Mars is the fourth planet, counting from the Sun, and is the planet in our solar system that most closely resembles Earth.
Mars has a diameter of approximately 6800 km. Its orbit lies at a mean distance of 1.52 AU away from the Sun.
A day on Mars is called a sol. One sol lasts 24 hours and 39 minutes on average. There are 668.6 sols per sidereal Martian year, compared to Earth's 365.25 days.
Its axis is inclined by 25.2° which is similar to Earth's 23.5° inclination, thus causing comparable seasons. Recent studies suggest this inclination varied drastically throughout Mars' history, because Mars lacks the presence of a big natural satellite (like Earth's Moon). Template:MainArticle
Despite being much smaller than Earth, the fact that there are no oceans on Mars gives it an equal amount of dry surface, compared to Earth. However, recently water had been found on the surface of the planet, embedded in the soil. Template:MainArticle
The gravity on Mars is 3.71 m/s2, approximately one third (0.38) that on Earth. Very little is known with certainty about the effects of living in lower gravity.
The Martian atmosphere has a much lower mean surface pressure (6.36 mb) than that of Earth (1013 mb), varying from 4.0 mb to 8.7 mb, depending on season. It is composed mainly on Carbon Dioxide (95.3%), Nitrogen (2.7%), Argon (1.6%) and traces of other gases. This has several consequences such as requiring pressurized suits or vehicles for surface excursions and the construction of pressurized habitats. One of the goals of terraforming is to raise the atmospheric pressure in order to dispense with these requirements. Template:MainArticle
The average global temperature on Mars is approximately 218 K (-57° C, -70° F), with a minimum of 133 K (-140° C, -220° F) measured at the poles during winter and a maximum of 300 K (+27° C, +80° F) measured near the equator during summer. Temperatures at the Viking I landing site cycled daily between 186 K (-87° C, -125° F) and 241 K (-32° C, -25° F), while temperatures at the Viking II landing site nearer the pole cycled between 158 K (-115° C, -175° F) and 200 K (-73° C, -100° F) and stayed closer to the minimum during winter. For comparison, temperatures at the Amundsen-Scott South Pole Station, which is manned year round, vary between an average of 245 K (-27°C, -18° F) in the summer to 213 K (-60° C, −76° F) in winter, with a recorded minimum of 190 K (-83° C, −117° F) and a maximum of 260 K (-14°C, +7° F). Special measures are required to live in such low temperatures. Template:MainArticle
Unlike Earth, Mars has no strong global magnetic field, only weak local ones are present. That, combined with Mars' thin atmosphere means that much more high energy radiation reaches the surface of Mars, which can be dangerous to Terran biology, for example, it can raise the chance of cancer. Two types of radiation, in particular require defensive measures: solar energetic particle events (SEP) and galactic cosmic radiation (GCR). Template:MainArticle
Mars' surface presents some very spectacular features, like
- Valles Marineris: a huge system of canyons, 4000 km long and as much as 7 km deep;
- Olympus Mons: the largest mountain in the Solar System, 24 km high;
- Hellas Planitia: a huge impact crater in the southern hemisphere, 2000 km in diameter and 6 km deep;
- Tharsis: a bulge that is 4000 km across and 10 km high;
Exploration of Mars
The first probe to visit Mars was Mariner 4, taking closeup images of the surface at an altitude of 9.846 kilometers. In doing so, it revealed that there was no advanced civilization living there, an idea that gained popularity in the late 19th century.
The first landers were the Vikings in 1976. Those landers carried cameras that showed the first glimpses of frost during winter. They also carried life-science experiments with them, but the outcome of those were negative although the man that designed the experiment says that's debatable
The most successful mission to date is undoubtedly the twin Mars Exploration Rovers or MER Called Spirit and Opportunity. These rovers, sporting an array of sophisticated camera's and science-packages, were designed for a 90-ish Martian day mission, but are still going strong after 550 days. Template:MainArticle
Mars has two small moons:
There is currently a current of opinion believing to be appropiate to rename Mars' moons, because of the translations of their name, "Terror" and "Fear". (see also: Renaming of Mars' Moons) Template:MainArticle