There are lots of objects in our solar system, but only eight of them are planets. What do all planets have in common?

• They are all made of rock or ice
• They all have rings or moons as satellites
• They are all nearly round and orbit the Sun
• They all rotate on an axis and orbit the Earth

Which answer describes how the inner planets are similar to each other?

• They are all the same size
• They all have solid surfaces
• They all have at least one moon
• They all have a thick atmosphere

Which of the inner planets listed below is closest to the Sun?

• Earth
• Mars
• Mercury
• Venus

Tom and his friends were talking about what it would be like if they could go live on Mars someday. Mandy said it would be much colder there than on Earth and it would hardly ever get above freezing even in summer. Jose said there would be time periods on Mars like there are on Earth.  
What else might they experience if they ever went to live on Mars?

• A year on Mars would last almost as long as two Earth years
• Water would run in the canals on Mars on the warmest days
• They would see four big moons and several smaller ones at night on Mars
• They could breathe the air since Mars and Earth have similar atmospheres

When comets come close to the Sun they develop a tail that glows so we can see it from Earth. Asteroids do not develop tails like this. In what other way are asteroids different from comets?

• Asteroids orbit planets while comets orbit the Sun
• Asteroids are rocky while comets are balls of ice and dust
• Asteroids orbit outside of the Solar System while comets do not
• Asteroids are smooth and round while comets are lumpy shapes

Ann and Cheryl are trying to write a general description of a planet that could apply to any planet in our Solar System. So far, their list looks like this:   
1.  Orbits the Sun  
 2.  Is nearly round  
What else can they add to their list?

• spins on its axis
• has at least one moon
• has water on its surface
• is always the same distance from the sun

Demarcus wants his friend, Alvin, to guess which planet he is describing. He tells Alvin that the planet is rocky and doesn't have any moons. What other clue would let Alvin be certain which planet Demarcus is describing?

• It has rings around it
• It is very hot in the daytime
• It has a thick atmosphere
• It has liquid water on its surface

Of the outer planets, which one is closest to the Sun?

• Jupiter
• Neptune
• Saturn
• Uranus

Which of the following describes one way that Mars and Earth are different?

• Mars has a moon but Earth does not.
• Earth has an atmosphere but Mars does not
• Earth is an inner planet and Mars is an outer planet
• A year on Earth is about half as long as a year on Mars

Comets and asteroids both crash into planets or their moons sometimes. In what other way are comets and asteroids similar?

• They both have a smooth, round shape
• They are both found in orbit around the Sun
• They both develop glowing tails near the Sun
• They are both made of ice and rock particles