Ch. 9: Asteroid, Comets, and Dwarf Planets

A few hundred tons of comet dust are added to Earth daily from the millions of meteors that enter our atmosphere: Choose the approximate time it would take for Earth to get 0.1% heavier at this rate. Is this mass accumulation significant for Earth as a planet?

10^14 years This extra mass is unimportant compared to Earth's existing mass.

Choose all the pieces of the evidence suggesting that an impact caused the mass extinction that killed off the dinosaurs.

A worldwide layer of Earth's surface that is rich in iridium. Existence of the crater Chicxulub, on the Yucatán Peninsula, which is the right size and age. Different geological samples that show evidence of having experienced high temperatures and high pressures at the corresponding time.

Which statement is NOT thought to be true of all comets in our solar system?

Comets always have tails.

Listed following are some distinguishing characteristics of comets, meteors, and asteroids. Match these to the appropriate category of objects.

Comets: form a coma when near the Sunmost are located either in Kuiper belt or Oort cloudvisible in the sky as a fuzzy patch of light that rises and sets with the stars Meteors: visible in the sky as a bright streak of light for only a few secondsdust particles entering Earth's atmosphere at high speed Asteroids: compositions similar to that of the terrestrial planetstypically orbit the Sun at approximately 3 AU

What would happen if a 1-kilometer object struck the Earth?

It would cause widespread devastation and climate change.

In the case of the Oort cloud, close gravitational encounters between icy planetesimals and the ______________ caused the comets to move outwards to huge distances where they formed the Oort cloud. Nudges from other stars affected their orbits enough that most comets never reenter in the inner solar system.

Jovian planets

Sort each statement below into the appropriate bin based on whether it is something that scientists knew about Pluto or its moon Charon before the New Horizons flyby, is something learned as a result of the New Horizons flyby, or is something that seems possible from the New Horizons mission but for which we'll need additional data to establish it with certainty.

Known prior to New Horizons mission: Pluto is sometimes nearer to the Sun than Neptune/Pluto has a comet-like composition of ice and rock/Pluto is less massive than any of the terrestrial planets/Pluto is a member of the Kuiper belt Learned from New Horizons mission: Charon has huge, deep canyons/Pluto has smooth plains of nitrogen ice/Pluto's thin atmosphere contains haze particles that can fall to the surface/Pluto has tall mountains built of water ice Possible but not proven from New Horizons mission: Pluto has active volcanoes/Pluto has a subsurface ocean of liquid water

The _______________ extends from about beyond the orbit of Neptune to about twice the distance of Neptune from the Sun.

Kuiper belt

Which are thought to have formed farthest from the Sun?

Kuiper belt comets

After the New Horizons flyby, scientists concluded that Pluto has probably been geologically active within the past 100 million years or less. Why?

Large regions of the surface have very few impact craters.

The asteroid belt lies between the orbits of

Mars and Jupiter

Did a large terrestrial planet ever form in the region of the asteroid belt?

No, because Jupiter prevented one from accreting.

Which of the following statements about asteroids, Kuiper belt objects, and Oort cloud objects is true?

Objects in the asteroid belt and Kuiper belt orbit the Sun in nearly the same plane as the planets, but objects in the Oort cloud do not.

About a trillion comets are thought to be located far, far beyond Pluto in the

Oort Cloud

Which have the most elliptical and tilted orbits?

Oort cloud comets

Why didn't a planet form in the region of the solar system now occupied by the asteroid belt?

Orbital resonances with Jupiter disrupted orbits in this region.

In another star system, astronomers discover an object the size of Earth orbiting its star at the distance of the Kuiper belt.

Surprising. Terrestrial planets are not expected to form in regions where ice is common.

The evidence for recent geological activity on Pluto came as a surprise to most scientists, because they did not expect Pluto to retain enough heat to drive such activity. Which of the following best explains why Pluto is so geologically active despite its small size?

The activity involves nitrogen ice, so Pluto does not need much heat to cause this ice to undergo change.

Can an asteroid be pure metal?

Yes, it must have been the core of a shattered asteroid.

What does Pluto most resemble?

a comet

How big an object causes a typical shooting star?

a grain of sand or a small pebble

According to current evidence, Pluto is best explained as ______.

a large member of the Kuiper belt

A rock found on Earth that crashed down from space is called _________.

a meteorite

Scientist knew the_________________ of Pluto from Pluto's calculated density.

approximate composition

Scientist knew the_____________ of Pluto because the 1978 discovery of its moon Charon allowed them to calculate it with Newton's version of Kepler 19s third law.

approximate mass

Leftover planetesimals that formed inside the frost line are known as

asteroid

The jovian planets have profoundly affected the orbits of small bodies. Through the action of orbital resonances, Jupiter affects the ___________ belt and Neptune affects the ____________ belt.

asteroid/Kuiper

Among discovered meteorites, we have found some with all the following origins EXCEPT _________.

being a fragment from Comet Halley

The asteroid belt is located _________.

between the orbits of Mars and Jupiter

The bright spherical part of a comet observed when it is close to the Sun is the

coma

Leftover planetesimals that formed in the region of the solar system now occupied by the jovian planets are called

comets

Meteor showers are associated with debris from

comets

The objects that are sometimes visible in the night sky with long tails are

comets

In what ways might the impact have led to the mass extinction?

dust and smoke blocking sunlight acid rain changing chemistry in the atmosphere and oceans global wildfires

Ceres, Pluto, and Eris are all round in shape and classified as

dwarf planets

About how often does a 1-kilometer object strike the Earth?

every million years

A comet entering the inner solar system from afar will __________.

form a coma and some time later form a tail

Which direction do a comet's dust and plasma tails point?

generally away from the Sun

Scientists knew that Pluto is a ____________________ because they had discovered hundreds of other objects orbiting in the same region of the solar system.

member of the Kuiper belt

Particles ejected from a comet can cause a(n) ______________ on Earth.

meteor shower

Pieces of asteroids that have fallen to Earth are called

meteorites

A comet's ________ the frozen portion of a comet.

nucleus

A comet's plasma tail always points directly away from the Sun because __________.

of pressure exerted by the fast-moving charged particles in the solar wind

Jupiter nudges the asteroids through the influence of

orbital resonances

A typical meteor is created by a particle about the size of a _________.

pea

A comet's __________ stretches directly away from the Sun.

plasma tail

In the case of the asteroid belt the jovian influence _______________ the formation of a terrestrial planet. In both of the asteroid belt and the Kuiper belt cases, resonances further nudge the objects onto very elliptical orbits, which can result in ____________________.

prevented/collisions with the other planets

The biggest surprise from the New Horizons flyby of Pluto was learning that Pluto _________.

shows clear evidence of recent or ongoing geological activity

Scientists knew that Pluto is _________________________ because decades of observation at allowed them to precisely plot its orbit.

sometimes nearer to the Sun than Neptune

During the time that a comet passes through the inner solar system, the comet can appear quite bright because __________.

sunlight reflects off the comet's tail and coma

When a comet passes near the Sun, part of it takes on the appearance of a large, bright ball from which the tail extends. This part is called _________.

the coma