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2006-04-08T14:06:28Z

‎Natural satellites

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[[Image:Marsglobe1.jpg|thumb|200px|right|Mars, population 0]]
[[Image:Mars_topographic.jpg|thumb|200px|right|Topographical map of Mars - Stake your claim]]

Mars is the fourth planet, counting from the Sun, and is the planet in our solar system that most closely resembles Earth.

== General information ==
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).
{{MainArticle|[[Orbit of Mars]]}}

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.
{{MainArticle|[[Water on Mars]]}}

The gravity on Mars is 3.71 m/s<sup>2</sup>, 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 [[Requirements for living in low pressure|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.
{{MainArticle|[[Martian atmosphere]]}}

Mars has a significantly elliptical orbit, which influences a lot [[Climate of Mars|the Marsian climate]]. Thus, the temperature difference between aphelion and perihelion is as much as 30 K at the same [[subsolar point]].

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 [[Requirements for living in low temperature|required to live in such low temperatures]].
{{MainArticle|[[Climate of Mars]]}}

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 [[Radiation hazard mitigation|defensive measures]]: [[solar energetic particle events]] (SEP) and [[galactic cosmic radiation]] (GCR).
{{MainArticle|[[Magnetic fields of Mars]]}}

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;
{{MainArticle|[[Topography of Mars]]}}

== 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 [[Viking]]s 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.
{{MainArticle|[[Exploration of Mars]]}}

== Natural satellites ==

Mars has two small moons:
* [[Phobos]] with an orbit of 7 h 39 m 26.6s; and
* [[Deimos]] with an orbit of 30 h 18 m.
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]])
{{MainArticle|[[Mars' natural satellites]]}}

== External links ==

* [http://www-mars.lmd.jussieu.fr/ Mars Climate Database]
* Mars from [http://www.nineplanets.org/mars.html The Nine Planets]
* Mars from [http://marsprogram.jpl.nasa.gov/ JPL]
* NASA fact sheet on [http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html Mars]
*[http://pds.jpl.nasa.gov/ NASA Planetary Data System Database]
*[http://www.astronautix.com Encyclopedia Astronautica]
*[http://www.astronautix.com/craftfam/martions.htm Proposed Expeditions to Mars]

[[Category:Planets]]

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