Scholars Online Astronomy - Chapter 8: Solar System Origins
Reading: Astronomy, Chapter 8: The Origins of our Solar System
Study Notes: notes on your assigned reading from the text
- Section 8.1 Models of the origin of the solar system must explain why the terrestrial and Jovian planets have different densities and size (probably as a function of their differenced from the sun), why all planets orbit in the same direction (along with their moons), mostly in the same plane, and revolve mostly the same way.
- Section 8.2 The early universe was hydrogen and helium; heavier elements formed during star evolution and nova events, so all the atoms of elements other than H and He were formed elsewhere and condensed to form our planets. The overall abundance of the elements in the solar system, despite local concentrations in the different composition of the planets themselves, reflects their abundance in the universe.
- Section 8.3 Radioactive elements are used to date surface rocks and meteorites to give the age of the solar system as around 4.5 billion years old. We know that for some materials to form, elements must have been present in particular abundances, which gives us a starting amount from which to calculate the age of various substances.
- Section 8.4 The nebular hypothesis is a model that explains the formation of solar/planetary objects from a diffuse spinning cloud that condensed under gravitation force to form a sun and planetary disk. The laws of concentration of angular momentum require the speed of rotation to compensate for the loss of kinetic energy when the radius of the planetary object shrinks.
- Section 8.5 Computer models support the possibilities planets formed by condensing into lumps from individual small objects, a process called accretion. Some never were captured by larger bodies and became asteroids or comets; others went into orbit around larger nearby bodies rather than the sun and became moons.
- Section 8.6 A core accretion model accounts for the formation of Jovian planets with their hydrogen-rich envelopes surrounding rocky cores in a band 4-10 AU from the sun. The planets were later flung to their current orbits by gravitational interaction with each other, particularly with Jupiter.
- Section 8.7 By looking at stars that "wobble" in their movements through space, astronomers have discovered extrasolar planets, that is, non-luminescent bodies orbiting other stars. The size and rate of the wobble, detected using astrometric or radial velocity methods, allows astronomers to determine the size and orbital distance of the planet from its primary.
Key Formulae to Know
Read the following weblecture before chat: The Solar System's Formation
- Planetarium Program:
- If your program supports it, observe our solar system from at least 60AU above the north pole of the Sun and then move to observe it from the side "edge-on". Try to describe your observations in words — what you actually see, not what you "know" is happening.
- If your program supports viewing extrasolar planets, identify planets within 90 LY of Earth. What characteristics do they share (type of central sun, mass, likely composition, distance from central sun)? How do the planets you can find compare to Jupiter? to Earth?
- Optional Websites: StarDate is the website of McDonald Observatory at the University of Texas. It includes a number of resources, including information about currently visible planetary objects (good for planning observing sessions), as well as online and physical exhibits at the observatory. Check out the solar system link for pictures an information about the planets and minor bodies.
Chat Preparation Activities
- Essay question: The Moodle forum for the session will assign a specific study question for you to prepare for chat. You need to read this question and post your answer before chat starts for this session.
- Go over the list of Key Words and Key Ideas at the end of the chapter. If you don't remember the definition of the key word, review its use (the page number on which it is explained is given).
- Read through the Review Questions and be prepared to discuss them in class. If any of them confuses you, ask about it!
- Mastery Exercise: The Moodle Mastery exercise for the chapter will contain sections related to our chat topic. Try to complete these before the chat starts, so that you can ask questions.
- Required: Complete the Mastery exercise with a passing score of 85% or better.
- Go to the Moodle and take the quiz for this chat session to see how much you already know about astronomy!
Read through the lab for this week; bring questions to chat on any aspect of the lab, whether you intend not perform it or not. If you decide to perform the lab, be sure to submit your report by the posted due date.
- Lab instructions: Observe Saturn and Jupiter -- see Moodle assignment notes.
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