The four planets closest to the Sun (Mercury, Venus, Earth, and Mars) are known as the rocky planets. Each has a solid surface and a core of heavy metals. None have rings. If we could weigh these planets, we'd find they have a high density for their size. In other words, they're heavy.
Jupiter, Saturn, Uranus, and Neptune are known as the gas planets because they are large spinning bodies of gases with no solid surfaces. These planets are located far from the Sun, and have rings made of rock, ice, and dust. If we could weigh these large planets, we'd find they have a very low density compared to their gigantic size. In other words, they're light.
Pluto is the smallest planet in our solar system. It has no rings. Although Pluto is made of rock and ice, it's not considered a rocky planet. It's not a gas planet either, and so is in a category of its own.
Mission: Learn the main differences between rocky planets and gas planets.
Locate the four planets labeled A, B, C, and D.
Pick up planet A and observe it closely.
Weigh planet A on the scale provided.
Repeat steps 2 and 3 for planets B, C, and D.
A. Which two planets weigh the most?
B. Which two planets weigh the least?
C. Which of the four planets do you think are rocky planets? Why?
D. Which of the four planets do you think are gas planets? Why?