origin of the solar system

PTYS/ASTR 206 Origin of the Solar System2/13/07

Origin of the Solar System

Solar nebula

Formation of planetismals

Formation of terrestrial planets


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


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!


Radioactivity

• The number of protons in an atom determines the element; however, the number of neutrons can vary– Isotope

• 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


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


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


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

ANSWER: 4.56 Billion Years !


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 Sun – primarily H, He

?


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?


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”


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)


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


The Solar Nebula• Elements that make up the solar nebula• Hydrogen and Helium are most abundant, Oxygen is third-

most abundant, C, N, Ne, Mg, Si, S, Fe, Ni are also fairly common


• 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 known as a protoplanetary disk

The Formation of the Protoplanetary disk


Concept of Angular Momentum


Hubble Spce Telescope Images of protoplanetary disks (or proplyds) in the Orion nebula


The sequence of solar-system formation and how long it takes


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


• 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 system


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 iron-rich core (differentiation)

– A terrestrial planet!


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” of H and He


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


Finding Extrasolar Planets 1


Finding Extrasolar Planets 2

• The planets themselves are not visible; their presence is detected by the “wobble” of the stars around which they orbit


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


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


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%).


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!


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 Earth-

centered system, elliptical orbits, Kepler’s laws, Newton’s laws, gravity


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, light-

gathering ability, resolution, CCDs, adaptive optics


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

origin of the solar system

Documents

solar system form

solar systemmeteorites

planets surfaceradioactive

oldest rocks

sunjovian planets

radioactive age dating

ages of rocks

gyoldest earth rocks