Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, being larger than only Mercury. Mars is often referred to as the “Red Planet ”, which refers to the effect of the iron oxide prevalent on Mars’s surface, which gives it a reddish appearance distinctive among the objects visible to the naked eye.Its apparent magnitude reaches −2.94, which is surpassed only by Venus, the Moon and the Sun.

Some facts about Mars

Diameter-  6,780km

Orbital period-  1.88yrs

Length of a Day-   24hr, 37min

Axis tilt-  25 degrees

Distance from the Sun- 228 million kilometer ( 1.52AU )

Moons- Phobos and deimos

Special features

 Mars is a terrestrial planet with a thin atmosphere, with surface features reminiscent of the impact craters of the Moon and the valleys, deserts and polar ice caps of Earth. The days and seasons are comparable to those of Earth, because the rotational period as well as the tilt of the rotational axis relative to the ecliptic plane are similar. Mars is the site of Olympus Mons, the largest volcano and highest known mountain on any planet in the Solar System, and of Valles Marineris, one of the largest canyons in the Solar System. The smooth Borealis basin in the Northern Hemisphere covers 40% of the planet and may be a giant impact feature. Mars has two moons, Phobos and Deimos, which are small and irregularly shaped. 

Exploration

Mars has been explored by several uncrewed spacecraft. Mariner 4 was the first spacecraft to visit Mars; launched by NASA on 28 November 1964, it made its closest approach to the planet on 15 July 1965. The Soviet Mars 3 mission included a lander, which achieved a soft landing in December 1971; however, contact was lost seconds after touchdown. On 20 July 1976, Viking 1 performed the first successful landing on the Martian surface. On 4 July 1997, the Mars Pathfinder spacecraft landed on Mars and on 5 July released its rover, Sojourner, the first robotic rover to operate on Mars. The Mars Express orbiter, the first European Space Agency (ESA) spacecraft to visit Mars, arrived in orbit on 25 December 2003. In January 2004, NASA’s Mars Exploration Rovers, named Spirit and Opportunity, both landed on Mars. NASA landed its Curiosity rover on August 6, 2012, as a part of its Mars Science Laboratory (MSL) mission to investigate Martian climate and geology. On 24 September 2014, the Indian Space Research Organisation (ISRO) became the fourth space agency to visit Mars when its maiden interplanetary mission, the Mars Orbiter Mission spacecraft, arrived in orbit.  China National Space Administration (CNSA)’s Tianwen-1 spacecraft arrived in Martian orbit on 10 February 2021. NASA’s Perseverance rover and Ingenuity helicopter successfully landed on Mars on 18 February 2021. On 14 May 2021, CNSA’s Tianwen-1 lander and Zhurong rover successfully landed on Mars. The Zhurong rover was successfully deployed on 22 May 2021, which makes China the second country to successfully deploy a rover on Mars, after the United States. 

Phobos and Deimos

Phobos has a diameter of 22.2 km (13.8 mi) and a mass of 1.08×10¹⁶ kg, while Deimos measures 12.6 km (7.8 mi) across, with a mass of 2.0×10¹⁵ kg. Phobos orbits closer to Mars, with a semi-major axis of 9,377 km (5,827 mi) and an orbital period of 7.66 hours; the semi-major axis of Deimos’s orbit is 23,460 km (14,580 mi), with an orbital period of 30.35 hours.

Atmosphere

Mars lost its magnetosphere 4 billion years ago, possibly because of numerous asteroid strikes, so the solar wind interacts directly with the Martian ionosphere, lowering the atmospheric density by stripping away atoms from the outer layer. The atmosphere of Mars consists of about 96% carbon dioxide, 1.93% argon and 1.89% nitrogen along with traces of oxygen and water. The atmosphere is quite dusty, containing particulates about 1.5 µm in diameter which give the Martian sky a tawny color when seen from the surface. It may take on a pink hue due to iron oxide particles suspended in it.

Structure

Mars has a dense core at its center between 930 and 1,300 miles (1,500 to 2,100 kilometers) in radius. It’s made of iron, nickel, and sulfur. Surrounding the core is a rocky mantle between 770 and 1,170 miles (1,240 to 1,880 kilometers) thick, and above that, a crust made of iron, magnesium, aluminum, calcium, and potassium.

Mars – Wikipedia
In Depth | Mars – NASA Solar System Exploration