MARS

       Mars is the fourth planet from the Sun and the second smallest planet in the Solar System, after Mercury. It is often described as the "Red Planet" because the iron oxide prevalent on its surface gives it a reddish appearance. Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the volcanoes, valleys, deserts, and polar ice caps of Earth. The rotational period and seasonal cycles of Mars are likewise similar to those of Earth, as is the tilt that produces the seasons. Mars is the site of Olympus Mons, the second highest known mountain within the Solar System (the tallest on a planet), and of Valles Marineris, one of the largest canyons.  Mars has two moons, Phobos and Deimos, which are small and irregularly shaped. These may be captured asteroids. Its equatorial radius is equivalent to 0.533 Earths.

       Mars can easily be seen from Earth with the naked eye, as can its reddish coloring. Its apparent magnitude is only surpassed only by Jupiter, Venus, the Moon, and the Sun.

       Mars has approximately half the diameter of Earth. It is less dense than Earth, having about 15% of Earth's volume and 11% of the mass. Its surface area is only slightly less than the total area of Earth’s dry land. While Mars is larger and more massive than Mercury, Mercury has a higher density. This results in the two planets having a nearly identical gravitational pull at the surface – that of Mars is stronger by less than 1%. The red-orange appearance of the Martian surface is caused by iron oxide, more commonly known as hematite, or rust. It can also look butterscotch, and other common surface colors include golden, brown, tan, and greenish, depending on minerals.

       Like Earth, this planet has undergone differentiation, resulting in a dense, metallic core region overlaid by less dense materials. the planet's interior imply a core region consisting primarily of iron and nickel with about 16–17% sulfur. This iron sulfide core is partially fluid, and it has twice the concentration of the lighter elements that exist at Earth's core. The core is surrounded by a silicate mantle that formed many of the tectonic and volcanic features on the planet, but it now appears to be dormant. Besides silicon and oxygen, the most abundant elements in the Martian crust are iron, magnesium, aluminum, calcium, and potassium. The average thickness of the planet's crust is about 50 km (31 mi), with a maximum thickness of 125 km (78 mi). Earth's crust, averaging 40 km (25 mi), is only one third as thick as Mars's crust, relative to the sizes of the two planets.

      Liquid water cannot exist on the surface of Mars due to low atmospheric pressure, except at the lowest elevations for short periods. The two polar ice caps appear to be made largely of water. The volume of water ice in the south polar ice cap, if melted, would be sufficient to cover the entire planetary surface to a depth of 11 meters.