Mars is a harsh, cold world. It is much colder than Earth; but then, it is also farther from the sun. The small, barren planet also has a thin atmosphere that is 95 percent carbon dioxide.
Mars's atmosphere is about 100 times thinner than Earth's. Without a "thermal blanket," Mars can't retain any heat energy. On average, the temperature on Mars is about minus 80 degrees F (minus 60 degrees C). In winter, near the poles temperatures can get down to minus 195 degrees F (minus 125 degrees C). A summer day on Mars may get up to 70 degrees F (20 degrees C) near the equator, but at night the temperature can plummet to about minus 100 degrees F (minus 73 C). Frost forms on the rocks at night, but as dawn approaches and the air gets warmer, the frost turns to vapor, and there is 100 percent humidity until it evaporates.
Seasons on Mars
Like Earth, Mars has four seasons because the planet tilts on its axis. The seasons vary in length because of Mars' eccentric orbit around the sun. In the northern hemisphere, spring is the longest season at seven months. Summer and fall are both about six months long. Winter is only four months long.
During a Martian summer, the polar ice cap, composed mainly of carbon dioxide ice, shrinks and may disappear altogether. When winter comes, the ice cap grows back. There may be some liquid water trapped beneath the carbon dioxide ice sheets, scientists say.
— Tim Sharp, Reference Editor