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1. Has a reddish hue over 60 percent of the planet, which we now known to be caused by red dust and rocks on the surface of the planet. |
2. Has polar ice caps waxing and waning with the seasons that we now know to be composed both of dry ice (frozen carbon dioxide) and water ice. |
3. Has surface markings that some originally thought looked like "canals" from Earth. These are now known to be features like the edges of mountain ranges. |
4. Has areas of changing color that were once thought to correspond to vegetation. We now believe these regions of changing color to be due to blowing sand, not vegetation. |
5. Has an atmosphere with clouds. |
Many of these features, particularly the "canals," made Mars and conjectured life
there a favorite of science fiction
writers early in this century (see the box below).
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