What You Need


  • Poster Paper (one for each student)
  • Markers, colored pencils
  • Sketch paper
  • Photo Paper (for printing pictures)
  • Any other supplies that students could use to make an interesting poster about one of the terrestrial planets
  • Box filled with sand
  • Marble
  • Cardboard box with lid
  • Various common objects


To explore the geological history of Mercury and the other terrestrial planets, Venus, Earth, and Mars and to form hypotheses about them.


This lesson is part of the MESSENGER: A Mission to Mercury Project, which examines the science behind space exploration. MESSENGER: A Mission to Mercury is developed by AAAS and funded by NASA's MESSENGER Project. For more lessons, activities, and interactives that take a closer look at the science behind space exploration, be sure to check out the MESSENGER: A Mission to Mercury Project page.

In this lesson, students will explore the geological history of Mercury and the other terrestrial planets, Venus, Earth, and Mars. This lesson assumes that students already have some general knowledge of the planet Mercury. Students at this age know many things about our solar system already, such as what the planets are, their order in the solar system, and scales of size. They even may be familiar with the various profiles of planets, including which are terrestrial and which are gas planets.

This lesson assumes that students already have some general knowledge about the planet Mercury. If students do not, or if you would like to cover the information as a refresher, we recommend preceding this lesson with another Science NetLinks lesson, Mercury. A faster way to achieve the same goal is to assign a preliminary reading at either the MESSENGER site, Mercury the Elusive Planet (students should click on each menu item at the top of this page), or NASA's Mercury page.

At this grade level, students should add more detail to what they know of the solar system. The focus of this lesson will be the geology of terrestrial planets and how scientists take data and interpret the information to come up with a planetary history. Features of many of the planets and their moons show evidence of developmental processes similar to those that occur on the earth (such as earthquakes, lava flows, and erosion). This idea is covered in the lesson as well.

Because the development of the lesson revolves around GeoHunter, an interactive in which students explore the geology of Mercury, students will learn about MESSENGER, the spacecraft mission to Mercury. Throughout the lesson, they also will discuss the geology of Mars, Venus, and Earth.

Other aspects of this lesson that are presented in a subtle manner delve into Habits of Mind benchmarks. Since students will discuss data and give various interpretations for the data, they will discuss how different explanations can be given for the same evidence.

Make a Mission is a lesson that is about the mission as a whole and can precede or follow this lesson, however each stands on its own. Since this lesson is one that covers the area of planetary geology, the lesson will complement any geology or astronomy lesson.


To start this lesson, set up a small, sand-filled box on a table at the front of the room. If there is space, have students stand around the table. Then, pick up a marble and show it to your students. Tell them that you will now demonstrate an impact crater. To do this, simply drop the marble into the sand-filled box.

Follow the demonstration with these questions:

  • What happened to the sand when I dropped the marble into the box?
  • Why do you think this happened?
  • Do you think the impression made by the marble is in any way like the craters found on our moon or other planets? If so, how?
  • How do you think the surfaces of the different terrestrial planets (Mercury, Venus, Earth, and Mars) were formed?

(Answers may vary. Encourage students to explain their answers.)

Now, students should use their Terrestrial Terrain student esheet to explore these brief articles and view one video:

These resources briefly introduce ideas of how a terrestrial planet's surface may have formed. Students can answer these questions on their Terrestrial Terrain student sheet.

  • What are some geological structures or formations found on the terrestrial planets Mercury, Venus, Earth, and Mars? (Students mostly have read about craters and volcanoes, but may know of others, or bring up the land formations of channels [gulches] that indicate there could have been water on Mars.)
  • What kind of information can evidence of craters on the surface of a planet or moon help scientists figure out? (The number of craters can indicate the age of the surface, generally speaking. For instance, on Venus, students will read that there are few craters, which indicates that the surface has been "paved" over and is young. A surface like our moon with numerous craters indicates an older surface.)
  • What are some geological formations on Earth? Do you think that our understanding of these features could be applied to other planets? (Students may come up with numerous ideas, any of which could be discussed in the context of another planet. For instance, the "waterways" on Mars look like "waterways" because of what they look like on Earth. Another interesting idea is plate tectonics and whether or not other planets could possibly have plate tectonics.)
  • When scientists get pictures and data back from Venus, Mars, and Mercury, do you think that they will all come up with the same "explanation" or hypothesis for the planet's geological history? (This question will take the discussion in another direction, but is worth exploring, particularly in the case of planetary geology, because scientists rely on data that can certainly be interpreted in a number of ways. Students should reason that due to many factors involved in geology, different scientists may come up with different hypotheses. In the case of Mars, some scientists say that because there was likely water on the planet, this is an indication of past life on the red planet. Other scientists think that there wasn't enough time for life to evolve even if there was water. These are two very different ideas that have grown out of the same geological data.)

Follow this last question with a demonstration using a closed cardboard box filled with various common objects. Have students observe this mystery box to try to determine its contents. They may hold it, shake it, weigh it, etc. They will all be faced with the same data but come to different conclusions, much like scientists do.


Armed with their knowledge about the geological features of terrestrial planets, students should now examine some of Mercury's features in more detail. To do so, students can use their esheet to view some images of Mercury that were taken by the MESSENGER mission. Students should view these images:

Students should consider these questions as they are studying the images:

  • What do you notice about the distribution of the craters, scarps, and volcanoes in the images? Is there any kind of pattern? If so, what is it?
  • Can you form a hypothesis about the distribution of these features on the planet? What would it be?
  • Are these images of Mercury how you expected the planet to look?
  • Do these images look like the images of any other planets, moons, meteors, etc. in the solar system?
  • Why do you think Mercury appears to have so many craters, volcanoes, and scarps?

(Answers to these questions may vary. Encourage students to explain their answers.)

In this part of the lesson, students should use their esheet to do an online, interactive activity called GeoHunter, where they explore the geology of the planet Mercury. They are instructed to collect fifteen pieces of data (pictures of geological formations). Follow up with these questions:

  • What types of geological formations did you collect pictures of? (They collected pictures of dormant volcanoes, impact craters, and scarps.)
  • What can these geological formations tell you and scientists about Mercury? (There are probably more than several answers to this question. Craters can indicate surface history and dates and students may remember from past readings that Mercury has more meteoroid impacts because its atmosphere is thin. Scarps, which are long, rounded cliffs that stand around a mile tall, have lead scientists to believe they formed when Mercury cooled and shrank.)
  • Is the process of analyzing the data something that happens right away when information is sent back from MESSENGER? (The Learn More section mentions that this data will be used for decades to come. This may be important in students' understanding of how interpretations can differ and change over time.)
  • Do you think that all geologists who look at this data will come up with the same explanations for why Mercury has these surface features? (The answer to this question is not in the interactive, but students should reason from prior discussion that there could be a variety of hypotheses.)
  • Do you think this new information from MESSENGER will lead to new hypotheses about the planet's geological history? If so, why? (The purpose of a mission such as this one is to learn more about the planet, which may lead to new hypotheses about the planet's surface history as well as what is happening there now.)


The assessment is two-fold. Each student should become an expert in one of the terrestrial planets and create a poster on that planet. Encourage them to include pictures and a geological profile of several hundred words. Though they may include other information, the focus should be geology. Students can use the resources on the esheet to help them perform their research.

The second part of the exercise should address, in part, the Habits of Mind benchmarks, that hypotheses are valuable. Students should quickly write up one solid observation that they would make about Mercury based on their knowledge of the terrestrial planet they have just profiled. They should explain what they would look for in the new data returned from the MESSENGER Mission and what hypothesis this information could lead to, based on their knowledge of the planet they profiled.


For some other Science NetLinks lessons about the solar system and the universe, see:

To further extend some of the ideas in this lesson, students could visit The Nine Planets, which provides a comprehensive overview and often-detailed discussion of the planets in our solar system and their related satellites, with accompanying graphics and photos to enhance any learner's understanding.

If students want to learn more about the MESSENGER Mission or Mercury itself, they could go to the MESSENGER website, which provides all the information about the mission and the planet.

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Lesson Details

Grades Themes Project 2061 Benchmarks National Science Standards