User:Chrisjj/Mars Ed

Gravity and magnetosphere
The surface gravity of Mars is 38% that of Earth. Although microgravity is known to cause health problems such as muscle loss and bone demineralization, it is not known if Martian gravity would have a similar effect. The Mars Gravity Biosatellite was a proposed project designed to learn more about what effect Mars' lower surface gravity would have on humans, but it was cancelled due to a lack of funding.

Due to the lack of a magnetosphere, solar particle events and cosmic rays can easily reach the Martian surface.

The atmosphere
Atmospheric pressure on Mars is far below the Armstrong limit at which people can survive without pressure suits. Since terraforming cannot be expected as a near-term solution, habitable structures on Mars would need to be constructed with pressure vessels similar to spacecraft, capable of containing a pressure between 30 and 100 kPa. The atmosphere is also toxic as most of it consists of carbon dioxide (95% carbon dioxide, 3% nitrogen, 1.6% argon, and traces totaling less than 0.4% of other gases including oxygen.

This thin atmosphere does not filter out ultraviolet sunlight, which causes instability in the molecular bonds between atoms. For example, ammonia (NH3) is not stable in the Martian atmosphere and breaks down after a few hours. Also due to the thinness of the atmosphere, the temperature difference between day and night is much larger than on Earth, typically around 70 °C (125 °F). However, the day/night temperature variation is much lower during dust storms when very little light gets through to the surface even during the day, and instead warms the middle atmosphere.

Water and climate
Water on Mars is scarce, with rovers Spirit and Opportunity finding less than there is in Earth's driest desert.

The climate is much colder than Earth, with mean surface temperatures between 186 and 268 K (depending on the season and latitude). The lowest temperature ever recorded on Earth was 184 K (−89.2 °C, −128.6 °F) in Antarctica.

Because Mars is about 52% farther from the Sun, the amount of solar energy entering its upper atmosphere per unit area (the solar constant) is only around 43.3% of what reaches the Earth's upper atmosphere. However, due to the much thinner atmosphere, a higher fraction of the solar energy reaches the surface. The maximum solar irradiance on Mars is about 590 W/m2 compared to about 1000 W/m2 at the Earth's surface; optimal conditions on the Martian equator can be compared to those on Devon Island in the Canadian Arctic in June.

Global dust storms are common throughout the year and can cover the entire planet for weeks, blocking sunlight from reaching the surface. This has been observed to cause temperature drops of 4 °C (7 °F) for several months after the storm. In contrast, the only comparable events on Earth are infrequent large volcanic eruptions such as Krakatoa which threw large amounts of ash into the atmosphere in 1883, causing a global temperature drop of around 1 °C (2 °F). Perhaps more importantly, these storms affect electricity production from solar panels for long periods, as well interfering with communications with Earth.

Mars has no rain and virtually no clouds, so although cold, it is permanently sunny (apart from during dust storms). This means solar panels can always operate at maximum efficiency on dust-free days. And Mars' orbit is more eccentric than Earth's, increasing temperature and solar constant variations over the course of the Martian year.

Soil
The Martian soil is toxic due to relatively high concentrations of chlorine and associated compounds which are hazardous to all known forms of life.

Survivability
Although there are some extremophile organisms that survive in hostile conditions on Earth, including simulations that approximate Mars, plants and animals generally cannot survive the ambient conditions present on the surface of Mars.