THE INNER PLANETS

• Earth is just one of the planets in our solar system. The planets are large bodies that rotate around the Sun and reflect its light and warmth. The planets that are located closest to the Sun are made out of rocky material, and are relatively small and heavy. In contrast, the planets that are farther away from the Sun are much larger because they are formed of light gases. All of these planets follow a certain path around the Sun, held a specific distance from the Sun by the strong gravitational force of the Sun.
• The inner planets, those closest to the Sun, are Mercury, Venus, Earth, and Mars. Even though these planets are all small and rocky, they have more differences than they have things in common. Because Mercury is the closest to Sun, the side that faces the Sun gets as hot as 427º Celsius. At the same time, the side that faces away from the Sun is a freezing -173º Celsius. Mercury also has a slower rate of rotation than Earth, making days and nights much longer than ours. The extreme temperatures alone make it a very unlikely place for life. Add to that an atmosphere too thin for human breathing, and it’s obvious that people won’t be living on Mercury any time soon. The next planet from the Sun is Venus. Below clouds of sulfuric gas lies its 96% carbon dioxide atmosphere. That might be nice for a plant, but not a person. If you managed to survive the atmosphere, the bad news is that the surface of the planet is hot enough to melt solid metal. In addition, the pressure of the air would be strong enough to crush you.
• You are probably most familiar with Earth because it is your home planet. It has the perfect conditions for life as we know it. Earth’s atmosphere and oceans help control the trickiest part of making a planet life-friendly: temperature. Earth is the only planet known to have liquid water. Mars, the fourth farthest from the Sun, has about the same amount of land as Earth, but does not have vast oceans separating it as we do on Earth. Mars has been studied and photographed more than any of the other planets besides Earth. There is speculation that it may be possible for life to exist there. Although scientists have not been able to find actual water on Mars, there seems to be evidence of water erosion on its surface. Its canyons and mountains are very similar to those found on Earth, except that they are lacking vegetation. Some scientists believe that Mars may have been very much like Earth until something somehow happened to evaporate the water supply.

 Name:__________________________________

Answer the following questions based on the reading passage. Don’t forget to go back to the passage whenever necessary to find or confirm your answers.

1. Propose a theory for what could have happened to the water supply on Mars. 
2. Why do you think that scientists have explored Mars more than the other planets? 
3. Why might plants be able to survive in the atmosphere of Venus?
4. Attempt to explain the huge difference in temperature between the two sides of the planet Mercury 
5. Do you think that people will ever be able to colonize other planets in the future? Why, or why not?