Asteroids, Comets, and Meteoroids

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INTRODUCTION

On the night of July 23, 1995, astronomers Alan Hale and Tom Bopp discovered Comet Hale-Bopp from different locations. Hale and Bopp were the first people in more than 3000 years to view what is now officially known as Comet Hale-Bopp (Comet H-B for short). This may have been the biggest comet ever visible from Earth.

During this lesson, you will examine the orbits of asteroids and comets within the solar system and the possible effects of asteroid and comet impact on the planets. What do you already know and want to know about asteroids, comets, and meteoroids? How are they alike or different? What are some of the possible effects of their impact on Earth and other planets? In this les-son, you will explore these and other questions.

17 Asteroids, Comets,

and Meteoroids

OBJECTIVES FOR THIS LESSON

Analyze the position of the asteroid belt using mathematical patterns.

Brainstorm what you know and want to know about asteroids, comets, and meteoroids; make comparisons among them.

Analyze the ability of scientists to forecast asteroid and comet impact, and explore the challenges of making such forecasts.

Read to learn more about

Earth-Comet Hale-Bopp. The white dust tail is composed of large particles of dust and ice. The gas tail is blue.

ARREN/CORBIS

Getting Started

1.

With your class, review your homework from Lesson 16, Student Sheet 16: Bode’s Law.

2.

Read “Asteroids, Comets, and Meteoroids.” Carefully examine the photos in the read-ing selection. How are asteroids similar to or different from comets and meteoroids? Record a summary of your ideas in your science notebooks. Then discuss them as a class or within your group, as instructed by your teacher. MATERIALS FOR LESSON 17 For you 1 completed copy of Student Sheet 16: Bode’s Law 1 working copy of Student Sheet 10.1c: Planetary Chart

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INTRODUCTION

On the night of July 23, 1995, astronomers Alan Hale and Tom Bopp discovered Comet Hale-Bopp from different locations. Hale and Bopp were the first people in more than 3000 years to view what is now officially known as Comet Hale-Bopp (Comet H-B for short). This may have been the biggest comet ever visible from Earth.

During this lesson, you will examine the orbits of asteroids and comets within the solar system and the possible effects of asteroid and comet impact on the planets. What do you already know and want to know about asteroids, comets, and meteoroids? How are they alike or different? What are some of the possible effects of their impact on Earth and other planets? In this les-son, you will explore these and other questions.

17 Asteroids, Comets,

and Meteoroids

OBJECTIVES FOR THIS LESSON

Analyze the position of the asteroid belt using mathematical patterns.

Brainstorm what you know and want to know about asteroids, comets, and meteoroids; make comparisons among them.

Analyze the ability of scientists to forecast asteroid and comet impact, and explore the challenges of making such forecasts.

Read to learn more about

Earth-Comet Hale-Bopp. The white dust tail is composed of large particles of dust and ice. The gas tail is blue.

ARREN/CORBIS

Getting Started

1.

With your class, review your homework from Lesson 16, Student Sheet 16: Bode’s Law.

2.

Read “Asteroids, Comets, and Meteoroids.” Carefully examine the photos in the read-ing selection. How are asteroids similar to or different from comets and meteoroids? Record a summary of your ideas in your science notebooks. Then discuss them as a class or within your group, as instructed by your teacher. MATERIALS FOR LESSON 17 For you 1 completed copy of Student Sheet 16: Bode’s Law 1 working copy of Student Sheet 10.1c: Planetary Chart

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Inquiry 17.1

Examining Asteroids

PROCEDURE

1.

In the program Explore the Planets,

review the Asteroids segment in the “Tour the Planets” section. Discuss the concepts with your class.

2.

Make general observations about the asteroids shown on the program. Look back at Lesson 12. How do you think Barringer (Meteor) Crater and the craters on the surface of asteroids Gaspra and Ida were formed? Discuss or record your ideas, as instructed by your teacher.

REFLECTING ON WHAT YOU’VE DONE

Answer the following questions in your science notebook, and be prepared to discuss your ideas with the class:

A. How and when do scientists think asteroids may have formed?

B. Why do you think the belt of asteroids exists between Jupiter and Mars?

C. How are the orbits of asteroids similar to, or different from, planetary orbits?

Inquiry 17.2

Studying Asteroid Impact

PROCEDURE

1.

Read “A Fiery Necklace.” How did Dr. Eugene Shoemaker contribute to the understanding of asteroid and comet impacts? Record your ideas in your notebook.

1.

In your notebook, record your ideas to the following, and be prepared to discuss them with your class:

A. How has Earth’s history been influ-enced by occasional natural catastrophes, such as asteroid impacts?

B. An asteroid impact is considered a nat-ural hazard on Earth, but it is not consid-ered a natural hazard on any other planet or moon. Given this information, how would you define “natural hazard?” C. What is the scientist’s role in forecast-ing asteroid and comet impacts?

D. What challenges do scientists face when they forecast asteroid or comet impacts? E. What is the scientist’s role in reducing the risks of such an event?

2.

Return to your list of ideas about aster-oids, comets, and meteoroids. What new things do you want to add to your list? Make your changes and additions now.

3.

With your class, return to the Question J

folder for Lesson 1. Is there anything that you would now change or add? Discuss your ideas with the class.

4.

Read “Mission: Earth.” Add any new information about Earth to your working copy of Student Sheet 10.1c: Planetary Chart. Complete your planetary brochure. You will present your planetary brochure and your team’s mission design to the class in Lesson 19.

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Inquiry 17.1

Examining Asteroids

PROCEDURE

1.

In the program Explore the Planets,

review the Asteroids segment in the “Tour the Planets” section. Discuss the concepts with your class.

2.

Make general observations about the asteroids shown on the program. Look back at Lesson 12. How do you think Barringer (Meteor) Crater and the craters on the surface of asteroids Gaspra and Ida were formed? Discuss or record your ideas, as instructed by your teacher.

Answer the following questions in your science notebook, and be prepared to discuss your ideas with the class:

A. How and when do scientists think asteroids may have formed?

B. Why do you think the belt of asteroids exists between Jupiter and Mars?

C. How are the orbits of asteroids similar to, or different from, planetary orbits?

Inquiry 17.2

Studying Asteroid Impact

PROCEDURE

1.

Read “A Fiery Necklace.” How did Dr. Eugene Shoemaker contribute to the understanding of asteroid and comet impacts? Record your ideas in your notebook.

1.

In your notebook, record your ideas to the following, and be prepared to discuss them with your class:

A. How has Earth’s history been influ-enced by occasional natural catastrophes, such as asteroid impacts?

B. An asteroid impact is considered a nat-ural hazard on Earth, but it is not consid-ered a natural hazard on any other planet or moon. Given this information, how would you define “natural hazard?” C. What is the scientist’s role in forecast-ing asteroid and comet impacts?

D. What challenges do scientists face when they forecast asteroid or comet impacts? E. What is the scientist’s role in reducing the risks of such an event?

2.

Return to your list of ideas about aster-oids, comets, and meteoroids. What new things do you want to add to your list? Make your changes and additions now.

3.

With your class, return to the Question J

folder for Lesson 1. Is there anything that you would now change or add? Discuss your ideas with the class.

4.

Read “Mission: Earth.” Add any new information about Earth to your working copy of Student Sheet 10.1c: Planetary Chart. Complete your planetary brochure. You will present your planetary brochure and your team’s mission design to the class in Lesson 19.

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the asteroid belt—a vast, doughnut-shaped ring located between the orbits of Mars and Jupiter (see the illustration below). Gaspra and Ida, pictured on the next page, are two asteroids found in the main belt. Some scien-tists theorize that asteroids may be pieces of a planet that never formed because Jupiter’s great mass exerted too much gravitational force to allow the pieces to combine into one planet.

Among the planets in the solar system are countless numbers of asteroids, comets, and meteoroids. Let’s take a look at how these solar system objects are different from planets.

Asteroids

Asteroids are metallic, rocky objects in space. They have no atmospheres and move in inde-pendent orbits around the Sun. Tens of thou-sands of asteroids are found in an area called

The asteroid belt is located between Jupiter and Mars. Mars Jupiter

Asteroids, Comets,

and Meteoroids

Image of asteroid 951, Gaspra, taken by the Galileospacecraft

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Image of the asteroid 243, Ida, and its small satellite, Dactyl. Dactyl is the small object to the right of Ida.

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Because asteroids are too small to be classified as planets, they are often called “minor planets.” Some asteroids are the size of a small building. Ceres was the first asteroid scientists observed. Discovered in 1801, it is about 1000 kilometers across and one of the largest known asteroids. Another asteroid, discovered in 2001, is about half the size of Pluto (or 1150 kilometers). Most asteroids are actually less than a kilometer wide. If we could combine all of these asteroids, they would be smaller than half the size of the Moon.

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the asteroid belt—a vast, doughnut-shaped ring located between the orbits of Mars and Jupiter (see the illustration below). Gaspra and Ida, pictured on the next page, are two asteroids found in the main belt. Some scien-tists theorize that asteroids may be pieces of a planet that never formed because Jupiter’s great mass exerted too much gravitational force to allow the pieces to combine into one planet.

Among the planets in the solar system are countless numbers of asteroids, comets, and meteoroids. Let’s take a look at how these solar system objects are different from planets.

Asteroids

Asteroids are metallic, rocky objects in space. They have no atmospheres and move in inde-pendent orbits around the Sun. Tens of thou-sands of asteroids are found in an area called

The asteroid belt is located between Jupiter and Mars. Mars Jupiter

Asteroids, Comets,

and Meteoroids

Image of asteroid 951, Gaspra, taken by the Galileospacecraft

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ACE ADMINISTRA

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ATES GEOLOGICAL SUR

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Image of the asteroid 243, Ida, and its small satellite, Dactyl. Dactyl is the small object to the right of Ida.

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TION/JET PROPULSION LABORA

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Because asteroids are too small to be classified as planets, they are often called “minor planets.” Some asteroids are the size of a small building. Ceres was the first asteroid scientists observed. Discovered in 1801, it is about 1000 kilometers across and one of the largest known asteroids. Another asteroid, discovered in 2001, is about half the size of Pluto (or 1150 kilometers). Most asteroids are actually less than a kilometer wide. If we could combine all of these asteroids, they would be smaller than half the size of the Moon.

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This photo shows two tails shed by Comet Hale-Bopp. The blue tail points directly away from the Sun. The white tail is cre-ated by bits of grit that have come off the comet’s nucleus. They are being pushed away by the solar winds from the Sun. Comets

A comet is a mass of frozen gas, cosmic dust, and ice crystals. Comets are often described as “dirty icebergs.” They circle the Sun in long, narrow orbits, mainly located in the cold outer reaches of our solar system. They orbit the Sun in the Kuiper Belt, which begins just past Neptune. A trillion more comets may live even farther out in a cold area called the “Oort Cloud.”

Some comets leave their orbits in the Kuiper Belt or the Oort Cloud and journey toward the Sun. When a comet flies near the Sun, its ice begins to “boil” away. As it vaporizes, a tail of glowing gases and dust forms behind it, always pointing away from the Sun. If Earth happens to pass through comet

dust, burning particles can be seen streaking through the sky in a spectacular display called a “meteor shower.”

The parts of a comet

Nucleus Tail Coma

A meteorite stone discovered on Earth weighing 452.6 grams. A 1-cm square cube is shown for scale.

Meteors streak through the night sky.

COURTESY OF OFER GABZO

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Meteoroids, Meteors, and Meteorites

Meteoroids are pieces of rock and metal dislodged from comets, planets, asteroids, or moons. Most meteoroids are made up of dust-sized particles. When a meteoroid enters a planet’s atmosphere, it burns up due to fric-tion. As it burns, a meteoroid creates a bright streak of light in the sky that we call a “meteor.” Sometimes large mete-oroids do not burn up completely— one may make it all the way through a planet, moon, or asteroid’s atmos-phere and land on its surface, after which it is called a “meteorite.”

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This photo shows two tails shed by Comet Hale-Bopp. The blue tail points directly away from the Sun. The white tail is cre-ated by bits of grit that have come off the comet’s nucleus. They are being pushed away by the solar winds from the Sun. Comets

A comet is a mass of frozen gas, cosmic dust, and ice crystals. Comets are often described as “dirty icebergs.” They circle the Sun in long, narrow orbits, mainly located in the cold outer reaches of our solar system. They orbit the Sun in the Kuiper Belt, which begins just past Neptune. A trillion more comets may live even farther out in a cold area called the “Oort Cloud.”

Some comets leave their orbits in the Kuiper Belt or the Oort Cloud and journey toward the Sun. When a comet flies near the Sun, its ice begins to “boil” away. As it vaporizes, a tail of glowing gases and dust forms behind it, always pointing away from the Sun. If Earth happens to pass through comet

dust, burning particles can be seen streaking through the sky in a spectacular display called a “meteor shower.”

The parts of a comet

Nucleus Tail Coma

A meteorite stone discovered on Earth weighing 452.6 grams. A 1-cm square cube is shown for scale.

Meteors streak through the night sky.

COURTESY OF OFER GABZO

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ACE ADMINISTRA

TION/JOHNSON SP

ACE CENTER

Meteoroids, Meteors, and Meteorites

Meteoroids are pieces of rock and metal dislodged from comets, planets, asteroids, or moons. Most meteoroids are made up of dust-sized particles. When a meteoroid enters a planet’s atmosphere, it burns up due to fric-tion. As it burns, a meteoroid creates a bright streak of light in the sky that we call a “meteor.” Sometimes large mete-oroids do not burn up completely— one may make it all the way through a planet, moon, or asteroid’s atmos-phere and land on its surface, after which it is called a “meteorite.”

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A

FIERY

NECKLACE

A NASA Hubble Space Telescope image of comet Shoemaker-Levy 9, taken on May 17, 1994. When the comet was observed, its train of 21 icy fragments stretched across 1.1 million km of space, or three times the distance between Earth and the Moon.

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It’s not often that you get to see a comet strike a planet. Until July 1994, only one comet strike had ever been observed. That was in 1178, when five English monks reported seeing “a flaming torch” on the Moon “spewing out fire, hot coals, and sparks.” Modern astronomers have con-firmed that those monks had seen a comet or a

small asteroid hit the Moon, forming the crater that is now named Giordano Bruno.

Those 12th_{century monks weren’t equipped}

with cameras. But in 1994, astronomers all over the world got a chance to see and photograph a similar event when Comet Shoemaker-Levy 9 collided with Jupiter.

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A

FIERY

NECKLACE

A NASA Hubble Space Telescope image of comet Shoemaker-Levy 9, taken on May 17, 1994. When the comet was observed, its train of 21 icy fragments stretched across 1.1 million km of space, or three times the distance between Earth and the Moon.

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ACE ADMINISTRA

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It’s not often that you get to see a comet strike a planet. Until July 1994, only one comet strike had ever been observed. That was in 1178, when five English monks reported seeing “a flaming torch” on the Moon “spewing out fire, hot coals, and sparks.” Modern astronomers have con-firmed that those monks had seen a comet or a

small asteroid hit the Moon, forming the crater that is now named Giordano Bruno.

Those 12th_{century monks weren’t equipped}

with cameras. But in 1994, astronomers all over the world got a chance to see and photograph a similar event when Comet Shoemaker-Levy 9 collided with Jupiter.

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Ringing the Bell

Between July 16 and July 22, 1994, Shoemaker-Levy 9’s fragments hit Jupiter’s upper atmos-phere one by one. Virtually every large telescope on Earth recorded the collisions. The Hubble Space Telescope recorded the event as it orbited Earth, and so did the Galileospacecraft, which was on its way to Jupiter.

The 21 fragments hit Jupiter at speeds of more than 60 kilometers per second. The impacts cre-ated plumes of hot gas that rose thousands of kilometers high. They left marks on the planet’s surface that lasted for nearly a year. The pieces plowed into the planet’s atmosphere with enor-mous energy. One astronomer described the impacts as “ringing Jupiter like a bell.”

The impact of a fragment of Comet Shoemaker-Levy 9 Big News

In 1993, astronomers Eugene and Carolyn Shoemaker, a husband-and-wife team, and David Levy discovered the comet Shoemaker-Levy 9. The three astronomers were working at the Mt. Palomar Observatory in California. New comets are discovered all the time, but this one made headlines. Shoemaker-Levy 9 was a comet that had been ripped to pieces. Instead of being a single ball, the comet was made up of 21 fragments, each one trailing a large cloud of ice and dust. It looked like a fiery necklace blaz-ing across the night sky. The astronomers calcu-lated that about 9 months before they spotted it, Shoemaker-Levy 9 had passed within about 21,000 kilometers of Jupiter. Jupiter’s gravita-tional force (which is 2.36 times that of Earth’s) had pulled the comet apart.

A NASA Hubble Space Telescope image of comet A NASANext came even bigger news: The pieces of Shoemaker-Levy 9 were on a collision course with Jupiter. Astronomers predicted that Jupiter’s gravitational force was about to grab those fragments, once and for all. That set the stage for one of the most photographed events in astronomical history.

R. EV

ANS, J. TRAUGER, H. HAMMEL, AND THE HST COMET SCIENCE TEAM AND THE NA

ACE ADMINISTRA

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Ringing the Bell

Between July 16 and July 22, 1994, Shoemaker-Levy 9’s fragments hit Jupiter’s upper atmos-phere one by one. Virtually every large telescope on Earth recorded the collisions. The Hubble Space Telescope recorded the event as it orbited Earth, and so did the Galileospacecraft, which was on its way to Jupiter.

The 21 fragments hit Jupiter at speeds of more than 60 kilometers per second. The impacts cre-ated plumes of hot gas that rose thousands of kilometers high. They left marks on the planet’s surface that lasted for nearly a year. The pieces plowed into the planet’s atmosphere with enor-mous energy. One astronomer described the impacts as “ringing Jupiter like a bell.”

The impact of a fragment of Comet Shoemaker-Levy 9 Big News

In 1993, astronomers Eugene and Carolyn Shoemaker, a husband-and-wife team, and David Levy discovered the comet Shoemaker-Levy 9. The three astronomers were working at the Mt. Palomar Observatory in California. New comets are discovered all the time, but this one made headlines. Shoemaker-Levy 9 was a comet that had been ripped to pieces. Instead of being a single ball, the comet was made up of 21 fragments, each one trailing a large cloud of ice and dust. It looked like a fiery necklace blaz-ing across the night sky. The astronomers calcu-lated that about 9 months before they spotted it, Shoemaker-Levy 9 had passed within about 21,000 kilometers of Jupiter. Jupiter’s gravita-tional force (which is 2.36 times that of Earth’s) had pulled the comet apart.

A NASA Hubble Space Telescope image of comet A NASANext came even bigger news: The pieces of Shoemaker-Levy 9 were on a collision course with Jupiter. Astronomers predicted that Jupiter’s gravitational force was about to grab those fragments, once and for all. That set the stage for one of the most photographed events in astronomical history.

R. EV

ANS, J. TRAUGER, H. HAMMEL, AND THE HST COMET SCIENCE TEAM AND THE NA

ACE ADMINISTRA

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UNITED ST

ATES GEOLOGICAL SUR

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Tribute to Eugene Shoemaker

In July 1997, three years after Shoemaker-Levy 9 collided with Jupiter, Eugene Shoemaker met his own end. He was killed in a car crash in Australia, where he was studying an ancient impact crater.

The following year, Shoemaker’s ashes were carried aboard the Lunar Prospector

spacecraft in a small capsule. In a fitting tribute, the spacecraft was deliberately crashed onto the Moon’s surface on July 31, 1999.

“I don’t think Gene ever dreamed his ashes would go to the Moon,” said his wife, Carolyn. “He would be thrilled.”

Eugene Shoemaker and wife, Carolyn

Mission:

Earth

polar caps—like those on Mars—that cover Earth’s poles. Swirling clouds, flashes of light-ning, and volcanic gases are evidence of an active atmosphere.

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IMAGE CREA

TED BY RETO STOCKLI, NAZMI EL SALEOUS, AND MARIT JENTOFT-NILSEN

This image came from a single remote-sensing device flying more than 700 kilometers above the Earth on the Terra Earth-observing satellite.

We have learned much about Earth’s neighbor-ing planets in the solar system. We’ve sent flyby spacecraft to photograph them, put orbiters around them for longer study, deposited landers on their surfaces, and flown probes through their atmospheres. But what have we learned about Earth as a planet using space technology?

Earth’s seven continents and vast oceans set it apart from the other planets. Liquid water surrounds its continents, which are covered by contrasting lush vegetation and desert land-scapes. From space we can see frozen white

The presence of life on planet Earth is one of its unique features. Macro- and microscopic organisms are teeming on land and in water. One hint that life exists on Earth can be detected from space—the electromagnetic noise caused by radios and TV broadcasts. But the presence of life is only one aspect of our world when con-sidered as a whole.

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UNITED ST

ATES GEOLOGICAL SUR

VEY

Tribute to Eugene Shoemaker

In July 1997, three years after Shoemaker-Levy 9 collided with Jupiter, Eugene Shoemaker met his own end. He was killed in a car crash in Australia, where he was studying an ancient impact crater.

The following year, Shoemaker’s ashes were carried aboard the Lunar Prospector

spacecraft in a small capsule. In a fitting tribute, the spacecraft was deliberately crashed onto the Moon’s surface on July 31, 1999.

“I don’t think Gene ever dreamed his ashes would go to the Moon,” said his wife, Carolyn. “He would be thrilled.”

Eugene Shoemaker and wife, Carolyn

Mission:

Earth

polar caps—like those on Mars—that cover Earth’s poles. Swirling clouds, flashes of light-ning, and volcanic gases are evidence of an active atmosphere.

NA

ACE ADMINISTRA

TION/GODDARD SP

ACE FLIGHT CENTER/

IMAGE CREA

TED BY RETO STOCKLI, NAZMI EL SALEOUS, AND MARIT JENTOFT-NILSEN

This image came from a single remote-sensing device flying more than 700 kilometers above the Earth on the Terra Earth-observing satellite.

We have learned much about Earth’s neighbor-ing planets in the solar system. We’ve sent flyby spacecraft to photograph them, put orbiters around them for longer study, deposited landers on their surfaces, and flown probes through their atmospheres. But what have we learned about Earth as a planet using space technology?

Earth’s seven continents and vast oceans set it apart from the other planets. Liquid water surrounds its continents, which are covered by contrasting lush vegetation and desert land-scapes. From space we can see frozen white

The presence of life on planet Earth is one of its unique features. Macro- and microscopic organisms are teeming on land and in water. One hint that life exists on Earth can be detected from space—the electromagnetic noise caused by radios and TV broadcasts. But the presence of life is only one aspect of our world when con-sidered as a whole.

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Let’s look at a few examples of how the ESE mission helps scientists and engineers observe Earth as a planet.

The Cooling and Warming Power of Clouds

Clouds act to regulate Earth’s climate. Cirrus clouds—high, wispy clouds—warm Earth by trapping radiation from Earth’s surface.

Stratocumulus clouds—soft, gray clouds in glob-ular patches or rolls—cool Earth’s surface by reflecting incoming solar radiation back into space. Scientists who work with Earth-observing satellites are studying how clouds affect Earth’s climate. By using global cloud observations from EOS satellites, scientists can determine to what extent warming or cooling caused by clouds has an impact on the global climate.

Earth System Enterprise

The key to a better understanding of Earth is to explore how its systems of atmosphere (air), geosphere (land), hydrosphere (water), and bio-sphere (life) interact with each other. And the best way to study all of these systems together is from space. Mission to Planet Earth—now called Earth System Enterprise (ESE)—was established in 1991 and is the foundation of NASA’s Earth-observing program.

This program has three main components: a series of Earth Observing System (EOS) satellites, a system to collect data, and teams of scientists around the world who study the data. ESE uses satellites, such as Terra, and other tools to study Earth. Through ESE, NASA hopes to explain how natural processes affect life on Earth—and how life on Earth is affecting Earth’s natural processes. Data from these studies may help improve weath-er forecasts, help manage agriculture and forests, provide information to fishermen and local

planners, and, eventually, help predict how the climate may change in the future.

(continued)

BARBARA SUMMEY, NATIONAL AERONAUTICS AND SPACE ADMINISTRATION/GODDARD SPACE FLIGHT CENTER

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Let’s look at a few examples of how the ESE mission helps scientists and engineers observe Earth as a planet.

The Cooling and Warming Power of Clouds

Clouds act to regulate Earth’s climate. Cirrus clouds—high, wispy clouds—warm Earth by trapping radiation from Earth’s surface.

Stratocumulus clouds—soft, gray clouds in glob-ular patches or rolls—cool Earth’s surface by reflecting incoming solar radiation back into space. Scientists who work with Earth-observing satellites are studying how clouds affect Earth’s climate. By using global cloud observations from EOS satellites, scientists can determine to what extent warming or cooling caused by clouds has an impact on the global climate.

Earth System Enterprise

The key to a better understanding of Earth is to explore how its systems of atmosphere (air), geosphere (land), hydrosphere (water), and bio-sphere (life) interact with each other. And the best way to study all of these systems together is from space. Mission to Planet Earth—now called Earth System Enterprise (ESE)—was established in 1991 and is the foundation of NASA’s Earth-observing program.

This program has three main components: a series of Earth Observing System (EOS) satellites, a system to collect data, and teams of scientists around the world who study the data. ESE uses satellites, such as Terra, and other tools to study Earth. Through ESE, NASA hopes to explain how natural processes affect life on Earth—and how life on Earth is affecting Earth’s natural processes. Data from these studies may help improve weath-er forecasts, help manage agriculture and forests, provide information to fishermen and local

planners, and, eventually, help predict how the climate may change in the future.

(continued)

BARBARA SUMMEY, NATIONAL AERONAUTICS AND SPACE ADMINISTRATION/GODDARD SPACE FLIGHT CENTER

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NA

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CENTER/MITI/ERSDAC/DARDS AND U.S./JAP

AN ASTER SCIENCE TEAM.

This photo of the San Quintín Glacier was taken nearly 6 years later in May 2000. Like many glaciers worldwide, San Quintin appears to be retreating.

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This photo of the San Quintín Glacier in southern Chile was taken by the crew of mission STS-068 in October 1994.

Global Ice and Sea Level Changes

Earth’s glacial ice contains more than 77 percent of Earth’s fresh water. Over the last century, many of the world’s mountain glaciers and ice caps have been retreating (getting smaller). Melting glaciers cause sea levels to rise. One of the jobs of the EOS scientists is to figure out whether Greenland and Antarctic ice sheets are grow-ing or shrinkgrow-ing by studygrow-ing changes in sea level. Scientists examine changes in sea level by looking at satellite, laser, and radar data.

Greenhouse Effect

Scientists use the EOS satellites to measure levels of greenhouse gases such as carbon dioxide, methane, and chlorofluorocar-bons (CFCs) in our atmosphere. Carbon dioxide is released into the atmosphere when solid waste, fossil fuels (oil, natural gas, and coal), and wood and wood products are burned. CFCs are found in aerosol sprays, in blowing agents for foams and packing materials, as solvents, and as refrigerants. CFCs do not occur naturally; therefore, their increase in the

imagery to study El Niño—an occurrence of unusually warm surface water in the Pacific Ocean. EOS can help scientists investigate the role Earth’s oceans play in regulating the amount of greenhouse gases in the atmosphere.

atmosphere is entirely the result of human activity. The levels of these gases have been increasing steadily. These gases trap heat within Earth’s atmosphere preventing it from escaping into space.

Ocean Processes

Oceans cover more than 70 percent of Earth’s surface. These bodies of water transport heat and weather conditions around the globe. Satellites can measure sea surface temperatures. These temperatures are each assigned a color on the satellite image. A global view of Earth can show the locations of the warmest and coolest ocean temperatures. Scientists can also use satellite

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TIONS, INC.

Sea surface temperatures: Cold waters are black and dark green. Blue, purple, red, yellow, and white represent progressively warmer water.

The EOS satellite called Terracollects detailed measurements of the ocean’s surface temperatures every day all over the globe. This sensor acts like a sophisticated thermometer in space. It helps scientists understand how Earth’s oceans and atmosphere interact and drive weather patterns. These patterns define our climate.

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NA

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CENTER/MITI/ERSDAC/DARDS AND U.S./JAP

AN ASTER SCIENCE TEAM.

This photo of the San Quintín Glacier was taken nearly 6 years later in May 2000. Like many glaciers worldwide, San Quintin appears to be retreating.

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This photo of the San Quintín Glacier in southern Chile was taken by the crew of mission STS-068 in October 1994.

Global Ice and Sea Level Changes

Earth’s glacial ice contains more than 77 percent of Earth’s fresh water. Over the last century, many of the world’s mountain glaciers and ice caps have been retreating (getting smaller). Melting glaciers cause sea levels to rise. One of the jobs of the EOS scientists is to figure out whether Greenland and Antarctic ice sheets are grow-ing or shrinkgrow-ing by studygrow-ing changes in sea level. Scientists examine changes in sea level by looking at satellite, laser, and radar data.

Greenhouse Effect

Scientists use the EOS satellites to measure levels of greenhouse gases such as carbon dioxide, methane, and chlorofluorocar-bons (CFCs) in our atmosphere. Carbon dioxide is released into the atmosphere when solid waste, fossil fuels (oil, natural gas, and coal), and wood and wood products are burned. CFCs are found in aerosol sprays, in blowing agents for foams and packing materials, as solvents, and as refrigerants. CFCs do not occur naturally; therefore, their increase in the

imagery to study El Niño—an occurrence of unusually warm surface water in the Pacific Ocean. EOS can help scientists investigate the role Earth’s oceans play in regulating the amount of greenhouse gases in the atmosphere.

atmosphere is entirely the result of human activity. The levels of these gases have been increasing steadily. These gases trap heat within Earth’s atmosphere preventing it from escaping into space.

Ocean Processes

Oceans cover more than 70 percent of Earth’s surface. These bodies of water transport heat and weather conditions around the globe. Satellites can measure sea surface temperatures. These temperatures are each assigned a color on the satellite image. A global view of Earth can show the locations of the warmest and coolest ocean temperatures. Scientists can also use satellite

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ACE ADMINISTRA

TION/ GODDARD SP

ACE FLIGHT

CENTER. IMAGE BY JESSE ALLEN, SCIENCE SYSTEMS AND APPLICA

TIONS, INC.

Sea surface temperatures: Cold waters are black and dark green. Blue, purple, red, yellow, and white represent progressively warmer water.

The EOS satellite called Terracollects detailed measurements of the ocean’s surface temperatures every day all over the globe. This sensor acts like a sophisticated thermometer in space. It helps scientists understand how Earth’s oceans and atmosphere interact and drive weather patterns. These patterns define our climate.

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ACE ADMINISTRA

TION/ GODDARD SP

ACE FLIGHT CENTER SCIENTIFIC VISUALIZA

TION STUDIO, IMAGES BY GREG SHIR

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These images clearly show that since 1979, the protective ozone layer had declined in concentration and area. In fact, the ozone hole had grown so much over the years that in 1999, it was about the size of the entire Antarctic continent.

Satellites can monitor snow cover as well. A decrease in the amount of snow cover may indicate increased global temperatures.

The Future of Earth as a Planet

In its natural state, Earth is in perfect balance. Water exists in all three states (liquid, gas, and solid). Its atmosphere is oxygen rich, and life is abundant. To maintain this balance, humans must have an understanding of how Earth func-tions as a system. The technology of the Earth System Enterprise mission promotes the study of Earth as an integrated system.

Ozone, Vegetation, and Snow

Both satellite and ground-based measurement tools have detected a hole in the ozone over the Antarctic. The ozone is a layer of O3in the stratosphere, the second layer of the atmos-phere above Earth’s surface. Decreased ozone levels allow more ultraviolet radiation from the Sun to reach Earth’s surface. Ultraviolet radia-tion can harm organisms, including humans. In New Zealand, for example, school children are required to wear hats while outside, since expo-sure to the Sun’s rays due to ozone depletion is particularly dangerous in that region. EOS ana-lyzes the natural and human activities on Earth that cause the decrease in the ozone.

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ACE ADMINISTRA

TION IMAGE BY BRIAN MONTGOMER

Y,

ROBERT SIMMON, AND RETO STÖCKLI, BASED ON DA

TA PROVIDED BY THE MODIS SCIENCE TEAM.

Madagascar was once covered in lush green vegetation. Today, an estimated 80 percent of its forests have been destroyed. The reddish-brown exposed terrain can be seen in this true-color image of northern Madagascar taken in May 2000.

monitors the rate of deforestation (the process of taking down trees) in the Brazilian rainforest. Satellite images of Africa can show characteristics of vegetation. Instruments can measure how much sunlight the leaves absorb.

Scientists at NASA also can evaluate processes that directly affect Earth’s energy and water cycles. For example, satellite imagery continuously

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NA

ACE ADMINISTRA

TION/ GODDARD SP

ACE FLIGHT CENTER SCIENTIFIC VISUALIZA

TION STUDIO, IMAGES BY GREG SHIR

AH

These images clearly show that since 1979, the protective ozone layer had declined in concentration and area. In fact, the ozone hole had grown so much over the years that in 1999, it was about the size of the entire Antarctic continent.

Satellites can monitor snow cover as well. A decrease in the amount of snow cover may indicate increased global temperatures.

The Future of Earth as a Planet

In its natural state, Earth is in perfect balance. Water exists in all three states (liquid, gas, and solid). Its atmosphere is oxygen rich, and life is abundant. To maintain this balance, humans must have an understanding of how Earth func-tions as a system. The technology of the Earth System Enterprise mission promotes the study of Earth as an integrated system.

Ozone, Vegetation, and Snow

Both satellite and ground-based measurement tools have detected a hole in the ozone over the Antarctic. The ozone is a layer of O3in the stratosphere, the second layer of the atmos-phere above Earth’s surface. Decreased ozone levels allow more ultraviolet radiation from the Sun to reach Earth’s surface. Ultraviolet radia-tion can harm organisms, including humans. In New Zealand, for example, school children are required to wear hats while outside, since expo-sure to the Sun’s rays due to ozone depletion is particularly dangerous in that region. EOS ana-lyzes the natural and human activities on Earth that cause the decrease in the ozone.

NA

ACE ADMINISTRA

TION IMAGE BY BRIAN MONTGOMER

Y,

ROBERT SIMMON, AND RETO STÖCKLI, BASED ON DA

TA PROVIDED BY THE MODIS SCIENCE TEAM.

Madagascar was once covered in lush green vegetation. Today, an estimated 80 percent of its forests have been destroyed. The reddish-brown exposed terrain can be seen in this true-color image of northern Madagascar taken in May 2000.

monitors the rate of deforestation (the process of taking down trees) in the Brazilian rainforest. Satellite images of Africa can show characteristics of vegetation. Instruments can measure how much sunlight the leaves absorb.

Scientists at NASA also can evaluate processes that directly affect Earth’s energy and water cycles. For example, satellite imagery continuously

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Earth: Quick Facts

Diameter 12,756 km Average distance from the Sun 149,600,000 km

Mass 597 ×1022_kg

Surface gravity 1*

Average temperature –55 °C to 70 °C Length of sidereal day 23.93 hours

Length of year 365.25 days Number of observed moons 1

Did You Know?

•The oldest rocks on Earth date back 4 billion years.

•Only Earth has the temperature range that permits liquid water to exist, and only Earth has developed an oxygen-rich atmosphere. These two factors enable Earth to support life.

Inner core

Relative size

Earth atmosphere

Nitrogen (78%)

Argon, carbon dioxide, and water vapor (trace amounts) (1%) Oxygen (21%) Earth Outer core Mantle Crust

PLANETARY FACTS:

Earth

Moon

Q:

How often are comets discovered? Are they named the same way as asteroids?

A:

Many new comets are dis-covered every month. They are generally named for their discoverers. Comet Halley was named after astronomer Edmund Halley, who was the first to predict the return of this particular comet. But like aster-oids, comets are given codes that reflect their discovery date.

Q:

What about stars?

A:

A few bright stars easily seen from Earth have ancient, traditional Arabic names, such as Sirius. We have identified hundreds of millions of stars. To study them, we need to be able to find them, so they are simply known by catalog numbers. By looking up its number in a huge catalog, we can find a star’s precise coordinates, or position in the sky.

Q:

Is it true that people can pay to have a star or a planet named after them?

A:

Some companies claim to offer such services for a fee. However, those names are completely invalid. As an international scientific organization, the IAU has nothing to do with the commercial practice of “selling” fictitious names of stars, planets, moons, or any other space “real estate.” If you’re interested in stars and space, go to your nearest planetarium or local observatory. Have someone show you real stars through a telescope. You also may want to join a local astronomy club. Someday you may discover a new asteroid or comet that could be named after you!

Dr. Michael F. A’Hearn knows his way around space. Dr. A’Hearn, a professor of astronomy at the University of Maryland, is also an office-holder in the International Astronomical Union (IAU), the organization responsible for naming celestial bodies. Scientists, space agencies, and authorities around the world recognize and use IAU’s names. Here,

Dr. A’Hearn answers some common questions about the space “name game,” or how astro-nomical bodies get their names.

Q:

How are asteroids named?

A:

First, an asteroid is given a set of numbers and letters that tells when it was first discovered. Once the asteroid’s orbit is well known, a perma-nent number is assigned—in numerical order. After that, a name is assigned. The discoverer of the asteroid can suggest a name, but the IAU has final approval.

For example, an asteroid discovered by P. Wild on March 5, 1973, was given the designation “1973 EB.” This means that the asteroid was identified in 1973 in the first half of March (E) and was the second (B) asteroid discovered in the first half of that month. Once we under-stood the orbit of 1973 EB, we gave it the per-manent number of 2001 because that’s how many asteroids had been discovered by then. This asteroid was named Einstein in memory of Albert Einstein, the greatest scientist of the 20th century.

Q:

How often are asteroids discovered?

A:

New asteroids are discovered nearly every day! However, people tend not to search during the full Moon because the background light interferes too much. Most discoveries are made around the new Moon, when our cameras can “see.”

Dr. Michael F. A’Hearn

COURTESY OF ELIZABETH W

ARNER