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Mars is the fourth planet from the Sun.

Mars is a desert-like rocky planet with a tenuous atmosphere that is primarily carbon dioxide (CO2). Mars retains some water, in the ground as well as thinly in the atmosphere, forming cirrus clouds, fog, frost, larger polar regions of permafrost and ice caps (with seasonal CO2 snow), but no bodies of liquid surface water. Its mean diameter, 6,779 km (4,212 mi), is about half the Earth's, or twice the Moon's, and its surface area is the size of all the dry land of Earth. The terrain of Mars roughly follows a north–south divide, the Martian dichotomy, with the northern hemisphere mainly consisting of relatively flat, low lying plains, and the southern hemisphere of cratered highlands. Mars has two natural satellites that are small and irregular in shape: Phobos and Deimos. With a significant axial tilt of 25 degrees, Mars experiences seasons, like Earth (which has an axial tilt of 23.5 degrees). A Martian solar year is equal to 1.88 Earth years (687 Earth days), a Martian solar day (sol) is equal to 24.6 hours. Mars formed along with the other planets approximately 4.5 billion years ago. During the martian Noachian period (4.5 to 3.5 billion years ago), its surface was marked by meteor impacts, valley formation, erosion, the possible presence of water oceans and the loss of its magnetosphere. Because of Mars's geological history, the possibility of past or present life on Mars remains an area of active scientific investigation, with some possible traces needing further examination. Being visible with the naked eye in Earth's sky as a red wandering star, Mars has been observed throughout history, acquiring diverse associations in different cultures. In 1963 the first flight to Mars took place with Mars 1, but communication was lost en route. In 1971 Mariner 9 entered orbit around Mars, being the first spacecraft to orbit any body other than the Moon, Sun or Earth; following in the same year were the first uncontrolled impact (Mars 2) and first successful landing (Mars 3) on Mars. At times, more than ten probes have simultaneously operated in orbit or on the surface, more than at any other planet beyond Earth. Mars is an often proposed target for future crewed exploration missions, though no such mission is currently planned.

A 2023 study shows evidence, based on the orbital inclination of Deimos (a small moon of Mars), that Mars may once have had a ring system 3.5 billion years to 4 billion years ago.

Both Mars Global Surveyor and Mars Express have detected ionized atmospheric particles trailing off into space behind Mars, and this atmospheric loss is being studied by the MAVEN orbiter.

The amount of Martian deuterium (D/H = 9.3 ± 1.7 10−4) is five to seven times the amount on Earth (D/H = 1.56 10−4), suggesting that ancient Mars had significantly higher levels of water.

The history of observations of Mars is marked by oppositions of Mars when the planet is closest to Earth and hence is most easily visible, which occur every couple of years.

In 1997 Mars Pathfinder became the first successful rover mission beyond the Moon and started together with Mars Global Surveyor (operated until late 2006) an uninterrupted active robotic presence at Mars that has lasted until today.

Eight are in orbit: 2001 Mars Odyssey, Mars Express, Mars Reconnaissance Orbiter, MAVEN, ExoMars Trace Gas Orbiter, the Hope orbiter, and the Tianwen-1 orbiter.

After the Mariner and Viking spacecraft had returned pictures of Mars as a lifeless and canal-less world, these ideas about Mars were abandoned; for many science-fiction authors, the new discoveries initially seemed like a constraint, but eventually the post-Viking knowledge of Mars became itself a source of inspiration for works like Kim Stanley Robinson's Mars trilogy.

Magnetic field of Mars – Past magnetic field of the planet Mars

Quick Facts

• Mars formed along with the other planets approximately 4.5 billion years ago.
• In 1963 the first flight to Mars took place with Mars 1, but communication was lost en route.
• A Martian solar year is equal to 1.88 Earth years (687 Earth days), a Martian solar day (sol) is equal to 24.6 hours.
• Because of Mars's geological history, the possibility of past or present life on Mars remains an area of active scientific investigation, with some possible traces needing further examination.
• Magnetic field of Mars – Past magnetic field of the planet Mars

Source material: Wikipedia - "Mars". Adapted and summarized for DiscoverScroll. Original contributors are credited through the linked Wikipedia article. Read original on Wikipedia. CC BY-SA 4.0. Changes were made from the original.