Image of Mars centered near the Schiaparelli crater (color-reinforced photographic composition)
|Date||Known since ancient times|
|Stellar distance||54,600,000 kilometers|
|Apparent magnitude||+1,6 a –3|
|Longitude of the ascending node||49,562°|
|Major semi-axis||227 392 100 km (1.523679 etc. )|
|Derived orbital elements|
|Periastro o perihelio||206 669 000 km (1.381497 etc. )|
|Apoastro o afelio||249 209 300 km (1.665861 etc. )|
|Sidereal orbital period||686,971 days|
|Orbital period sinódico||779.96 days|
|Average orbital velocity||24,077 km/s|
|Radio orbital medio||227 936 640 km (1.523662 etc. )|
|Time||6,4185 × 1023 kg|
|Volume||1,6318 × 1011 km³|
|Density||3,9335 ± 0,0004 g/cm³|
|Area surface||144 798 500 km²|
|Radio||3 389.50 kilometers|
|Escape velocity||5,027 km/s|
|Rotation period||24.6229 hours|
|Pressure||0,636 (0,4-0,87) kPa|
Compared size of Earth and Mars
Mars is the fourth planet in order of distance from the Sun and the second smallest in the solar system , after Mercury . It was named in honor of the god of war in Roman mythology ( Ares in Greek mythology), and is also known as the "Red Planet" [ 3 ] [ 4 ] because of the reddish appearance [ 5 ] that It gives it the predominant iron oxide on its surface. Mars is the inner planet farthest from the sun . Is atelluric planet with an atmosphere thin carbon dioxide , and has two small and irregularly shaped satellites, Phobos and Deimos (children of the Greek god), which could be asteroids captured [ 6 ] [ 7 ] Similar to the Trojan asteroid (5261 ) Eureka . Its surface characteristics are reminiscent of craters on the Moon as well as valleys, deserts, and polar caps on Earth.
The rotation period and the seasonal cycles are similar to those of the Earth, since the inclination is what generates the seasons. Mars is home to Mount Olympus , the largest volcano and the second highest known mountain in the solar system , and the Valles Marineris , one of the largest canyons in the solar system. The flat Boreal basin in the northern hemisphere covers 40% of the planet and can be characteristic of a gigantic impact. [ 8 ] [ 9 ]Although it might appear to be a dead planet on the surface, it is not. Its dune fields continue to be swayed by the Martian wind, its polar caps change with the seasons, and it even appears that there are some small seasonal flows of water. [ 10 ]
Ongoing research is evaluating its potential habitability in the past, as well as the current possibility of life. Future astrobiology investigations, including the planned Mars 2020 of NASA and the ExoMars of ESA . [ 11 ] [ 12 ] [ 13 ] [ 14 ] The liquid water can not exist on the surface of Mars due to low atmospheric pressure, which is about 100 times lower than that of the Earth, [ 15 ]Except in the less elevated areas for short periods of time. [ 16 ] [ 17 ] His two polar ice caps appear to be made up mostly of water. [ 18 ] [ 19 ] The volume of the water ice southern polar cap, if melted, it would be enough to cover the entire planetary surface with a depth of 11 meters (36 feet). [ 20 ]
Mars can be easily seen with the naked eye from Earth, as well as its reddish coloration. Its apparent magnitude reaches -2.97 [ 21 ] , and is second only to Jupiter , Venus , the Moon, and the Sun. Optical ground-based telescopes are normally limited to resolutions of approximately 300 km (190 miles) away, when Earth and Mars are closer, due to the Earth's atmosphere. [ 22 ]
The 16th century Danish astronomer Tycho Brahe measured the motion of Mars in the sky with great precision. Data on apparent retrograde motion (so-called "loops") [ note 1 ] enabled Kepler to find the elliptical nature of its orbit and to determine the laws of planetary motion known as Kepler's laws .
Mars is one of the planets superior to Earth, since its orbit never crosses that of the Earth around the Sun. Its phases (illuminated portion seen from Earth) are poorly marked, a fact that is easy to demonstrate geometrically. Considering the Sun-Earth-Mars triangle, the phase angle is that formed by the Sun and the Earth seen from Mars; this reaches its maximum value in the quadratures when the STM triangle is right on Earth. For Mars, this phase angle is never greater than 42 °, and its aspect of a gibbous disk is analogous to that of the Moon 3.5 days before or after the full Moon.. This phase, visible with an amateur telescope, could not be seen by Galileo , who only assumed its existence. [ 24 ]
Mars is slightly ellipsoidal , with an equatorial diameter of 6,794.4 km and a polar diameter of 6,752.4 km (approximately half that of Earth), and a total surface area somewhat less than that of the landmass on our planet. [ 25 ] Very precise micrometric measurements have shown a flattening three times greater than that of the Earth, with a value of 0.01. Because of this flattening, the axis of rotation is affected by a slow precession due to the attraction of the Sun on the equatorial bulge of the planet. Lunar precession, which is twice as high on Earth as solar, has no equivalent on Mars. [ 26 ]
With this diameter, its volume is 15% of the earth's and its mass approximately 11%. Consequently, the density of Mars is lower than that of Earth and its gravity is 38% of Earth's gravity. The red-orange appearance of its surface is due to iron oxide III or rust. [ 27 ] It can appear toffee, and also other colors such as gold, brown, beige or greenish, depending on the minerals present on its surface. [ 28 ]
A the like Earth, Mars has differentiated dense metallic core coated with less dense materials. [ 29 ] Current models suggest a core with a radius of approximately 1,794 ± 65 kilometers (1,115 ± 40 mi), consisting mainly of nickel and iron with approximately 16-17% sulfur . [ 30 ] This iron (II) sulfide core is believed to contain twice as many light elements as Earth's. [ 31 ] The core is surrounded by a mantleof silicate where many of the tectonic and volcanic features of the planet were formed, now in a latent state. Along with silicon and oxygen, the most abundant elements in the crust of Mars are iron, magnesium , aluminum , calcium, and potassium . The average thickness of the planet's crust is about 50 km (31 mi), with a maximum thickness of 125 km (78 mi). The average thickness of the Earth's crust is 40 km (25 mi). [ 31 ]
Mars is a rocky planet made up of minerals that contain silicon , oxygen , metals, and other elements that normally make up rocks. The surface of Mars is mainly composed of toleitic basalt [ 32 ] with a high content of iron oxides that provide the characteristic red color of its surface. By its nature it resembles limonite, highly hydrated iron oxide. Just as silicates and aluminates predominate in the crusts of the Earth and the Moon, ferrosilicates are predominant in the soil of Mars. Its three main constituents are, in order of abundance, oxygen, silicon and iron. Contains: 20.8% silica, 13.5% iron, 5% aluminum, 3.8% calcium, and also titanium and other minor components. [ citation needed ] Some areas are richer in silica than basalt and may be similar to andesite rocks on Earth or silica glass . In parts of the mountainous areas in the south there are detectable amounts of pyroxeneshigh in calcium. Localized concentrations of hematites and olivines have also been detected . [ 33 ] Most of its surface is deeply covered with fine-grained iron (III) oxide dust . [ 34 ] [ 35 ]
Mars is a notably smaller planet than Earth. Its main characteristics, in proportion to those of the terrestrial globe, are the following: diameter 53%, surface area 28%, mass 11%. Since the oceans cover about 70% of the Earth's surface and Mars lacks them, both planets have roughly the same amount of walkable surface.
Although there is no evidence of a global magnetic field structure on Mars [ 36 ] , parts of the planetary crust show evidence of having been magnetized, suggesting the reversal of polarity of its dipole field in the past. This paleomagnetism of magnetically susceptible minerals is similar to that of the alternating fringes found on the ocean floor of the Earth. One theory, published in 1999 and revised in October 2005 (with the help of the Mars Global Surveyor ), is that these fringes suggest activity from Mars plate tectonics 4 billion years ago, before the dynamoplanetary will stop working and the magnetic field of the planet will vanish. [ 37 ]
It is believed that Mars was created, during the formation of the solar system, as a result of a stochastic process of accumulation of material from the protoplanetary disk orbiting the Sun. Mars has many peculiar chemical characteristics due to its position in the solar system. Elements with relatively low boiling points, such as chlorine , phosphorus, and sulfur , are much more common on Mars than on Earth; these elements were probably expelled by the strong solar wind of the young sun. [ 38 ]
After the formation of the planets, all were subjected to the so-called late heavy bombardment . Around 60% of the surface of Mars shows an impact record from that era, [ 39 ] [ 40 ] while the rest of the remaining area is probably under immense impact craters produced by these events. There is evidence for a huge impact basin in the northern hemisphere of Mars that spans between 10,600 by 8,500 km (6,600 by 5,300 mi), or about four times the size of the Aitken basin at the south pole of the Moon, the largest basin. impact discovered so far. [ 8 ] [9 ] This theory suggests that Mars was impacted by a body the size of Pluto about four billion years ago. The event, believed to be the cause of the Martian hemispheric dichotomy , created the Borealis basin that covers 40% of the planet. [ 41 ] [ 42 ]
The surface of Mars is remarkably differentiated in its hemispheres, while the northern hemisphere is quite homogeneous and uniform in terms of its landscape; the southern hemisphere is chaotic terrain, with extensive tectonic faults, abysses and colossal depressions, and each region of that hemisphere presents a geological aspect that is difficult to model on Earth scales.
- Noeic Period (named after Noachis Terra ) ː from the formation of Mars to 3.5 billion years ago. Areas from this era are marked by large and numerous impact craters. It is believed that during this period Tharsis , the volcanic plateau, was formed and that there were great floods by liquid water at the end of it.
- Hesperian Period (for Hesperia Planum ) ː between 3,500 ~ 3,300 and 2,900 million years ago. This period is marked by the formation of extensive lava plains.
- Amazonian Period (by Amazonis Planitia ) ː between 3,300 and 2,900 million years to the present. Impact craters are rare but quite varied. During this period Mount Olympus was formed , along with lava flows elsewhere on Mars.
Geological activity continues to take place on Mars. Athabasca Valles is the base of the lava beds formed 200 million years ago. The water currents in the rifts called Cerberus Fossae occurred less than 20 million years ago, indicating relatively recent volcanic intrusions. [ 44 ]
Thanks to the images taken by the HiRISE camera , mounted on the Mars Reconnaissance Orbiter , in orbit since March 2006, many of the main morphological characteristics of its surface have been revealed. [ 45 ] The surface of Mars has morphological characteristics of both the Earth and the Moon : impact craters, lava fields, volcanoes, dry river beds, and sand dunes. [ citation required ]
- From Earth, through telescopes, dark and bright spots are observed that do not correspond to topographic features but appear if the ground is covered with dark dust ( albedo characteristics ). These can change slowly when the wind blows the dust away. The most characteristic dark spot is Syrtis Major , a slope less than 1% and without noticeable features.
- The surface of Mars also has bright reddish-orange regions, which are called deserts , and which extend over three-quarters of the planet's surface, giving it its characteristic reddish coloration. These deserts are actually more like an immense scree, since the ground is covered with stones, ridges and blocks.
- An enormous step, close to the equator, divides Mars into two clearly differentiated regions: a flat, young and deep north and a high, old and steep south, with craters similar to the high regions of the Moon. In contrast, the northern hemisphere has much younger plains, and with a more complex history. There appears to be a sharp rise of several kilometers at the boundary. The reasons for this global dichotomy are unknown.
- There are impact craters scattered throughout Mars , but in the southern hemisphere there is an old basaltic lava plateau similar to the seas of the Moon , strewn with lunar-like craters. However, the general aspect of the Martian landscape differs from that of our satellite as a consequence of the existence of an atmosphere. In particular, the wind loaded with solid particles produces an ablation that, in the course of geological times, has washed away many craters. These are, therefore, much less numerous than on the Moon.and most of them have the walls more or less worn by erosion. On the other hand, the enormous volumes of dust blown by the wind cover the minor craters, the uneven terrain and other minor features of the relief. Among the prominent impact craters in the southern hemisphere is the Hellas Planitia impact basin , 6 km deep and 2,000 km in diameter. Many of the more recent impact craters have a morphology that suggests that the surface was wet or muddy when the impact occurred.
- The Martian magnetic field is very weak, with a value of about 2 thousandths of the Earth's and reversed polarity with respect to that of the Earth.
The Phoenix probe provided data that Martian soil is slightly alkaline and contains elements such as magnesium , sodium , potassium, and chlorine . These nutrients are found in terrestrial soils, and are necessary for plant growth. [ 46 ] Space probe experiments showed that Martian soil has a basic pH of 7.7 and contains 0.6% perchlorate salts . [ 47 ] [ 48 ] [ 49 ]
Striations are common across Mars, and new stripes often appear on steep crater slopes, depressions, and valleys. These stripes are dark at first and with time they become lighter. They can start in a tiny area and then spread out for hundreds of meters. They have been observed to skirt boulders and other obstacles in their path. Commonly accepted theories suggest that these are dark subsurface layers exposed after avalanches of dust clouds or dust devils . [ 51 ] Some other explanations have been proposed, including those concerning water or even the development of organisms. [ 52 ] [ 53 ]
The surface of Mars is chaotic in many sectors and retains the traces of great cataclysms that have no equivalent on Earth:
A characteristic of the northern hemisphere is the existence of a huge bulge that contains the Tharsis volcanic complex . In it is Mount Olympus , the largest volcano in the solar system . It has a calculated height between 21 and 26 km [ a ] (more than two and a half times the height of Everest on a globe much smaller than Earth's) and its base is 600 km wide. The lava flows have created a plinth whose edge forms a 6 km high cliff. We must add the great collapsed structure of Alba Patera. Volcanic areas occupy 10% of the planet's surface. Some craters show signs of recent activity and have petrified lava on their slopes. Despite this evidence, it was not until May 2007 that Spirit discovered, with a high degree of certainty, the first volcanic deposit sign of ancient volcanic activity in the area called Home Plate, [ 54 ] (an area with rocky bed about two meters high and fundamentally basaltic, which must have formed due to lava flows in contact with liquid water), located at the inner base of the Gusev crater . One of the best tests is what researchers call bomb sag(the brand of the pump). When lava and water meet, the explosion throws chunks of rock upward, some of which fall back into softer deposits.
Close to the equator and with a length of more than 3,000 km, a width of up to 600 km and a depth of up to 8 km, Valles Marineris is a canyon that dwarfs the Colorado Canyon . It was formed by the subsidence of the land due to the formation of the Tharsis bulge. [ 55 ]
There is clear evidence of erosion in various places on Mars, both by wind and water. There are long winding valleys on the surface that resemble river beds (currently dry as liquid water cannot exist on the planet's surface under current atmospheric conditions). Those immense valleys may be the result of fractures along which streams of lava and, later, water have flowed.
The surface of the planet preserves true hydrographic networks, today dry, with their sinuous valleys carved by the waters of the rivers, their tributaries, their arms, separated by banks of alluvium that have survived to this day. All these surface details suggest a past with other environmental conditions in which water caused these beds through catastrophic flooding. Some suggest the existence, in the remote past, of lakes and even a vast ocean in the boreal region of the planet. Everything seems to indicate that it was about 4000 million years ago and for a brief period, in the so-called Noeic era .
Like the Moon and Mercury , Mars does not have active plate tectonics , like Earth. There is no evidence of recent horizontal surface movements such as the folding mountains so common on Earth. However, the Mars Global Surveyor in orbit around Mars has detected extensive low-intensity magnetic fields in various regions of the planet. This unexpected finding of a probable global magnetic field, active in the past and now missing, may have interesting implications for the interior structure of the planet.
Recently, studies carried out with the help of the Mars Reconnaissance Orbiter and Mars Global Surveyor probes have shown that quite possibly the northern hemisphere of Mars is a huge elliptical impact basin, known as the Borealis Basin, 8500 kilometers in diameter that covers a 40 % of the planet's surface (the largest in the solar system, far exceeding the Aitken Basin of the Moon), which could have been formed 3.9 billion years ago by the impact of an object about 2000 kilometers in diameter. After the formation of this basin, giant volcanoes arose along its edge, which have made its identification difficult. [ citation required ]
The atmosphere of Mars is very thin, with a surface pressure of only 7 to 9 hPa compared to 1013 hPa for the Earth 's atmosphere . This represents one hundredth of the earth's. Atmospheric pressure varies considerably with altitude , from almost 9 hPa in the deepest depressions to 1 hPa at the top of Mount Olympus . Recent discoveries regarding Martian exploration allow the conclusion that the data on atmospheric pressure should be revised. Specifically because with such atmospheric pressure data it would be unfeasible to use large parachutes to land the modules sent to Mars (see Mars Science Laboratory).
On the basis of data fundamentally observed from Martian orbit, it has been deduced that the atmospheric composition of the planet is fundamentally: 95.3% carbon dioxide , 2.7% nitrogen , 1.6% argon and traces of molecular oxygen (0.15%), carbon monoxide (0.07%) and steam water(0.03%). The proportion of other elements is negligible and its dosage is beyond the sensitivity of the instruments used up to now. However, due to the confirmation in 2015 of the presence of seasonal water on the Martian surface by NASA, the data on the proportion of atmospheric oxygen and water vapor must be revised. With a temporal criterion, it has also been assumed that the ozone content is 1000 times lower than on Earth, so that this layer, which is 40 km high, would be unable to block ultraviolet radiation.
The atmosphere is dense enough to host very strong winds and large dust storms that can sometimes sweep across the entire planet for months. This wind is responsible for the existence of sand dunes in Martian deserts. Clouds can come in three colors: white, yellow, and blue. White clouds are condensed water vapor or carbon dioxide at polar latitudes. The yellow ones, which are hairy in nature, are the result of dust storms and are made up of particles around 1 micron in size . The Martian sky dome is a soft salmon-pink color due to the scattering of light by very fine dust grains from the ferruginous soil.
In winter, in the middle latitudes, water vapor condenses in the atmosphere and forms light clouds of very fine ice crystals. At extreme latitudes, the condensation of carbon dioxide forms other clouds consisting of dry ice crystals.
The weak Martian atmosphere produces a greenhouse effect that increases the surface temperature by about 5 degrees; much less than that observed on Venus and on Earth.
The Martian atmosphere has undergone a considerable process of evolution making it a second generation atmosphere. The original atmosphere, formed shortly after the planet, has given way to another, whose elements come from its geological activity. Thus, volcanism discharges certain gases into the atmosphere, among which carbon dioxide and water vapor predominate. The former remains in the atmosphere, while the latter tends to freeze on the cold ground. The nitrogen and oxygen are not produced on Mars more than negligible proportions. In contrast, argon is relatively abundant in the Martian atmosphere. This is not surprising: the light elements in the atmosphere ( hydrogen , helium, etc.) are the ones that escape more easily in interplanetary space since their atoms and molecules reach the escape velocity ; the heavier gases end up combining with the elements of the soil; the argon , albeit slight, is heavy enough to their hydrodynamic exhaust into interplanetary space is difficult and, moreover, to being a neutral gas or inert, not combined with other elements so will accumulate with weather.
In the beginning of its history Mars may have been very similar to Earth. As on our planet, most of its carbon dioxide was used to form carbonates in rocks. But lacking plate tectonics, it is unable to recycle any of this carbon dioxide into the atmosphere and thus cannot maintain a significant greenhouse effect.
The atmosphere of Mars escapes into outer space slowly, but continuously, over time. The main cause of this leak is the solar wind . In the absence of a significant magnetic field, electrically charged particles from the solar wind penetrate the atmosphere. The magnetism of these particles interacts with the ions in the atmosphere and gives them enough acceleration for some to achieve escape velocity and leave the planet. They also hit the neutral particles, also giving them a similar acceleration in some cases. In 2015 the MAVEN space probemeasured the rate of loss of the atmosphere, and the result was that every second more than 100 grams of Mars' atmosphere escapes into outer space, the loss being between 10 and 20 times higher during solar flares . [ 57 ]
Although there is no evidence of current volcanic activity, recently the European Mars Express spacecraft and Earth measurements obtained by the Keck telescope from Earth have found traces of methane gas at a ratio of 10 parts per 1 billion. This gas can only have a volcanic or biological origin. Methane cannot stay in the atmosphere for long; the time it takes to disappear from the atmosphere of Mars is estimated at 400 years, which implies that there is an active source that produces it. The small proportion of methane detected, very little above the limit of instrumental sensitivity, prevents for the moment to give a clear explanation of its origin, be it volcanic and / or biological. [ 56 ]The Mars Science Laboratory (Curiosity) lander mission includes equipment to compare the proportions of the C-12 , C-13 and C-14 isotopes , present in carbon dioxide and in methane, to determine the origin of the latter.
Water on mars
Water in a liquid state cannot exist on Mars due to low atmospheric pressure, which is less than 1% of that on Earth, [ 15 ] except on lower surfaces for short periods. [ 16 ] [ 17 ] The two polar caps appear to be formed largely of water. [ 18 ] [ 19 ] The volume of water ice in the south polar cap would suffice, if melted, to cover all the surface of the planet to a depth of 11m. [ 20 ] A permafrost mantleit extends from the pole to latitudes of about 60 °. [ 18 ] Large amounts of icy water are believed to be trapped in the thick layer of Mars' cryosphere . Data from the Mars Express and Mars Reconnaissance Orbiter radars showed large amounts of icy water at both poles (July 2005) [ 58 ] and at mid-latitudes (November 2008). [ 59 ] The probe samples taken directly Phoenix ice water on the surface of Mars soil 31 July 2008. [ 60 ]
A study published in September 2013, based on data collected by the Curiosity rover , states that there would be between 1.5 and 3% water on the surface of Mars. [ 61 ] However, today this calculation falls short and is considered as erroneous or subject to revision after the announcement in 2006 and the confirmation in 2015 by NASA, of the presence of liquid water on the surface of Mars that appears seasonally in certain regions of the planet. [ 62 ] [ 63 ]
Over time there have been numerous discoveries of clues that suggest the probable existence of water in the past. A study published in 2015 by NASA concluded that 4.3 billion years ago, and for 1.5 billion years, [ 64 ] the planet had an extensive ocean in the northern hemisphere [ 65 ] with a volume greater than that of the Arctic, [ 66 ] enough to cover the entire Martian territory with 130 m of water. [ 67 ]
In the images taken by the Mars Reconnaissance Orbiter orbiting probe, descending surface veins with seasonal variations were detected in the Martian hills, which was interpreted as the most promising indication of the existence of liquid water currents on the planet. [ 68 ] On February 14, 2014, in photographs taken by the Martian orbiters, evidence was observed that there are water flows in the so-called recurring slope lines (RSL). [ 69 ]On September 28, 2015, during a press conference, NASA announced that it had found strong evidence that liquid water, probably mixed with perchlorinated salts, flows intermittently across the surface of Mars. [ 70 ]
In December 2013 it was announced the possibility that about 3.6 billion years ago, in the so-called Yellowknife Bay, in Gale crater, near the planet's equator, there would have been a freshwater lake that could harbor some type of microbial life . [ 71 ]
The possibility that there is water on Mars is conditioned by several physical aspects. The boiling point depends on the pressure and if this is excessively low, the water cannot exist in a liquid state. That is what happens on Mars: if the planet had abundant water courses it was because it also had a much denser atmosphere that also provided higher temperatures. As most of that atmosphere dissipated into space, thus lowering the pressure and lowering the temperature, the water disappeared from the surface of Mars. However, it subsists in the atmosphere, in a state of vapor, although in scant proportions, as well as in the polar caps, made up of great masses of perpetual ice.
Everything allows us to suppose that there is frozen water between the grains of the soil, a phenomenon that, moreover, is common in very cold regions of the Earth. Lobe-shaped formations are observed around certain Martian craters, the formation of which can only be explained by admitting that the soil of Mars is frozen. There are also photographs of another type of relief accident perfectly explained by the existence of a gelisuelo . It is about a subsidence of the ground from whose depression a dry riverbed starts with the imprint of its arms separated by banks of alluvium.
It is also found on crater walls or in deep valleys where sunlight never falls, accidents that look like ravines formed by torrents of water and the deposits of earth and rocks transported by them. They only appear at high latitudes in the southern hemisphere.
Comparison with terrestrial geology suggests that it is the remnants of a surface water supply similar to an aquifer. In fact, the Mars Reconnaissance Orbiter probe has detected large buried glaciers with stretches of dozens of kilometers and depths of the order of a kilometer, which extend from the cliffs and the slopes of the mountains and which are found at latitudes lower than that. expected. That same probe has also discovered that the northern hemisphere of Mars has a greater volume of icy water. [ 72 ]
Another proof in favor of the existence of large amounts of water in the Martian past, in the form of oceans that covered a third of the planet, has been obtained by the gamma ray spectrometer of the Mars Odyssey probe , which has delimited what which appear to be the coastlines of two ancient oceans. [ 73 ]
Martian water also subsists in the planet's atmosphere, although in such a tiny proportion (0.01%) that, if it were completely condensed on the surface of Mars, it would form a liquid film on it whose thickness would be approximately one hundredth of a millimeter. Despite its scarcity, this water vapor participates in an annual cycle. On Mars, the atmospheric pressure is so low that water vapor solidifies on the ground, in the form of ice, at a temperature of –80 ° C. When the temperature rises above that limit again, the ice sublimates, turning into vapor without going through the liquid state.
The surface of the planet presents various types of permanent formations, among which the easiest to observe are two large white spots located in the polar regions, a kind of polar caps of the planet. When the cold season arrives, the perpetual ice store begins to be covered with a layer of frost due to the condensation of atmospheric water vapor. Then, as the temperature continues to drop, the frozen water disappears under a blanket of dry ice that surpasses the polar cap, sometimes exceeding the parallel of 60 °. This is so because part of the CO 2 atmosphere is frozen. Reciprocally in the opposite hemisphere, spring causes the temperature to rise above –120 ° C, which causes the sublimation of dry ice and the retreat of the polar cap; then, when the thermometer rises above –80 ° C, the frost in turn sublimates; then only permanent ice remains, but the cold is returning and these will not undergo significant ablation.
The perpetual ice mass is about 100 km in diameter and about 10 m thick. So the polar caps are made up of a very thin layer of CO 2 ice ("dry ice") and perhaps underneath the southern cap there is water ice. In one hundred years of observation, the South polar cap has disappeared twice completely, while the North has never done so.
The polar caps show a layered structure with alternating layers of ice and varying amounts of dark dust.
The total mass of ice in the North Polar Cap is equivalent to half the ice that exists in Greenland . In addition, the ice at the North Pole of Mars sits on a large depression in the ground and is covered by "dry ice."
On June 19, 2008, NASA claimed that the Phoenix probe must have found ice while digging near the North Pole of Mars. Chunks of material sublimated after being discovered on June 15 by a robot arm . [ 75 ] [ 76 ]
On July 31, 2008, NASA confirmed that one of the Martian soil samples introduced into one of the furnaces of the TEGA ( Thermal and Evolved-Gas Analyzer ), an instrument that is part of the probe, contained water ice. [ 77 ]
Geysers at the South Pole
During 1998-1999 NASA's Mars Global Surveyor orbital system detected dark patches in the dunes of the South Pole ice sheet, between latitudes 60 ° -80 °. The peculiarity of these spots is that 70% of them recur annually in the same place of the previous year. Dune spots appear at the beginning of each spring and disappear at the beginning of each winter, which is why a team of scientists from Budapest has proposed that these spots could be of a biological origin and of a extremophilic nature . [ 78 ] [ 79 ]
For its part, NASA has concluded that the spots are the product of cold eruptions of geysers , which are powered not by geothermal energy but by solar energy. NASA scientists explain that sunlight heats the interior of polar ice and sublimates it to a maximum depth of one meter, creating a network of horizontal tunnels with carbon dioxide gas (CO 2 ) under pressure. Eventually, the gas escapes through a fissure and carries basalt sand particles to the surface. [ 80 ] [ 81 ] [ 82 ] [ 83 ] [ 84 ]
There is still insufficient data on Martian thermal evolution. Because Mars is much further from the Sun than Earth, its climates are colder, and all the more so because the atmosphere, being so thin, retains little heat: hence the difference between daytime and nighttime temperatures is more pronounced than on our planet. The low thermal conductivity of Martian soil also contributes to this.
The surface temperature depends on the latitude and exhibits seasonal variations . The average surface temperature is about 218 K (–55 ° C). The diurnal variation of temperatures is very high as corresponds to such a thin atmosphere. Daytime highs, at the equator and in summer, can reach 20 ° C or more, while nighttime lows can easily reach –80 ° C. In the polar caps, in winter temperatures can drop to –130 ° C [ citation needed ] .
Huge dust storms can suddenly arise, persisting for weeks and even months, darkening the entire planet, caused by winds of more than 150 km / h. and they can reach planetary dimensions.
During a Martian year, part of the CO 2 in the atmosphere condenses in the hemisphere where it is winter, or sublimates from the pole to the atmosphere when it is summer. Consequently the atmospheric pressure has an annual variation.
Seasons on Mars
As on Earth, the Martian equator is inclined with respect to the plane of orbit at an angle of 25.19 °. Spring begins in the Northern Hemisphere on the vernal equinox when the Sun passes through the Vernal point passing from the Southern Hemisphere to the North (Ls = 0 and growing). In the case of Mars this also makes a climatic sense. Days and nights last the same and spring begins in the Northern Hemisphere. This lasts until Ls = 90 ° summer solstice in which the day has a maximum duration in the Northern hemisphere and minimum in the South.
Similarly, Ls = 90 °, 180 °, and 270 ° indicate for the northern hemisphere the summer solstice , autumnal equinox, and the winter solstice, respectively, while in the southern hemisphere it is the other way around. Since the length of the Martian year is roughly twice that of the Earth year, so is the length of the seasons.
The difference between their durations is greater because the eccentricity of the Martian orbit is much greater than that of the Earth. Comparison with ground stations shows that, just as their duration differs by at most 4.5 days (eccentricity of less than 2%), on Mars, due to the great eccentricity of the orbit, the difference reaches be initially 51 days (eccentricity of almost 10%).
Currently the Northern Hemisphere enjoys a milder climate than the Southern Hemisphere. The reason is obvious: the Northern Hemisphere has short autumns and winters and also when the Sun is in perihelion which, given the eccentricity of the planet's orbit, makes them more benign. In addition, spring and summer are long, but being the Sun in the aphelion they are colder than those of the Southern hemisphere. For the southern hemisphere the situation is the reverse. There is thus a partial compensation between both hemispheres due to the fact that the seasons of less duration take place with the planet in perihelion and it receives more light and heat from the Sun. Due to the retrogradation of the Vernal point and the advance of the perihelion, the situation goes away decanting more and more.
Martian weather in the past
There is a great debate regarding the past history of Mars. For some, Mars once housed large amounts of water and had a warm past, with a much denser atmosphere, and water flowing through the surface and excavating the great channels that furrow its surface.
The orography of Mars presents a northern hemisphere that is a great depression and where the supporters of wet Mars place the Oceanus Borealis , a sea whose size would be similar to the Mediterranean Sea .
The water in the Martian atmosphere has five times more deuterium than that of Earth. [ 85 ] [ 86 ] This anomaly, also registered in Venus, is interpreted as the two planets had much water in the past but ended up losing it , because water is heavier more likely to remain on the planet and not get lost in space.
The recent discoveries of the NASA Opportunity robot support the hypothesis of a wet past.
At the end of 2005, the controversy arose about the interpretations given to certain rock formations that required the presence of water, proposing an alternative explanation that reduced the need for water to much smaller quantities and reduced the great sea or equatorial lake to a simple pond where never had there been more than a foot of salt water. Some scientists have criticized the fact that NASA only investigated in one direction looking for evidence of a wet Mars and discarding the other hypotheses.
Thus, we would have three eras on Mars. During the first 1000 million years a Mars heated by an atmosphere that contained sufficient greenhouse gases for water to flow over the surface and form clays, the Noeic era , which would be the ancient stronghold of a humid Mars and capable of harboring lifetime. The second era lasted from 3800 to 3500 million years and in it climate change occurred. The most recent and longest era, lasting almost the entire history of the planet and stretching from 3.5 billion years to the present, with a Mars as we know it today, cold and dry. [ citation required ]
In summary, the paradigm of a wet Mars that would explain the orographic features of Mars is giving way to the paradigm of a dry and cold Mars where water has had a much more limited importance.
Translation and rotation
The average distance between Mars and the Sun is approximately 230 million kilometers, and its orbital period is 687 Earth days. Mars' solar day is only slightly larger than Earth's — 24 hours, 39 minutes, and 35.244 seconds. [ 87 ] A year on Mars equals 1.8809 Earth years, or 1 year, 320 days, and 18.2 hours. [ 21 ]
The axial tilt of Mars is 25.19 ° with respect to its orbital plane , similar to the axial tilt of the Earth. [ 21 ] Consequently, Mars has stations like Earth, although there they are almost twice as long because their orbital period is much longer. At present, the orientation of the Martian north pole is similar to that of the star Deneb . [ 88 ]
Mars has a relatively pronounced orbital eccentricity of approximately 0.09 [ 89 ] between its aphelion and its perihelion , the planet's distance from the Sun differs by about 42.4 million kilometers. Of the remaining planets in the solar system, only Mercury has a higher orbital eccentricity. This effect has a great influence on the Martian climate; the difference in distances from the Sun causes a temperature variation of about 30 ° C at the subsolar point between aphelion and perihelion. Thanks to the excellent observations of Tycho Brahe , Keplerhe realized this separation and came to discover the elliptical nature of planetary orbits, previously considered circular. It is known that in the past the orbit of Mars was much more circular. 1.35 million Earth years ago, the orbital width of Mars was just 0.002, much lower than that of Earth today. [ 90 ]
Distance between Mars and Earth
The distance between Mars and Earth varies according to their relative positions. The greatest distances, of about 399 million kilometers, occur when the planets are in conjunction , that is, the sun is between them. The apparent diameter of Mars is small, only about 3.5 ″. The shortest distances, between 90 and 56 million kilometers, occur in an interval of ± 8½ days with respect to the opposition between them. [ 91 ] When the distance is less than 60 million kilometers, the apparent diameter of Mars is 25 ″, reaching a magnitude of –2.8, making it the brightest planet with the exception of Venus.. Given the smallness of the Martian globe, its telescopic observation is of particular interest between the periods preceding and following the oppositions.
On August 27, 2003, Mars made its closest approach to Earth in approximately 60,000 years , at just 55.76 million km. The last time it had been this close, according to the calculations of the Italian astronomer Dr. Aldo Vitagliano, was in the year 57 617 BC. C. , and the next time that Mars is closer than it was in 2003 will be on August 28, 2287.
In general, in its orbits around the Sun, the Earth overtakes Mars once every 780 days (26 months). The last Mars oppositions took place on April 8, 2014 [ 92 ] , on May 22, 2016, and on July 27, 2018. The shortest distance between the planets for this opposition was 57.28 million kilometers and It happened five days later, on July 31, 2018.
It is known exactly how long the rotation of Mars takes because the dark and well-defined spots on its surface are excellent points of reference. They were first observed in 1659 by Christiaan Huygens who assigned the duration of one day to their rotation. In 1666 , Giovanni Cassini set it at 24 h 40 min, a value very close to the true one. Three hundred years of observations of Mars have resulted in establishing the value of 24 h 37 min 22.7 s for the sidereal day (the period of rotation of the Earth is 23 h 56 min 4.1 s). Mars rotates counterclockwise, just like Earth . [ 93 ]
From the length of the sidereal day it follows that the solar day on Mars has a duration of 24 h 39 min 35.3 s . The mean solar day or time between two consecutive passes of the mean Sun through the meridian of the place, lasts 24 h 41 min 18.6 s . The solar day on Mars has, like that of the Earth , a variable duration. However, on Mars the variation is greater due to its high eccentricity.
For greater operational convenience, those responsible for the US missions to explore Mars using robotic probes have unilaterally decided to name the Martian day the sun , despite having other meanings in other languages ("ground" in French, or the name of our star in Spanish).
The Martian year lasts 1 year, 321 days and 7 Earth hours, or 668.6 Martian days .
The poles of Mars are marked by two dazzling white polar caps, which have greatly facilitated the determination of the angle that the planet's equator forms with the plane of its orbit, an angle equivalent for Mars to the obliquity of the ecliptic on Earth . The measurements made by Camichel on photographs obtained by the French Pic du Midi observatory , have given for this angle 24 ° 48 ′. From space exploration a value of 25.19 ° is accepted [ citation needed ] , a little higher than the obliquity of the ecliptic (23 ° 27 ′), which is why Mars has seasonal periods similar to those of Earth, although its seasons are longer, since a Martian year is almost twice as long as an Earth year .
Synodic orbital period
It is the period of your synodic cycle or period that elapses between two oppositions with the Earth. The average is 779.96 days or 780 days (practically 111 weeks) during which the Earth makes two orbits and 14% of another, and Mars one and 14% of another. This is the average of 7 intervals of 7 examinations every 14.9 years (15 years minus 2 weeks). The intervals are irregular, which is due to the fact that the Martian orbit is very eccentric, with which its speed of translation is highly variable and each step of the Earth in front of Mars (opposition of Mars seen from Earth) occurs with weeks early or late. The difference between the maximum and minimum duration of your synodic cycles becomes practically 6 weeks, plus a synodic cycle of the Moon.
The synodic period of Mars is used in Mayan astronomy in relation to two cycles: the Tzolkin and the Ahau. The period is equivalent to three cycles of 260 days, which in Mayan terms are 3 Tzolkin, called the 'Sacred Calendar'. Also, one of the sub-cycles of the Mayan cycle is the Ahau of 93,600 days (360 Tzolkin) which are exactly 120 periods of 780 days, that is, 120 synodic cycles of Mars. In turn, the Ahau is the 20th part of the Long Count (5th part of the complete cycle and 1800 Tzolkin) with which each Long Count is equivalent to 2,400 synodic cycles. In turn, the Long Count is the 5th part of the Mayan cycle, with which during this —100 Ahau cycles— 12,000 synodic cycles of Mars occur.
Mars has two small natural satellites, called Phobos and Deimos , whose orbits are very close to the planet. They are believed to be two captured asteroids. Both were discovered in 1877 by Asaph Hall .
Their names were put in honor of the two characters from Greek mythology that accompanied Ares (Mars for Roman mythology).
From the surface of Mars, Deimos, the farthest and smallest, rises in the East like the Moon. However, Phobos, larger and closer, moves around the planet faster than the planet itself rotates. For this reason it appears in the west, moves comparatively quickly across the sky (in 4 hours 15 minutes or less) and sets in the east, approximately twice for each Martian day (every 11 hours and 6 minutes). .
Mars has, like Jupiter , some Trojan asteroids at Lagrange points L4 and L5; The three asteroids officially recognized by the International Astronomical Union and the Minor Planet Center are: 5261 Eureka , 101429 VF31 and 121514 UJ7 . The following Trojan asteroids have also been discovered on Mars: 1999 UJ7 (at point L 4), 1998 VF31, 2001 DH47, 2001 FG24, and 2001 FR127 (at point L 5). The coorbital asteroids 1998 QH56 and 1998 SD4 are not considered Trojans because they are not stable and will be pulled away by the gravitation of Mars in the next 500,000 years.
Current theories that predict the conditions in which life can be found require the availability of water in a liquid state, which is why your search is so important. A study published in 2015 by NASA concluded that 4.3 billion years ago and for 1.5 billion years, [ 94 ] the planet had an extensive ocean in the northern hemisphere, [ 95 ] with a volume greater than that of the Arctic, [ 96 ] enough to cover the entire Martian territory with a depth of 130 m. [ 97 ]
2003 were detected in trace gas methane in the atmosphere of Mars [ 98 ] [ 99 ] [ 100 ] [ 101 ] [ 102 ] , which is considered a mystery, since under atmospheric conditions of Mars and From solar radiation , methane is unstable and disappears after several years, which would indicate that there must be a methane-producing source on Mars that maintains that concentration in its atmosphere and that produces a minimum of 150 tons of methane each year. [ 103 ] [104 ] The Mars Science Laboratory probe(known by its nickname "Curiosity") includes a mass spectrometer that seeks to measure the difference between 14 C and 12 C to determine whether methane is of biological or geological origin. [ 105 ]
However, in the past liquid water existed in abundance and a denser and more protective atmosphere; These are the conditions that are believed to be most favorable for life on Mars to have developed. The ALH84001 meteorite , which is considered to originate from Mars, was found in Antarctica in December 1984 by a group of researchers from the ANSMET project and some researchers believe that the regular forms could be fossilized microorganisms . [ 106 ] [ 107 ] [ 108 ]
Christiaan Huygens made the first observations of dark areas on the surface of Mars in 1659 and was also one of the first to detect the polar caps. Other astronomers who contributed to the study of Mars were G. Cassini (calculated in 1666 the rotation of the planet in 24 hours and 40 minutes and in 1672 deduced the existence of an atmosphere on the planet), W. Herschel (discovered the obliquity of the axis of rotation of Mars and observed Martian clouds), and J. Schroeter.
The year 1877 Mars presented a position very close to Earth, which is why it was a key year for studies of the planet. The American astronomer A. Hall discovered the satellites Phobos and Deimos , while the Italian astronomer G. Schiaparelli carefully mapped Mars; Indeed, today, the nomenclature invented by him is used for the names of the Martian regions (Syrtis Major; Mare Tyrrhenum; Solis Lacus, etc.). Schiaparelli also believed he observed fine lines on Mars, which he named canali 'canals'.
However, this last word was translated into English as canals , a word that implies something artificial, which sparked the imagination of many people, especially those of the astronomer C. Flammarion and the aristocrat P. Lowell . These were dedicated to speculating with the possibility of life on Mars, the Martians . Lowell was so enthusiastic about this idea that he built his own observatory in Flagstaff in 1894., Arizona, to study the planet. His observations convinced him that there was not only life on Mars, but that it was intelligent life: Mars was a planet that was drying up and a wise ancient Martian civilization had built those canals to drain water from the polar ice caps and send it towards the thirsty ice caps. cities.
However, the great Barcelona astronomer Josep Comas i Solà , based on his own observations, was one of the first prestigious astronomers in the world who defended that in reality the Martian channels of Schiaparelli did not exist. First in scientific articles such as the one published in 1901 in the Bulletin de la Société Astronomique de Franceand later also in newspaper articles, such as the one published on August 16, 1903 in the Barcelona newspaper La Vanguardia, where he said: «(…) It is useless, then, that we waste time torturing our imagination, looking for hypotheses that give us a more or less satisfactory account of the channels of Mars. These, at least in the sense in which they had been accepted until now, do not exist. There will be details that in their general lines will offer a certain geometric aspect, but we already observe this on our own planet, and it obeys only natural laws, be they geological, mechanical, crystallographic, etc., without human work intervening in it at all (... ) ». Later, the other great astronomer who also refuted the existence of the canals,Eugène Antoniadi .
With the passage of time the fury of the Martian channels was dissipating, since many astronomers could not even see them; in fact, the canals were an optical illusion. By the 1950s, hardly anyone believed in Martian civilizations, but many were convinced that there was indeed life on Mars in the form of primitive mosses and lichens, a fact that was questioned when Mars was first visited by a spacecraft in 1965.
The first probe to visit Mars was the Soviet Mars 1 , which passed 193,000 km from Mars on June 19, 1963, without being able to send information.
The Mariner 4 in 1965 would be the first to broadcast from nearby. Together with the Mariner 6 and 7 that arrived at Mars in 1969 they only managed to observe a Mars full of craters and similar to the Moon . Was the Mariner 9 the first probe got placed in Martian orbit. She made observations in the middle of a spectacular dust storm and was the first to glimpse a Mars with channels that looked like water networks, water vapor in the atmosphere, and that suggested a different Mars past. The first spacecraft to land and transmit from Mars was the Soviet Mars 3 , which touched down at 45 ° S and 158 ° W at 13:50:35 GMT.of December 2, 1971. Later the Viking 1 and Viking 2 would do it in 1976 . NASA concluded the results of its biological experiments as negative.
The 4 as July as 1997 's Mars Pathfinder landed successfully on Mars and proved that it was possible for a small robot pasease the planet. In 2004 a more scientifically ambitious mission led two robots, Spirit and Opportunity , which landed on two diametrically opposite parts of Mars to scan rocks for water, finding evidence of an ancient sea or salt lake.
The European Space Agency ( ESA ) launched the Mars Express probe in June 2003 , which is currently orbiting Mars. To this last artificial satellite of Mars is added the NASA spacecraft Mars Odyssey , in orbit around Mars since October 2001 . The NASA launched the August 12, 2005 the probe Mars Reconnaissance Orbiter , which reached Mars orbit on March 10 of 2006 and its main objectives the search for water, past or present, and the study of climate.
The 25 of maypole of 2008 the probe Phoenix landed near the north pole of Mars; Its primary objective was to deploy its robotic arm and make surveys at different depths to examine the subsurface, determine if there was or could be life on Mars , characterize the climate of Mars , study the geology of Mars and carry out studies of the geological history of water , key factor to decipher the past of the planet's climatic changes.
On November 26, 2011, the Mars Science Laboratory (abbreviated MSL), known as Curiosity , was launched . It is a space mission that includes a NASA -led Martian exploration spacecraft that focuses on placing a rover- type rover on the Martian surface.. This vehicle will be three times heavier and twice as large as the vehicles used in the Mars Exploration Rover mission, which landed on Mars in 2004, and will carry the most advanced scientific instruments. The international community will provide some of these instruments and it is planned to launch it via an Atlas V 541 rocket. After landing, the rover will take dozens of samples of Martian soil and rocky dust for analysis. The duration of the mission will be 1 Martian year (1.88 Earth years), and with a range of exploration higher than those previously sent, it will investigate the past and present capacity of Mars to host life. [ 109 ]
On August 6, 2012, eight months after its launch, Curiosity landed on the surface of Mars, specifically in Gale crater , after going through the so-called 7 minutes of panic , a period of time during which Curiosity passed through the atmosphere of Mars and during which the technical team in charge of supervising the trip could not do anything, due to the 14-minute delay experienced by the signals emitted by the rover before reaching Earth from Mars. [ 110 ]
Since 2008 NASA maintains a catalog of 57 meteorites considered to have come from Mars and recovered in various countries. [ 111 ] These are extremely valuable as they are the only physical samples from Mars available for analysis. The three meteorites listed below exhibit characteristics that some researchers consider indications of possible natural organic molecules or probable microscopic fossils :
The ALH84001 meteorite was found in Antarctica in December 1984 by a group of researchers from the ANSMET project and weighs 1.93 kg. [ 112 ] Some researchers assume that the regular forms could be fossilized microorganisms , similar to nanobios or nanobacteria . [ 106 ] [ 107 ] [ 108 ] It has been detected content of magnetite on Earth is only on certain microorganisms. 
A team from NASA , from the Johnson Space Center division, obtained a small sample of this meteorite in March 1998, which was analyzed by means of optical microscopy and an electron microscope and other techniques to determine its content; the researchers observed spherical particles of homogeneous size. [ 116 ] They also performed gas chromatography and mass spectrometry (GC-MS) analyzes to study aromatic hydrocarbons.high molecular weight. In addition, "cellular structures and exopolymeric secretions" were identified inside. NASA scientists concluded that "at least 75% of organic material cannot be terrestrial pollution." [ 113 ] [ 117 ]
This caused additional interest so in 2006, NASA requested a larger sample of the Nakhla meteorite from the Natural History Museum in London. In this second specimen, a high carbon content was observed in the form of branches. When the respective images were published in 2006, a debate was opened by independent researchers considering the possibility that the charcoal is of biological origin. However, other researchers have emphasized that carbon is the fourth most abundant element in the Universe , so finding it in curious shapes or patterns does not suggest the possibility of biological origin. [ 118 ] [ 119 ]
The Shergotty meteorite , of Martian origin and with a mass of 4 kg, fell in Shergotty, India on August 25, 1865 , where it was immediately recovered by witnesses. [ 120 ] It is composed of pyroxene and is estimated to have been formed on Mars 165 million years ago, and was exposed and transformed by liquid water over many years. Certain characteristics of this meteorite suggest the presence of remains of membranes or films of possible biological origin, but the interpretation of its mineralized forms varies. [ 113 ]
Astronomy from Mars
Viewed from Mars, the Sun has an apparent diameter of 21 ′ (instead of 31.5 ′ to 32.6 ′ seen from Earth). The scientists who piloted Spirit and Opportunity had it observe a sunset. It was observed how the Sun disappears hidden among the dust suspended in the atmosphere .
Observation of satellites
Mars has two tiny satellites , two rocks of irregular shape: Phobos which measures 27 x 21 x 19 km ; and orbits the planet 6100 km above its surface; and Deimos , which measures 15 x 12 x 11 km , and orbits at an altitude of 20,000 km .
Despite being so close together, these satellites are only visible in the Martian sky as very bright points of light. The brightness of Deimos can be comparable to that of Venus seen from Earth ; that of Phobos is several times more intense.
Phobos goes around Mars in 7 hr 39 min 14 s . As its revolution is much faster than the rotation of the planet on itself, it seems as if the satellite described a retrograde movement : it is seen sunrise in the West and set in the East . Deimos spends 30 h 17 min 55 s traveling its orbit . His revolution is therefore a little longer than the rotation of the planet, which makes the satellite move slowly in the sky: it takes 64 hours between its departure, in the East, and its setting, in the West. The most curious thing is that during that time in which it remains visible , it develops the complete cycle of its phases twice. Another peculiarity of these satellites is that, because they gravitate in the equatorial plane of the planet and so close to its surface, they are totally invisible from the polar regions : Deimos cannot be seen from above the 82 ° parallel and Phobos from latitudes over 69 °. Given its small dimensions, these tiny satellites can barely dispel the darkness of the Martian night, and this for short periods, since, gravitating so close to the planet and in equatorial orbits, they spend most of the night hidden in the cone of shadow projected by the planet, that is, without being illuminated by sunlight .
Phobos has been observed to undergo a secular acceleration that slowly brings it closer to the planet's surface (so slowly that it may still be a hundred million years before it falls). This acceleration is produced by the effect of the tides . It also raises the astronomers the problem of the origins of those little stars , as opposed to certain reasons that are asteroids captured and other bodies to be formed around the planet at the same time as him. In addition, Phobos has characteristics that suggest that this satellite may be a separate fragment of another larger star.
Observation of solar eclipses
|Eclipses between Phobos , Deimos and the Sun , as seen by Opportunity on March 10, 2004 Phobos (left) and March 4, 2004 Deimos (right)|
The cameras ship Opportunity captured the October to March of 2004 the eclipse partial sun caused by the satellite Phobos . The satellite covers a large part of the Sun because it is larger than Deimos and orbits much closer to Mars. The Deimos eclipse captured on March 4 , 2004 is comparable to a transit of a planet .
Seen from Mars by future astronauts, the Earth would be a magnificent blue star and as bright as Jupiter is seen from Earth, at least during the favorable periods (lower conjunctions of the Earth), since our globe will present, seen from Mars, the same phases as Venus seen from Earth . Also, the same as Venus and Mercury , the Earth is a star alternately morning and evening. With a telescopeinstalled on Mars, the spectacle resulting from the conjugation of the movements of the Earth and the Moon, as well as the combination of the phases of both stars, could be appreciated: passage of the half moon over the dark half of the Earth's disk; passage of the Earth-Moon system before the solar disk during eclipses .
Transits of the Earth through the solar disk
On 10 November of the 2084 , will take place next transit of Earth by the solar disk as seen from Mars. These transits repeat approximately every 79 years. The October-November transits occur when the planet Mars is in opposition and close to the ascending node ; the transits of April-May, when it is in the descending node. The transit of the November of maypole of 1984 , provided by J. Meeus , served as inspiration for the writer Arthur C. Clarke to write thirteen years in advance (1971), his account Transit of Earth , in which an astronautabandoned on Mars describes the rare astronomical phenomenon, shortly before dying due to lack of oxygen . [ citation required ]
Origin of the name of the planet Mars
Mars was the Roman god of war , and his Greek equivalent was called Ares . The red color of the planet Mars, related to blood , favored its being considered since ancient times as a symbol of the god of war. Mars is sometimes referred to as the Red Planet . The star Antares , close to the ecliptic in the constellation of Scorpio , receives its name as a rival (ant-) of Mars, due to its similar brightness in some of its approaches.
Presence in literature
In addition to the aforementioned Transit of Earth , there are numerous references to Mars in science fiction, such as:
- Martian Chronicles , by R. Bradbury , where humans, tired of wars and pollution on Earth, decide to colonize Mars;
- Homo Plus , by Frederik Pohl . Terrestrial astronauts are genetically altered to survive on the hostile surface of Mars;
- Mars trilogy : Red Mars , Green Mars and Blue Mars of Kim Stanley Robinson . Trilogy of novels in which the colonization and terraforming of Marsis narrated, in a realistic way,along with the technological, social and philosophical implications that this would entail for humanity;
- Martian series: A Princess from Mars , The Gods of Mars , The Warrior of Mars , Thuvia, the Maiden of Mars and The Living Chess of Mars , by Edgar Rice Burroughs . The creator of Tarzan recounts the adventures of John Carter on the planet Mars;
- Several novels and stories by Philip K. Dick take place on Mars, such as Time for Mars or We Can Remember It For You Wholesale ;
- Venus Prime 3: Arthur C. Clarke's hide and seek game . The action moves to the planet Mars and its moon Phobos after the Martian plate located in the Martian city of Labyrinth City was stolen.
- The Martian , by Andy Weir . Six astronauts are on the surface of Mars when their mission is canceled due to a sandstorm too strong for the vehicle that will take them off the planet to remain intact. An antenna downed by the storm makes one of the astronauts disappear and the mission commander has to abandon him to save the rest of the team.
- Mars exploration
- Landing on Mars
- Annex: Artificial satellites of Mars
- Annex: Artificial objects on Mars
- Mars geological time scale
- Satellites of mars
- Mars Flag
- Colonization of Mars
- Terraforming of Mars
- Manned trip to Mars
- Life on mars
- Annex: Planets of the solar system
- Annex: Data of the planets and rounded objects of the solar system
- History of Mars Observation
- Astronomy on Mars
- The earth
- is popularly known as "links" to the apparent paths with a loop that describe the planets when they are overwhelmed by the Earth (see image of the "loop" in reference 2010) [ 23 ]
- " Mars: By the Numbers Archived October 3, 2015, at the Wayback Machine ." In Solar System Exploration , NASA . Retrieved October 2, 2015.
- "They detect oxygen reserves on Mars that could support microbes" . Trade. EFE. October 22, 2018 . Retrieved October 23, 2018 .
- Zubrin, Robert; Wagner, Richard (1997). Touchstone, ed. The Case for Mars: The Plan to Settle the Red Planet and Why We Must. Nueva York. ISBN 978-0-684-83550-1.
- Martin Rees, ed. (2012). Universe: The Definitive Visual Guide. Nueva York: Dorling Kindersley. pp. 160-161. ISBN 978-0-7566-9841-6.
- Science @ NASA (March 28, 2001). "The Lure of Hematite" (in English) . Retrieved October 12, 2016 .
- Millis, John P. (April 27, 2016). "Mars Moon Mystery" (in English) . Retrieved October 12, 2016 .
- Adler, M .; Owen, W .; Riedel, J. (June 12, 2012). "Use of Optical Navigation Camera MRO to Prepare for Mars Sample Return ' (in English) . Retrieved October 12, 2016 .
- Yeager, Ashley (June 25, 2008). "Impact May Have Transformed Mars" (in English) . Retrieved October 12, 2016 .
- Sample, Ian (June 26, 2008). "Cataclysmic impact created the north-south divide on Mars" (in English) . Retrieved October 12, 2016 .
- Nahum Mendez Chazarra. Una (Breve) Geología de Marte Journal of Feelsynapsis (JoF). . 2012.(2): 34-41
- Jarrell, Elizabeth M. (February 26, 2015). "Using Curiosity to Search for Life" . Mars Daily (English) . Retrieved October 13, 2016 .
- NASA (November 2013). "The Mars Exploration Rovers: Spirit and Opportunity" (in English) . p. 20. Archived from the original on October 10, 2015 . Retrieved October 13, 2016 .
- Wilks, Jeremy (May 21, 2015). "Mars mystery: ExoMars mission to finally resolve question of life on red planet" . EuroNews (English) . Retrieved October 13, 2016 .
- Howell, Elisabeth (January 5, 2015). « " Life on Mars? NASA's next rover aims to find out. " . The Christian Science Monitor (in English) . Retrieved on October 13, 2016 .
- Webster, Guy. Jones, Nancy Neal. Brown, Dwayne (February 11, 2012). "NASA Rover Finds Clues to Changes in Mars 'Atmosphere' (in English) . Retrieved October 13, 2016 .
- "Mars: By the Numbers" . Archived from the original on October 7, 2016 . Retrieved October 13, 2016 .
- Heldmann, J. L.; Toon, O. B.; Pollard, W. H.; et al. (7 de mayo de 2005). «Formation of Martian gullies by the action of liquid water flowing under current Martian environmental conditions». Journal of geophysical Research. doi:10.1029/2004JE002261. Consultado el 13 de octubre de 2016.
- Kostama, W. -P; Kreslavsky, M. A.; Head, J. W. (3 de junio de 2006). «Recent high-latitude icy mantle in the northern plains of Mars: Characteristics and ages of emplacement». Geophysical Research Letters 33. doi:10.1029/2006GL025946.
- Byrne, Shane; Ingersoll, Andrew P. (14 de febrero de 2003). «A Sublimation Model for Martian South Polar Ice Features». Science 299: 1051-1053. doi:10.1126/science.1080148.
- "Mars' South Pole Ice Deep and Wide" . NASA (in English) . March 15, 2007 . Retrieved October 13, 2007 .
- Williams, David R. "Mars Fact Sheet" . National Space Science Data Center. NASA (in English) . Retrieved October 13, 2016 .
- "The Red Planet: A Survey of Mars" . Lunar and Planetary Institute . Retrieved October 13, 2016 .
- "Astronomy Picture of the Day ' (in English) . Retrieved September 22, 2010 .
- «Academic | Digital Community of Knowledge » . academica.mx . Retrieved November 19, 2019 .
- David R. Williams (April 19, 2016). "Mars Fact Sheet" . National Space Science Data Center. NASA (in English) . Retrieved October 21, 2016 .
- "Mars" .
- Mark Peplow (May 6, 2004). "How Mars got its rust . " Nature . doi : 10.1038 / news040503-6 . Retrieved October 21, 2016 .
- NASA. "Mars in a Minuteː Is Mars Really Red?" (in English) . Archived from the original on October 22, 2016 . Retrieved October 21, 2016 .
- Nimmo, Francis; Tanaka, Ken (29 de noviembre de 2004). «Early crustal evolution of Mars». Annual Review of Earth and Planetary Sciences 33: 133-161. doi:10.1146/annurev.earth.33.092203.122637.
- Rivoldini, A.; Van Hoolst, T.; Verhoeven, O.; Mocquet, A.; Dehant, V. (Junio de 2011). «Geodesy constraints on the interior structure and composition of Mars». Icarus 213 (2): 451-472. doi:10.1146/annurev.earth.33.092203.122637. Consultado el 24 de octubre de 2016.
- Dave, Jacqué (September 26, 2003). "APS X-rays Reveal Secrets of the Martian Core" . Argonne National Laboratory . Retrieved October 24, 2016 .
- McSween, Harry Y. Jr; Taylor, G. Jeffrey; Wyatt, Michael B. (mayo 2009). Science, ed. Elemental Composition of the Martian Crust. 324 (5928). pp. 736-739. Bibcode:2009Sci...324..736M. doi:10.1126/science.1165871.
- Bandfield, Joshua L. (Junio de 2002). «Global mineral distributions on Mars». Journal of Geophysical Research: Planets 107 (E6): 9-1. Bibcode:2002JGRE..107.5042B. doi:10.1029/2001JE001510.
- Christensen, Philip R.; et al. (27 de junio de 2003). «Morphology and Composition of the Surface of Mars: Mars Odyssey THEMIS Results». Science 300 (5628): 2056-2061. PMID 12791998. doi:10.1126/science.1080885. Consultado el 19 de diciembre de 2016.
- Golombek, Matthew P. (27 de junio de 2003). «The Surface of Mars: Not Just Dust and Rocks». Science 300 (5628): 2043-2044. PMID 12829771. doi:10.1126/science.1082927. Consultado el 19 de diciembre de 2016.
- Valentine, Theresa. "Magnetic fields and Mars" . Mars Global Surveyor (in English) . NASA . Retrieved December 19, 2016 .
- Neal-Jones, Nancy; Cynthia O'Carroll (December 5, 20101). "New Map Provides More Evidence Mars Once Like Earth" . NASA Goddard Space Flight Center (in English) . Retrieved December 19, 2016 .
- Halliday, A. C. H., Birck, J. L. et al., A.; Wänke, H.; Birck, J. L.; Clayton, R. N.; et al.. «The Accretion, Composition and Early Differentiation of Mars». Space Science Reviews 96 (1/4). Bibcode:2001SSRv...96..197H. doi:10.1023/A:1011997206080.
- Zharkov, V. N. (1993). «The role of Jupiter in the formation of planets.». Evolution of the Earth and planets: 7-17. Bibcode:1993GMS....74....7Z. doi:10.1029/GM074p0007.
- Lunine, Jonathan I.; Chambers, John; Morbidelli, Alessandro; Leshin, Laurie A. (septiembre de 2003). «The origin of water on Mars». Icarus 165 (1): 1-8. Bibcode:2003Icar..165....1L. doi:10.1016/S0019-1035(03)00172-6.
- JR Minkel (June 25, 2008). "Giant Asteroid Flattened Half of Mars, Studies Suggest" . Scientific American (in English) . Retrieved December 19, 2016 .
- Chang, Kenneth (June 26, 2008). "Huge Meteor Strike Explains Mars's Shape, Reports Say" . The New York Times . Retrieved December 19, 2016 .
- Tanaka, K. L. (30 de noviembre de 1986). «The Stratigraphy of Mars». Journal of Geophysical Research 91 (B13): E139-E158. Bibcode:1986JGR....91..139T. doi:10.1029/JB091iB13p0E139.
- Mitchell, Karl L.; Wilson, Lionel (agosto de 2003). «Mars: recent geological activity : Mars: a geologically active planet». Astronomy & Geophysics 44 (4): 4.16-4.20. Bibcode:2003A&G....44d..16M. doi:10.1046/j.1468-4004.2003.44416.x.
- Méndez-Chazarra, Nahúm (November 2014). "Mars as art . " Beginning . ISSN 2386-5997 .
- "Martian soil 'could support life ' " . June 27, 2008 . Retrieved December 21, 2016 .
- Chang, Alicia (August 5, 2008). "Scientists: Salt in Mars soil not bad for life . " USA Today . Retrieved December 21, 2016 .
- Jet Propulsion Laboratory (August 4, 2008). "NASA Spacecraft Analyzing Martian Soil Data" . Jet Propulsion Laboratory. NASA . Retrieved December 21, 2016 .
- "Zigzagging of the dust whirlpool" . HIRISE . July 2, 2009 . Retrieved December 21, 2016 .
- Schorghofer, Norbert; Aharonson, Oded; Khatiwala, Samar (12 de diciembre de 2002). «Slope streaks on Mars: Correlations with surface properties and the potential role of water». Geophysical Research Letters 29 (23): 41-1, 41-4. Bibcode:2002GeoRL..29w..41S. doi:10.1029/2002GL015889.
- Gánti, T.; Horváth, A.; Bérczi, S.; et al. (octubre de 2003). «Dark Dune Spots: Possible Biomarkers on Mars?». Origins of life and evolution of the biosphere 33 (4): 515-557. Bibcode:2003OLEB...33..515G. doi:10.1023/A:1025705828948.
- «News | NASA's Mars Rover Finds Evidence of Ancient Volcanic Explosion " (in English) . May 3, 2007 . Retrieved September 23, 2016 .
- / Valle Marineris. Nave Viking 1970. Accessed: April 8, 2011
- "Earth-based telescopes detect methane on Mars" (digital) . The Country . 2009 . Retrieved December 9, 2009 .
- Daniel Marín (November 7, 2015). "The MAVEN probe and the shrinking atmosphere of Mars" . Eureka blog . Retrieved November 8, 2015 .
- "Water ice in crater at Martian north pole" . ESA . July 28, 2005 . Retrieved February 15, 2015 .
- Beard, JB (November 20, 2008). "Scientists Discover Concealed Glaciers on Mars at Mid-Latitudes . " The University of Texas at Austin . Archived from the original on July 25, 2011 . Retrieved February 15, 2017 .
- "NASA Spacecraft Confirms Martian Water, Mission Extended" . NASA . July 31, 2008 . Retrieved February 15, 2017 .
- Cf. L. A. Leshin et alii, «Volatile, Isotope, and Organic Analysis of Martian Fines with the Mars Curiosity Rover», Science, 27 de septiembre de 2013, vol. 341, no. 6153.
- "Mars Global Surveyor: Mars For Press" . nasa.gov (in English) . December 6, 2006 . Retrieved November 7, 2016 .
- Cf. Alfred S. McEwen, "Mars in motion", Research and Science , 442, July 2013, pp. 34-41.
- "NASA Mars Orbiters See Clues to Possible Water Flows' (in English) . POT. 2014 . Retrieved September 29, 2015 .
- "NASA Confirms Liquid Evidence That Water Flows on Today's Mars" (in English) . POT. 2015 . Retrieved September 29, 2015 .
- Cf. Teresa Guerrero, "'Curiosity' finds evidence of a Martian lake with microbial life." elmundo.es, December 9, 2013.
- MRO space probe discovers buried glaciers in mid-latitudes of Mars.
- «Space probes. Mars had ancient oceans, gamma ray data suggest. "
- "The Phoenix spacecraft sends images that could be drops of liquid water on Mars."
- «Bright Chunks at Phoenix Lander's Mars Site Must Have Been Ice.» June 19, 2008. NASA (in English) .-
- "NASA thinks it has found proof of the existence of water on Mars". June 20, 2008. Spanish Radio and Television .
- "NASA Spacecraft Confirms Martian Water, Mission Extended" . Retrieved August 1, 2008 .
- Gánti, T. et al., "Evidence For Water by Mars Odyssey is Compatible with a Biogenic DDS-Formation Process". (PDF) Lunar and Planetary Science Conference XXXVI (2003)
- Horváth, A., et al., "Annual Change of Martian DDS-Seepages". (PDF) Lunar and Planetary Science Conference XXXVI (2005).
- "NASA Findings Suggest Jets Bursting From Martian Ice Cap" . Jet Propulsion Laboratory (NASA). August 16, 2006 . Retrieved September 15, 2009 .
- Piqueux, Sylvain; Shane Byrne, and Mark I. Richardson (8 de agosto de 2003). «Sublimation of Mars's southern seasonal CO2 ice cap formation of spiders» (PDF). JOURNAL OF GEOPHYSICAL RESEARCH 180 (no. E8): 5084. doi doi:10.1029/2002JE002007. Consultado el 5 de septiembre de 2009.
- "BEHAVIOR OF SOLID CO" , Third Mars Polar Science Conference (2003) , 2003 , accessed September 6, 2009
- «SIMULATIONS OF GEYSER-TYPE ERUPTIONS IN CRYPTIC REGION OF MARTIAN SOUTH» (PDF), Fourth Mars Polar Science Conference, 2006, consultado el 11 de agosto de 2009
- Kieffer, H. H. (2000), «ANNUAL PUNCTUATED CO2 SLAB-ICE AND JETS ON MARS.» (PDF), Mars Polar Science 2000, consultado el 6 de septiembre de 2009
- "SAM has also found large amounts of deuterium on Mars." Archived May 14, 2014, at the Wayback Machine . Retrieved May 13, 2014.
- "NASA: The water on Mars is much heavier than that on Earth." Retrieved May 13, 2014.
- Badescu, Viorel (2009). Mars: Prospective Energy and Material Resources . Springer Science & Business Media. p. 600. ISBN 978-3-642-03629-3 . Retrieved November 23, 2016 .
- Barlow, Nadine G. (2008). Mars: an introduction to its interior, surface and atmosphere. Cambridge planetary science 8. Cambridge University Press. p. 21. ISBN 0-521-85226-9.
- Kastrenakes, Jacob (September 20, 2013). "Alien frontier: see the haunting, beautiful weirdness of Mars" . The Verge . Retrieved November 23, 2016 .
- Vitagliano, Aldo (2003). "Mars' Orbital eccentricity over time" . Archived from the original on June 29, 2015 . Retrieved November 23, 2016 .
- Meeus, Jean (marzo de 2003). «When Was Mars Last This Close?». Planetarian: 13.
- "The opposition of Mars" .
- Anderson, Howard C. (2003-08-23). «A webcam captures the rotation of Mars from Earth | Daily astronomy image - Observatory » . Observatory . Retrieved August 2, 2016 .
-  The Country .
-  ABC.
- Mumma, M. J.; Novak, R. E.; DiSanti, M. A.; Bonev, B. P., "A Sensitive Search for Methane on Mars" (abstract only). American Astronomical Society, DPS meeting #35, #14.18.
- Mumma, Michael J. "Mars Methane Boosts Chances for Life" . Skytonight.com. Archived from the original on February 20, 2007 . Retrieved August 16, 2008 .
- V. Formisano, S. Atreya T. Encrenaz, N. Ignatiev, M. Giuranna (2004). «Detection of Methane in the Atmosphere of Mars». Science 306 (5702): 1758-1761. doi:10.1126/science.1101732.
- Krasnopolskya, V. A.; J. P. Maillard, T. C. Owen (2004). «Detection of methane in the martian atmosphere: evidence for life?». Icarus 172 (2): 537-547. doi:10.1016/j.icarus.2004.07.004.
- ESA Press release. «Mars Express confirms methane in the Martian atmosphere». ESA. Consultado el 16 de agosto de 2008.
- Vladimir A. Krasnopolsky (February 2005). «Some problems related to the origin of methane on Mars». Icarus. Volume 180 (Issue 2): 359-367. doi:10.1016/j.icarus.2005.10.015.
- "Mars Express" . European Space Agency. August 2008 . Retrieved August 17, 2008 .
- Remote Sensing Tutorial, Section 19-13a Archivado el 21 de octubre de 2011 en la Wayback Machine. - Missions to Mars during the Third Millennium, Nicholas M. Short, Sr., et al., NASA
- Crenson, Matt (August 6, 2006). "After 10 years, few believe life on Mars" . Associated Press (on space.com . Archived from the original on August 9, 2006. Accessed on August 6, 2006 .
- McKay, David S., et al. (1996) "Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001". Science, Vol. 273. no. 5277, pp. 924 - 930. URL accessed August 17, 2008.
- McKay D. S., Gibson E. K., ThomasKeprta K. L., Vali H., Romanek C. S., Clemett S. J., Chillier X. D. F., Maechling C. R., Zare R. N. (1996). «Search for past life on Mars: Possible relic biogenic activity in Martian meteorite ALH84001». Science 273: 924-930. PMID 8688069. doi:10.1126/science.273.5277.924.
- "Mars Mars Planet SOLAR SCIENCE" . Archived from the original on March 12, 2016 . Retrieved December 18, 2012 .
- "Miguel San Martín explained the secrets of Curiosity's descent to Mars", September 28, 2012 La Nación . Retrieved May 13, 2014.
- "Mars Meteorites" . NASA . Retrieved August 15, 2008 .
- "Allan Hills 84001" . The Meteorolitical Society. April 2008 . Retrieved August 17, 2008 .
- EVIDENCE FOR ANCIENT MARTIAN LIFE. E. K. Gibson Jr., F. Westall, D. S. McKay, K. Thomas-Keprta, S. Wentworth y C. S. Romanek, Mail Code SN2, NASA Johnson Space Center, Houston TX 77058, USA.
- Baalke, Ron (1995). "The Nakhla Meteorite" . Jet Propulsion Lab . NASA . Retrieved August 17, 2008 .
- «Rotating image of a Nakhla meteorite fragment». London Natural History Museum. 2008. Consultado el 17 de agosto de 2008.
- Rincon, Paul (February 8, 2006). "Space rock re-opens Mars debate" . BBC News . Retrieved August 17, 2008 .
- C Meyer, C. (2004). "Mars Meteorite Compendium" (PDF) . NASA . Retrieved August 21, 2008 .
- Whitehouse, David (27 August 1999). «Life on Mars - new claims» . BBC News . Consulted on August 17, 2008 .
- NASA compilation of research references on the Nakhla meteorite: "Archived copy . " Archived from the original on September 4, 2008 . Retrieved August 21, 2008 .
- Meteorito Shergoti
- Raeburn, Paul. (2003). Mars: discovering the secrets of the red planet . RBA Magazines. Barcelona , Spain. ISBN 84-8298-130-7 .
- Asimov, Isaac. (2001). Mars, the red planet . The Pocket Book Collection, 1169. Alianza Editorial. Madrid , Spain. ISBN 84-206-0169-1 .
- Observe Mars: discover and explore the red planet . (2005). Spes Editorial. Barcelona, Spain. ISBN 84-8332-706-6 .
- Lizondo Fernández, Joaquín (1999). The enigmatic Mars . Editorial Telstar. Barcelona, Spain. ISBN 84-7237-033-X .
- Raeburn, Paul. (2003). Mars: discovering the secrets of the red planet . RBA Magazines. Barcelona, Spain. ISBN 84-8298-130-7 .
- Sersic, José Luis. (2002). The exploration of Mars . Labor Collection. Editorial Labor. Sardañola del Vallés , Spain. ISBN 84-335-2400-3 .
- Lizondo Fernández, Joaquín. (2000). : Beyond the horizons of the earth: Mars, the new frontier . Editorial Ronsel. Barcelona, Spain. ISBN 84-88413-19-X .
- Multimedia in Commons.
- Definitions in Wiktionary.
- Dating on Wikiquote.
- News on Wikinews.
- Solar System Web
- Video: Triangle formed by Mars, Saturn and Spica
- 35 high resolution images of Mars obtained thanks to the HiRISE (High Resolution Imaging Science Experiment) camera aboard NASA's MRO (Mars Reconnaissance Orbiter)
- Mars Odissey Mission. NASA
- Google Mars - Geography of Mars
- Mars Educational Activity: The Solar System
- New Papers about Martian Geomorphology