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Which of the following statements about comets and asteroids is true?

Comets are balls of ice and dust.

What do asteroids and comets have in common?

Most are unchanged since their formation in the solar nebula.

A rocky leftover planetesimal orbiting the Sun is

an asteroid.

An icy leftover planetesimal orbiting the Sun is

a comet.

We know that there are large gaps in the average distances of asteroids from the Sun (within the asteroid belt) because we

have plotted distributions of the orbital radii of the asteroids.

Why do we sometimes observe asteroids at the distances of the gaps in the asteroid belt?

A gap is located at an average orbital distance, and asteroid orbits often have large eccentricities.

Why are small asteroids not spherical in shape?

The strength of gravity on small asteroids is less than the strength of the rock.

What is a meteorite?

a fragment of an asteroid from the solar system that has fallen to Earth's surfac

A typical shooting star in a meteor shower is caused by a ________ entering Earth's atmosphere.

pea-size particle from a comet

Primitive stony meteorites can be distinguished from other meteorites and terrestrial rocks because they

contain a noticeable fraction of pure metallic flakes.

Processed meteorites with high metal content probably are

chunks of a larger asteroid that was shattered by a collision

What part of a comet points most directly away from the Sun?

the plasma tail

Why does the plasma tail of a comet always point away from the Sun?

The solar wind blows the ions directly away from the Sun.

Where did comets that are now in the Oort cloud originally form?

near the jovian planets

Where did comets that are now in the Kuiper belt originally form?

near the radius at which they orbit today

Comets with extremely elliptical orbits, like comets Hyakutake and Hale-Bopp,

come from the Oort cloud.

What is the typical size of comets that enter the inner solar system?

10 km

According to the nebular theory, how did the Kuiper belt form?

It is made of planetesimals that formed beyond Neptune's orbit and never accreted to form a planet.

According to the nebular theory, how did the Oort cloud form?

It is made of planetesimals formed in the outer solar system that were flung into distant orbits by encounters with the jovian planets.

Rather than being a planet, Pluto is really just a large member of

the Kuiper belt.

Which of the following is furthest from the Sun?

a comet in the Oort cloud

What is the name of the largest known Kuiper Belt Object?


Why do asteroids and comets differ in composition?

Asteroids formed inside the frost line, while comets formed outside.

Why was the Shoemaker-Levy 9 impact so important to astronomers?

It dredged up material that gave us our first direct look at Jupiter's interior composition.

On average, how often do impactors about 10 km in size, large enough to produce mass extinction, hit Earth?

once every hundred million years

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