Astronomy chapter 6

The dwarf planet Eris was discovered in 2005, orbiting the Sun at an average distance about twice that of Pluto. In which of the following ways do Pluto and Eris differ from the terrestrial and jovian planets in our solar system?

1. Both Pluto and Eris are smaller than any of the terrestrial planets. 2. Both Pluto and Eris travel in more elliptical orbits than any of the terrestrial or jovian planets. 3. Both Pluto and Eris are less massive than any of the terrestrial or jovian planets.

Based on the nebular theory as it explains our own solar system, which of the following should we expect to be true for other star systems?

1. Planetary systems should generally have all planets orbiting in nearly the same plane. 2. Planetary systems should be common. 3. Jovian planets always form farther from their star than terrestrial planets. 4. Many extrasolar planets should fall into the terrestrial or jovian categories.

About how old is the solar system?

4.5 billion years

As you've seen, the nebular theory predicts that a cloud that gives birth to planets should have the shape of a spinning disk. Which observable property of our solar system supports this prediction?

All the planets orbit the Sun in the same direction and in nearly the same plane.

The nebular theory also predicts that the cloud will flatten into a disk as it shrinks in size. Which of the following best explains why the collapsing cloud should form a disk?

Colliding cloud particles exchange angular momentum and, on average, end up with the rotation pattern for the cloud as a whole.

The materials that made up the solar nebula can be categorized into the four general types as follows. Rank these materials from left to right based on their abundance in the solar nebula, from highest to lowest.

Hydrogen and helium gas constituted about 98 percent of the mass in the solar nebula. Most of the rest was hydrogen compounds, which were nearly three times as abundant as rock and metal combined.

The solar system has two types of planets, terrestrial and jovian. According to the nebular theory, why did terrestrial planets form in the inner solar system and jovian planets in the outer solar system?

Ices condensed only in the outer solar system, where some icy planetesimals grew large enough to attract gas from the nebula, while only metal and rock condensed in the inner solar system, making terrestrial planets.

Rank these materials from left to right based on the distance from the Sun at which they could condense into a solid in the solar nebula, from farthest to closest.

In the inner regions of the solar nebula, where temperatures were high, only metal and rock could condense, which is why the inner planets ended up being made of metal and rock. Farther out, hydrogen compounds could condense into ices, which is why comets and outer solar system moons contain large amounts of ice. And because hydrogen compounds are more abundant than metal or rock, some of the solid objects in the outer solar system grew so large that their gravity could pull in hydrogen and helium gas, which explains how the jovian planets formed.

What's unusual about our Moon?

It's surprisingly large relative to the planet it orbits.

What substances existed as solid flakes within the innermost regions (within about the inner 0.3 AU) of the solar system before planets began to form?

None. Although all the materials were present in gaseous form, the innermost regions (within about the inner 0.3 AU) of the newly forming solar system was too warm for even rocks or metals to condense into solid flakes.

Assuming that other planetary systems form in the same way as our solar system formed, where would you expect to find terrestrial planets?

Terrestrial planets will likely be located nearer the planetary system's star than any jovian planets.

Which planet is approximately halfway between Pluto's orbit and the Sun?

Uranus, the seventh planet from the Sun

Are there any exceptions to the rule that planets rotate with small axis tilts and in the same direction as they orbit the Sun?

Venus and Uranus are exceptions

How many of the planets orbit the Sun in the same direction as Earth does?

all

Where would you expect terrestrial planets to form in the solar nebula?

anywhere between the innermost regions (within about the inner 0.3 AU) and the frost line

Which lists the major steps of solar system formation in the correct order?

collapse, condensation, accretion

Leftover ice-rich planetesimals are called

comets

Which of the following did not occur during the collapse of the solar nebula?

concentrating denser materials nearer the Sun

Planetary orbits in our solar system are:

fairly circular and in the same plane.

The composition of the solar nebula was 98%

hydrogen and helium

What is Jupiter's main ingredient?

hydrogen and helium

Compared to terrestrial planets, jovian planets are __________.

more massive and lower in average density

The jovian planets are thought to have formed as gravity drew hydrogen and helium gas around planetesimals made of __________.

rocks, metals, and ices

What substances were found in the innermost regions (within about the inner 0.3 AU) of the solar system before planets began to form?

rocks, metals, hydrogen compounds, hydrogen, and helium, all in gaseous form

Observations show that interstellar clouds can have almost any shape and, if they are rotating at all, their rotation is not perceptible. However, the nebular theory predicts that a cloud will rotate rapidly once it shrinks to a relatively small size. What physical law explains why a collapsed cloud will rotate rapidly?

the law of conservation of angular momentum

The nebular theory also predicts that the cloud should heat up as it collapses. What physical law explains why it heats up?

the law of conservation of energy