Astronomy Chapter 6: Formation of Planetary Systems

Why is direct detection of extra solar planets so difficult? What can we learn from direct detection?

Direct detection is when pictures or spectra of planets themselves constitute direct evidence of their existence. It is preferable because it tells us far more about a planet's properties. Direct detection is difficult because of the great distances and the glare from the stars.

List the four categories of material in the solar nebula by their condensation properties and abundance. Which ingredients are present in terrestrial planets? In Jovian planets? Explain why.

1. Hydrogen and Helium: (98% of SN) never condense under the conditions present in a nebula. 2. Hydrogen compound: (1.4% of SN) materials such as water, methane, and ammonia can solidify into ice at low temps, below 15K 3. Rock: (0.4%) various minerals that are gaseous at high temps but condenses into solid form at temps between 500K-1300K 4. Metals: (0.2%) Includes iron, nickle, and aluminum, are also gaseous at high temps but condenses into solid form at temps higher than rocks, at 1000k-1600K

What was the heavy bombardment? When did it occur?

A period of time where impacts occurred during the first few hundred million years of our solar system's history. When every world of the solar system was pelted by impacts. Occurred 4.0-3.8 billion years ago.

What are asteroids and comets? How and why are they different?

Asteroids are the rocky leftover planetesimals of the inner solar system. Comets are the icy leftover planetesimals of the outer solar system.

What properties of extra solar planets and their orbits have forced a re-examination of the nebular theory? How have we modified the theory to explain these properties?

Because the extra solar planets orbit in an elliptical

What are the four major features of out solar system that provide clues to how it formed? Describe each one briefly.

Four major features provide clues: (1) The Sun, planets, and large moons generally rotate and orbit in a very organized way. (2) With the exception of Pluto, the planets divide clearly into two groups: terrestrial and jovian. (3) The solar system contains huge numbers of asteroids and comets. (4) There are some notable exceptions to these general patterns.

Briefly describe the layout of the solar system as it would appear from beyond the orbit of Neptune

It wouldn't look like much because the sun and the planets are all quite small compared to the distance between them. Planets orbiting the sun include Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Then Keipler Belt and Oort Cloud.

What is the nebular theory, and why is it widely accepted by scientists today?

Nebular theory is the idea that our solar system formed from the gravitational collapse of an interstellar cloud of gas. The nebula theory is the solar systems birth. Back then, people tried to find different explanations and alter the theory. Now, new discoveries have lead to modifications that favors the hypothesis.

Describe three major methods used to describe extra solar planets indirectly, what does each method tell you about the planet?

Observing the motion of a star to detect the subtle gravitational affects of orbiting planets and observing changes to a stars brightness that occur when one of its planets passed in front of the star as viewed from Earth.

Briefly summarize the known characteristics of extra solar planets.

Orbits: most orbit very closely to their host stars (closer than mercury to our sun). Many of the orbits are elliptical instead of circular. Masses: Most of these planets are more massive than Jupiter but less massive than Uranus and Neptune. Most extra solar planets are Jovian instead of terrestrial. Composition: Evidence of water and methane

Briefly explain the technique of radiometric dating, and describe how we use it to determine the age of the solar system.

Radiometric dating is a method for measuring the age of a rock and how long a rock has been solidified. It relies on careful measurement of the proportions of various atoms and isotopes of a rock. Atoms undergo a change with time, which allows us to determine how long they've been held w/ in the rock. We can find the time that passed once the rock has solidified.

What do we mean by the solar nebula? What is it made of, and where did it come from?

Solar nebula is the idea that our solar system was born from a cloud of gas and collapsed under its own gravity. The gas that made up the solar nebula contained hydrogen and helium from the Big Bang and heavier elements produced by stars.

What are the basic differences between terrestrial and Jovian planets? Which planets in our solar system fall into each group?

Terrestrial: four planets of the inner solar system include Mercury, Venus, Earth, and Mars. They are small and dense with rocky surfaces and an abundance of metals in their cores. They are close to the sun, have no rings, and have few moons. Jovian: Four large planets of the outer solar system include Jupiter, Saturn, Uranus, and Neptune. The are much larger in size and average density than terrestrial planets. They are made mostly of hydrogen and helium. They have rings and multiple moons.

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 is the minimum distance at which it was cold enough for ice to condense- which lay between the present day orbits of Jupiter and Mars. Temp differences birth two types of planets because the warmer inner regions are from seeds of metal and rock while the cool outer regions are born from seeds of ice.

Describe each of the three key processes that left the solar nebula to take the form of a spinning disk. What observational evidence supports this scenario?

The solar nebula shrank in size and altered its density, temp, and shape by three different processes changing it from a large diffuse, spread out, cloud to a smaller spinning disk: (1.) Heating: temp of solar nebula increased as it collapsed. As cloud shrank, GPE was converted to KE of individual gas particles falling inward. (2.) Spinning: like an ice skater pulling her arms in as she spins, the solar nebula rotated faster as the radius shrank. This increase in rotation rate represents conservation of angular momentum. Rapid rotation helped ensure that not all material collapsed at the center. (3.) Flattening: this flattening is a natural consequence of collision btwn particles in a spinning cloud. **b/c conservation of rotational motion even though gravity wants it to collapse. It can only collapse parallel to the axis.

Briefly describe the process by which terrestrial planets are thought to have formed. How was the formation of Jovian planets similar? How was is different? Why did the Jovian planets end up with so many moons

The terrestrial planets formed inside the frost line where accretion allowed tiny, small grains of metal and rock to grow into planetesimals which merged together to create the planets we have today. Jovian planets form through accretion but also with the addition of gas.

How do we think the moon formed, and what evidence supports this hypothesis?

We think the moon was formed by material that was ejected from Earth in a giant impact. The material in this impact was collected and the accretion with debris could have formed the moon. Evidence to support the hypothesis include two features of the moons composition: moons overall comp is similar to earth and moon has smaller proportion of vaporized ingredients that Earth.