Astronomy: Chapter 12

Question 1

Name and describe the two main categories of planets in our solar system and explain their differences.

Answer 1

•Terrestrial planets: 
     - Formed slowly from accretion disks. 
     -High density. 
     -Inner four planets. 
     -Smaller, rocky
     -No rings, fewer moons. 
     -Mercury, earth, Venus, and mars. 
•Jovial Planets
     -Formed by gravitational collapse
     -Low density
     -Outer four planets
     -Larger, gaseous
     -Jupiter, Saturn, Uranus, Neptune.

Question 2

Any theory of the formation of the solar system must explain what characteristics of the solar system?

Answer 2

1. Disk shape of the solar system
   
   • Orbits in nearly the same plane
   • Common direction of revolution and rotation
2. Two planetary types
   
   • Terrestrial—inner planets; small, high density
   • Jovian—outer planets; large, low density
3. Planetary rings and large satellite systems around the jovian planets, not around the terrestrial planets.
4. Space debris—asteroids, comets, and meteors.
   
   • Composition: two types, rocky versus icy
   • Orbits: two types, inner versus outer solar system
5. Common age of about 4.6 billion years for earth, the moon, mars, meteorites, and the sun.

Question 3

Explain the evidence for the roles of condensation and accretion in the formation of the planets.

Answer 3

Planets begin growing by accreting solid material but once a planet appraches about 15 earth masses, it can begin growing by gravitational collapse as it pulls gas from the solar nebula.
- Accreting: the sticking together of solid particles to produce a larger particle.

• the condensation sequence explains that the Terrestrail planets formed in the inner solar system where only denser minerals could condense to form solids, while the Jovian planets formed farther out where ices could condense.
  
  • Condensation sequence: the sequence in which different materials condense from the solar nebula depending on distance from the sun.
  • condensation: the growth of a particle by addition of material from surrounding gas, atom by atom.

Question 4

Describe the recent efforts of astronomers to detect planets around other stars.

Answer 4

• Debris disks appear to be produced by dust released by collisions among objects in other planetary systems ans may contain planets.
• Planets orbiting other stars have been detected because they create small doppler shifts in the stars’ spectra. Planets have also been detected as they cross in front of their star and dim the star’s light.
• nearly all extrasolar planets found so far are massive, Jovian worlds. Lower mass terrestrial planets are harder to detect but are presumably common.

Question 5

Solar Nebula Theory

Answer 5

• the solar nebula contracts and flattens into a spinning disk. the large blob in the center will become the sun. the small blobs in the outer regions may become jovial planets.
• Dust grains act as condensation Nuclei, forming clumps of matter that collide, stick together, and grow into moon sized planetesimals.
• strong winds from the still-forming sun expel the nebular gas
• planetesimals continue to collide and grow.
• over the course of 100 million years ot so, planetesimals form a few large planets that travel in roughly circular orbits.

Question 6

Growth of planets.

Answer 6

Condensation: particles begin to grow when atoms of gas begin to attach themselves and the particles grow atom by atom.

• accretion: over time, these particles begin to stick together within a few 100 of millions years between mili to centi till we have planetesimals.
• planetesimals: Kilometer scale objects. they then will smash into each other more violently and rapidly. eventually they will form protoplanets.
• Protoplanets: they are no longer homogenous bodies of material. they contain many different elements and compounds. heat generated by the core, either by the protoplanet’s rapid growth or through radioactive decay, melts the material, which then separates by density through a process called differentiation.
• Differentiation: heavy materials like iron sink to the center to form the core, and lighter materials float to the outer layers to form the crust of the protoplanets.
• these hot protoplanets continue to grow as they sweep up material along their orbital paths around the sun.