Mars (planet)

Mars (planet)
Name	Mars
Caption	Mars in true color, taken by the Rosetta probe's OSIRIS instrument.
Adjectives	Martian
Discovery	Known to antiquity

Mars (planet). Mars is the fourth planet from the Sun and the second-smallest in the Solar System, often called the "Red Planet" due to the prevalence of iron oxide on its surface. It is a terrestrial planet with a thin atmosphere, featuring surface characteristics reminiscent of both the Moon's impact craters and Earth's valleys, deserts, and polar ice caps. The planet has been a prime target for space exploration due to its potential for past habitability and as a future destination for human exploration.

Physical characteristics

Mars has a mean radius of approximately 3,390 kilometers, roughly half that of Earth, resulting in a surface gravity about 38% of Earth's. Its internal structure is believed to consist of a dense core composed primarily of iron and sulfur, a silicate mantle, and a crust averaging about 50 kilometers thick. Unlike Earth, Mars lacks a global magnetic field, though residual magnetized crustal regions suggest it once possessed an active dynamo. The planet's distinctive red color is caused by fine iron-oxide dust, known as regolith, covering its surface. Key topographic features include the stark dichotomy between the heavily cratered southern highlands and the smoother northern lowlands, which may be the site of an ancient ocean.

Orbit and rotation

Mars orbits the Sun at an average distance of about 1.52 astronomical units, completing one revolution, or a Martian year, in approximately 687 Earth days. Its orbit is more eccentric than Earth's, leading to significant variations in solar insolation. The Martian day, called a sol, is only slightly longer than an Earth day at 24 hours, 39 minutes, and 35.244 seconds. The planet's axial tilt of about 25.2 degrees is similar to Earth's, giving rise to distinct seasons, though they are nearly twice as long due to the longer orbital period. These seasons are further complicated by the orbital eccentricity, making southern hemisphere seasons more extreme than those in the north.

Surface and geology

The Martian surface is a geological record of ancient volcanic, fluvial, and impact processes. It hosts the largest volcano in the Solar System, Olympus Mons, and a vast canyon system, Valles Marineris. Widespread features like outflow channels and valley networks provide strong evidence that liquid water once flowed across the surface. Significant mineralogical evidence, including hematite and phyllosilicates detected by orbiters like Mars Reconnaissance Orbiter, supports past aqueous activity. The current surface is dominated by basaltic rocks and vast dune fields, such as those within Proctor Crater. The polar regions are covered by permanent caps of water ice and CO₂ ice, which wax and wane with the seasons.

Atmosphere and climate

The Martian atmosphere is thin, with a surface pressure less than 1% of Earth's, and is composed primarily of carbon dioxide (95%), with minor amounts of nitrogen, argon, and trace oxygen and water vapor. This tenuous atmosphere is insufficient to retain significant heat, leading to large temperature swings from about 20 °C at the equator during day to below −100 °C at night. Despite its thinness, the atmosphere supports dynamic weather phenomena, including planet-encircling dust storms, local dust devils, and the formation of water ice clouds, often observed by the Mars Global Surveyor. The climate of Mars has likely undergone major shifts, with evidence suggesting it was once thicker and warmer, capable of sustaining liquid water.

Exploration

Mars has been extensively explored by robotic spacecraft since the first successful flyby by Mariner 4 in 1965. A series of successful missions, including the Viking program landers in the 1970s, the Mars Pathfinder rover, and more recently the Curiosity and Perseverance rovers, have transformed our understanding of the planet. Orbiters like Mars Odyssey, the Mars Express, and the MAVEN mission have mapped the surface, probed the subsurface for water, and studied atmospheric loss. The United Arab Emirates' Hope probe and China's Tianwen-1 mission mark the latest phase of international exploration, focusing on global weather and comprehensive orbital and surface study.

Habitability and future human missions

The search for evidence of past or present life on Mars is a central goal of exploration, with missions like Perseverance caching samples for potential return to Earth by a future NASA-ESA campaign. Regions like Jezero Crater and the Columbia Hills, investigated by the Spirit rover, are of high astrobiological interest due to their aqueous histories. Plans for future human mission to Mars are being developed by agencies including NASA and private entities like SpaceX, with concepts focusing on in-situ resource utilization, such as extracting water from the regolith. Long-term challenges for human habitation include radiation exposure, the toxic soil containing perchlorates, and the psychological effects of isolation during the long journey, which may be informed by experiences aboard the International Space Station.

Category:Mars (planet) Category:Terrestrial planets Category:Planets of the Solar System