 ### Overview

Students will use average straight-line distances to the planets and average rate of travel of several modes of transportation to compute the length of time it would take a spacecraft launched from Earth to travel to another planet.

### Management

• Download images of the planets and display them around the classroom for reference.
• Project or copy the tables from the student worksheet onto large chart paper or a whiteboard.
• Students can work individually or in groups in which they divide the work among team members.
• If time is limited, assign each group one mode of transportation or one planet for which to perform the calculations.

### Background

The solar system is enormous. Making a scale model of the solar system can help students understand the vast distances between planets. Take their understanding a step further with this lesson, which has them determine how long it would take to travel to each of the major planets and the dwarf planet Pluto.

How big are the planets and how far away are they compared to each other? See how the sizes of planets and the distances between them compare in this video. Credit: NASA/JPL-Caltech | Watch on YouTube

For this lesson, we take a simplified approach to having students compute straight-line distances to the planets from Earth. While this approach is effective for aiding student understanding, it’s not practical for real space travel because straight-line distances to the planets vary every day and spacecraft don’t travel in a straight line.

When we send a spacecraft to another planet, it follows a curved path, or trajectory, because of the gravitational pull of the Sun and the other solar system objects it passes near. Additionally, the planets are always moving, which can affect the time it takes to travel to them. A destination planet might be on the same side of the Sun as Earth when a spacecraft launches, but on the complete opposite side by the time it arrives.

Removing those factors allows young students to estimate the length of time it would take them to get to the planets by walking, riding their bikes, driving a car, riding on a rocket or traveling at the speed of light. Of course, most of these modes of transportation are impossible for space travel, but because they are most tangible to young students, they can help students gain a conceptual understanding of the vast distances in our solar system. Note that the rate of travel used for the rocket is the top speed of NASA’s Parker Solar Probe, the fastest spacecraft in existence.

### Procedures

1. Provide students with student worksheets, pencils, scratch paper and, if desired, calculators.
2. Have a volunteer read the instructions from the student worksheet.
3. Ask the class how the distance from Earth to each of the planets and Pluto should be computed. Answer: Subtract the appropriate distances.
4. Have students represent the problems to be solved using equations with a letter standing for the unknown quantity.
5. Have the class work together to compute the distance from Earth to each of the planets and Pluto. Fill in the class chart together as students fill in the charts on their worksheets.
6. Ask students to guess how long it would take them to travel to the planets using the various modes of transportation. Fill these guesses into the class chart.
7. Ask students how we should determine actual travel times by each mode of transportation to a given planet. Answer: Divide the distance by the rate of travel.
8. Have students represent the problems to be solved using equations with a letter standing for the unknown quantity.
9. Have students work individually or in small groups to perform the calculations and record their answers on their worksheets.
10. Compare actual answers to guesses and determine how they differ. Were student guesses close? Did they follow the same pattern?
11. If time allows, have students convert some of the larger numbers of hours into days or years.
12. Point out to students that we cannot travel at the speed of light, but as technology improves, we may be able to travel faster and get to other planets sooner.
13. Ask students to research how far away the closest star and neighboring planetary system are, then determine how long it would take by rocket to get there.
14. Ask students to identify some of the challenges of sending humans on such long journeys. Some challenges they might mention include taking enough food, water and air to breathe, being away from their families so long, physiological effects of being in space for extended periods, the length of time it would take them to return, and more.

### Assessment

1. Students should be able to understand which calculations are needed to yield the desired answers.
2. Students should be able to perform these calculations either by hand or using a calculator.