Discovery
Which inner planet has been known since ancient times and can be seen without a telescope?
Mercury
Which inner planet is the smallest?
Mercury
What is the closest planet to the Sun?
What is Mercury?
About how old are the inner planets?
4.6 billion years old?
How many moons does Earth have?
1
Who discovered the phases of Venus using a telescope?
Galileo Galilei
Which inner planet is the hottest?
Venus
Which planet is third from the Sun?
What is Earth?
What was the solar system formed from?
A rotating cloud of gas and dust called the solar nebula.
How many moons does Mercury have?
0
Who used observations of Mars to help develop the laws of planetary motion?
Johannes Kepler
Which inner planet is known as the Red Planet?
Mars
Which planet is fourth from the Sun?
What is Mars?
Why are the inner planets mostly rock and metal?
They formed close to the hot young Sun, where rock and metal could remain solid while lighter materials were less likely to condense.
What is unusual about Venus compared with the other inner planets?
It has an extremely thick carbon-dioxide atmosphere and is the hottest planet.
Which spacecraft orbited Mercury and greatly expanded scientists' knowledge of it?
MESSENGER
Which inner planet has liquid water and the only confirmed life?
What is Earth?
Which planet is second from the Sun?
What is Venus?
What is the main theory explaining how our solar system formed?
The solar nebular theory/model.
What evidence suggests Mars once had liquid water on its surface?
Ancient valleys, channels, minerals, and other geological features indicate past water activity.
Why is saying Earth was 'discovered' different from saying Mercury was discovered?
Humans have always lived on Earth, while Mercury was observed as a separate celestial object.
What do all four inner planets have in common?
What are terrestrial, rocky planets with solid surfaces?
Put the inner planets in order from the Sun outward.
What is Mercury → Venus → Earth → Mars
Why are the inner planets smaller than the outer planets?
The hot inner solar system had less solid material available to build very large planets, while farther out there was more ice and material to form giant planets.
How do the inner planets support theories about other star systems?
Their rocky compositions and their location close to the Sun match predictions that hot regions near young stars tend to form smaller rocky planets, supporting models of planetary system formation.