Question 1

The description of a comet as a "dirty snowball" applies to the:

Accepted Answer

The "dirty snowball" description refers to the nucleus, which is the solid central part of the comet made up of ice and dust.

Question 2

The expected (and now measured, at least for Halley's Comet) size of the nucleus of a typical comet is about:

Accepted Answer

The nucleus of a typical comet, including Halley's Comet, is expected to be about 10 kilometers in diameter. This size has been confirmed through observations and measurements.

Question 3

The Deep Impact mission to Comet Tempel 1 measured the density of the comet's nucleus. This was found to be:

Accepted Answer

The Deep Impact mission found that the density of Comet Tempel 1's nucleus is less than the density of water, indicating it is not solid rock or iron but rather a "dirty snowball" composed of ice mixed with dust and rocky materials.

Question 4

As of 2013, we had done all of the following comet investigations EXCEPT ONE. Which is the EXCEPTION?

Accepted Answer

As of 2013, we had not yet achieved landing on the surface of a comet. This milestone was later achieved in November 2014 by the European Space Agency's Rosetta mission, which successfully landed its Philae probe on comet 67P/Churyumov-Gerasimenko.

Question 5

What experimental technique was used to discover the huge hydrogen cloud that surrounds the nucleus and the coma of a comet?

Accepted Answer

Rocketborne ultraviolet photography was used to discover the huge hydrogen cloud surrounding the nucleus and the coma of a comet. This technique is effective because hydrogen emits strongly in the ultraviolet part of the spectrum, which cannot be observed from the ground due to the Earth's atmosphere blocking most ultraviolet wavelengths.

Question 6

The huge hydrogen cloud that surrounds the nucleus of a comet has a typical diameter of about:

Accepted Answer

The huge hydrogen cloud that surrounds the nucleus of a comet is called the coma. Its typical diameter is about 1 million km. Therefore, the correct choice is C.

Question 7

The hydrogen envelope of a bright comet is:

Accepted Answer

The hydrogen envelope of a bright comet is not visible to the naked eye from Earth's surface due to its emission in the ultraviolet part of the spectrum, which is absorbed by Earth's atmosphere. It can be observed using ultraviolet telescopes that are positioned above the atmosphere.

Question 8

Comet tails are the result of:

Accepted Answer

Comet tails are formed due to the melting and evaporation of ices from the comet's nucleus as it approaches the sun. The heat causes the ices to sublimate and form a gas cloud around the nucleus, which is then blown away by solar wind particles, creating the tail.

Question 9

A comet's gas and ion tail:

Accepted Answer

The gas and ion tail of a comet is always blown away from the comet in the direction opposite to the Sun. This is due to the solar wind, which consists of charged particles emitted by the Sun, pushing the comet's material away from it.

Question 10

Which of the following governs the direction in which a comet's ion tail is aligned in space?

Accepted Answer

The direction of a comet's ion tail is governed by the solar wind, which is a stream of charged particles emanating from the Sun. The solar wind affects the ionized particles in the comet's tail, causing it to be aligned in a direction away from the Sun. This means that the ion tail will generally point away from the Sun, but the precise direction will depend on various factors such as the comet's velocity and orientation relative to the solar wind.

Question 11

Which one of the following parts of a comet is not visible to the naked eye?

Accepted Answer

The hydrogen envelope of a comet is not visible to the naked eye as it is made up of neutral hydrogen atoms that do not interact with visible light. The dust tail is visible as it is composed of small particles reflecting sunlight, the ion tail is visible due to the interaction of charged particles with the solar wind, and the coma is a visible atmosphere surrounding the nucleus of the comet.

Question 12

Comets that we find in the Kuiper belt are believed to have formed:

Accepted Answer

Comets in the Kuiper Belt are believed to have formed in the region where we currently observe them, which is in a band beyond the orbit of Pluto. This region is thought to be a reservoir of small icy bodies left over from the formation of the solar system.

Question 13

Why do most comets have very elliptical orbits, often extending far out beyond the orbit of Pluto?

Accepted Answer

Comets formed outside the orbit of Pluto in the Kuiper Belt or Oort Cloud and were then flung into highly elliptical orbits by the gravitational interactions with the giant planets. This explains why most comets have very elongated orbits that extend far beyond the orbit of Pluto.

Question 14

What is the approximate orbital period of an object that is moving in a circular orbit around the Sun at the inner edge of the doughnut-shaped part of the Oort cloud?

Accepted Answer

The inner edge of the Oort cloud is thought to be about 2,000 to 5,000 astronomical units (AU) from the Sun. Using Kepler's third law of planetary motion, which relates the orbital period of a body to its average distance from the Sun, an object at this distance would have an orbital period of approximately 100,000 years.

Question 15

The nearest star beyond the Sun is Proxima Centauri, which is approximately 4.22 ly away. Suppose Proxima Centauri is surrounded by an Oort cloud the same size as our own. What would be the distance between these Oort clouds as a fraction of the distance between these two stars?

Accepted Answer

The distance between the two Oort clouds would be proportional to the distance between the two stars. The ratio of the distances can be calculated as follows:

Distance between Oort clouds = 2 x distance from star to Oort cloud
Distance between Proxima Centauri and its Oort cloud = 4.22 ly
Distance between our Sun and its Oort cloud = 0.5 ly (approximately)
Distance between the two Oort clouds = 2 x (4.22 ly + 0.5 ly) = 9.44 ly
Ratio of distances = (9.44 ly) / (4.22 ly) = 2.234
Therefore, the distance between the two Oort clouds is 2.234 times the distance between the two stars. Expressed as a fraction, this is approximately 0.63. Therefore, the answer is B.

Question 16

A typical comet loses what fraction of its mass each time it passes close to the Sun (i.e., at each perihelion passage)?

Accepted Answer

A typical comet loses about 0.5% to 1% of its mass each time it passes close to the Sun. This is due to the heat causing some of the ice and dust on the comet's surface to vaporize into space. Over time, this can significantly affect the comet's size and composition.

Question 17

The number of times that a typical comet can pass close to the Sun (i.e., the number of orbits that the comet can complete) before it completely vaporizes is between:

Accepted Answer

The answer of The number of times that a typical...

Question 18

Showers of shooting stars or meteors are seen at regular times each year on Earth because:

Accepted Answer

Showers of shooting stars or meteors are typically caused by Earth passing through a cloud of debris left behind by a comet. This debris is made up of dust and small rock fragments that burn up as they enter Earth's atmosphere, creating the visible streaks of light in the sky. These showers are regular because Earth passes through debris clouds at the same time each year as it orbits the Sun, corresponding to the path of the comet that left the debris behind.

Question 19

Suppose an intense meteor shower occurs on a certain date this year, but there was no shower last year on that date, and it turns out that there is no shower next year on that date. A likely explanation is that:

Accepted Answer

The fact that there was no shower last year and there will be no shower next year suggests that the source of the meteor shower is not a regular occurrence. Option A provides a likely explanation for this: Earth passed through the orbit of a recently disintegrated comet, one for which the debris is not yet distributed along the entire orbit. This would account for the singular occurrence of the meteor shower on this date.

Question 20

When the solar system first formed, there were numerous icy planetesimals in the vicinity of the newly formed jovian planets. What happened to most of these planetesimals?

Accepted Answer

Most of the icy planetesimals were expelled from the solar system by gravitational interactions with the massive jovian planets, particularly Jupiter.

Quiz 15: Asteroids, Comets, and Impacts