Solar System — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. Astronauts on the International Space Station experience weightlessness. What is the best explanation for this?
A) The space station is so far from Earth that gravity no longer reaches it.
B) The station and astronauts are in constant free fall around Earth, creating the sensation of weightlessness.
C) The station's engines cancel out the force of gravity inside the cabin.
D) There is no air in space, and without air there is no gravity.
The ISS and its astronauts are constantly falling toward Earth while moving forward fast enough to keep missing it — this continuous free fall creates the floating sensation we call weightlessness.
2. Scientists want to build a base on the Moon before attempting a crewed mission to Mars. Which reason best supports this plan?
A) The Moon has a thick atmosphere that protects against radiation just like Earth.
B) The Moon is much closer than Mars, so it is a safer place to test life-support technology.
C) The Moon has abundant liquid water that could supply a Mars-bound crew.
D) Rockets cannot carry enough fuel to reach Mars without stopping on the Moon first.
The Moon is only about 240,000 miles from Earth (a three-day trip), while Mars is over 30 million miles away at its closest. Testing life-support systems on the nearby Moon lets astronauts return quickly if problems arise.
3. Europa, a moon of Jupiter, has an icy surface with a possible ocean underneath. Why are scientists excited about this?
A) An underground ocean could provide drinking water for astronauts visiting Jupiter.
B) Liquid water beneath the ice could potentially support simple forms of life.
C) The ice could be mined and shipped back to Earth to solve water shortages.
D) Europa's ocean proves that all moons in the solar system contain water.
Liquid water is considered essential for life as we know it. If Europa has a vast ocean beneath its icy crust, warmed by tidal forces from Jupiter's gravity, it could harbor simple organisms like bacteria.
4. A trip to Mars takes about seven months. Which challenge would be the greatest concern for the crew?
A) The spacecraft would run out of sunlight for its solar panels during the trip.
B) Crew members would face long-term exposure to radiation and the effects of low gravity on their bodies.
C) Radio signals between Earth and Mars are instant, so mission control would constantly interfere.
D) The spacecraft would overheat because it moves closer to the Sun on the way to Mars.
During a seven-month trip to Mars, astronauts would face dangerous cosmic radiation without Earth's magnetic field to protect them, and prolonged low gravity would weaken their bones and muscles.
Part B: Fill in the Blank
Write the correct answer on each line.
1. NASA's Artemis program aims to return astronauts to the Moon for the first time since 1972.
NASA's Artemis program plans to land astronauts on the Moon again after a gap of more than 50 years since the last Apollo mission (Apollo 17) in December 1972.
2. Solar panels provide electricity to spacecraft by converting sunlight into energy.
Solar panels contain special cells that convert sunlight directly into electricity, giving spacecraft a renewable power source as long as they are close enough to the Sun.
3. Communication between Mars and Earth can be delayed by up to 20 minutes because of the vast distance.
Radio signals travel at the speed of light, but Mars can be so far from Earth that a message takes up to 20 minutes each way — meaning a round-trip conversation could take 40 minutes.
4. The James Webb Space Telescope launched in 2021 to study the earliest galaxies and distant exoplanets.
The James Webb Space Telescope launched in December 2021 and uses infrared sensors to peer deeper into space than ever before, studying the oldest galaxies and the atmospheres of distant exoplanets.
5. A planet orbiting a star outside our solar system is called an exoplanet.
The prefix exo- means "outside," so an exoplanet is a planet that orbits a star outside our solar system. Scientists have confirmed thousands of exoplanets so far.