Week 7

Approximately how old is the Solar System?

4.6 billion years

Which of the following assumptions of the original solar nebula hypothesis is probably WRONG in light of the evidence provided by extrasolar planets?

A planet's orbit does not change after the planet forms.

The material that would eventually make all the major bodies in our solar system first gathered together as smaller pieces which astronomers call

planetesimals.

Astronomers now believe that the differences in composition among the planets reflect what characteristic in the early solar system?

temperature

Our best evidence and theoretical calculations indicate that the solar system began with a giant spinning system of gas and dust that scientists call

the solar nebula.

One group of smaller objects in the solar system composed mainly of ices (frozen gases) that usually orbit far from the Sun are called

Kuiper Belt objects (KBOs).

All the planets (without exception)

revolve around the Sun in the same direction

From what did the Solar System form?

An interstellar cloud

Which of the following features of the Solar System does the solar nebula hypothesis explain?

1. All the planets orbit the Sun in the same direction. 2. All the planets move in orbits that lie in nearly the same plane. 3. The planets near the Sun don't contain a lot of ices compared to the planets far from the Sun. 4. All the planets and the Sun, to the extent that we know, are the same age.

Which of the following ways that Jovian (giant) planets differ from the terrestrial planets is NOT correct?

Jovians are made primarily of heavy elements like lead and uranium.

How did planetesimals form?

By the accumulation and sticking of dust and solid particles in the solar nebula.

One of the most perplexing issues raised by the discovery of thousands of exoplanets is the existence of "hot Jupiters" - planets with the masses and compositions of Jupiter, but orbiting closer to their stars than Mercury does in our solar system. What is our best idea currently about how such "hot Jupiters" came to be?

Hot Jupiters formed further out in their star system, and then migrated inward somehow.

Some of the early planetesimals that formed the solar system still survive today. Where would you find such planetesimals?

In the asteroid and Kuiper belts

Which of the following is a reason that astronomers have not found many giant planets with the orbit of Neptune around other stars?

Neptune takes 165 years to go around the Sun; getting information about just one cycle of such a planet's orbit around another star would take astronomers 165 years.

How do astronomers know that the age of the solar system is about 4.6 billion years old?

Radioactive dating of the primitive meteorites indicates they have that age (since they are left-over building blocks of the solar system).

Three kinds of worlds are round in our solar system. Which of the following is NOT a type of world that is typically round?

Small Solar System bodies (asteroids, comets, etc.)

Which of the following is NOT a characteristic that worlds in our solar system have in common?

That all the planets have solid surfaces on which we can see impact craters.

Which of the following characteristics do all four terrestrial planets have in common?

They all have solid surfaces made of silicate (rock).

The smaller objects in the solar system made of rock and metal (most of which orbit between Jupiter and Mars) are called

asteroids

One piece of evidence that can help astronomers sort out how the planets in our solar system formed is

finding circumstellar disks of material around nearby stars.

If you were to take a large sample of the four giant planets, the most common element you would find in them is

hydrogen.

The big surprise about the first planet discovered around another regular star was that it

orbited so close to its star it took only 4 days to go around.

One reason the planets near the Sun are composed mainly of rock and iron may be that

the Sun's heat made it difficult for ices to condense near it.

A key difference between the planetesimals that formed in the outer solar system and those that formed in the inner solar system was that

those in the outer solar system were in a place where ice, not just rock, condensed and thus could grow larger.

Which of the following is NOT one of the reasons planets around other stars are so difficult to detect?

planets only form very late in the life of a star, just when it is ready to die, and thus last only a very short fraction of the star's life.