals
•
Many smaller objects collected into just
a few large ones.
Formation of Jovian Planets
•
Ice could also form small particles outside the
frost line.
•
Larger planetesimals and planets were able to
form.
•
The gravity of these larger planets was able to
draw in surrounding H and He gases.
The gravity of
rock and ice in
jovian planets
draws in H and
He gases.
Nebular Capture and the Formation of the Jovian Planets
Moons of jovian planets form in miniature disks.
Summary of Key Ideas
Formation of the Solar System



Hydrogen, helium, and traces of lithium, the three
lightest elements, were formed shortly after the creation
of the universe. The heavier elements were produced
much later by stars and are cast into space when stars
die. By mass, 98% of the observed matter in the
universe is hydrogen and helium.
The solar system formed 4.6 billion years ago from a
swirling, disk-shaped cloud of gas, ice, and dust, called
the solar nebula.
The four inner planets formed through the accretion of
dust particles into planetesimals and then into larger
protoplanets. The four outer planets probably formed
through the runaway accretion of gas and ice onto rocky
protoplanetary cores over millions of years, but possibly
by gravitational collapse in under 100,000 years.
Formation of the Solar System


The Sun formed at the center of the solar nebula. After
about 100 million years, the temperature at the
protosun’s center was high enough to ignite
thermonuclear fusion reactions.
For 800 million years after the Sun formed, impacts of
asteroid-like objects on the young planets dominated the
history of the solar system.
Comparative Planetology



The four inner planets of the solar system share many
characteristics and are distinctly different from the four
giant outer planets.
The four inner, terrestrial planets are relatively small,
have high average densities, and are composed
primarily of rock and metal.
Jupiter and Saturn have large diameters and low
densities and are composed primarily of hydrogen and
helium. Uranus and Neptune have large quantities of
water as well as much hydrogen and helium.
Comparative Planetology



Pluto, once considered the smallest planet, has a size,
density, and composition consistent with the known
Kuiper Belt Objects (KBOs).
Asteroids are rocky and metallic debris in the solar
system, larger than about a kilometer in diameter, and
found primarily between the orbits of Mars and Jupiter.
Meteoroids are smaller pieces of such debris. Comets
are debris that contain both ice and rock.
Planets Outside Our Solar System




Astronomers have observed disks of gas and dust
orbiting young stars.
At least 250 extrasolar planets have been discovered
orbiting other stars.
Most of the extrasolar planets that have been discovered
have masses roughly the mass of Jupiter.
Extrasolar planets are discovered indirectly as a result of
their effects on the stars they orbit.
Key Terms
accretion
albedo
asteroid
asteroid belt
average density
comet
core-accretion model
crater
gravitational instability
model
meteoroid
microlensing
moon (natural
satellites)
orbital inclination
planet
planetesimal
protoplanet
protoplanetary disks
(proplyds)
protosun
solar nebula
solar system
terrestrial planet
WHAT DID YOU THINK?


Were the Sun and planets among the first generation of
objects created in the universe?
No. All matter and energy were created by the Big Bang.
However, much of the material that exists in our solar
system was processed inside stars that evolved before
the solar system existed. The solar system formed
billions of years after the Big Bang occurred.
WHAT DID YOU THINK?


How long has Earth existed, and how do we know this?
Earth formed along with the rest of the solar system,
about 4.6 billion years ago. The age is determined from
the amount of radioactive decay that has occurred in it.
WHAT DID YOU THINK?


What typical shape(s) do moons have, and why?
Although some moons are spherical, most look roughly
like potatoes. Those that are spherical are held together
by the force of gravity, pulling down high regions. Those
that are potato-shaped are held together by the
electromagnetic interaction between atoms, just like
rocks. These latter moons are too small to be reshaped
by gravity.
WHAT DID YOU THINK?


Have any Earthlike planets been discovered orbiting
Sunlike stars?
Not really. Most extrasolar planets are Jupiter-like gas
giants. The planets similar in mass and size to Earth are
either orbiting remnants of stars that exploded or, in the
case of Gliese 581, a star much less massive and much
cooler than the Sun.