Mars, the fourth planet from the Sun, is colloquially referred to as the "Red Planet" due to its distinctive orange-red coloration. This terrestrial body features a desert-like, rocky terrain and possesses a thin atmosphere composed predominantly of carbon dioxide (CO2). Its average surface atmospheric pressure is merely a few thousandths of Earth's, with temperatures fluctuating between −153 and 20 °C (−243 and 68 °F), and it is characterized by elevated levels of cosmic radiation. While Mars retains water in its subsurface and as a sparse atmospheric component, manifesting as cirrus clouds, fog, frost, and extensive polar permafrost and ice caps (which include seasonal CO2 snow), no persistent bodies of liquid surface water exist. The planet's surface gravity is approximately one-third that of Earth, or twice that of the Moon. With a diameter of 6,779 km (4,212 mi), Mars is roughly half the size of Earth and twice the size of the Moon, possessing a surface area equivalent to Earth's total landmass.
Mars is the fourth planet from the Sun. It is also known as the "Red Planet", for its orange-red appearance. Mars is a desert-like rocky planet with a tenuous atmosphere that is primarily carbon dioxide (CO§56§). At the average surface level the atmospheric pressure is a few thousandths of Earth's, atmospheric temperature ranges from −153 to 20 °C (−243 to 68 °F), and cosmic radiation is high. 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 CO§910§ snow), but no bodies of liquid surface water. Its surface gravity is roughly a third of Earth's or double that of the Moon. Its 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.
Fine dust particles are ubiquitous across both the Martian surface and atmosphere, readily mobilized and dispersed by the planet's weak winds, despite its low gravitational pull. The Martian terrain exhibits a distinct north–south division, known as the Martian dichotomy, characterized by relatively flat, low-lying plains in the northern hemisphere and heavily cratered highlands in the southern hemisphere. Geologically, Mars demonstrates moderate activity, evidenced by subsurface marsquakes, and features numerous colossal extinct volcanoes, including Olympus Mons (standing 21.9 km or 13.6 mi tall), alongside one of the Solar System's most extensive canyons, Valles Marineris (stretching 4,000 km or 2,500 mi). The planet is orbited by two small, irregularly shaped natural satellites: Phobos and Deimos. Possessing a substantial axial tilt of 25 degrees, Mars undergoes seasonal variations analogous to those on Earth (which has an axial tilt of 23.5 degrees). A Martian solar year spans 1.88 Earth years (equivalent to 687 Earth days), while a Martian solar day, or sol, lasts 24.6 hours.
Mars originated approximately 4.5 billion years ago, concurrently with the formation of other planets in the Solar System. The Martian Noachian period, spanning from 4.5 to 3.5 billion years ago, was characterized by extensive meteor impacts, the development of valleys, significant erosion, the potential existence of water oceans, and the eventual loss of its magnetosphere. Subsequently, the Hesperian period, commencing 3.5 billion years ago and concluding between 3.3 and 2.9 billion years ago, witnessed pervasive volcanic activity and catastrophic flooding events that sculpted vast outflow channels. The Amazonian period, which persists to the present day, represents the prevailing influence on the planet's geological processes. Given Mars's complex geological history, the prospect of past or extant life on the planet continues to be a subject of rigorous scientific inquiry, with certain potential indicators requiring additional scrutiny.
Historically, Mars has been observed from Earth as a conspicuous red "wandering star," leading to varied cultural interpretations and associations across civilizations. The inaugural mission to Mars, Mars 1, launched in 1963, but communication with the spacecraft was lost during its transit. A successful flyby exploration of Mars was first achieved in 1965 by Mariner 4. Mariner 9 became the first spacecraft to orbit a celestial body other than the Moon, Sun, or Earth when it entered Martian orbit in 1971; that same year also saw the first uncontrolled impact (Mars 2) and the first successful landing (Mars 3) on the planet. Robotic probes have maintained continuous operations on Mars since 1997. Periodically, over ten probes have simultaneously functioned in orbit or on the Martian surface, surpassing the number of active missions at any other planet beyond Earth. Mars is frequently identified as a prospective destination for future crewed exploration missions, although no such endeavors are presently scheduled.
Natural History
Formation
Scientific theories propose that Mars originated during the Solar System's formation through a stochastic process of runaway accretion, involving material from the protoplanetary disk orbiting the Sun. The planet exhibits several unique chemical characteristics attributable to its specific location within the Solar System. Elements possessing relatively low boiling points, including chlorine, phosphorus, and sulfur, are considerably more abundant on Mars than on Earth; it is hypothesized that the energetic solar wind from the nascent Sun propelled these elements outwards.
Late Heavy Bombardment
Following planetary formation, the inner Solar System may have undergone a period known as the Late Heavy Bombardment. Approximately 60% of the Martian surface preserves evidence of impacts from this era, with vast underlying impact basins likely characterizing much of the remaining terrain. Nevertheless, recent modeling has contested the existence of the Late Heavy Bombardment. Significant evidence points to an immense impact basin in Mars's Northern Hemisphere, measuring 10,600 by 8,500 kilometers (6,600 by 5,300 mi). This feature, roughly four times the size of the Moon's South Pole–Aitken basin, would be the largest impact basin yet discovered if its existence is confirmed. It is hypothesized that this basin formed approximately four billion years ago when Mars was struck by a Pluto-sized celestial body. This catastrophic event is thought to have caused the Martian hemispheric dichotomy and created the smooth Borealis basin, which covers 40% of the planet's surface.
A 2023 study, based on the orbital inclination of Deimos, a small Martian moon, provides evidence suggesting that Mars may have possessed a ring system between 3.5 and 4 billion years ago. This hypothetical ring system is proposed to have formed from a moon, twenty times more massive than Phobos, that orbited Mars billions of years ago, with Phobos itself potentially representing a remnant of this ancient ring.
Geological Periods
Epochs:
The geological history of Mars is conventionally divided into several periods, with the following three identified as primary:
- Noachian Period: This period, dating from 4.5 to 3.5 billion years ago, marks the formation of Mars's oldest extant surfaces. Noachian-age terrains are extensively scarred by large impact craters. The Tharsis bulge, a significant volcanic upland, is hypothesized to have formed during this epoch, which also featured widespread flooding by liquid water in its later stages. The period derives its name from Noachis Terra.
- Hesperian Period: Extending from 3.5 billion years ago to between 3.3 and 2.9 billion years ago, the Hesperian period is characterized by the formation of extensive lava plains. It is named after Hesperia Planum.
- Amazonian Period: This period spans from between 3.3 and 2.9 billion years ago to the present. Amazonian regions are characterized by a low density of meteorite impact craters but exhibit significant geological variation. Olympus Mons formed during this epoch, accompanied by other lava flows across Mars. The period is named after Amazonis Planitia.
Recent Geological Activity
Geological activity persists on Mars. The Athabasca Valles features sheet-like lava flows dating back approximately 200 million years. Furthermore, water flows within the Cerberus Fossae grabens occurred less than 20 million years ago, indicating recent volcanic intrusions. The Mars Reconnaissance Orbiter has also captured images of avalanches.
Physical Characteristics
Mars has approximately half the diameter of Earth, or twice that of the Moon, and its surface area is only slightly less than Earth's total dry landmass. Mars is less dense than Earth, possessing about 15% of Earth's volume and 11% of its mass, which results in approximately 38% of Earth's surface gravity. It is currently the only known example of a desert planet, a rocky body with a surface analogous to Earth's deserts. The characteristic red-orange appearance of the Martian surface is caused by iron(III) oxide (nanophase Fe2O3) and the iron(III) oxide-hydroxide mineral goethite. While often resembling butterscotch, other common surface colors include golden, brown, tan, and greenish, depending on the specific minerals present.
Internal Structure
Similar to Earth, Mars is differentiated into a dense metallic core overlain by less dense rocky layers. The outermost layer, the crust, averages 42–56 kilometers (26–35 mi) in thickness, with a minimum of 6 kilometers (3.7 mi) in Isidis Planitia and a maximum of 117 kilometers (73 mi) in the southern Tharsis plateau. For comparative purposes, Earth's crust averages 27.3 ± 4.8 km in thickness. The most abundant elements within the Martian crust are silicon, oxygen, iron, magnesium, aluminum, calcium, and potassium. Mars is confirmed to be seismically active; in 2019, it was reported that the InSight mission had detected and recorded over 450 marsquakes and related seismic events.
The Martian crust is underlain by a silicate mantle, which significantly contributes to the planet's tectonic and volcanic surface characteristics. Within the upper Martian mantle, a low-velocity zone exists, characterized by seismic wave velocities that are reduced compared to adjacent depth ranges. This mantle exhibits rigidity to a depth of approximately 250 km, resulting in a lithosphere considerably thicker than Earth's. Beneath this rigid layer, the mantle progressively increases in ductility, and seismic wave velocities subsequently rise. Unlike Earth's lower mantle, the Martian mantle lacks a thermally insulating layer; instead, at depths exceeding 1050 km, its mineralogical composition resembles Earth's transition zone. A basal liquid silicate layer, estimated to be 150–180 km thick, is situated at the base of the mantle. The Martian mantle exhibits significant heterogeneity, containing dense fragments up to 4 km in diameter. These fragments are thought to have been introduced deep into the planet by immense impacts approximately 4.5 billion years ago. Observations from eight marsquakes revealed that high-frequency waves decelerated upon traversing these localized regions. Modeling suggests these heterogeneities represent compositionally distinct debris, preserved due to Mars's absence of plate tectonics and its sluggishly convecting interior, which impedes complete homogenization.
Mars possesses an iron and nickel core that is at least partially molten, with the potential presence of a solid inner core. This core constitutes approximately half of Mars's radius, measuring between 1650 and 1675 km, and is characterized by an enrichment in light elements including sulfur, oxygen, carbon, and hydrogen. Core temperatures are estimated to range from 2000–2400 K, significantly lower than the 5400–6230 K recorded for Earth's solid inner core. The existence of a solid inner core within Mars remains an active area of scientific inquiry. A 2023 investigation utilizing data from the InSight lander indicated the absence of such a core. However, a subsequent 2025 study, re-analyzing the same data, reported the detection of a solid inner core with a radius of 613 kilometres (381 mi) ± 67 kilometres (42 mi).
Surface Geology
As a terrestrial planet, Mars possesses a surface composed of minerals containing silicon, oxygen, metals, and other common rock-forming elements. The Martian surface predominantly consists of tholeiitic basalt; however, certain areas exhibit higher silica content than typical basalt, potentially resembling terrestrial andesitic rocks or silica glass. Low albedo regions indicate concentrations of plagioclase feldspar, with northern low albedo areas specifically showing elevated levels of sheet silicates and high-silicon glass. Detectable quantities of high-calcium pyroxenes are present in portions of the southern highlands. Furthermore, localized concentrations of hematite and olivine have been identified. A significant portion of the surface is extensively covered by fine-grained iron(III) oxide dust.
Data acquired by the Phoenix lander revealed that Martian soil is slightly alkaline and contains elements such as magnesium, sodium, potassium, and chlorine. These elements, which are essential for plant growth, are also present in terrestrial soils. Lander experiments further demonstrated that Martian soil exhibits a basic pH of 7.7 and contains 0.6% perchlorate by weight, concentrations considered toxic to humans.
Linear streaks are prevalent across the Martian surface, with new formations frequently observed on the steep slopes of craters, troughs, and valleys. Initially dark, these streaks progressively lighten over time. Originating from small points, these features can extend for hundreds of meters. Observations indicate that they often conform to the contours of boulders and other obstructions. Prevailing hypotheses suggest these streaks represent darker subsurface material exposed by avalanches of bright dust or by dust devils. Alternative explanations have also been proposed, encompassing mechanisms involving water or even the proliferation of organisms.
The average environmental radiation levels on the Martian surface are approximately 0.64 millisieverts per day, which is considerably lower than the 1.84 millisieverts per day (or 22 millirads per day) experienced during transit to and from Mars. In contrast, radiation levels in low Earth orbit, where space stations are situated, average around 0.5 millisieverts per day. Hellas Planitia records the lowest surface radiation, approximately 0.342 millisieverts per day. Within this region, lava tubes southwest of Hadriacus Mons could potentially exhibit levels as low as 0.064 millisieverts per day, a value comparable to radiation exposure during terrestrial flights.
Magnetic Characteristics
Despite the absence of a structured global magnetic field on Mars, observational data indicate localized magnetization within the planet's crust, implying a history of alternating polarity reversals in its ancient dipole field. This paleomagnetic signature, present in magnetically susceptible minerals, bears resemblance to the alternating bands observed on Earth's oceanic crust. A hypothesis, initially proposed in 1999 and subsequently re-evaluated in October 2005 with data from the Mars Global Surveyor, posits that these magnetic bands signify plate tectonic activity on Mars approximately four billion years ago, preceding the cessation of the planetary dynamo and the subsequent dissipation of the planet's magnetic field.
Martian Geography and Surface Features
While primarily recognized for their lunar cartography, Johann Heinrich von Mädler and Wilhelm Beer are credited as the pioneering areographers. Their initial contributions involved confirming the permanence of most Martian surface features and accurately calculating the planet's rotational period. By 1840, Mädler synthesized a decade of observations to produce the inaugural map of Mars.
Martian surface features derive their nomenclature from diverse origins. Albedo features are typically designated with names from classical mythology. Craters exceeding approximately 50 kilometers in diameter are named in honor of deceased scientists, writers, and other individuals who have significantly advanced Martian studies. Conversely, smaller craters are assigned names of towns and villages globally with populations under 100,000. Extensive valleys bear names derived from the terms 'Mars' or 'star' in different languages, while smaller valleys are named after terrestrial rivers.
Many extensive albedo features retain their historical designations, though these are frequently revised to incorporate contemporary understanding of their characteristics. For instance, Nix Olympica (meaning 'the snows of Olympus') was reclassified as Olympus Mons ('Mount Olympus'). From Earth, the Martian surface appears bifurcated into two distinct regions characterized by varying albedo. The lighter plains, composed of dust and sand rich in reddish iron oxides, were historically perceived as Martian 'continents' and consequently named, for example, Arabia Terra (land of Arabia) or Amazonis Planitia (Amazonian plain). Conversely, the darker features were initially interpreted as seas, leading to designations such as Mare Erythraeum, Mare Sirenum, and Aurorae Sinus. Syrtis Major Planum represents the most prominent dark feature observable from Earth. The permanent northern polar ice cap is designated Planum Boreum, while its southern counterpart is known as Planum Australe.
While Mars's equator is rotationally defined, its Prime Meridian, analogous to Earth's Greenwich Meridian, was established through the selection of an arbitrary reference point. Mädler and Beer initially designated a specific line for this purpose in their 1830 Martian maps. Following the comprehensive imagery provided by the Mariner 9 spacecraft in 1972, Merton E. Davies, Harold Masursky, and Gérard de Vaucouleurs selected a small crater, subsequently named Airy-0 and situated within the Sinus Meridiani ('Middle Bay' or 'Meridian Bay'), to define 0.0° longitude, aligning with the earlier chosen reference.
Given the absence of oceans and, consequently, a 'sea level' on Mars, a zero-elevation surface required designation as a reference datum. This reference is termed the areoid of Mars, drawing an analogy to Earth's geoid. Zero altitude is specifically defined as the elevation where the atmospheric pressure measures 610.5 Pascals (6.105 millibars). This pressure value corresponds to the triple point of water and constitutes approximately 0.6% of Earth's sea-level surface pressure (0.006 atmospheres).
For cartographic purposes, the United States Geological Survey partitions the Martian surface into thirty quadrangles, each named after a prominent classical albedo feature within its boundaries. In April 2023, The New York Times documented the release of an updated global map of Mars, compiled from imagery acquired by the Hope spacecraft. Concurrently, NASA published a significantly more detailed global Martian map on April 16, 2023.
Martian Volcanism
The extensive Tharsis upland region hosts several colossal volcanoes, notably the shield volcano Olympus Mons. This volcanic edifice spans more than 600 km (370 mi) in width. Due to its immense size and intricate marginal structures, precisely determining its height presents a challenge. Its local relief, measured from the base of the cliffs along its northwestern flank to its summit, exceeds 21 km (13 mi), which is more than double the height of Mauna Kea when measured from its oceanic base. The total elevation differential from the Amazonis Planitia plains, situated over 1,000 km (620 mi) to the northwest, to the peak approaches 26 km (16 mi), approximately three times the height of Mount Everest, which measures just over 8.8 kilometers (5.5 mi). Consequently, Olympus Mons ranks as either the tallest or second-tallest mountain within the Solar System; the sole known contender for greater height is the Rheasilvia peak on the asteroid Vesta, estimated at 20–25 km (12–16 mi).
Impact Topography
Martian topography exhibits a striking dichotomy: the northern plains, smoothed by lava flows, sharply contrast with the southern highlands, which are extensively pitted and cratered by ancient impacts. Hypothetically, approximately four billion years ago, Mars's Northern Hemisphere may have been impacted by an object ranging from one-tenth to two-thirds the size of Earth's Moon. Should this hypothesis prove accurate, the Martian Northern Hemisphere would host an impact crater measuring 10,600 by 8,500 kilometers (6,600 by 5,300 mi), an area roughly equivalent to Europe, Asia, and Australia combined, thereby exceeding Utopia Planitia and the Moon's South Pole–Aitken basin as the largest known impact crater in the Solar System.
Mars bears the scars of 43,000 impact craters, each with a diameter of 5 kilometers (3.1 mi) or more. The most prominent exposed crater is Hellas, spanning 2,300 kilometers (1,400 mi) in width and reaching 7,000 meters (23,000 ft) in depth, presenting a high-albedo feature distinctly observable from Earth. Additional significant impact features include Argyre, approximately 1,800 kilometers (1,100 mi) in diameter, and Isidis, measuring around 1,500 kilometers (930 mi) in diameter. Owing to its comparatively smaller mass and size, Mars experiences approximately half the probability of impact events compared to Earth. Its proximity to the asteroid belt, however, increases its susceptibility to impacts from materials originating there. Furthermore, Mars is more frequently impacted by short-period comets, i.e., those whose orbits are confined within Jupiter's.
The morphology of some Martian craters suggests that the subsurface material became saturated with water following the meteoritic impact.
Tectonic Features
Valles Marineris, an immense canyon system (Latin for 'Mariner Valleys,' also historically referred to as Agathodaemon on older canal maps), extends for 4,000 kilometers (2,500 mi) and reaches depths of up to 7 kilometers (4.3 mi). Its length is comparable to the entire continent of Europe, spanning approximately one-fifth of Mars's circumference. In contrast, Earth's Grand Canyon measures only 446 kilometers (277 mi) in length and nearly 2 kilometers (1.2 mi) in depth. The formation of Valles Marineris is attributed to the uplift of the Tharsis region, which subsequently led to the collapse of the crust within the canyon's vicinity. A 2012 proposal suggested that Valles Marineris functions not merely as a graben, but as a plate boundary exhibiting 150 kilometers (93 mi) of transverse motion, implying the potential existence of a two-plate tectonic system on Mars.
Subsurface Features and Caves
Data acquired by the Thermal Emission Imaging System (THEMIS) on NASA's Mars Odyssey orbiter has identified seven potential cave entrances situated on the flanks of the Arsia Mons volcano. These caves, informally designated the "seven sisters" and named after the discoverers' loved ones, represent significant subsurface openings. The entrances to these caverns range from 100 to 252 meters (328 to 827 ft) in width, with estimated minimum depths of 73 to 96 meters (240 to 315 ft). Given that sunlight does not penetrate to the floors of most of these caves, their actual depths may significantly exceed these initial estimates, potentially expanding considerably beneath the surface. The sole exception is "Dena," whose floor is visible and was measured at a depth of 130 meters (430 ft). The interiors of these subterranean formations could offer protection from micrometeoroids, ultraviolet radiation, solar flares, and high-energy particles that incessantly impact the Martian surface.
Other Geological Features
Atmosphere
Mars experienced the loss of its magnetosphere approximately 4 billion years ago, potentially as a consequence of numerous asteroid impacts. This absence allows the solar wind to interact directly with the Martian ionosphere, thereby reducing atmospheric density by stripping atoms from the outer layer. Both the Mars Global Surveyor and Mars Express missions have detected ionized atmospheric particles dissipating into space behind Mars, a phenomenon currently under investigation by the MAVEN orbiter. Compared to Earth, the Martian atmosphere is considerably rarefied. Surface atmospheric pressure presently ranges from a minimum of 30 Pa (0.0044 psi) on Olympus Mons to over 1,155 Pa (0.1675 psi) in Hellas Planitia, with a mean surface pressure of 600 Pa (0.087 psi). The peak atmospheric density on Mars is equivalent to that found at an altitude of 35 kilometers (22 mi) above Earth's surface. Consequently, the mean surface pressure constitutes only 0.6% of Earth's 101.3 kPa (14.69 psi). The atmospheric scale height is approximately 10.8 kilometers (6.7 mi), which exceeds Earth's 6 kilometers (3.7 mi) due to Mars's surface gravity being only about 38% of Earth's.
The Martian atmosphere is composed of approximately 96% carbon dioxide, 1.93% argon, and 1.89% nitrogen, alongside trace amounts of oxygen and water. This atmosphere is notably dusty, containing particulates with an approximate diameter of 1.5 μm, which impart a tawny coloration to the Martian sky when viewed from the surface. The presence of suspended iron oxide particles can also contribute to a pink hue.
Despite recurrent detections of methane on Mars, a definitive scientific consensus regarding its origin remains elusive. One hypothesis suggests that methane is present on Mars and exhibits seasonal fluctuations in concentration. The existence of methane could result from non-biological processes, such as serpentinization involving water, carbon dioxide, and the mineral olivine—which is known to be prevalent on Mars—or alternatively, from extant Martian life.
Relative to Earth, the higher concentration of atmospheric CO2 and lower surface pressure on Mars likely contribute to increased sound attenuation, where natural acoustic sources are scarce apart from wind. Analysis of acoustic recordings gathered by the Perseverance rover indicates that the speed of sound on Mars is approximately 240 m/s for frequencies below 240 Hz and 250 m/s for higher frequencies.
Auroras have been observed on Mars. Given Mars's lack of a global magnetic field, the characteristics and spatial distribution of its auroras differ from those on Earth; rather than being predominantly confined to polar regions, a Martian aurora can encompass the entire planet. In September 2017, NASA reported a temporary doubling of radiation levels on the Martian surface, which correlated with an aurora 25 times brighter than any previously recorded, attributed to an intense and unanticipated solar storm that occurred mid-month.
Climate
Mars experiences seasons that alternate between its northern and southern hemispheres, analogous to Earth. Furthermore, Mars's orbit possesses a greater eccentricity compared to Earth's, leading to perihelion occurring during the southern hemisphere's summer and northern hemisphere's winter, and aphelion coinciding with the southern hemisphere's winter and northern hemisphere's summer. Consequently, the southern hemisphere's seasons are more extreme, while the northern hemisphere's seasons are milder than they would otherwise be. Summer temperatures in the south can exceed equivalent northern summer temperatures by up to 30 °C (54 °F).
Martian surface temperatures fluctuate significantly, ranging from lows of approximately −110 °C (−166 °F) to highs of up to 35 °C (95 °F) during equatorial summer. This substantial temperature range is attributable to the thin atmosphere's limited capacity to retain solar heat, the low atmospheric pressure (approximately 1% of Earth's atmosphere), and the low thermal inertia of Martian soil. The planet is situated 1.52 times farther from the Sun than Earth, resulting in only 43% of the solar insolation received by Earth.
Mars is home to the largest dust storms in the Solar System, with wind speeds exceeding 160 km/h (100 mph). These storms can range in scale from localized events to colossal systems that envelop the entire planet. They typically manifest when Mars is closest to the Sun and have been demonstrated to elevate global temperatures. Additionally, seasonal processes lead to the formation of dry ice coverings on the polar ice caps.
Hydrology
Although Mars possesses substantial quantities of water, the majority exists as dust-covered water ice within its polar ice caps. Should the water ice in the southern polar cap melt, it would yield sufficient volume to inundate most of the planetary surface to a depth of 11 meters (36 ft).
Liquid water is unable to persist on the Martian surface because of the planet's extremely low atmospheric pressure, which constitutes less than 1% of Earth's. Only in the lowest topographical regions do pressure and temperature conditions become adequate for the transient existence of liquid water.
Despite the minimal presence of water in the atmosphere, it is sufficient to generate water ice clouds, various forms of snow, and frost, frequently intermingled with carbon dioxide dry ice snow.
Ancient Hydrosphere
Martian geomorphological features provide compelling evidence for the past existence of liquid water on the planet's surface. Approximately 25 extensive linear tracts of eroded terrain, termed outflow channels, traverse the surface. These formations are generally interpreted as erosional remnants from the catastrophic discharge of water from subterranean aquifers, although alternative hypotheses propose their origin from glacial or volcanic activity. A prominent example, Ma'adim Vallis, extends 700 kilometers (430 mi) in length, significantly surpassing the Grand Canyon, with a width of 20 kilometers (12 mi) and localized depths reaching 2 kilometers (1.2 mi). This feature is believed to have been sculpted by flowing water during the early stages of Martian history. The most recent of these channels is estimated to have formed merely a few million years ago.
In other regions, particularly within the most ancient Martian terrains, intricate dendritic valley networks are extensively distributed across substantial portions of the landscape. The morphological characteristics and spatial arrangement of these valleys strongly suggest their formation through runoff generated by precipitation in early Martian history. While subsurface water flow and groundwater sapping might have contributed as significant secondary factors in certain networks, precipitation is considered the primary mechanism responsible for the incision in nearly all instances.
Thousands of features resembling terrestrial gullies are observed along crater and canyon walls. These gullies are predominantly located in the Southern Hemisphere highlands, oriented towards the Equator, and situated poleward of 30° latitude. Several researchers propose that their formation process entails liquid water, likely derived from melting ice, while others contend for mechanisms involving carbon dioxide frost or the transport of dry dust. The absence of partially degraded gullies due to weathering and the lack of superimposed impact craters suggest that these are geologically recent features, potentially remaining active. Additional geological formations, including deltas and alluvial fans preserved within craters, provide further corroboration for periods of warmer, wetter conditions during Mars's ancient history. These conditions inherently necessitate the extensive presence of crater lakes across a significant portion of the surface, a hypothesis supported by independent mineralogical, sedimentological, and geomorphological data. Moreover, the detection of specific minerals like hematite and goethite, both of which typically precipitate in the presence of water, offers additional evidence for the past existence of liquid water on the Martian surface.
Historical Observations and Discoveries of Water Evidence
The spectroscopic detection of water vapor's chemical signature on Mars was first unequivocally established in 1963 using an Earth-based telescope. In 2004, the Opportunity rover identified the mineral jarosite. Jarosite's formation exclusively occurs in acidic aqueous environments, thereby indicating the past presence of water on Mars. The Spirit rover discovered concentrated silica deposits in 2007, suggesting historical wet conditions, and in December 2011, NASA's Mars rover Opportunity located gypsum, another mineral formed in the presence of water, on the surface. The estimated water content in Mars's upper mantle, manifested as hydroxyl ions within Martian minerals, is comparable to or exceeds that of Earth, ranging from 50 to 300 parts per million of water, a quantity sufficient to cover the entire planet to a depth of 200–1,000 meters (660–3,280 ft).
On March 18, 2013, NASA disclosed findings from instruments aboard the Curiosity rover, indicating mineral hydration, specifically hydrated calcium sulfate, within various rock samples. These samples included fragments from "Tintina" and "Sutton Inlier" rocks, alongside veins and nodules in other formations such as "Knorr" and "Wernicke" rocks. Subsequent analysis by the rover's Dynamic Albedo of Neutrons (DAN) instrument revealed subsurface water, with concentrations up to 4% by mass, extending to a depth of 60 centimeters (24 inches). This evidence was collected during the rover's journey from the Bradbury Landing site to the Yellowknife Bay region within the Glenelg terrain. In September 2015, NASA further announced substantial evidence of hydrated brine flows within recurring slope lineae, derived from spectrometer data of darkened slope areas. These streaks exhibit downhill flow during the Martian summer, when temperatures exceed −23 °C, and solidify at colder temperatures. These observations initially corroborated prior hypotheses, based on formation timing and growth rates, suggesting that these dark streaks were caused by subsurface water flow. Nevertheless, subsequent research has proposed that these lineae might instead represent dry, granular flows, with water playing at most a minor role in their initiation. Consequently, a conclusive determination regarding the presence, extent, and function of liquid water on the Martian surface remains unresolved.
A prevailing hypothesis among researchers posits that a significant portion of the planet's low northern plains was once submerged under an ocean hundreds of meters deep, although this theory continues to be debated. In March 2015, scientists estimated that such an ancient Martian ocean could have rivaled the size of Earth's Arctic Ocean. This estimation was based on comparing the protium-to-deuterium ratio in the contemporary Martian atmosphere with that of Earth. The observed Martian deuterium abundance (D/H = 9.3 ± 1.7 10−4) is five to seven times greater than Earth's (D/H = 1.56 10−4), implying that ancient Mars possessed substantially higher water volumes. Earlier data from the Curiosity rover had also detected an elevated deuterium ratio within Gale Crater, though not sufficiently high to definitively indicate a former ocean. However, other scientists advise caution, noting that these findings lack independent confirmation and that current Martian climate models do not yet demonstrate past conditions warm enough to sustain extensive liquid water bodies. Adjacent to the northern polar cap lies the 81.4-kilometer (50.6-mile) wide Korolev Crater, which the Mars Express orbiter has identified as containing approximately 2,200 cubic kilometers (530 cubic miles) of water ice.
In November 2016, NASA announced the discovery of a substantial reservoir of subsurface ice within the Utopia Planitia region. The estimated volume of this detected water is comparable to that of Lake Superior, which contains 12,100 cubic kilometers. Furthermore, between 2018 and 2021, the ExoMars Trace Gas Orbiter identified evidence of water, likely in the form of subsurface ice, within the Valles Marineris canyon system.
Orbital Motion
Mars maintains an average orbital distance of approximately 230 million kilometers (143 million miles) from the Sun, completing an orbit in 687 Earth days. A Martian solar day, or sol, is marginally longer than an Earth day, lasting 24 hours, 39 minutes, and 35.244 seconds. Consequently, one Martian year equates to 1.8809 Earth years, or 1 year, 320 days, and 18.2 hours. The gravitational potential difference, and thus the delta-v required for interplanetary transfer between Mars and Earth, is the second lowest among solar system bodies relative to Earth.
Mars exhibits an axial tilt of 25.19° relative to its orbital plane, a value comparable to Earth's axial inclination. This similarity results in the presence of distinct seasons on Mars, analogous to those on Earth, albeit nearly twice as long due to Mars's extended orbital period. Currently, the Martian north pole is oriented in proximity to the star Deneb.
Mars possesses a notably pronounced orbital eccentricity, approximately 0.09, which is surpassed only by Mercury among the other seven planets in the Solar System. Historical astronomical data indicate that Mars's orbit was considerably more circular in the past. For instance, 1.35 million Earth years ago, its eccentricity was approximately 0.002, significantly lower than Earth's current eccentricity. The cycle of Mars's orbital eccentricity spans 96,000 Earth years, in contrast to Earth's 100,000-year cycle.
The closest approach of Mars to Earth, known as opposition, occurs within a synodic period of 779.94 days. This phenomenon should not be conflated with a Mars conjunction, which describes a configuration where Earth and Mars are positioned on opposing sides of the Solar System, forming a collinear alignment with the Sun. While the average interval between successive Martian oppositions, its synodic period, is 780 days, the actual duration can fluctuate from 764 to 812 days. The distance during these close approaches ranges from approximately 54 to 103 million km (34 to 64 million mi), a variability attributed to the elliptical nature of both planets' orbits, consequently affecting their apparent angular size. Conversely, at their maximum separation, Mars and Earth can be up to 401 million km (249 million mi) distant from each other. Martian opposition relative to Earth occurs approximately every 2.1 years. Notably, oppositions coinciding with Mars's perihelion occurred in 2003, 2018, and 2035, with the 2020 and 2033 events exhibiting a particularly close proximity to perihelic opposition.
Mars exhibits a mean apparent magnitude of +0.71, with a standard deviation of 1.05. Due to the eccentricity of Mars's orbit, its magnitude during opposition from the Sun can vary between approximately −3.0 and −1.4. The planet's minimum brightness, recorded at magnitude +1.86, occurs when it is near aphelion and in conjunction with the Sun. When at its brightest, Mars, alongside Jupiter, ranks second only to Venus in terms of apparent luminosity. Typically, Mars presents a distinct yellow, orange, or red hue. At its maximum distance from Earth, Mars is over seven times more remote than during its closest approach. Optimal viewing conditions for Mars, characterized by its proximity, generally occur once or twice within 15-year or 17-year cycles. Even during the closest approaches of Earth and Mars, optical ground-based telescopes are typically constrained to resolving features approximately 300 kilometers (190 mi) in size, primarily due to atmospheric interference on Earth.
Upon approaching opposition, Mars initiates a phase of retrograde motion, during which it appears to traverse backward in a looping trajectory relative to the background stellar field. This retrograde period extends for approximately 72 days, with Mars attaining its maximum apparent brightness midway through this interval.
Satellites
Mars possesses two comparatively small natural satellites, Phobos (approximately 22 km (14 mi) in diameter) and Deimos (approximately 12 km (7.5 mi) in diameter), which orbit the planet at distances of 9,376 km (5,826 mi) and 23,460 km (14,580 mi), respectively. The genesis of these moons remains uncertain, though a prevalent hypothesis posits their origin as asteroids gravitationally captured into Martian orbit.
These two satellites were discovered in 1877 by Asaph Hall and subsequently named after the mythological Greek twins Phobos (the personification of panic and fear) and Deimos (the personification of terror and dread), who served as companions to their father Ares, the god of war, in combat. Mars, the Roman deity, is the counterpart to the Greek Ares. In contemporary Greek, the planet continues to be referred to by its ancient designation, Ares (Aris: Άρης).
Observed from the Martian surface, the orbital dynamics of Phobos and Deimos diverge significantly from those of Earth's Moon. Phobos exhibits an anomalous motion, rising in the west, setting in the east, and reappearing within a mere 11-hour interval. Deimos, positioned just beyond a synchronous orbit—a state where its orbital period would align with the planet's rotational period—ascends predictably in the east, albeit at a reduced pace. Given that Phobos's orbit lies beneath a synchronous altitude, Martian tidal forces are progressively diminishing its orbital radius. Within approximately 50 million years, Phobos is projected to either impact the Martian surface or disintegrate, forming a ring system around the planet.
The genesis of these two satellites remains incompletely understood. Their low albedo and composition, characteristic of carbonaceous chondrites, have been interpreted as indicative of asteroidal origins, thereby lending credence to a capture hypothesis. Phobos's inherently unstable orbit further suggests a relatively recent capture event. However, both satellites maintain circular orbits in close proximity to the Martian equator, a configuration atypical for captured bodies, and the requisite capture dynamics are inherently intricate. While accretion during the early stages of Martian history presents a plausible formation mechanism, it would not adequately explain a composition more akin to asteroids than to Mars itself, assuming such compositional similarity is substantiated. Furthermore, Mars is hypothesized to possess undiscovered moons, potentially ranging from 50 to 100 meters (160 to 330 ft) in diameter, and a dust ring is predicted to reside within the orbital region between Phobos and Deimos.
A third hypothesis regarding their origin as Martian satellites involves the participation of an additional celestial body or a form of impact disruption. More recent evidence, indicating Phobos possesses a highly porous interior and a composition primarily of phyllosilicates and other minerals found on Mars, suggests Phobos originated from material ejected by a Martian impact that subsequently reaccreted in orbit, mirroring the prevailing theory for Earth's moon. While the visible and near-infrared (VNIR) spectra of Mars' moons resemble those of outer-belt asteroids, the thermal infrared spectra of Phobos have been reported as inconsistent with any class of chondrites. Alternatively, Phobos and Deimos may represent fragments of an older, larger moon, formed from debris following a significant impact on Mars, which was then destroyed by a more recent impact on that satellite.
More recently, a multinational research study proposed the past existence of a lost moon, estimated to be at least fifteen times the size of Phobos. Through the analysis of geological formations on Mars indicative of tidal processes, it is hypothesized that these tides may have been regulated by this ancient moon.
Human observations and exploration
The historical record of Martian observations is characterized by oppositions, periods when the planet is closest to Earth and thus most readily visible, occurring approximately every two years. Particularly noteworthy are perihelic oppositions, distinguished by Mars' proximity to its perihelion, which results in an even closer approach to Earth.
Ancient observations
The ancient Sumerians designated Mars as Nergal, the deity of war and plague. During the Sumerian era, Nergal held minor significance, but in later periods, his primary cult center was established in Nineveh. Mesopotamian texts identify Mars as the "star of judgement of the fate of the dead." Ancient Egyptian astronomers also documented Mars as a wandering celestial object, and by 1534 BCE, they had recognized the planet's retrograde motion. During the Neo-Babylonian Empire, Babylonian astronomers meticulously recorded planetary positions and systematically observed their behavior. For Mars, they determined that the planet completed 37 synodic periods, or 42 circuits of the zodiac, every 79 years, and developed arithmetic methods for minor corrections to predicted planetary positions. In Ancient Greece, the planet was known as Πυρόεις. The common Greek appellation for the planet now identified as Mars was Ares. The Romans subsequently bestowed the name Mars, honoring their god of war, frequently symbolized by the sword and shield associated with the planet's namesake.
In the fourth century BCE, Aristotle observed an occultation of Mars by the Moon, inferring that the planet was situated at a greater distance. Ptolemy, a Greek scholar residing in Alexandria, endeavored to model the orbital motion of Mars. Ptolemy's astronomical model and his comprehensive body of work were compiled into a multi-volume collection later termed the Almagest (derived from the Arabic for "greatest"), which served as the authoritative treatise on Western astronomy for the subsequent fourteen centuries. Ancient Chinese literature confirms that Mars was recognized by Chinese astronomers no later than the fourth century BCE. Within East Asian cultures, Mars is conventionally termed the "fire star" (火星), consistent with the Wuxing system.
Early modern observations
In 1609, Johannes Kepler published a decade-long investigation into the Martian orbit, utilizing Tycho Brahe's measurements of Mars' diurnal parallax to establish a preliminary calculation of the planet's relative distance. From Brahe's observations of Mars, Kepler deduced that the planet traversed an elliptical, rather than circular, path around the Sun. Furthermore, Kepler demonstrated that Mars' orbital velocity increased upon approach to the Sun and decreased when receding, a phenomenon subsequently elucidated by physicists as a manifestation of the conservation of angular momentum.
The initial astronomical application of a telescope, encompassing observations of Mars, was conducted by the Italian astronomer Galileo Galilei in 1610. Subsequently, the diurnal parallax of Mars was remeasured using a telescope to ascertain the Sun-Earth distance, a feat first accomplished by Giovanni Domenico Cassini in 1672. However, the precision of these early parallax measurements was constrained by the rudimentary quality of the available instrumentation. Notably, the sole recorded occultation of Mars by Venus occurred on October 13, 1590, and was observed by Michael Maestlin in Heidelberg.
Martian "Canals"
During the 19th century, advancements in telescope resolution enabled the identification of Martian surface features. A perihelic opposition of Mars transpired on September 5, 1877, prompting Italian astronomer Giovanni Schiaparelli to utilize a 22-centimetre (8.7 in) telescope in Milan for the creation of the first comprehensive map of Mars. This map conspicuously depicted features he designated as canali, which, apart from the natural canyon Valles Marineris, were subsequently determined to be optical illusions. These purported canali were described as extensive, linear formations on the Martian surface, to which Schiaparelli assigned names of prominent terrestrial rivers. Although his original term signifies "channels" or "grooves," it was widely and inaccurately rendered in English as "canals."
Inspired by these observations, the orientalist Percival Lowell established an observatory equipped with 30- and 45-centimetre (12- and 18-in) telescopes. This facility was dedicated to Martian exploration during the optimal opposition of 1894 and subsequent less favorable alignments. Lowell authored several influential books concerning Mars and potential extraterrestrial life, significantly impacting public perception. The canali were also independently reported by other astronomers, including Henri Joseph Perrotin and Louis Thollon in Nice, who employed one of the era's largest telescopes.
The observed seasonal variations, characterized by the recession of polar caps and the emergence of dark regions during Martian summers, coupled with the presence of "canals," fueled extensive speculation regarding life on Mars. For an extended period, it was widely believed that Mars harbored vast seas and vegetation. However, with the deployment of progressively larger telescopes, the number of observed long, straight canali diminished. Notably, during Antoniadi's observations in 1909 using an 84-centimetre (33 in) telescope, irregular surface patterns were identified, but no canali were discernible.
Initial Spacecraft Exploration
The Soviet Union's Mars 1 represented the inaugural Earth-launched spacecraft intended for Mars, executing a flyby in 1963, though communication was lost during its transit. Subsequently, NASA's Mariner 4 became the first spacecraft to successfully transmit data from Mars. Launched on November 28, 1964, it achieved its closest planetary approach on July 15, 1965. Mariner 4 identified a faint Martian radiation belt, approximately 0.1% the strength of Earth's, and acquired the first deep-space images of another planet.
The arrival of spacecraft at Mars during the 1960s and 1970s fundamentally challenged numerous pre-existing perceptions of the planet. Following the outcomes of the Viking life-detection experiments, the prevailing scientific consensus shifted towards the hypothesis of a geologically inactive planet. Data acquired from Mariner 9 and Viking facilitated the creation of more accurate Martian maps.
Resumption of Exploration
Between the shutdown of Viking 1 in 1982 and 1997, Mars was the destination of only three unsuccessful probes: Phobos 1 (1988) and Mars Observer (1993), which performed flybys without establishing contact, and Phobos 2 (1989), which experienced an orbital malfunction prior to reaching its intended target, Phobos.
In 1997, Mars Pathfinder achieved distinction as the first successful rover mission beyond the Moon. This mission, alongside Mars Global Surveyor (operational until late 2006), initiated a continuous and active robotic presence on Mars that persists to the present day. These missions generated comprehensive and highly detailed maps of Martian topography, its magnetic field, and surface mineral composition.
Subsequent to these pioneering missions, a diverse array of advanced uncrewed spacecraft, comprising orbiters, landers, and rovers, has been dispatched to Mars. Successful missions have been conducted by NASA (United States), JAXA (Japan), ESA, the United Kingdom, ISRO (India), Roscosmos (Russia), the United Arab Emirates, and CNSA (China). These endeavors aim to investigate the planet's surface, climate, and geology, thereby elucidating the historical components and dynamic processes of the Martian hydrosphere, as well as potential evidence of ancient life.
Ongoing Missions
As of 2023, Mars hosts ten operational spacecraft.
Currently, eight operational spacecraft are orbiting Mars: 2001 Mars Odyssey, Mars Express, Mars Reconnaissance Orbiter, MAVEN, ExoMars Trace Gas Orbiter, the Hope orbiter, and the Tianwen-1 orbiter.
Additionally, two rovers are active on the Martian surface: the Mars Science Laboratory Curiosity and the Perseverance.
Comprehensive Martian maps are accessible online through various platforms, such as Google Mars. NASA offers two dedicated digital resources: Mars Trek, which presents planetary visualizations derived from five decades of exploratory data, and Experience Curiosity, an interactive simulation allowing users to navigate Mars in 3D with the Curiosity rover.
Future Missions
Upcoming missions targeting Mars encompass:
- NASA's EscaPADE spacecraft, scheduled for launch on November 13, 2025.
- The Rosalind Franklin rover mission, purposed for detecting evidence of ancient life, initially aimed for a 2018 launch but has experienced multiple postponements, with its earliest projected launch now set for 2028. The initiative received renewed funding and was restarted in 2024.
- A collaborative NASA-ESA mission concept, focused on retrieving Martian samples, is currently envisioned for a 2026 launch.
- China's Tianwen-3, a mission designed for sample return, is slated for launch in either 2028 or 2030.
By February 2024, the accumulated debris from such missions exceeded seven tons, primarily comprising crashed and defunct spacecraft along with jettisoned components.
In April 2024, NASA commissioned several commercial entities to conduct studies on delivering services that would advance robotic scientific endeavors on Mars. Primary focus areas encompass telecommunications infrastructure, payload transportation, and surface imaging capabilities.
Habitability and Potential for Human Habitation
In the late 19th century, the astronomical community largely presumed Mars possessed attributes conducive to life, such as oxygen and water. Nevertheless, in 1894, W. W. Campbell of Lick Observatory reported that "if water vapor or oxygen occur in the atmosphere of Mars it is in quantities too small to be detected by spectroscopes then available." This finding challenged numerous contemporary measurements and initially met with skepticism. Campbell and V. M. Slipher replicated the investigation in 1909, employing enhanced instrumentation, yet yielded identical conclusions. The prevailing notion of Mars's Earth-like habitability was not definitively disproven until W. S. Adams corroborated these findings in 1925. Despite this, publications concerning Martian biology persisted into the 1960s, often attributing seasonal Martian changes to biological processes rather than alternative explanations.
Contemporary scientific understanding of planetary habitability—defined as a world's capacity to foster environmental conditions conducive to the genesis of life—prioritizes planets featuring surface liquid water. This typically necessitates a planetary orbit within the habitable zone, which for the Sun is estimated to span from Earth's orbit to approximately Mars's. While Mars briefly enters this zone during perihelion, its tenuous, low-pressure atmosphere precludes the sustained presence of liquid water across extensive areas. Historical evidence of liquid water flow on Mars indicates its past potential for habitability. However, recent findings propose that any extant Martian surface water might have been excessively saline and acidic to sustain typical terrestrial life forms.
The Martian environmental conditions present significant obstacles to the sustenance of organic life. The planet exhibits minimal heat transfer across its surface, possesses inadequate shielding against solar wind bombardment due to the absence of a magnetosphere, and lacks sufficient atmospheric pressure to maintain water in a liquid state, causing it to sublimate directly into gas. Mars appears to be largely, if not entirely, geologically inert; the cessation of volcanic activity has seemingly halted the crucial recycling of chemicals and minerals between the planet's surface and interior.
Planetary evidence indicates that Mars was once substantially more conducive to life than its current state; however, the past existence of living organisms remains an unresolved question. The Viking probes of the mid-1970s conducted experiments aimed at identifying microorganisms in Martian soil at their respective landing sites and yielded positive indications, such as a transient elevation in CO§34§ generation upon exposure to water and nutrient solutions. These initial findings were subsequently contested by the scientific community, initiating an ongoing discourse. Notably, NASA scientist Gilbert Levin maintains that the Viking missions may indeed have detected biological activity. A 2014 examination of the Martian meteorite EETA79001 revealed chlorate, perchlorate, and nitrate ions present in concentrations high enough to imply their pervasive distribution across Mars. Ultraviolet and X-ray radiation would convert these chlorate and perchlorate ions into highly reactive oxychlorine compounds, thereby suggesting that any extant organic molecules would necessitate subsurface burial for preservation.
The detection of trace amounts of methane and formaldehyde by Mars orbiters has been posited as potential evidence for biological processes, given the rapid degradation of these chemical compounds within the Martian atmosphere. Conversely, these compounds could be continuously regenerated through volcanic activity or other geological mechanisms, such as serpentinization. Impact glass, a material generated by meteoritic impacts and known on Earth for its capacity to preserve biosignatures, has also been identified within Martian impact craters. Similarly, this impact glass on Mars could potentially have encapsulated evidence of life, assuming its presence at the impact location.
In June 2024, the Cheyava Falls rock, identified on Mars, was classified by NASA as a "potential biosignature." The Perseverance rover subsequently acquired a core sample for potential transport to Earth and comprehensive analysis. While highly compelling, the existing data preclude a conclusive determination regarding the rock's biological or abiotic genesis.
Proposals for Human Missions
Numerous proposals for crewed missions to Mars have been advanced; however, none have yet been realized. The NASA Authorization Act of 2017 mandated a feasibility study for a crewed Mars mission in the early 2030s, which subsequently determined such an endeavor to be impractical. Furthermore, in 2021, China articulated plans for a crewed Mars mission targeting 2033. Private entities, including SpaceX, have similarly put forth initiatives for human expeditions to Mars, with the ultimate objective of planetary settlement. By 2024, SpaceX had advanced the development of its Starship launch vehicle, specifically designed for Mars colonization. According to plans disseminated by the company in April 2024, Elon Musk projects the establishment of a Martian colony within the next two decades. This ambitious undertaking would rely on the mass production of Starship vehicles, initial logistical support from Earth, and the implementation of in-situ resource utilization on Mars, ultimately aiming for the colony's complete self-sufficiency. Prospective human missions to Mars are anticipated to align with the optimal launch window, which recurs approximately every 26 months. Phobos, one of Mars's moons, has been suggested as a potential anchor for a space elevator. Beyond governmental space agencies and private aerospace firms, organizations like The Mars Society and The Planetary Society actively champion human exploration of Mars.
Cultural Significance
Mars derives its name from the Roman god of war (Ares in Greek mythology) and was additionally linked to the demigod Heracles (Roman Hercules) by ancient Greek astronomers, as documented by Aristotle. This martial association of Mars originates at least from Babylonian astronomy, where the planet was designated after Nergal, the deity of war and destruction. This thematic connection has endured into contemporary culture, notably exemplified by Gustav Holst's orchestral suite The Planets, in which the prominent first movement characterizes Mars as "The Bringer of War." The planet's astronomical symbol, depicting a circle with an upward-right pointing spear, also serves as a conventional representation for the male gender. This symbol's provenance extends at least to the 11th century, with a potential precursor identified within the Greek Oxyrhynchus Papyri.
During the late 19th century, the concept of Mars being inhabited by intelligent beings gained considerable traction. Schiaparelli's observations of "canali," coupled with Percival Lowell's extensive writings, popularized the perception of Mars as a desiccating, cooling, and moribund planet, home to ancient civilizations engaged in constructing elaborate irrigation systems. Numerous other observations and pronouncements from prominent figures further fueled what became known as "Mars Fever." Contemporary high-resolution mapping of the Martian surface has yielded no evidence of artificial structures or habitation; nevertheless, pseudoscientific conjectures regarding intelligent Martian life persist. Echoing the canali observations, these speculations frequently derive from interpretations of small-scale features identified in spacecraft imagery, including purported "pyramids" and the "Face on Mars." Planetary astronomer Carl Sagan, in his work Cosmos, articulated this phenomenon, stating: "Mars has become a kind of mythic arena onto which we have projected our Earthly hopes and fears."
The portrayal of Mars in fictional narratives has been significantly influenced by its distinctive red hue and by 19th-century scientific hypotheses suggesting that its surface conditions could sustain not only life but intelligent civilizations. This fertile ground led to numerous science fiction works exploring these themes, including H. G. Wells's The War of the Worlds, where Martians attempt to flee their dying world by invading Earth; Ray Bradbury's The Martian Chronicles, depicting human explorers inadvertently eradicating a Martian civilization; Edgar Rice Burroughs's Barsoom series; C. S. Lewis's 1938 novel Out of the Silent Planet; and several stories by Robert A. Heinlein published prior to the mid-1960s. Subsequently, Martian portrayals expanded into animated media. Marvin the Martian, an intelligent comic character, debuted in Haredevil Hare (1948) within Warner Brothers' Looney Tunes animated cartoons and has since maintained a prominent role in popular culture. Following the data returned by the Mariner and Viking spacecraft, which depicted Mars as a barren world devoid of canals, earlier notions about the planet were largely discarded. While these new scientific findings initially presented a creative limitation for many science fiction writers, the post-Viking understanding of Mars ultimately served as a fresh wellspring of inspiration for works such as Kim Stanley Robinson's Mars trilogy.
Astronomy on Mars
- Astronomy on Mars
- Outline of Mars – A comprehensive overview and thematic guide to the planet Mars.
- List of missions to Mars
- Magnetic field of Mars – Historical magnetic field characteristics of the planet Mars.
- Mineralogy of Mars
Notes
References
Weinersmith, K., & Weinersmith, Z. (2023). A city on Mars: Can we settle space, should we settle space, and have we really thought this through?. New York: Penguin Press. ISBN 978-1-9848-8172-4.
- Weinersmith K, Weinersmith Z (2023). A city on Mars: can we settle space, should we settle space, and have we really thought this through?. New York: Penguin Press. ISBN 978-1-9848-8172-4.Shindell, M. (2023). For the love of Mars: A human history of the red planet. Chicago; London: The University of Chicago Press. ISBN 978-0-226-82189-4.
- Mars Trek, an integrated map browser of maps and datasets for Mars
- First TV image of Mars (15 July 1965), CNN News; 15 July 2023