Astronomy- Ch. 8
Describe the technique of radiometric dating. What is a half-life?
...
How do we think the Moon formed, and what evidence supports this hypothesis?
...
How old is the solar system, and how do we know?
...
In the context of planet formation, what are asteroids and comets? Briefly explain why we find asteroids in the asteroid belt and comets in the Kuiper belt and Oort cloud.
...
Our bodies (and most living things) are made mostly of water: H20. Summarize the "history" of a typical hydrogen atom from its creation to the formation of Earth. Do the same for a typical oxygen atom.
...
Suppose our solar nebula had begun with much more angular momentum than it did. Do you think planets could still have formed? Why or why not? What if the solar nebula had started with zero angular momentum?
...
Suppose the entire solar nebula had cooled to 50 K before the solar wind cleared it away. How would the composition and sizes of the planets of the inner solar system be different from what we see today? Explain your answer in a few sentences.
...
Suppose the solar wind had cleared away the solar nebula before the seeds of the jovian planets could gravitationally draw in hydrogen and helium gas. How would the planets of the outer solar system be different? Would they still have many moons? Explain your answer in a few sentences.
...
What is the solar wind, and what roles did it play in the early solar system?
...
What was the heavy bombardment, and when did it occur?
...
Why did the jovian planets end up with so many moons?
...
How was the formation of jovian planets similar to that of the terrestrial planets? How was it different?
Condensation of ices farther out in the solar nebula meant there were more solid materials in addition to the metal and rock. Jovian planets formed as gravity drew gas around ice-rich planetesimals much larger than Earth; (when it gets about 10 Earth masses) therefore they had a strong enough gravity that it could capture and hold hydrogen and helium that made up a vast majority of the material in the solar nebula. After collecting and collecting, they hardly resembled the icy seeds from which they grew.
List the four categories of materials in the solar nebula by their condensation properties and abundance. Which ingredients are present in terrestrial planets? In jovian planets? In comets and asteroids? Explain why.
Hydrogen and helium: 98% of solar nebula. NEVER CONDENSE Hydrogen compounds (1.4% of solar nebula. Condense into ices below 150K .these include water, methane, and ammonia Rock: 0.4% of solar nebula, Condenses into solid bits of mineral b/t 500-1300K Metal: 0.2% of solar nebula. Condense into solid form at temps b/t 1000-1600K ---The ingredients present in terrestrial planets include rocks and metals because it is hotter closer to the sun where the rocks and metals could condense to form a planet. Farther away from the sun where it requires less temperature to condense hydrogen and helium and hydrogen compounds are where the jovian planets formed. In comets and asteroids, it is carbon-rich minerals that condensed because of the low enough temperature.
What was the frost line in the solar nebula? Explain how temperature differences led to the formation of two distinct types of planets.
The frost line in the solar nebula lies between Mars and Jupiter. It is the distance where it was cold enough for hydrogen compounds to condense into ices. Temperature differences led to the formation of two distinct types of planets (terrestrial and jovian) b/c of the temperature at which the materials that make up each type of planet could condense. (Ex. Takes a higher temp to condense rock and metal [terrestrial] and a lower temp to condense hydrogen, helium, and hydrogen compounds [jovian]). This also tells us why the jovian planets are so much larger than the terrestrials (b/c hydrogen is most abundant and could only condense farther out from the Sun).
What is the nebular theory, and why is it widely accepted by scientists today?
The nebular theory is a modification of the nebular hypothesis which said that the solar system formed from the gravitational collapse of an interstellar cloud of gas. It was formed when scientists used more sophisticated models of the processes that occur in a collapsing cloud of gas. It became a theory because it offered natural explanations for all four of the general features of the solar system (listed in question 1). It is so widely accepted because it successfully predicted the existence of other planetary systems (that we are found recently).
Briefly describe the process by which terrestrial planets are thought to have formed.
The process by which terrestrial planets formed is called accretion. It begins with the microscopic solid particles that condensed from the solar nebula's gas. Because the particles orbited the Sun just like the gas that orbited, the particles "collisions" were really just gentle touches- sticking together through electrostatic forces (static electricity). Small particles became larger ones; then, gravity began helping the process of sticking together, which made the growth much faster. These particles became planetesimals ("pieces of planets"). Only the largest planetesimals avoided being shattered and could grow into terrestrial planets.
What do we mean by the solar nebula? What was it made of, and where did it come from?
The solar nebula is the cloud of gas from which our solar system was born when it collapsed under its own gravity. By using the compositions of the Sun, other stars, and interstellar gas clouds, we know that the solar nebula contained 98% hydrogen and helium and only 2% of all other elements combined. This came from the billion of years of galactic recycling that occurred before the Sun and planets were born.
Describe each of the three key processes that led the solar nebula to take the form of a spinning disk. What observational evidence supports this scenario?
The solar nebula took the form of a spinning disk, instead of a sphere, because of three main processes: heating, spinning, and flattening. -Heating: means that the temperature increased as it collapsed representing energy conservation. As it shrank, the PE was converted into the KE of individual gas particles falling inward. These crashed into each other, converting their inward, falling KE into the random motions of thermal energy. The Sun formed in the center, where temperatures and densities were the highest. -Spinning: Like an ice skater, the solar nebula became faster as it shrank in radius representing conservation of angular momentum. Before the collapse, the rotation was very slow, but as it shrank, fast rotation was inevitable. It helped ensure that everything in the nebula didn't crash into the center because the greater the angular momentum, the more spread out it would be. -Flattening: consequence of collisions between particles in a spinning cloud. Randomly shaped and sized clumps of gas collide and merge as the cloud collapses and each clump gets the average velocity of the clumps that formed it. Basically, it becomes more orderly as the cloud collapses. The observational evidence supporting this scenario include the infrared radiation we've detected from many nebulae where star systems appear to be forming. Also, other stars have flattened, spinning disks. Other support comes from computer simulations. Also, we see other examples (like the Milky Way, planetary rings, and accretion disks of neutron stars and black holes) of where flattening should occur because of the orbiting particles colliding.
What are the four major features of our solar system that provide clues to how it formed? Describe each one briefly.
a. Patterns of motion among large bodies- Sun, planets, large moons rotate in an organized way (co-planar)—nearly circular orbits in the same direction (coplanar and prograde) b. Two major types of planets- terrestrial vs. jovian planets c. Asteroids and comets- locations, orbits, and compositions follow distinct patterns—Asteroids are b/t Mars and Jupiter in the asteroid belt. Also located in the Kuiper belt and Oort Cloud d. Exceptions to the rules- Earth is inner planet with large moon, Uranus is only side tilted axis, etc.
