Transcript Lec10-021307 - Lunar and Planetary Laboratory

Solar nebula
Formation of
planetismals
Origin of the Solar
System
Formation of
terrestrial planets
PTYS/ASTR 206
Origin of the Solar System
2/13/07
Announcements
• There will be another preceptor-led study group
Wednesday at 10:30AM in room 330 of Kuiper
• Be sure to pick up all assignments in the box – it will be
completely cleared out by Thursday PM.
• Exam on Thursday (2/15)
– Closed book, closed note, no electronic devices
– Brief review today
• Reading for next class (next Tuesday)
– 7-6, 7-7 (review), 9-2, 9-3
PTYS/ASTR 206
Origin of the Solar System
2/13/07
How Old is the Solar System ?
• How can we determine this ?
– Radioactive dating
– Need to find the right material to
date !
– Because of plate tectonics and
geological activity, Earth rocks are
not a good indicator of the age of
the Solar System
– Meteorites!
PTYS/ASTR 206
Origin of the Solar System
2/13/07
• The number of protons in an
atom determines the element;
however, the number of
neutrons can vary
– Isotope
Radioactivity
• Some elements are stable
(never changing)
• Others are unstable, and
“disintegrate” into a more-stable
isotope of the same element
• This “decay” of the unstable
isotope happens spontaneously
and the element is radioactive
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Origin of the Solar System
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Radioactive Dating
• Each type of radioactive
nucleus decays at its own
characteristic rate, called its
half-life, which can be
measured in the laboratory
• This is the key to a
technique called
radioactive age dating,
which is used to determine
the ages of rocks
PTYS/ASTR 206
Origin of the Solar System
2/13/07
Some Naturally Occurring Radioactive
Isotopes and their half-lives
Radioactive
Isotope (parent)
Product
(Daughter)
Half Life
(years)
Uranium-238
Lead-216
4.5 Billion
Potassium-40
Argon-40
1.26 Billion
Uranium-235
Lead-207
0.7 Billion
Carbon-14
Nitrogen-14
5,715
PTYS/ASTR 206
Origin of the Solar System
2/13/07
How Old is the Solar System?
• The oldest rocks found anywhere in
the solar system are meteorites,
the bits of meteoroids that survive
passing through the Earth’s
atmosphere and land on our planet’s
surface
• Radioactive age-dating of
meteorites, reveals that they are all
nearly the same age, about 4.56
billion years old (4.56 Gy)
– Oldest Earth rocks – about Gy
– Zircons (ancient sand grains) – over 4
Gy
– Moon rocks – oldest are about 4.3 Gy
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ANSWER: 4.56 Billion Years !
Origin of the Solar System
2/13/07
How did the Solar System Form?
• What we know:
– The planets have orbits that are in a
plane (the ecliptic plane)
– The planets orbit the Sun in the
same direction!
– Terrestrial planets: small, rocky
bodies made of heavy elements
• Close to the Sun
– Jovian planets: large bodies made
of light elements (H, He)
• Far from the Sun
the Solar System
– The Sun – primarilyOrigin
H, ofHe
2/13/07
PTYS/ASTR 206
?
The Big Bang
• The theory of the origin of
the Universe
• Only Hydrogen and
Helium (perhaps small
amounts of Li and Be)
would survive the
enormous temperatures
of the Big Bang
• Where did all the heavy
elements (like Iron,
Oxygen, etc.) come
from?
PTYS/ASTR 206
Origin of the Solar System
2/13/07
The formation of Stars
• Hydrogen and Helium gas clouds are
formed due to mutual gravitational
effects
• The gas cloud begins to collapse -Jeans instability
• Kelvin-Helmholtz contraction
– Gravitational energy  thermal
energy
– As the gas/dust cloud contracts, it
heats up
• The birth of a “protostar”
PTYS/ASTR 206
Origin of the Solar System
2/13/07
The protostar
• As the protostar continues to
“accrete” material, its center is under
extreme pressure
• As the core is put under more
pressure and gets hotter and
hotter, thermonuclear fusion starts
to occur
– It is now a full-fledged star
• Formation of different atomic
elements
– These are released as the star
evolves and eventually dies
(either gradually, or by supernova)
PTYS/ASTR 206
Origin of the Solar System
2/13/07
We are made out of “star dust” !
• Space has mostly H and
He, but heavier elements
also exist (resulting from
nuclear reactions that
occurred in now-dead
stars)
• The material from which
our solar system formed
is called the Solar
Nebula
PTYS/ASTR 206
Origin of the Solar System
2/13/07
The Solar Nebula
• Elements that make up the solar nebula
• Hydrogen and Helium are most abundant, Oxygen is thirdmost abundant, C, N, Ne, Mg, Si, S, Fe, Ni are also fairly
common
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Origin of the Solar System
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The Formation of the
Protoplanetary disk
• As the original gas cloud (which
rotates slowly about a common
axis) collapses, it begins to
rotate faster
– conservations angular momentum
• As the cloud shrinks, it also
flattens
• The flattened, rotating disk of
gas and dust from which our
solar system is made of is
PTYS/ASTRas
206 a protoplanetary
Origin disk
of the Solar System
known
2/13/07
Concept of Angular Momentum
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Origin of the Solar System
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Hubble Spce
Telescope Images
of protoplanetary
disks (or proplyds)
in the Orion nebula
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Origin of the Solar System
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The sequence of
solar-system
formation and how
long it takes
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Origin of the Solar System
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Condensation
• Dust in the early solar nebula acted as
condensation nuclei (nuclei upon which
other elements attach to)
• If an element has a temperature above
the condensation temperature – it
will be a gas
• It the temperature is below the
condensation temperature – it is solid
(or liquid)
– Iron, nickel have high
condensation temperatures
– Hydrogen and Helium have very
low condensation temperatures
PTYS/ASTR 206
Origin of the Solar System
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• The composition of
the solar system
was arranged
largely by how far it
was from the
protostar
• Elements with high
condensation
temps. (iron, nickel,
rocky material, etc.)
in the inner solar
system
– Terrestrial
planets!
• methane, ammonia,
etc. remained as ice
in the outer solar
PTYS/ASTR 206
system
Origin of the Solar System
2/13/07
Formation of terrestrial planets
• Small dust particles accreted
to make “planetesimals”
• Planetesimals accreted (and
collided with other
planetesimals) to form
protoplanets
• The protoplanets were at
least partially molten
– denser iron-rich material
fell to the center,
bringing heavier metals
with it, making an ironrich core (differentiation)
–
A terrestrial
planet!Origin of the Solar System
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206
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There are currently two theories for the
formation of Gas Giants
• Core accretion model
– Bottom up model
– Started with a core, then accreted
H and He
– Ices and rocky material provided
the core
– Once large enough, they could
attract H and He
• Disk instability model
– “top down” model
– Formed directly from the
protoplanetary disk as a “clump”
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Origin of the Solar System
of H206and He
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Extrasolar Planets
• About 10 years ago,
astronomers began finding
extrasolar planets, or planets
orbiting other stars
– More than 100 have been
detected
– Can be detected by
amateurs
• They are not actually seen,
instead, their effects on their
parent star are observed
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Origin of the Solar System
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Finding Extrasolar Planets 1
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Origin of the Solar System
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Finding Extrasolar Planets 2
• The planets themselves are not visible; their
presence is detected by the “wobble” of the stars
around which theyOrigin
orbit
PTYS/ASTR 206
of the Solar System
2/13/07
Extrasolar Planets
Most of the extrasolar planets discovered to date are quite massive and
have orbits that are very different from planets in our solar system
PTYS/ASTR 206
Origin of the Solar System
2/13/07
First Exam
• Format:
– 5 short-answer questions
– 30 multiple choice questions
• To be answered on the scantron sheets
• BRING A #2 PENCIL !
– Closed book, closed notes, no electronic
devices (including calculators!)
– The allotted time will be ~72 minutes
PTYS/ASTR 206
Origin of the Solar System
2/13/07
First Exam
• What will it cover?
– Mostly material discussed in the lectures
– Reading – Chapters 1-8
– Note: some lecture topics are discussed more in the
textbook
– The exam is usually balanced by lecture material (~4
questions per lecture, typically)
• How much does it count towards the final grade?
– Either 20% or 10% of your overall grade depending on
how you do on the second exam (the best score of the 2
is 20%, the worst is 10%).
PTYS/ASTR 206
Origin of the Solar System
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First Exam
• What should you study?
– Go over lecture slides
– Textbook
• Go over guiding questions at the beginning of each chapter
• Go over key ideas and review questions at the end of each
chapter
– Review in-class activities, homework, and quizzes
• All solutions are posted on the website
– Go over the practice exam
– Note that to ensure the maximum possibility of success,
you should do all of the above and not just the practice
exam!
• What should you ignore when studying?
– There won’t questions like the quantitative problems found
on the homework
– Do NOT bring a calculator!
PTYS/ASTR 206
Origin of the Solar System
2/13/07
First exam: A brief review
• Chapter 1
– powers-of-ten notation
• Chapter 2
– The sky, diurnal motion, celestial sphere, reason for
the seasons, equinoxes
• Chapter 3
– Reason for lunar phases, when they rise/set, lunar
eclipses, solar eclipses
• Chapter 4
– Copernicus heliocentric system vs. Ptolemaic Earthcentered system, elliptical orbits, Kepler’s laws,
Newton’s laws, gravity
PTYS/ASTR 206
Origin of the Solar System
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First Exam: A brief review
• Chapter 5
– radiation and spectroscopy, Kirchoff’s laws, Wien’s
law, Stefan-Boltzman law
• Basic properties of waves
• Electromagnetic spectrum
• Blackbody radiation
• Absorption and Emission lines
• Doppler effect
• Chapter 6
– Telescopes (how they work), magnification, lightgathering ability, resolution, CCDs, adaptive optics
PTYS/ASTR 206
Origin of the Solar System
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First exam: A brief review
• Chapter 7
– Layout of the solar system, properties of the
planets, average density, kinetic energy,
escape speed, spectroscopy
• Chapter 8
– Origin of the solar system, the nebular
hypothesis, extrasolar planets, radioactive
dating
PTYS/ASTR 206
Origin of the Solar System
2/13/07