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Dear Dr. Staff: How come Mars is red? I hear you're going to be passing it in a few weeks on your way back from Neptune, and would be curious to know how the planet got to be red. My Uncle Smiley said that the planet is red because there have been a lot of wars on it, and people have the habit of bleeding in wars. I think he's wrong, though, because I read somewhere that Martians have green blood.

--Colorful, Completely Confused Kid

Dear Confused: Well, sonny, here's how it works. On earth, all the trees and shrubs, algae, and flower stems are green, the color of chlorophyll. Chlorophyll is the chemical the plants use to convert carbon dioxide in our atmosphere into little flecks of energy that the plants can use to get bigger. On Mars, there just isn't enough carbon dioxide for these plants to live, so they don't, and they die. The planet Mars is covered with dead plants. These plants don't have any chance to decompose with the same bacteria that plants on earth do, so they just sit there, forever. You would think that the plants would still have their natural color after they died, but they don't, because of the way they died. When you hold your breath real hard, your face turns red. When the plants don't have any air to breathe, they also turn red, and so that's the color they are when they die. That's why Mars looks red, even from as far away as earth.

--Space-Traveling Super Science Sentience

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