Science Chapter 21

Which shape describes a planet’s orbit?

• a circle

• an ellipse

• a straight line

Why is Venus hotter than Mercury?

• Venus’s surface is covered with lava.

• Venus has a strong greenhouse effect.

• Venus is closer to the Sun than Mercury is

How are the outer planets similar?

• They have solid surfaces.

• They are about the same size

• They have atmospheres that are mostly hydrogen

Pluto was known as a planet but is now a(n)

• asteroid

• meteoroid

• dwarf planet

An astronomical unit is the average distance

• from Earth to Mars.

• from Earth to the Sun.

• from Earth to the Moon.

orbit close to the Sun and have rocky surfaces

• asteroids

• inner planets

• outer planets

have gaseous surfaces and more than one moon

• inner planets

• outer planets

• meteors

chunks of rocks and ice that form a belt just beyond Mars

• asteroids

• comets

• meteors

light streaks in the atmosphere due to objects from space

• asteroids

• comets

• meteors

objects made of ice, rock, and dust that glow near the Sun

• asteroids

• comets

• meteors