Astronomy Chapter 6

According to modern scientific dating techniques, approximately how old is the solar system?

4.5 billion years

According to modern science, what was the approximate chemical composition of the solar nebula?

98% hydrogen and helium, 2% everything else (the sun still has this basic composition today)

Suppose you view the solar system from high above Earth's North Pole. Which of the following statements about planetary orbits will be true?

All the planets orbit counterclockwise around the Sun. (This is a consequence of the way the planets formed in a spinning disk around the young Sun.

Which of the following types of material can condense into what we call ice at low temperatures?

Hydrogen compounds

According to our theory of solar system formation, what three major changes occurred in the solar nebula as it shrank in size?

It got hotter, its rate of rotation increased, and it flattened into a disk. (Heating is a consequence of conservation of energy, faster rotation is a consequence of conservation of angular momentum, and flattening is a consequence of collisions between objects in a spinning system.

What do we mean by the frost line when we discuss the formation of planets in the solar nebula?

It is a circle at a particular distance from the Sun, beyond which the temperature was low enough for ices to condense.

Jovian

Jupiter,Saturn,Uranus, and Neptune

According to our theory of solar system formation, what are asteroids and comets?

Leftover planetesimals that never accreted into planets (Asteroids are the rocky leftovers of the inner solar system and comets are the icy leftovers of the outer solar system.)

Terrestrial Plantes

Mercury,Venus,Earth and Mars (Note that the Moon isn't technically a planet, though we'll discuss its properties along with the terrestrial planets in later chapters.)

What is the giant impact hypothesis for the origin of the Moon?

The Moon formed from material blasted out of the Earth's mantle and crust by the impact of a Mars-size object.

Our Sun

The Sun is made mostly of hydrogen and helium. The Sun contains more than 98% of all the mass in our solar system. The Sun is a star.

What do we mean by the period of heavy bombardment in the context of the history of our solar system?

The first few hundred million years after the planets formed, which is when most impact craters were formed

What do we mean by accretion in the context of planet formation?

The growth of planetesimals from smaller solid particles that collided and stuck together

The terrestrial planets are made almost entirely of elements heavier than hydrogen and helium. According to modern science, where did these elements come from?

They were produced by stars that lived and died before our solar system was born.

The planet in our solar system with the highest average surface temperature is _____.

Venus (Venus's extreme temperature is caused by its very strong greenhouse effect.)

Statements about Mars

We have landed spacecraft on its surface. It is frozen today, but once had flowing water. It is considered part of our inner solar system.

When we say that jovian planets contain significant amounts of hydrogen compounds, we mean all the following chemicals except __________.

YES, methane-ammonia-water NO, carbon dioxide

Suppose you start with 1 kilogram of a radioactive substance that has a half-life of 10 years. Which of the following statements will be true after 20 years pass?

You'll have 0.25 kilogram of the radioactive substance remaining.

According to our present theory of solar system formation, which of the following lists the major ingredients of the solar nebula in order from the most abundant to the least abundant?

hydrogen and helium gas; hydrogen compounds; rock; metal

In essence, the nebular theory holds that

our solar system formed from the collapse of an interstellar cloud of gas and dust (this cloud of gas and dust that gave birth to our solar system is called the solar nebula)