This red planet has a very thin _____________________________ that consists of 95% carbon dioxide (CO2), 3% nitrogen, and 1.6% argon (there is no oxygen). The surface of Mars is dry, rocky, and mostly covered with iron-rich dust. There are low-lying plains in the northern hemisphere, but the southern hemisphere is dotted with impact _____________________________. The ground is frozen; this _____________________________ extends for several kilometers. The north and _____________________________ poles of Mars are covered by _____________________________ caps composed of frozen water and carbon dioxide. Mars is much _____________________________ than the Earth. Mars' surface _____________________________ ranges from a high of 68° F(20° C) to a low of -220° F(-140° C).

Each _____________________________ on Mars takes 1.03 Earth days (24.6 hours). A year on Mars takes 687 Earth days; it takes this long for Mars to orbit the _____________________________ once.

Mars has 2 tiny _____________________________, Phobos and _____________________________. They were probably _____________________________ that were pulled into orbit around Mars.