Solar System Formation Solar System Formation

Solar System Formation Solar System Formation

Solar System Formation Solar System Formation Question: How did our solar system and other planetary systems form? “Comparative planetology” has helped us understand • Compare the differences and similarities among the objects in our solar system • Figure out what physical processes could have led to them • Then construct a model of how our solar system formed based on this ------- • This model must explain our own solar system… • …but might or might not explain other planetary systems • If not, modify the model to accommodate discrepancies • In other words, carry out the scientific process ------- • Let’s look at the solar system characteristics comparative planetology has to work with… Solar System Formation -- Characteristics of Our Solar System 1. Large bodies have orderly motions and are isolated from each other – All planets and most moons have nearly circular orbits going in the same direction in nearly the same plane Solar System Formation -- Characteristics of Our Solar System 1. Large bodies have orderly motions and are isolated from each other – All planets and most moons have nearly circular orbits going in the same direction in nearly the same plane – The Sun and most of the planets rotate in this same direction as well Solar System Formation -- Characteristics of Our Solar System 1. Large bodies have orderly motions and are isolated from each other – All planets and most moons have nearly circular orbits going in the same direction in nearly the same plane – The Sun and most of the planets rotate in this same direction as well – And most moons orbit their planet in the direction it rotates Solar System Formation -- Characteristics of Our Solar System 2. Planets fall into two main categories Small, rocky “terrestrial” planets near the Sun Large, hydrogen-rich “jovian” planets far from the Sun Solar System Formation -- Characteristics of Our Solar System 2. Planets fall into two main categories Solar System Formation -- Characteristics of Our Solar System 3. Swarms of asteroids and comets populate the solar system – Asteroids are concentrated in the asteroid belt Solar System Formation -- Characteristics of Our Solar System 3. Swarms of asteroids and comets populate the solar system – Asteroids are concentrated in the asteroid belt – Comets populate the regions known as the Kuiper belt and the Oort cloud Solar System Formation -- Characteristics of Our Solar System 4. Several notable exceptions to these general trends stand out – Planets with unusual axis tilts – Surprisingly large moons – Moons with unusual orbits Summary of Characteristics of Our Solar System 1. Large bodies in the solar system have orderly motions and are isolated from each other – All planets and most moons have nearly circular orbits going in the same direction in nearly the same plane – The Sun and most of the planets rotate in this same direction as well – Most moons orbit their planet in the direction it rotates 2. Planets fall into two main categories – Small, rocky terrestrial planets near the Sun – Large, hydrogen-rich jovian planets farther out • The jovian planets have many moons and rings of rock and ice 3. Swarms of asteroids and comets populate the solar system – Asteroids are concentrated in the asteroid belt – Comets populate the regions known as the Kuiper belt and the Oort cloud 4. Several notable exceptions to these general trends stand out – Planets with unusual axis tilts – Surprisingly large moons – Moons with unusual orbits any successful theory of solar system formation must account for these Solar System Formation – The Nebular Theory • The nebular theory is the best current explanation of our solar system • It is not a new idea… …the philosophers Emanuel Swedenborg and Immanuel Kant suggested it in the 1700s • And like all scientific theories, it is still being refined and improved Solar System Formation – The Nebular Theory • It starts with cold interstellar clouds of gas and dust • These clouds are mostly hydrogen and helium from the Big Bang • But they contain heavier elements that were not formed in the Big Bang • Astronomers call these “metals” (even though they’re not necessarily metallic elements) • Where did these heavier elements come from? • They came from stars! Solar System Formation – The Nebular Theory • Stars make heavier elements from lighter ones through nuclear fusion Solar System Formation – The Nebular Theory • Stars make heavier elements from lighter ones through nuclear fusion • The heavy elements (the “metals”) mix into the interstellar medium when the stars die Solar System Formation – The Nebular Theory • Stars make heavier elements from lighter ones through nuclear fusion • The heavy elements (the “metals”) mix into the interstellar medium when the stars die • And then new stars form from the enriched gas and dust • And the cycle continues Solar System Formation – The Nebular Theory • And at the same time stars are forming… …planetary systems can form • Here’s how it works… Solar System Formation – The Nebular Theory • A large cloud -- a nebula perhaps 1 light year across -- floats in space Solar System Formation – The Nebular Theory • A large cloud -- a nebula perhaps 1 light year across -- floats in space • The cloud begins to collapse …WHY would this happen?... Local density increase Solar System Formation – The Nebular Theory • A large cloud -- a nebula perhaps 1 light year across -- floats in space • The cloud begins to collapse -- local density increase • As it collapses it begins to spin faster …WHY would this happen?... Conservation of angular momentum Solar System Formation – The Nebular Theory • A large cloud -- a nebula perhaps 1 light year across -- floats in space • The cloud begins to collapse -- local density increase • As it collapses it begins to spin faster -- conservation of angular momentum • And as it spins faster, it flattens out …WHY would this happen?... Collisions and conservation of angular momentum Solar System Formation – The Nebular Theory • A large cloud -- a nebula perhaps 1 light year across -- floats in space • The cloud begins to collapse -- local density increase • As it collapses it begins to spin faster -- conservation of angular momentum • And as it spins faster, it flattens out – collisions and conservation of angular momentum • At the same time, it begins to heat up in the center …WHY would this happen?... Conversion of gravitational potential energy into thermal energy Solar System Formation – The Nebular Theory • A large cloud -- a nebula perhaps 1 light year across -- floats in space • The cloud begins to collapse -- local density increase • As it collapses it begins to spin faster -- conservation of angular momentum • And as it spins faster, it flattens out -- collisions • At the same time, it begins to heat up in the center -- conversion of potential to thermal energy • And when it gets hot enough, a star forms in the center • And in the disk around the forming star, planets can form • What type of planets can form depends on what the cloud is made of… Solar System Formation – The Nebular Theory • This is what our own cloud—the solar nebula—was made of • But how do we know this? Solar System Formation – The Nebular Theory • This is what our own cloud—the solar nebula—was made of • But how do we know this? This is how… • …the absorption line spectrum of the Sun • It tells us the composition of the gas on the surface of the Sun Solar System Formation – The Nebular Theory • This is the composition of the Sun’s surface gas – its atmosphere • We think the solar nebula had the same composition • But a skeptic might say, is it reasonable to say this? Solar System Formation – The Nebular Theory • After all, the solar nebula collapsed 4.6 billion years ago • The Sun’s been making new atoms with nuclear fusion ever since • That’s how it generates the energy that gives us sunlight • Wouldn’t this change the composition of the Sun’s atmosphere? • The answer has to do with where the new atoms are being made… Solar System Formation – The Nebular Theory • The sunlight-generating fusion reactions happen in the Sun’s core • The core is in the Sun’s center, far from the surface, and held in by intense gravity • So the surface layers should be essentially unchanged • And their composition should be very similar to the solar nebula the Sun formed from Solar System Formation – The Nebular Theory • So it seems reasonable that the Sun’s atmosphere is similar to the nebula it formed from Solar System Formation – The Nebular Theory • The key to the nebular theory is the condensation temperature of these materials • That’s the temperature at which they condense into solid form • The nebula was initially very cold, so everything except H and He was in solid form • But it heated up as it collapsed… • …and the temperature was different at different distances from the center Solar System Formation – The Nebular Theory • This image shows a graph of a modeled temperature profile of the solar nebula… …along with an artist’s rendition of the nebula • The temperature was hottest in the center, and went down away from the center • There was a mixture of metals, rocks, and hydrogen compounds throughout the nebula • These could only be solid where the temperature was below their condensation temperature • So different chemical components of the nebula condensed at different distances • A mixture of solid rock and metal existed out to about 4.5 AU from the center • At 4.5 AU, the temperature dropped low enough for hydrogen compounds to condense, too • The boundary between where they

View Full Text

Details

  • File Type
    pdf
  • Upload Time
    -
  • Content Languages
    English
  • Upload User
    Anonymous/Not logged-in
  • File Pages
    101 Page
  • File Size
    -

Download

Channel Download Status
Express Download Enable

Copyright

We respect the copyrights and intellectual property rights of all users. All uploaded documents are either original works of the uploader or authorized works of the rightful owners.

  • Not to be reproduced or distributed without explicit permission.
  • Not used for commercial purposes outside of approved use cases.
  • Not used to infringe on the rights of the original creators.
  • If you believe any content infringes your copyright, please contact us immediately.

Support

For help with questions, suggestions, or problems, please contact us