Asteroids
Asteroids are rocky and metallic objects that orbit the Sun but are too small to be
considered planets. They are also known as minor planets. Asteroids are made of iron,
nickel, and stone. Asteroids range in size from a diameter of about 500 miles, down to the
size of pebbles. One famous asteroid is called Ceres, it is one of the biggest asteroids.
Most are found in the asteroid belt which exists between the orbits of Mars and Jupiter.
Asteroids are material left over from the formation of the solar system. There are 2
theories about how they formed. One theory suggests that they are the remains of a
planet that was destroyed in a massive collision long ago. The second theory is that
asteroids are material that never formed a planet. In fact, if the estimated total mass of all
asteroids was gathered into a single object, the object would be less than 932 miles
across -- less than half the diameter of our Moon.
Most asteroids are irregularly shaped. They are not round like the planets but look more
like giant rocks orbiting in space. Asteroids also have many craters that were formed by
collisions with other asteroids or comets.
1. What is another name for asteroids? ________________________________
2. Where is the asteroid belt located? ______________________________________
3. What are asteroids made of? ____________________________________________
4. What object do asteroids look like? _______________________________________
5. Asteroids have craters from ______________________________ with other asteroids
in space.
6. What is the name of one famous asteroid? ____________________________
7. What are 2 possible explanations or theories about how the asteroids were formed?
a. ________________________________________________________
b. ________________________________________________________
8. Name one difference and one similarity between planets and asteroids.
Similarity - _______________________________________________
Difference - _____________________________________________
Comets
Comets are commonly called dirty snowballs because of the frozen gases, water, and dust
that they are made of. They also orbit around the sun but their orbits are much more
elliptical or oval shaped than the planets’ orbits.
Comets reflect light from the sun. When their orbit crosses earth’s orbit, they can look
like fuzzy stars in the night sky. All comets have three main parts: the coma, the nucleus,
and the tail.
The nucleus, or center, is made of frozen gases, water and dirt. As it travels through
space, the sun warms the outside of the nucleus and a cloud of gas is formed around the
nucleus. This cloud is called the coma and it is what makes comets look fuzzy.
When the comet gets closer to the sun, the coma becomes larger and the solar winds
blow the coma into a tail that streams from the nucleus. Because of the solar winds
blowing on the coma, the tail of the comet always points away from the sun. When the
comet is traveling towards the sun, the tail is behind the nucleus. However, when the
comet is traveling away from the sun, the tail is in front of the nucleus!
Two famous comets are Halley’s Comet and Hale-Bopp comet. Halley’s comet can be
seen every 76 years. Its tail has been measured at about 93 million miles, which is the
same distance as the Earth to the sun! It will next be visible in 2061.
1. What are comets made of? ______________________________________
2. Which is more elliptical, a planet’s orbit around the sun or a comet’s orbit around the
sun?
3. Describe each part of the comet: - coma, tail, nucleus.
A. the frozen center ____________________
B. as the ice melts, this forms around the nucleus ___________________
C. this is a stream of water vapor and dust particles __________________
4. What part of the comet makes it look fuzzy? _________________________
5. Why does a coma form around the nucleus to make it appear fuzzy?
6. Which direction does the tail of a comet ALWAYS POINT? ___________________
7. What famous comet has a revolution time of 76 years?
8. What object do comets revolve around? ____________________________________
Meteoroids, Meteors, Meteorites
The word meteor is used to describe the streak of light produced as a rock in the solar
system falls into Earth's atmosphere creating temporary light as a result of the friction
between the atmosphere and the object. This typically occurs at heights of 50 to 68 miles
above Earth's surface. Meteors are also known as shooting stars or falling stars.
A meteoroid is an object that is revolving around the sun or any object in space that is too
small to be called an asteroid or a comet. Most meteoroids are made of stone, nickel, and
iron. As meteoroids come close to Earth, they can be pulled into Earth’s atmosphere by
Earth’s gravity. Once they are in Earth’s atmosphere, the friction between the rock and
the air molecules cause the rock to ignite or catch on fire. This is what causes them to
look like “shooting stars” because as they burn up, the light shoots across the sky.
Most meteors burn up in Earth’s atmosphere and disintegrate before they reach the
ground. If a meteor does reach the ground, it is called a meteorite. Meteorites can form
craters on Earth but because of rain and wind the craters do not last very long.
The planet Mercury and Earth’s moon do not have an atmosphere so meteors are more
likely to land there and create craters on the surface. Without an atmosphere, there is
nothing to create the friction for the meteor to burn up.
A meteor shower is when you are able to see hundreds of meteors at one time. These
often happen when the tail of a comet is close enough for the tiny particles in the tail to be
pulled in by Earth’s gravity.
1. What causes a meteoroid to be pulled in to Earth’s atmosphere? _________________
2. What are meteoroids made of? ___________________________________
3. Why are meteors sometimes called falling stars or shooting stars?
4. Why do you think more meteors hit the surface of Mercury than Earth?
5. What is a meteor shower?
6. Explain the meaning for each word:
Meteoroid:
Meteorite:
Meteor:
7. What causes a meteor to burn up in Earth’s atmosphere?