The Planets
Which planet is closest to the Sun?
Mercury
Explanation: It is the first planet.
What are comets mostly made of?
Ice, dust, and rock
Explanation: They melt and form tails near the Sun.
What effect does Earth’s moon have on Earth?
Tides
Explanation: The moon’s gravity pulls on the oceans.
What two factors determine gravitational force?
Mass and distance
Explanation: More mass = stronger pull; more distance = weaker pull.
Why are outer planets colder than inner planets?
They are farther from the Sun
Explanation: They receive less solar energy.
Which two planets are too hot for liquid water because they are inside the habitable zone?
Mercury and Venus
Explanation: They are too close to the Sun
A comet develops a tail when it gets closer to the Sun. Why?
Heat causes ice to melt and gas to be released
Explanation: Solar radiation produces the tail.
Do planets or moons orbit in a circle or an elliptical (oval) shape?
Elliptical
Explanation: Orbits are slightly stretched ovals, not perfect circles.
Why does a comet or planet keep moving forward even as gravity pulls it inward?
Because of inertia
Explanation: Newton’s First Law — objects resist changes in motion.
Which planet is known for its rings?
Saturn
Explanation: It has the most visible ring system.
Which planet has the most moons?
Jupiter
Explanation: It has the greatest confirmed number.
Which one stays in space and which one burns up in Earth’s atmosphere: a meteor or a meteoroid?
A meteoroid stays in space; a meteor burns in the atmosphere
Explanation: Meteors burn up as shooting stars.
At which point in orbit does the moon move the fastest?
When it is closest to Earth
Explanation: Gravity is stronger at shorter distances.
If the distance between a moon and a planet increases, what happens to the gravitational force?
The Gravity decreases
Explanation: More distance = weaker force.
If Earth were too far from the Sun, what would happen to water?
It would freeze
Explanation: Less heat means lower temperatures.
Earth and Mars are both in the habitable zone, but only one has liquid water on the surface.
Which Planet and Why?
Earth has the right atmosphere to support liquid water.
Explanation: Mars doesn’t have an atmosphere that creates a greenhouse effect to keep surface water liquid. Instead, its surface water evaporated, and deeper water is frozen underground.
Which starts farther from the Sun: comets or asteroids?
Comets
Explanation: Many begin in the Oort Cloud or Kuiper Belt.
What four things are required to make a planet habitable for life like on Earth?
Water, a source of energy, complex chemistry, and a stable environment
Explanation: These conditions support life as we know it.
A planet wants to move in a straight line, but gravity bends that motion. Which law explains the straight-line part?
Newton’s First Law (Inertia)
Explanation: Objects keep their motion unless acted on.
According to NASA, our moon moves about one inch away from Earth each year. If this continues, how would the increased distance affect the moon’s orbital motion?
The moon would orbit more slowly and have a larger orbital path
Explanation: More distance = weaker gravity = slower orbit.
Which planets have more than one moon?
Name at least three.
Mars, Jupiter, Saturn, Uranus, Neptune
Explanation: Only Mercury and Venus have zero; Earth has one.
What two factors affect the orbit of an asteroid if it gets close to Earth?
Mass and distance
Explanation: These control gravitational pull.
What percentage of Earth’s atmosphere is oxygen: 10%, 20%, 50%, or 100%?
20%
Explanation: Most of our atmosphere is nitrogen.
If Earth suddenly had no gravity acting on the moon, what would the moon do?
Move in a straight line at a constant speed
Explanation: Without gravity, inertia takes over.
What percentage of Earth’s atmosphere is oxygen: 10%, 20%, 50%, or 100%?
20%
Explanation: Most of the atmosphere is nitrogen.