Mars is the fourth planet from the Sun. Due to the proximity of Mars to Earth, curiosity about the habitability of Mars is not new. However, factors such as distance and climatic characteristics are significant impediments. Earth is approximately 93 million miles away from the Sun, while Mars is approximately 142 million miles away, and therefore receives less heat. Mars has an estimated average temperature of -81 °F. The planet takes 687 days to complete a revolution around the Sun, meaning seasons on Mars are roughly twice as long as seasons on Earth. The atmosphere of Mars is also fragile and consists primarily (95%) of CO2. For these reasons, Mars is too cold for humans to establish a permanent settlement.
Temperature on Mars
Mars has an atmosphere that is 100 times thinner than the atmosphere of Earth. As a result, Mars' atmosphere cannot retain heat and the surface of Mars has an average temperature of -81 °F. During winter, temperatures at the poles drop even further, reaching lows of -195 °F. Near the equator of Mars, daytime temperatures during the summer can reach 70 °F, but plummet to -100 °F at night. Frost is common on rocks during nights, but it melts and evaporates as the air get warmer near dawn. Even when Mars experiences 100% humidity, the conditions remain similar to those of the Atacama Desert in South America. Some forms of life, such as lichens, are known to survive this type of harsh climate by absorbing water from the humid environment, and researchers believe that a variety of Antarctic lichen that photosynthesizes at 70% humidity might be able to withstand the conditions on Mars.
Like Earth, Mars experiences four seasons, as both planets tilt on their axis at similar angles. However, seasons on Mars are much longer because of the planet's eccentric orbit. Spring lasts for seven months, both fall and summer last for six months, while winter is four months long. During the summer, the carbon dioxide ice caps in the polar regions shrink and disappear altogether, but redevelop during the winter. Researchers and astronomers believe that liquid water may be trapped beneath the carbon dioxide ice sheets.
Dust storms are a common feature on the surface of Mars. In 2018, space satellites and telescopes recorded the largest dust storm ever observed on the surface of the Red Planet. In fact, the storm was so severe that it ended the mission of NASA's Mars rover, Opportunity. The thin atmosphere allows heat to penetrate to the surface of Mars, where it is absorbed by dust, resulting in a warm and circulating atmosphere. The storms puff up the surface and atmosphere, making it easier for water vapor and other gases to escape into space, which might explain how the planet lost its atmosphere and oceans.
Some researchers suspect that Mars was wetter and warmer in the past, with an average temperature of about 50 °F, while others think the planet may have been an icy world with temperatures as low as -54 °F. Recent astronomical studies indicate that Mars might be emerging from an ice age. Shrinking ice caps and increased humidity at the polar regions suggest a rise in temperature, a feature that astronomers believe is the key to making the planet habitable for humans.