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Chapter 15: Problem 45

For many years it was thought that the Tunguska event was caused by a comet striking the Earth. This idea was rejected because a small comet would have broken up too high in the atmosphere to cause significant damage on the ground. Explain why, using your knowledge of a comet's structure.

Short Answer

Expert verified
A comet comprises primarily of ice, dust, and rocks. As it enters Earth's atmosphere, the heat and friction caused by the atmosphere cause the ice to sublimate and the comet to break apart. This effect would be significant in a smaller comet, resulting in its disintegration high in the atmosphere, thus preventing any major ground damage.

Step by step solution

01

Understanding a Comet's Composition

Comets are celestial bodies that orbit the sun, just like planets. They are composed primarily of ice, dust, and rocky material. The icy portion consists of water, carbon dioxide, ammonia, and other frozen gases. When the comet approaches the sun, the ice begins to vaporize and create a 'coma' - a bright, hazy cloud around the comet's nucleus.
02

The Role of Earth's Atmosphere

Earth's atmosphere acts as a protective shield against many celestial objects. As these objects enter the atmosphere, they face significant frictional force which results in intense heat. This intense heat is capable of disintegrating small objects before they reach the ground.
03

Why the Comet Breaks Up in the Atmosphere

Given a comet's composition being primarily fragile and volatile materials, it would start to disintegrate under the intense heat generated by the friction with Earth's atmosphere. Because the majority of a comet is made up of ices, the high thermal energy leads to rapid sublimation of this ice into gaseous form. Consequently, a small comet would not maintain its integrity and would break apart high in the atmosphere, before it could cause any significant damage on the ground.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Comet Structure
Comets are fascinating celestial bodies, known for their striking tails and distinctive glowing comas. A typical comet is made up of three main parts: the nucleus, the coma, and the tail. Each part plays a role in how a comet behaves and how it interacts with other objects, such as planets.

  • Nucleus: At the core of the comet lies the nucleus, which is made of ice, dust, and rocky materials. It's often compared to a 'dirty snowball' due to its icy makeup.
  • Coma: When a comet approaches the sun, the heat causes the ice to vaporize, forming a glowing atmosphere around the nucleus called the coma.
  • Tail: The released gases and dust form a tail that points away from the sun. This tail can stretch for millions of kilometers.
These components make comets intriguing but also fragile. The ice in the nucleus is prone to sublimation, especially when a comet nears a heat source like the sun or experiences the friction of an atmosphere.
Earth's Atmosphere
Earth's atmosphere serves as a protective barrier safeguarding our planet from many hazards. This layer of gases not only contains the oxygen we breathe but also acts as a shield against incoming celestial bodies. As objects such as meteors or small comets try to enter Earth's atmosphere, they encounter a significant hurdle due to:

  • Friction: The fast-moving object faces resistance from the air particles, generating intense heat.
  • Thermal Energy: This heat is crucial in breaking apart smaller objects due to their rapid increase in temperature.
This protective nature of the atmosphere means that smaller comets, rich in volatile materials like ice, tend to disintegrate upon entry. The increasing temperatures cause the icy core of a comet to vaporize quickly, mitigating the chance of them reaching Earth's surface.
Comet Composition
Understanding a comet's composition provides insight into its behavior and potential interactions with planets. Comets possess a unique blend of materials that define their structure and lifecycle.

  • Ice: A significant portion of a comet comprises various ices, including water, carbon dioxide, and methane. These ices are critical in determining how a comet behaves as it nears heat sources.
  • Dust and Rock: Along with ices, comets contain dust and rocky particles, contributing to the solid aspect of the nucleus.
  • Frozen Gases: In addition to ice, comets also hold gases like ammonia in a frozen state, which sublimates to form the coma when near the sun.
The interplay of these materials means that when a comet pierces through atmospheric layers, especially one as thick as Earth's, its fragile constitution often leads to quick disintegration.
Celestial Bodies
Celestial bodies encompass a diverse array of objects found in the universe, each with unique features and behaviors. Comets, as part of this group, present intriguing qualities that have intrigued humans for centuries. They share the universe with:

  • Planets: Bodies that orbit stars and do not emit their own light. Earth is our most familiar example.
  • Asteroids: Rocky objects, often found in belts, with compositions primarily of metal and rock.
  • Meteoroids: Smaller fragments often resulting from broken up comets or asteroids, which can become meteors upon entering a planet's atmosphere.
Each of these bodies interacts within the cosmos in a dance influenced by gravity, proximity to stars, and their intrinsic properties. This diversity results in varied interactions, such as comets sometimes vaporizing and forming tails when they spin close to the sun or planets.

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Most popular questions from this chapter

What led astronomers to suspect that there were members of the solar system that orbit between Mars and Jupiter?

Use the Starry Night Enthusiast ?M program to study the motion of a comet. First set up the field of view so that you are observing the inner solar system from a distance (select Solar System > Inner Solar system in the Favourites menu). In the toolbar, click on the Stop button to halt the animation, and then set the date to January 1,1995 , and the time step to 1 day. Select View \(>\) Solar System \(>\) Asteroids in the menu to remove the asteroids from the view. Open the Find pane and center on Comet Hyakutake by typing "Hyakutake" in the Search All Databases box and then pressing the Enter key. Use the Zoom controls to decrease the field of view to about \(25^{\circ} \times\) \(17^{\circ}\). Then click on the Run Time Forward button. (a) Watch the motion of Comet Hyakutake for at least two years of simulated time. Describe what you see. Is the comet's orbit in about the same plane as the orbits of the inner planets, or is it steeply inclined to that plane? (You can tilt the plane of the solar system by holding down the Shift key while clicking on and moving the mouse to investigate this off-ecliptic motion.) How does the comet's speed vary as it moves along its orbit? During which part of the orbit is the tail visible? In what direction does the tail point? (b) Click on the Stop button to halt the animation, and set up the field of view so that you are observing from the center of a transparent Earth by selecting Guides \(>\) Atlas in the Favourites menu. Set the date to January 1, 1995, and the Time Flow Rate to 1 day, and again center on Comet Hyakutake. Use the controls at the righthand end of the toolbar to zoom out as far as possible. Then click on the Run Time Forward button and watch the comet's motion for at least two years of simulated time. Describe the motion, and explain why it is more complicated than the motion you observed in part (a). (c) Stop the animation, set the date to today's date, set the Time Flow Rate to 1 month ("lunar m."), and restart the animation. Comet Hyakutake is currently moving almost directly away from the Sun and so, as seen from the Sun, its position on the celestial sphere should not change. Is this what you see in Stamy Night Enthusiast \(\mathrm{\text {??? }}\) Explain any differences. (Hint: You are observing from the Earth, not the Sun.)

A very crude model of a typical comet nucleus is a cube of ice (density \(1000 \mathrm{~kg} / \mathrm{m}^{3}\) ) \(10 \mathrm{~km}\) on a side. (a) What is the mass of this nucleus? (b) Suppose \(1 \%\) of the mass of the nucleus evaporates away to form the comet's tail. Suppose further that the tail is 100 million \(\left(10^{8}\right) \mathrm{km}\) long and 1 million \(\left(10^{6}\right) \mathrm{km}\) wide. Estimate the average density of the tail (in \(\mathrm{kg} / \mathrm{m}^{3}\) ). For comparison, the density of the air you breathe is about \(1.2 \mathrm{~kg} / \mathrm{m}^{3}\). (c) In 1910 the Earth actually passed through the tail of Comet Halley. At the time there was some concern among the general public that this could have deleterious effects on human health. Was this concern justified? Why or why not?

A NASA spacecraft called Dawn is intended to go into orbit around two asteroids, 1 Ceres and 4 Vesta. Search the World Wide Web for information about this mission. Why were these two particular asteroids selected for study? What types of observations will the spacecraft make?

The asteroid 243 Ida, which was viewed by the Galileo spacecraft, is a member of a Hirayama family. Discuss what this tells us about the history of this asteroid. Where might you look to find other members of the same family?
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