other objects in the solar system

meteorites

A meteoroid is dragged towards Earth by gravity and enters the atmosphere. Friction with the atmosphere heats the object quickly, so it starts to vaporize. As it flies through the atmosphere, it leaves a trail of glowing gases. The object is now a meteor. Most meteors vaporize in the atmosphere. They never reach Earths surface. Large meteoroids may not burn up entirely in the atmosphere. A small core may remain and hit the Earths surface. This is called a meteorite. Meteorites provide clues about our solar system. Many were formed in the early solar system (Figure 25.34). Some are from asteroids that have split apart. A few are rocks from nearby bodies like Mars. For this to happen, an asteroid smashed into Mars and sent up debris. A bit of the debris entered Earths atmosphere as a meteor.

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meteoroids

Before these small pieces of matter enter Earths atmosphere, they are called meteoroids. Meteoroids are as large as boulders or as small as tiny sand grains. Larger objects are called asteroids; smaller objects are interplanetary dust. Meteoroids sometimes cluster together in long trails. They are the debris left behind by comets. When Earth passes through a comet trail, there is a meteor shower. During a meteor shower, there are many more meteors than normal for a night or two.

meteors

If you look at the sky on a dark night, you may see a meteor, like in Figure 25.33. A meteor forms a streak of light across the sky. People call them shooting stars because thats what they look like. But meteors are not stars at all. The light you see comes from a small piece of matter burning up as it flies through Earths atmosphere.

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asteroid missions

Scientists are very interested in asteroids. Most are composed of material that has not changed since early in the solar system. Scientists can learn a lot from them about how the solar system formed. Asteroids may be important for space travel. They could be mined for rare minerals or for construction projects in space. Scientists have sent spacecraft to study asteroids. In 1997, the NEAR Shoemaker probe orbited the asteroid 433 Eros. The craft finally landed on its surface in 2001. The Japanese Hayabusa probe returned to Earth with samples of a small near-earth asteroid in 2010. The U.S. Dawn mission will visit Vesta in 2011 and Ceres in 2015.

pluto

For decades Pluto was a planet. But even then, scientists knew it was an unusual planet. The other outer planets are all gas giants. Pluto is small, icy and rocky. With a diameter of about 2400 kilometers, it has only about 1/5 the mass of Earths Moon. The other planets orbit in a plane. Plutos orbit is tilted. The shape of the orbit is like a long, narrow ellipse. Plutos orbit is so elliptical that sometimes it is inside the orbit of Neptune. Plutos orbit is in the Kuiper belt. We have discovered more than 200 million Kuiper belt objects. Pluto has 3 moons of its own. The largest, Charon, is big. Some scientists think that Pluto-Charon system is a double dwarf planet (Figure 25.37). Two smaller moons, Nix and Hydra, were discovered in 2005.

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dwarf planets

For several decades, Pluto was a planet. But new solar system objects were discovered that were just as planet-like as Pluto. Astronomers figured out that they were like planets except for one thing. These objects had not cleared their orbits of smaller objects. They didnt have enough gravity to do so. Astronomers made a category called dwarf planets. There are five dwarf planets in our solar system: Ceres, Pluto, Makemake, Haumea and Eris. Figure 25.36 shows Ceres. Ceres is a rocky body that orbits the Sun and is not a star. It could be an asteroid or a planet. Before 2006, Ceres was thought to be the largest asteroid. Is it an asteroid? Ceres is in the asteroid belt. But it is by far the largest object in the belt. Ceres has such high gravity that it is spherical. Is it a planet? Ceres only has about 1.3% of the mass of the Earths Moon. Its orbit is full of other smaller bodies. Its gravity was not high enough to clear its orbit. Ceres fails the fourth criterion for being a planet. Ceres is now considered a dwarf planet along with Pluto.

where comets come from

Some comets have periods of 200 years or less. They are called short-period comets. Short-period comets are from a region beyond the orbit of Neptune called the Kuiper Belt. Kuiper is pronounced KI-per, rhyming with viper. The Kuiper Belt is home to comets, asteroids, and at least two dwarf planets. Some comets have periods of thousands or even millions of years. Most long-period comets come from a very distant region of the solar system. This region is called the Oort cloud. The Oort cloud is about 50,000100,000 times the distance from the Sun to Earth. Comets carry materials in from the outer solar system. Comets may have brought water into the early Earth. Other substances could also have come from comets.

comets

Comets are small, icy objects that orbit the Sun. Comets have highly elliptical orbits. Their orbits carry them from close to the Sun to the solar systems outer edges. When a comet gets close to the Sun, its outer layers of ice melt and evaporate. The vaporized gas and dust forms an atmosphere around the comet. This atmosphere is called a coma. Radiation and particles streaming from the Sun push some of this gas and dust into a long tail. A comets tail always points away from the Sun, no matter which way the comet is moving. Why do you think that is? Figure Gases in the coma and tail of a comet reflect light from the Sun. Comets are very hard to see except when they have comas and tails. That is why they appear only when they are near the Sun. They disappear again as they move back to the outer solar system. The time between one visit from a comet and the next is called the comets period. The first comet whose period was known was Halleys Comet. Its period is 75 years. Halleys Comet last traveled through the inner solar system in 1986. The comet will appear again in 2061. Who will look up at it?

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makemake

Makemake is the third-largest and second-brightest dwarf planet we have discovered so far (Figure 25.39). Make- make is only 75 percent the size of Pluto. Its diameter is between 1300 and 1900 kilometers. The name comes from the mythology of the Eastern Islanders. Makemake was the god that created humanity. At a distance between 38.5 to 53 AU, this dwarf planet orbits the Sun in 310 years. Makemake is made of methane, ethane, and nitrogen ices.

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haumea

Haumea was named a dwarf planet in 2008. It is an unusual dwarf planet. The body is shaped like an oval! Haumeas longest axis is about the same as Plutos diameter, and its shortest axis is about half as long. The bodys orbit is tilted 28. Haumea is so far from the Sun that it takes 283 years to make one orbit (Figure 25.38). Haumea is the third-brightest Kuiper Belt object. It was named for the Hawaiian goddess of childbirth. Haumea has two moons, Hiiaka and Namaka, the names of the goddess Haumeas daughters. Haumeas odd oval shape is probably caused by its extremely rapid rotation. It rotates in just less than 4 hours! Like other Kuiper belt objects, Haumea is covered by ice. Its density is similar to Earths Moon, at 2.6 3.3 g/cm3 . This means that most of Haumea is rocky. Haumea is part of a collisional family. This is a group of astronomical objects that formed from an impact. This family has Haumea, its two moons, and five more objects. All of these objects are thought to have formed from a collision very early in the formation of the solar system.

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nearearth asteroids

Near-Earth asteroids have orbits that cross Earths orbit. This means that they can collide with Earth. There are over 4,500 known near-Earth asteroids. Small asteroids do sometimes collide with Earth. An asteroid about 510 m in diameter hits about once per year. Five hundred to a thousand of the known near-Earth asteroids are much bigger. They are over 1 kilometer in diameter. When large asteroids hit Earth in the past, many organisms died. At times, many species became extinct. Astronomers keep looking for near-Earth asteroids. They hope to predict a possible collision early so they can to try to stop it.

the asteroid belt

Hundreds of thousands of asteroids have been found in our solar system. They are still being discovered at a rate of about 5,000 new asteroids per month! The majority are located in between the orbits of Mars and Jupiter. This region is called the asteroid belt, as shown in Figure 25.32. There are many thousands of asteroids in the asteroid belt. Still, their total mass adds up to only about 4 percent of Earths Moon. Asteroids formed at the same time as the rest of the solar system. Although there are many in the asteroid belt, they were never were able to form into a planet. Jupiters gravity kept them apart.

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asteroids

Asteroids are very small, irregularly shaped, rocky bodies. Asteroids orbit the Sun, but they are more like giant rocks than planets. Since they are small, they do not have enough gravity to become round. They are too small to have an atmosphere. With no internal heat, they are not geologically active. An asteroid can only change due to a collision. A collision may cause the asteroid to break up. It may create craters on the asteroids surface. An asteroid may strike a planet if it comes near enough to be pulled in by its gravity. Figure 25.31 shows a typical asteroid.

eris

Eris is the largest known dwarf planet in the solar system. It is 27 percent larger than Pluto (Figure 25.40). Like Pluto and Makemake, Eris is in the Kuiper belt. But Eris is about 3 times farther from the Sun than Pluto. Because of its distance, Eris was not discovered until 2005. Early on, it was thought that Eris might be the tenth planet. Its discovery helped astronomers realize that they needed a new definition of planet. Eris has a small moon, Dysnomia. Its moon orbits Eris once about every 16 days. Astronomers know there may be other dwarf planets far out in the solar system. Look for Quaoar, Varuna and Orcus to be possibly added to the list of dwarf planets in the future. We still have a lot to discover and explore!

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instructional diagrams

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questions

Near-Earth asteroids

a. have orbits that cross Earths

b. number more than 4,500

c. could strike Earth

-->  d. all of these

Which two planets does the asteroid belt fall between?

a. Earth Mars

-->  b. Mars Jupiter

c. Jupiter Neptune

d. Mercury Venus

Why do scientists value meteorites?

-->  a. They are material from the earliest solar system.

b. They are an important source of valuable metals.

c. They contain metals not otherwise found on Earth.

d. none of these

What is the asteroid belt?

a. It is a large planet that was broken apart by an asteroid impact.

b. It is where the Suns gravity is perfect for asteroids.

-->  c. It is debris that couldnt form a planet due to Jupiters gravity.

d. none of these

Why is the dwarf planet Ceres not classified as a large asteroid?

-->  a. it is rounded

b. it is too large

c. it does not have craters

d. it is a moon of Pluto

Most asteroids in the solar system are located between Mars and Earth.

a. true

-->  b. false

Asteroids formed after the rest of the solar system formed.

a. true

-->  b. false

Small asteroids sometimes collide with Earth.

-->  a. true

b. false

All shooting stars become meteorites.

a. true

-->  b. false

After a meteor hits Earths surface, it is called a meteorite.

-->  a. true

b. false

Comet orbits are similar in shape to planet orbits.

a. true

-->  b. false

Meteoroids are usually larger than asteroids.

a. true

-->  b. false

Comets are commonly called shooting stars.

a. true

-->  b. false

The longest period comets come from the Kuiper belt.

a. true

-->  b. false

A comet has an atmosphere only when it gets close to the sun.

-->  a. true

b. false

Any object whose orbit crosses Earths can collide with Earth.

-->  a. true

b. false

Halleys Comet is it expected to return in 2061.

-->  a. true

b. false

Scientists think that comets may have brought water to early Earth.

-->  a. true

b. false

The dwarf planet Ceres was originally considered to be the largest asteroid.

-->  a. true

b. false

Pluto is always farther from the sun than Neptune is.

a. true

-->  b. false

event that occurs when Earth passes through the tail of a comet

a. asteroid

b. asteroid belt

c. comet

d. Kuiper belt

e. meteor

f. coma

-->  g. meteor shower

atmosphere of a comet

a. asteroid

b. asteroid belt

c. comet

d. Kuiper belt

e. meteor

-->  f. coma

g. meteor shower

small, irregularly shaped, rocky body that orbits the sun

-->  a. asteroid

b. asteroid belt

c. comet

d. Kuiper belt

e. meteor

f. coma

g. meteor shower

region from which many comets come

a. asteroid

b. asteroid belt

c. comet

-->  d. Kuiper belt

e. meteor

f. coma

g. meteor shower

region where most asteroids are located

a. asteroid

-->  b. asteroid belt

c. comet

d. Kuiper belt

e. meteor

f. coma

g. meteor shower

small chunk of space rock that burns up as it falls through Earths atmosphere

a. asteroid

b. asteroid belt

c. comet

d. Kuiper belt

-->  e. meteor

f. coma

g. meteor shower

small, icy object that orbits the sun

a. asteroid

b. asteroid belt

-->  c. comet

d. Kuiper belt

e. meteor

f. coma

g. meteor shower

Asteroids do not have any of the following except

-->  a. gravity.

b. internal heat.

c. an atmosphere.

d. geological activity.

Which of the following statements is true about short-period comets?

-->  a. They have periods of 200 years or less.

b. They come from the asteroid belt.

c. The originate in the Oort cloud.

d. none of the above

Which of the following is a dwarf planet?

a. Ceres

b. Haumea

c. Makemake

-->  d. all of the above

Pluto was once called a planet. Now it has been reclassified as a dwarf planet because

-->  a. its gravity is too weak to clear its orbit.

b. it does not have any moons.

c. it consists only of gases.

d. its orbit is not elliptical.

The only dwarf planet located in the asteroid belt is

a. Eris.

-->  b. Ceres.

c. Haumea.

d. Makemake.

Which dwarf planet is shaped more like an egg than a ball?

a. Ceres

-->  b. Haumea

c. Eris

d. Pluto

The dwarf planet named Eris

-->  a. is bigger than Pluto.

b. has more moons than Pluto.

c. was discovered before Pluto.

d. is closer to the sun than Pluto.

diagram questions

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