Solar System — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. Venus is closer to the Sun than Earth, yet Mercury has wider temperature swings than Venus. What best explains this?
A) Mercury spins faster than Venus so it heats and cools more quickly each day.
B) Venus has a thick atmosphere that traps heat, while Mercury has no atmosphere at all.
C) Mercury is smaller than Venus so it cannot hold onto heat as long.
D) Venus reflects all sunlight back into space while Mercury absorbs it.
Venus's thick CO₂ atmosphere traps heat (greenhouse effect) keeping it hot day and night. Mercury has no atmosphere so temperature swings wildly.
2. Why do the outer planets have many more moons than the inner planets?
A) Outer planets spin faster which pulls in more objects from space.
B) Outer planets are much larger and their stronger gravity captures more objects.
C) Inner planets are too hot for moons to form near them.
D) Moons can only form from rings and inner planets have no rings.
Larger mass = stronger gravitational pull = more ability to capture passing objects as moons. Jupiter has 90+ moons; Saturn has 140+.
3. A student says Neptune must be the coldest planet because it is farthest from the Sun. Which fact would best support this claim?
A) Neptune has the strongest winds in the solar system.
B) Neptune takes about 165 Earth years to orbit the Sun once.
C) Neptune receives very little solar energy due to its great distance from the Sun.
D) Neptune is an ice giant made of frozen water and ammonia.
The supporting reason is that Neptune's great distance from the Sun means very little solar energy reaches it, making it extremely cold.
4. Mars shows evidence of ancient river valleys and lake beds. What does this evidence most strongly suggest?
A) Mars once had active volcanoes that melted ice across the surface.
B) Mars once had conditions warm enough for liquid water to flow on its surface.
C) Mars currently has underground oceans hidden beneath its polar ice caps.
D) Mars was once closer to the Sun and has slowly drifted outward over time.
River valleys and lake beds require liquid water. This evidence strongly suggests ancient Mars had a warmer, wetter climate.
Part B: Fill in the Blank
Write the correct answer on each line.
1. Earth is the only planet in our solar system known to support life.
Earth's liquid water, oxygen-rich atmosphere, moderate temperature, and magnetic field make it uniquely suited for life.
2. The greenhouse effect on Venus causes its surface temperature to reach over 450 degrees Celsius.
Venus's thick CO₂ atmosphere traps solar heat, raising surface temperatures above any other planet.
3. Jupiter's strong magnetic field is the largest of any planet in the solar system.
Jupiter's magnetic field is 20,000 times stronger than Earth's, creating massive radiation belts and spectacular auroras.
4. Saturn's moon Titan has a thick atmosphere and lakes of liquid methane on its surface.
Titan is Saturn's largest moon and the only moon with a dense atmosphere. It has methane rain, rivers, and lakes.
5. Triton is an unusual moon of Neptune because it orbits the planet in a backward direction.
Triton has a retrograde orbit — it orbits Neptune in the opposite direction of Neptune's rotation, suggesting it was captured.