Chapter 12

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 isan asteroid
An icy leftover planetesimal orbiting the Sun isa comet
Why do asteroids and comets differ in composition?Asteroids formed INSIDE the frost line, while comets formed OUTSIDE.
What is the size of the largest asteroid?1,000 KM
How does the largest asteroid, Ceres, compare in size to other solar system worlds?It is about a quarter the size of the Moon
Which is closest to the average distance between asteroids in the asteroid belt?1 million km
The combined mass of all the asteroids in the asteroid belt isless than that of any terrestrial planet.
Where are the Trojan asteroids located?along Jupiter’s orbit, 60° ahead of and behind Jupiter
We know that there are large gaps in the average distances of asteroids from the Sun (within the asteroid belt) because wehave plotted distributions of the orbital radii of the asteroids.
The large gaps in the asteroid belt (often called Kirkwood gaps) are caused byorbital resonances with Jupiter.
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 isn’t there a planet where the asteroid belt is located?gravitational tugs from Jupiter prevented material from collecting together to form a planet.
How can we determine an asteroid’s reflectivity?by comparing its infrared thermal emission to its visible-light reflection
If we know the size of an asteroid, we can determine its density bydetermining its mass from its gravitational pull on a spacecraft, satellite, or planet.
Why aren’t small asteroids 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 surface
What do we call a small piece of solar system debris found on Earth?meteorite
A typical shooting star in a meteor shower is caused by a ________ entering Earth’s atmosphere.pea-size particle from a comet
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.

Primitive meteorites can be distinguished from other meteorites and terrestrial rocks because theycontain a noticeable fraction of pure metallic flakes.
Most meteorites arerocky and primitive.
Processed meteorites with low metal content probably arechunks of a larger asteroid that was shattered by a collision.
Meteorites can come fromall of the above
A.) the cores of asteroids
b.) the moon
c.) Mars
d.) comets
Halley’s comet is named after the English scientist Edmund Halley because hecalculated its orbit and predicted that it would return in 1758.
In order to have a comet named after you, you have tobe one of the first three discoverers who report it to the International Astronomical Union (IAU).
When do comets generally begin to form a tail?inside of Jupiter’s orbit
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 electromagnetically “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.
The number of comets in the Oort cloud is probably abouta trillion
What is the typical size of comets that enter the inner solar system?10 km
When was Pluto discovered?80 years ago
Why won’t Pluto collide with Neptune?The two planets have an orbital resonance that prevents them from colliding.
What is Charon?Pluto’s moon
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.
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 becausedust injected into the stratosphere from the impact absorbed visible light from the Sun, causing global temperatures to plummet.
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
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