Mars

## Atmosphere

### **Composition**

* Carbon Dioxide (95%)
* Nitrogen (3%)
* Argon (1.6%)

## General Information

**Mars** is the fourth planet and the furthest terrestrial planet from the Sun. The reddish color of its surface is due to finely grained iron oxide dust in the soil. Mars's radius is second smallest among the planets in the Solar System at 3,389.5 km (2,106 mi). Mars has a thin atmosphere made primarily of carbon dioxide and two irregularly shaped moons: Phobos and Deimos.

Geologically, Mars is fairly active, with dust devils and marsquakes. The surface of Mars hosts the largest mountain and one of the largest canyons in the Solar System. Like the other planets in the Solar System, Mars was formed approximately 4.5 billion years ago. Mars is among the brightest objects in Earth's sky, and thus has been known from ancient times.

### Properties

Mars is approximately half the diameter of Earth, with a surface area only slightly less than the total area of Earth's dry land. The red-orange appearance of the Martian surface is caused by rust.

Mars is a terrestrial planet with a surface that consists of minerals containing silicon and oxygen, and metals.

Although Mars has no evidence of a magnetic field, observations show that parts of the planet's crust have been magnetized, suggesting that alternating polarity reversals of its dipole field have occurred in the past.

Streaks are common across Mars and new ones appear frequently on steep slopes of craters, troughs, and valleys. The streaks are dark at first and get lighter with age. The streaks can start in a tiny area, then spread out for hundreds of metres. They have been seen to follow the edges of boulders and other obstacles in their path. The commonly accepted theories include that they are dark underlying layers of soil revealed after avalanches of bright dust or dust devils. Several other explanations have been put forward, including those that involve water or even the growth of organisms.

Craters larger than roughly 50 kilometers are named for deceased scientists and writers and others.

Water as a liquid cannot exist on the surface of Mars due to low atmospheric pressure. The two polar ice caps appear to be made largely of water.

Landforms visible on Mars suggest that liquid water has existed on the planet's surface. Outflow channels cut across the surface in about 25 places.

Mars has two permanent polar ice caps.

The caps at both poles consist primarily of water ice. Frozen carbon dioxide accumulates as a comparatively thin layer about one metre thick on the north cap in the northern winter only, whereas the south cap has a permanent dry ice cover about eight metres thick. The southern polar cap has a diameter of 350 kilometres (220 mi) and a thickness of 3 kilometres (1.9 mi). The total volume of ice in the south polar cap plus the adjacent layered deposits has been estimated at 1.6 million cubic km.

The seasonal frosting of areas near the southern ice cap results in the formation of transparent one meter thick slabs of dry ice above the ground. This process is rapid, observed happening in the space of a few days, weeks or months.

Mars has two moons, Phobos and Deimos, which orbit close to the planet. The origin of both moons is unclear, although a popular theory states that they were asteroids captured into Martian orbit.

Both satellites were discovered in 1877 by Asaph Hall.

### Valles

**Valles** on Mars are similar to valleys on Earth.

The large canyon, Valles Marineris, has a length of 4,000 kilometers and a depth of up to. In 2012, it was proposed that Valles Marineris is not just a graben, but a plate boundary where 150 kilometers of transverse motion has occurred, making Mars a planet with possibly a two-tectonic plate arrangement.