About the Activity

In the previous activity, Planetary Cycles, students learned how the presence or absence of a carbon cycle explains very important differences among Mars, Earth, and Venus. This activity examines the conditions necessary to support on-going life on a planet. After considering the conditions needed for life as we know it, students select the most habitable planet, in a fictitious planetary system, on which to crash land. This leads to a discussion about what makes a planet habitable. By explaining why Earth is able to support life, this activity serves as a lead-in for the next module, Origin of Life.

Learning Objectives

After completing this activity, students will be able to:

  • Analyze a fictional solar system and select a planet most likely to support life as we know it.

  • Describe what makes a planet habitable.

During the Activity

Activity Sequence in Brief

    discuss what makes a good environment for life, and watch a video on life in extreme environments.

    Students brainstorm the things they would need to survive on an extended trip into space, and choose a habitable planet in a crash-landing scenario.

    discuss their planet choices and why they considered them habitable.

    discuss the habitable zone and factors that make a planet habitable.

    The teacher collects the Crash Landing! Student Activity Sheets, and reviews the reasoning behind students' choices for habitable planets in the Explore activity.

Engage (10 minutes)

  1. Ask students to recap what they have learned about the differences in the environments of Mars, Venus, and Earth, and why the three planets are different. You should expect a variety of answers covering different factors studied in the Planetary Module. Discuss the student reader article "Goldilocks and the Three Planets" and answers to the questions assigned in Activity 5.1, The Greenhouse Effect using the "Goldilocks and the Three Planets" Teacher Answer Key as a guide. Collect student answers to the "Goldilocks and the Three Planets" questions.

  2. Ask students: What makes a planet habitable? What conditions need to exist in order for life to survive? Some prompting questions include: What temperature range is good for life? What sort of atmosphere does life need? Does life need liquid water? What do organisms need in order to eat? Do organisms need light? Does it matter how massive the planet is?

  3. Once students have described a good environment for life, show the video: Life in Extreme Conditions. Direct students to look for two types of extreme environments on Earth as they view the video. Expand students' definition of a good environment for life by discussing extreme environments, including black smokers (deep sea vents), algae in Antarctica, and bacteria in the Yellowstone hot springs. These organisms all live in places that would be uninhabitable for humans, yet they are able to thrive. Explain that students will now examine what makes a world habitable.

EXTENSION: Organism Cards. Have students examine the Organism Cards and consider what different organisms need to survive on a planet.

Explore (20 minutes)

  1. Divide students into small teams (three to five students each). Have them create a list of items they would need to bring with them to survive an extended trip on a spaceship into space (the supplies that are necessary for life as we know it). Encourage students to think beyond what humans would need, and to consider the needs of other forms of life that humans might bring along (for example, plants for food or medicine, animals for food or companionship, etc.). Each student should record on a piece of paper the list their team develops. (These will be collected at the end of class).

  2. Once the teams have developed lists of what they would need, inform them that something has gone terribly wrong on their well-packed space ship. They will need to crash land in the nearest planetary system. Give each team the Crash Landing! Student Activity Sheet (a profile of the planetary system) and instruct the teams to decide on which planet or moon to crash. Teams should discuss the planetary system for no more than 10 minutes. Tell students to record their selections and the reasons why they chose that planet or moon on the back of their student activity sheets.

Explain (10 minutes)

  1. Bring the whole class back together. Have each team share which planet or moon they thought was best for a crash landing. Remind presenters to elaborate on their group's reasoning.

Elaborate (10 minutes)

  1. Ask students if they think there is any one factor that is essential for life. Remind students about the extremophiles they saw in the video at the beginning of class. (The most obvious common element is liquid water.)

  2. Introduce the concept of the "habitable zone" as the area around a star where water can be liquid. Show the video: What is the Habitable Zone? While watching the video, ask students to listen for the planets in our solar system that are in the "habitable zone." Discuss where in our own solar system the habitable zone is located. (Just inside Earth's orbit to just outside Mars' orbit.)

  3. Discuss the possibility of a second habitable zone around large planets such as Jupiter. (See Science & Resources for help in leading this discussion.) Close the discussion by reexamining the list of planets and moons in the Nonog System. Review which of them have liquid water. Point out that some of the life forms that students have examined today could live on some liquid water worlds, but not others. Liquid water is the most basic requirement for all life as we know it, but other factors are important for the particular organisms that students examined as well. For example, while liquid water might exist on Moon 2 of Planet 7, it would be far too cold there for organisms such as hot spring bacteria (or other extremophiles) to live.


  1. Collect the Crash Landing! Student Activity Sheet and check to see if students' reasoning for choosing a habitable planet makes sense. Also collect students' lists of what they would need for an extended space trip.

  2. Remind students that the end-of-module assessments begin tomorrow with a concept map activity, and an end-of-module test on the following day.

EXTENSION: Earth's Cousins. If you have chosen to have student teams complete the project Earth's Cousins, assign the Earth's Cousins Evaluation Student Information Sheet on today. Students should bring their completed Evaluations on the next day; they will be collected at the beginning of the period. Announce that the next class meeting will be Earth's Cousins Poster Project Presentations, followed by a concept map activity on the following day, and end-of-the-module test on the day after that.



For Each Student

  • None

For Each Student Team

  • None

For Teacher

Student Handouts

Student Reader Articles


  1. Prepare any necessary handouts and transparencies. Familiarize yourself with the media. For background information on the topics covered in this activity, review "The Science & Resources" section (accessed from the menu bar above).

NOTE: All Teacher CD-ROMs in the complete Voyages Through Time curriculum (not this SAMPLE) provide both MS WORD and PDF versions of items such as student activity sheets and tests. In the complete VTT curriculum, teachers may use MS WORD (or other word processor) to modify any of the printable items if they wish to do so.