Solar System — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. Scientists want to send a rover to study a planet with evidence of ancient water. Which planet would be the best choice and why?
A) Venus, because it is closest in size to Earth and may have had oceans.
B) Mars, because it has ancient river valleys and is close enough to reach with current technology.
C) Jupiter, because its large size means it could hold the most water.
D) Mercury, because its craters could contain frozen water from comet impacts.
Mars has clear geological evidence of ancient water (river valleys, deltas, lake beds) and is reachable with current technology.
2. If the Sun suddenly lost half of its gravitational pull, what would most likely happen to the planets?
A) All planets would crash into each other because their orbits would become unstable.
B) Planets would drift farther from the Sun into wider orbits or escape into space.
C) Nothing would change because planets have their own gravity to keep them in orbit.
D) Only the inner planets would be affected because they are closest to the Sun.
The Sun's gravity is the centripetal force keeping planets in orbit. Reducing it would allow planets to drift outward or escape.
3. A spacecraft takes four years to reach Jupiter but twelve years to reach Neptune. What is the main reason for this difference?
A) Neptune has stronger gravity that slows the spacecraft down as it approaches.
B) Neptune is much farther from the Sun than Jupiter so the spacecraft must travel a greater distance.
C) Jupiter pulls the spacecraft toward it with its strong gravity, making the trip faster.
D) Neptune's thick atmosphere creates drag that slows the spacecraft during approach.
Neptune is about 30 AU from the Sun vs. Jupiter's ~5 AU. The greater distance is the primary reason for the longer travel time.
4. Why would a space colony on Mars need a greenhouse to grow food instead of planting crops outdoors?
A) Mars has too much sunlight which would burn the crops without a filter.
B) Mars has a thin atmosphere with little oxygen and extremely cold temperatures.
C) Mars soil contains too many nutrients which would cause crops to grow too fast.
D) Mars has constant rain storms that would flood any outdoor crops.
Mars's thin atmosphere (less than 1% of Earth's pressure), lack of oxygen, and temperatures averaging -60°C make outdoor farming impossible.
Part B: Fill in the Blank
Write the correct answer on each line.
1. Rovers like Curiosity and Perseverance explore the surface of Mars searching for signs of past life.
NASA's Mars rovers analyze soil, rock, and atmosphere to find biosignatures or conditions that could have supported life.
2. An astronomical unit is the average distance from Earth to the Sun, about 93 million miles.
1 AU (astronomical unit) = ~93 million miles / ~150 million km. Used to describe distances within the solar system.
3. The force of gravity keeps the Moon in orbit around Earth and Earth in orbit around the Sun.
Gravity is the attractive force between masses. It governs all orbital motion in the solar system.
4. Scientists study comets because the icy bodies may contain clues about the early solar system.
Comets are preserved from the early solar system. Their ice and dust provide information about solar system formation.
5. A planet's orbital period is the time it takes to complete one full trip around the Sun.
Orbital period is the time for one complete revolution around the Sun. Earth's orbital period is 365.25 days (1 year).