Chapter 9

Question 1

What are asteroids primarily composed of?

Answer 1

• Rocky remnants of planet formation
• Inner-solar system objects

Asteroids leave trails in long-exposure images due to their orbital motion around the Sun.

Question 2

What are comets primarily composed of?

Answer 2

• Icy remnants of the outer solar system
• Known for their appearance when near the Sun

Comets spend most of their time far from the Sun.

Question 3

What defines a dwarf planet?

Answer 3

• Large enough to be round
• Has not cleared its orbit

The category was adopted following the discovery of Eris.

Question 4

What is a meteor?

Answer 4

The flash of light produced as a small object enters the atmosphere

A meteorite is an object that survives its trip through the atmosphere and lands on the ground.

Question 5

What is the largest asteroid and its diameter?

Answer 5

Ceres, diameter ~1000 km

Ceres is also classified as a dwarf planet.

Question 6

What are the two types of meteorites?

Answer 6

• Primitive: Unchanged since formation
• Processed: Experienced processes like volcanism

Most meteorites are pieces of asteroids.

Question 7

Where do most asteroids orbit?

Answer 7

In a belt between Mars and Jupiter

Trojan asteroids follow Jupiter’s orbit, while near-Earth asteroids cross Earth’s orbit.

Question 8

What prevents the formation of a planet in the asteroid belt?

Answer 8

Orbital resonances with Jupiter

These resonances stirred up asteroid orbits and prevented their accretion into a planet.

Question 9

What is the nucleus of a comet often described as?

Answer 9

A ‘dirty snowball’

It is the source of material for the comet’s tail.

Question 10

What are the two main regions where comets originate?

Answer 10

• Oort Cloud: Random orbits
• Kuiper Belt: Orderly orbits at 30-100 AU

Comets in the Kuiper belt are aligned with the plane of planetary orbits.

Question 11

What is Pluto’s largest moon?

Answer 11

Charon

Charon is nearly as large as Pluto itself and likely formed from a major impact.

Question 12

What evidence suggests an impact caused the mass extinction of dinosaurs?

Answer 12

An iridium layer above dinosaur fossils

This layer was laid down about 65 million years ago, likely from a meteorite impact.

Question 13

True or false: Major impacts on Earth are very common.

Answer 13

FALSE

Major impacts are rare and occur approximately every 100 million years.

Question 14

What effect do jovian planets have on comets?

Answer 14

• Redirect comets toward Earth
• Eject many into the Oort Cloud

Jupiter’s gravity plays a significant role in this process.

Question 15

What is the Rosetta mission known for?

Answer 15

Orbiting comet 67P to observe its coma and tail growth

It provided valuable insights into comet behavior as they approach the Sun.

Question 16

What is the composition of Kuiper belt comets expected to be similar to?

Answer 16

Pluto

Not much is known about other Kuiper belt comets.

Question 17

What is the name of the first object of interstellar origin observed in the Solar System?

Answer 17

‘Oumuamua

It was designated as 1I/2017 U1.

Question 18

According to astronomers from Harvard, what may have been the purpose of ‘Oumuamua?

Answer 18

An alien spacecraft sent to investigate Earth

This hypothesis suggests an extraterrestrial origin.

Question 19

What did Micheli et al. (2018) report about ‘Oumuamua?

Answer 19

It showed deviations from a Keplerian orbit at high statistical significance

This indicates unusual acceleration not typical for comets.

Question 20

What natural phenomenon is suggested to explain ‘Oumuamua’s excess acceleration?

Answer 20

Solar radiation pressure

This is a force that can affect the trajectory of objects in space.

Question 21

What is the required mass-to-area ratio for ‘Oumuamua to explain its acceleration?

Answer 21

{m/A) 0.1 g cm²

This ratio is necessary for the object to be influenced by solar radiation pressure.

Question 22

What width is suggested for a thin sheet to achieve the required mass-to-area ratio for ‘Oumuamua?

Answer 22

• 0.3 — 0.9 mm

This dimension allows the object to survive interstellar travel.

Question 23

What potential origin for ‘Oumuamua is discussed in the text?

Answer 23

A lightsail of artificial origin

This suggests the possibility of advanced technology being involved.

Question 24

True or false: ‘Oumuamua is considered an active comet.

Answer 24

FALSE

Observational studies imply that ‘Oumuamua does not exhibit characteristics typical of active comets.

Question 25

What distances can an extremely thin object like **'Oumuamua** withstand during interstellar travel?

Answer 25

Galactic distances of 5 kpc ## Footnote This indicates its resilience against collisions with gas and dust.