Chapter 12

Which is closest to the average distance between asteroids in the asteroid belt?

1 million km

What is the size of the largest asteroid?

1,000 KM

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

10 km

When was Pluto discovered?

80 years ago

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 do asteroids and comets differ in composition?

Asteroids formed INSIDE the frost line, while comets formed OUTSIDE.

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

Comets are balls of ice and dust

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.

How does the largest asteroid, Ceres, compare in size to other solar system worlds?

It is about a quarter the size of the Moon

What do asteroids and comets have in common?

Most are unchanged since their formation in the solar nebula.

Which of the following does NOT lend support to the idea that Pluto is a Kuiper-belt object?

Pluto is regarded by many to be a planet.

What is Charon?

Pluto's moon

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

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

Why aren't small asteroids spherical in shape?

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

Why won't Pluto collide with Neptune?

The two planets have an orbital resonance that prevents them from colliding.

An icy leftover planetesimal orbiting the Sun is

a comet

What is a meteorite?

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

The number of comets in the Oort cloud is probably about

a trillion

What characteristic distinguishes a meteorite from a terrestrial rock?

all of the above A) A meteorite is usually covered with a dark crust from burning in Earth's atmosphere. B) A meteorite usually has a high metal content. C) Meteorites have different isotope ratios of particular elements when compared to terrestrial rocks. D) Meteorites contain rare elements, such as iridium, that terrestrial rocks do not.

Meteorites can come from

all of the above A.) the cores of asteroids b.) the moon c.) Mars d.) comets

Where are the Trojan asteroids located?

along Jupiter's orbit, 60° ahead of and behind Jupiter

A rocky leftover planetesimal orbiting the Sun is

an asteroid

In order to have a comet named after you, you have to

be one of the first three discoverers who report it to the International Astronomical Union (IAU).

How can we determine an asteroid's reflectivity?

by comparing its infrared thermal emission to its visible-light reflection

Halley's comet is named after the English scientist Edmund Halley because he

calculated its orbit and predicted that it would return in 1758.

Processed meteorites with low metal content probably are

chunks of a larger asteroid that was shattered by a collision.

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

come from the Oort cloud.

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

contain a noticeable fraction of pure metallic flakes.

If we know the size of an asteroid, we can determine its density by

determining its mass from its gravitational pull on a spacecraft, satellite, or planet.

Which of the following Pluto observations did not help convince scientists to change Pluto's status from that of a planet?

discovery of large Kuiper Belt Objects

In the asteroid impact theory of the extinction of the dinosaurs some 65 million years ago, the dinosaurs (and over half of all the other species on Earth at that time) died off largely because

dust injected into the stratosphere from the impact absorbed visible light from the Sun, causing global temperatures to plummet.

Why isn't there a planet where the asteroid belt is located?

gravitational tugs from Jupiter prevented material from collecting together to form a planet.

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.

When do comets generally begin to form a tail?

inside of Jupiter's orbit

The combined mass of all the asteroids in the asteroid belt is

less than that of any terrestrial planet.

What do we call a small piece of solar system debris found on Earth?

meteorite

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

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

once every hundred million years

The large gaps in the asteroid belt (often called Kirkwood gaps) are caused by

orbital resonances with Jupiter.

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

pea-size particle from a comet

Most meteorites are

rocky and primitive.

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

the plasma tail