This lesson is designed for middle school students with no previous knowledge of astronomy or the history of astronomy. I often prepare my images as a slideshow or printed, large size images for students to understand the planets we are studying. This lesson should take approximately thirty to forty-five minutes depending on how long you spend on each planet and any video you choose to show.

Group Size:


Learning Objectives:

  • Define terrestrial planet
  • Describe the interior, atmosphere, surface conditions of Mercury
  • Describe the interior, atmosphere, surface conditions of Venus
  • Describe the interior, atmosphere, surface conditions of Mars

Guiding Question:

Why was the Scientific Revolution important and how did it contribute to progress?


Images and video of the terrestrial planets.

Additional resources:




[Note: This lesson in its entirety with images can be found as an attached pdf and doc file]

Lesson Summary:

  • Define terrestrial planets
  • Describe the conditions of Mars
  • Describe the conditions of Venus
  • Describe the conditions of Mercury

Lesson: Terrestrial planets (ex. Earth)

The four inner planets are small, have rocky surfaces, and are called the terrestrial planets. They are more similar to each other than to any of the outer planets.

Mercury is the smallest of the planets and closest to the sun.

Mercury is not much larger than our moon and its core is made of dense metal iron. Its internal structure is a 100-200 km thick crust, a 600 km thick mantle and a core that’s approximately 3,600 km in diameter.

Mercury’s surface is overall very similar in appearance to that of the Moon, and it has virtually no atmosphere. Because of Mercury’s small mass, it has virtually no gravity to hold onto an atmosphere and because of the high daytime temperatures the gas particles that could form an atmosphere move faster, and therefore escape the gravitational pull more easily.

Mercury is a planet of extremes. Because of its proximity to the Sun, during the day, the side facing the Sun reaches temperatures of 430?C. But, at night, with no atmosphere to retain the heat, it can get as cols as -170?C!

Venus is so similar in size and mass to Earth that it is sometimes called Earth’s twin. Venus’ density and internal structure are similar to Earth’s, but that’s where the similarities end!

The similarity in size and density between Venus and Earth suggests that it has a similar internal structure: a core, mantle, and crust. Like that of Earth, the Venusian core is at least partially liquid. The slightly smaller size of Venus suggests that pressures are significantly lower in its deep interior than Earth.

The principal difference between the two planets is the lack of plate tectonics on Venus. Much of Venus' surface appears to have been shaped by volcanic activity. Overall, Venus has several times as many volcanoes as Earth, and it possesses some 167 giant volcanoes that are over 100 km across.

Venus takes about 7.5 Earth months to revolve around the Sun and it takes Venus about 8 months to rotate once on its axis. Oddly, Venus rotates from East to West, the opposite of most other planets in the solar system.

Venus’ atmosphere is so thick that it’s always cloudy. From Earth or space, astronomers can only ever see a smooth cloud cover over Venus. The pressure of Venus’ atmosphere is 90 times greater than the pressure of Earth’s and would quickly crush a person standing on the surface of Venus. Venus’ atmosphere is primarily composed of sulfuric acid, and the air is primarily carbon dioxide – neither of which supports human life.

Venus has the hottest surface of any planet at 460?C because of all the heat trapped by the intense cloud cover of its atmosphere. Because Venus is closer to the sun than Earth, it receives more solar energy than earth. The radiation that reaches the surface of Venus is given off as heat, and that heat is trapped in the atmosphere by the carbon dioxide.

Mars is called the Red Planet because it has a reddish tinge when seen from Earth. The reddish tinge is caused by the breakdown of iron rich rocks that create a rusty dust that coats the planet.

The atmosphere of Mars is more than 95% carbon dioxide, but unlike Venus, the atmosphere is much thinner. Temperatures on the surface of Mars range from -140?C to 20?C.

Because of certain geological features like canyons and coastlines, scientists think that a large amount of liquid water must have flowed on Mars’ surface in the distant past. At present, liquid water cannot exist on Mars because the atmosphere is so thin that any liquid water would quickly turn to gas.

Mars has two very small moons: Phobos and Deimos. Phobos, which is closer to Mars than Deimos is, is slowly spiraling towards Mars. Astronomers predict that Phobos will smash into Mars in about 40 million years.

It takes Mars 387 Earth days to orbit the sun. A Martian day is 24 hours, 39 minutes, and 35.244 seconds. A Martian year is equal to 1.8809 Earth years, or 1 year, 320 days, and 18.2 hours.


At the end of this lesson, students are asked to complete a Venn diagram activity where they need the information from this lesson to complete the diagrams.

The assessment can be found as a separate wiki page here, where there is also a pdf and doc version available for download. [Note: this assessment has not yet been added to the wiki, although it will be added soon...check back if you're looking for it.]

Attached Files:

Terrestrial Planets (ex. Earth) Lesson (pdf)

Terrestrial Planets (ex. Earth) Lesson (doc)

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