MARS
IMAGES
Unpiloted spacecraft from the United States, launched between 1964 and 1976, have supplied the most detailed information on Mars. From this data, scientists determined that the planet's atmosphere predominantly consists of carbon dioxide (CO2), with small amounts of nitrogen, oxygen, and water vapor also present. Due to the thinness of the atmosphere, daily temperatures often vary as much as 100 Celcius degrees (190 Fahrenheit degrees). In general, surface temperatures are too cold and surface pressures too low for water to exist in a liquid state on Mars, so the planet resembles a cold, high-altitude desert.
By Jordan Wood