Mars is the fourth planet from the Sun and is known as the "Red Planet" due to the iron(III) oxide on its surface. It's a terrestrial planet, the second smallest in the Solar System, with a diameter of 6,779 km. A Martian solar day is 24.6 hours, and a year is 1.88 Earth years. Mars is bright and easily viewed through telescopes due to its high-contrast albedo features. It has two small, irregularly shaped moons: Phobos and Deimos.
During observations in 1909 by Antoniadi with an 84-centimetre telescope, irregular patterns were observed on Mars, but no canali were seen.
In 1909, Campbell and V. M. Slipher repeated a study using better instruments, but had the same results.
It was not until the findings were confirmed by W. S. Adams in 1925 that the myth of the Earth-like habitability of Mars was finally broken.
In 1938, C.S. Lewis's novel "Out of the Silent Planet", depicting Mars, was published.
In 1948, Marvin the Martian, a comic figure of an intelligent Martian, appeared in Haredevil Hare as a character in the Looney Tunes animated cartoons of Warner Brothers.
NASA's Mariner 4 was launched on 28 November 1964, becoming the first spacecraft to visit Mars.
On 15 July 1965, Mariner 4 made its closest approach to Mars, detected a weak radiation belt, and captured the first images of another planet from deep space.
In 1965, the Mariner 4 probe performed the first flyby of Mars.
In 1971, the Mars 2 probe became the first spacecraft to orbit Mars.
In 1972, after Mariner 9 provided extensive imagery, Airy-0 crater was chosen to define 0.0° longitude.
In 1976, the Viking 1 probe achieved the first successful landing on Mars.
The Mars Global Surveyor mission launched in 1996, producing detailed maps of the Martian topography, magnetic field and surface minerals.
In 1999, a hypothesis suggested that alternating polarity reversals indicate plate tectonic activity on Mars four billion years ago.
As of 2023, 2001 Mars Odyssey is one of eight orbiters currently around Mars.
In 2004, the Opportunity rover detected the mineral jarosite, which forms in the presence of acidic water, indicating past water on Mars.
In October 2005, the hypothesis of plate tectonic activity on Mars was re-examined using data from the Mars Global Surveyor.
The Mars Global Surveyor mission, which launched in 1996, operated until late 2006, producing complete, extremely detailed maps.
In 2007, the Spirit rover found concentrated deposits of silica, further indicating wet conditions in Mars's past.
In December 2011, NASA's Mars rover Opportunity found the mineral gypsum, which forms in the presence of water, on the surface of Mars.
In 2012, it was proposed that Valles Marineris is a plate boundary with transverse motion, suggesting a two-tectonic plate arrangement on Mars.
On 18 March 2013, NASA reported evidence from the Curiosity rover of mineral hydration, likely hydrated calcium sulfate, in several rock samples.
In 2014, an analysis of the Martian meteorite EETA79001 revealed the presence of chlorate, perchlorate, and nitrate ions at concentrations suggesting their widespread presence on Mars. The analysis also indicated that UV and X-ray radiation would convert chlorate and perchlorate ions into highly reactive oxychlorines, meaning that organic molecules would have to be buried to survive.
In March 2015, scientists stated that an ocean on Mars might have been the size of Earth's Arctic Ocean, based on the ratio of protium to deuterium.
In September 2015, NASA announced they had found strong evidence of hydrated brine flows in recurring slope lineae.
In November 2016, NASA reported finding a large amount of underground ice in the Utopia Planitia region, estimated to be equivalent to the volume of water in Lake Superior.
In September 2017, NASA reported radiation levels on Mars doubled due to an aurora 25 times brighter than any observed earlier, caused by a solar storm.
In 2017, the NASA Authorization Act directed NASA to study the feasibility of a crewed Mars mission in the early 2030s, but the resulting report eventually concluded that this would be unfeasible.
During observations from 2018 through 2021, the ExoMars Trace Gas Orbiter spotted indications of water in the Valles Marineris canyon system.
In 2019, it was reported that InSight had detected and recorded over 450 marsquakes and related events, confirming Mars is seismically active.
The planets came into opposition near Mars's perihelion in 2020.
During observations from 2018 through 2021, the ExoMars Trace Gas Orbiter spotted indications of water in the Valles Marineris canyon system.
In 2021, China was planning to send a crewed Mars mission in 2033.
In April 2023, The New York Times reported an updated global map of Mars based on images from the Hope spacecraft and NASA released a more detailed map.
A 2023 study based on the orbital inclination of Deimos, suggests Mars may have had a ring system 3.5 to 4 billion years ago.
As of 2023, Mars hosts ten functioning spacecraft, including eight orbiters and two rovers on the surface.
As of 2023, there are at least 11 active probes orbiting Mars or on the Martian surface.
As of February 2024, debris from Mars missions has reached over seven tons, consisting of crashed spacecraft, inactive components and discarded parts.
In April 2024, NASA selected several companies to begin studies on providing commercial services to further enable robotic science on Mars, including telecommunications and surface imaging.
In June 2024, NASA designated the Cheyava Falls rock on Mars as a "potential biosignature." The Perseverance rover took a core sample for possible return to Earth and further examination, but no definitive determination on a biological or abiotic origin of this rock can be made with current data.
In 2033, China was planning to send a crewed Mars mission, as of their plans in 2021.
The planets will come into opposition near Mars's perihelion in 2033.
Mars is expected to come into opposition from Earth near its perihelion in 2035.