“Fear” and “Horror” of the red planet. Phobos and Deimos - natural satellites of Mars
“...In addition, they discovered two small stars, or two satellites, orbiting around Mars, of which the inner one is 3 times its diameter from the center of the planet, and the outer one is 5; the first rotates in space in 10 hours, and the second in 21.5 in such a way that the ratio of the squares of these periods is very close to the ratio of the cubes of their distances from the center of Mars; this was convincing evidence for them of the manifestation of the same law of gravity that governs movement around other massive bodies.”
There are many mysteries associated with Mars, and one of them is contained in this phrase from Jonathan Swift's novel about the adventures of Gulliver. One hundred and fifty years before the discovery of the satellites of Mars, an English writer managed to predict their existence!
The most surprising detail of this prediction is the short 10-hour orbital period of the inner satellite. It is significantly shorter than the 42-hour period for Io, the fastest of the 10 moons known at Swift's time, and at the same time roughly corresponds to Phobos's true 8-hour orbital period. Swift was not as clairvoyant as it seems at first glance. The choice of distance values of three and five planetary diameters coincides very closely with the distance from Jupiter to its moons Io and Europa. However, it is more difficult to explain why Swift predicted a 10-hour period for the first satellite. Even if we take the system of Jupiter’s satellites as a model for the spatial arrangement of the satellites of Mars, the periods cannot be derived by simple analogy. If Mars had the same density as the Earth, then the first satellite at a distance of three planetary diameters should orbit in about a day; if the density were the same as that of the planets of the Jupiter group, then the orbital period should be close to two days. A passage from Newton's Principia states that "the smaller planets, other things being equal, have a much greater density." The diameter of Jupiter is approximately 22 times larger than the diameter of Mars. If we accept the density of Mars to be 22 times greater than that of Jupiter (now this seems absurd high value), then the inner satellite must have a 10-hour period. Swift correctly applied Kepler's third law, but it seems that he had help from a professional.
By the way, Swift was not the only great writer of the 18th century who
"discovered" the satellites of Mars. Francois Marie Voltaire - master of thoughts of a brilliant century
Enlightenment, writing in 1752. I also mentioned the fantastic story “Micromegas”
"two moons of Mars." But in passing, without the details that Swift listed,
the only “proof” is this consideration: one moon would be
not enough to illuminate a planet so far from the Sun at night! (He says: “... travelers would have seen two moons of this planet Mars, which were not discovered by our astronomers. I am sure that Father Castel will argue against the existence of these two moons, and even quite wittily, but I agree with those who argue by analogy the best philosophers know how difficult it would be for Mars to have less than two moons, since he is next from the Sun."
Even earlier, Fontenelle, in his Discourses on the Plurality of Worlds, mentioned that Mars may have satellites. There, the student in a dispute gives the following arguments: “Nature has given so many moons to Saturn and Jupiter - this is a kind of proof that Mars cannot lack moons.”
The intuition that Mars has two moons can be found in the writings of Johannes Kepler, who repeatedly argued on principles based on harmony or analogy. In a letter to Galileo, Kepler wrote: “I am so far from doubting the discovery of the four planets surrounding Jupiter that I passionately desire to have a telescope so that I can, if possible, precede you in the discovery of two orbiting Mars (the number meets the requirements of proportionality), six or eight around Saturn and probably one near
Mercury and Venus." However, before a genuine, and not a “sci-fi” discovery of the satellites of Mars, humanity had to wait until 1877, which became truly “Martian”. Giovanni Schiaparelli at this time literally brought the entire astronomical world to its feet, reporting the existence of “channels” and “seas” on the Red Planet. This “Martian fever” also had an objective basis: 1877 was the year of the great confrontation, in which Mars and Earth came very close to each other. An experienced astronomer could not neglect such favorable conditions. Asaph Hall (1829-1907), who had already earned considerable prestige as one of the best observers and calculators at the Harvard Observatory and professor of mathematics at the Naval Observatory (Washington). August 12, 1877 In the evening, Hall looked through the 26-inch telescope of the M. Observatory and saw an object that he called the “Martian Star”. A week later, Hall was able to verify that this “star” was in fact a satellite of Mars, and, in addition, he discovered a second Martian satellite (August 17). From Earth, Phobos and Deimos are visible only through a large telescope as very faint points of light near the bright Martian disk. (It is possible to photograph them using a ground-based telescope only by covering the image of bright Mars with a special mask.)
Having learned about the discovery from the newspapers, one English schoolgirl suggested Hall names for new celestial bodies: the god of war in ancient myths is always accompanied by his offspring - Fear and Horror, so let the innermost of the satellites be called Phobos, and external Deimos, for this is how these words sound in ancient Greek. The names turned out to be successful and stuck forever.
Phobos orbits Mars at a distance of 9,400 km from the center of the planet, and its speed of revolution is so high that it completes one revolution in a third of a Martian day, overtaking the daily rotation of the planet. Because of this, Phobos rises in the west and sinks below the horizon in the east. Deimos behaves more familiar to us. Its distance from the center of the planet is more than 23 thousand kilometers, and it takes almost a day more to complete one revolution than Phobos.
The latest determinations of the orbits of Phobos and Deimos were published in the works of Sinclair (1972), Shore (1975) and Born and Duxbury (1975). The first two works are based on ground-based observations, the third on photo-television filming from Mariner 9. All three definitions have comparable accuracy, and ephemeris based on them make it possible to predict satellite positions with an error of 50 to 100 km.
Until more accurate data on the satellites of Mars were obtained, scientists tried to determine the mass of Phobos, erroneously assuming that the reason for the slowdown was its braking in the Martian atmosphere. However, the first results discouraged astronomers: it turned out that, despite its large size, the satellite was very light. The famous astrophysicist Joseph Samuilovich Shklovsky (1962) noted that atmospheric braking would be sufficient at a very low density of Phobos, and in connection with this he put forward a bold and unexpected hypothesis, according to which the satellites of Mars ... are empty inside and, therefore, are of artificial origin. Confirmation by Shklovsky was not confirmed, but it stimulated the research of others possible reasons secular acceleration of Phobos. One of them may be tides caused in the Martian crust by the gravity of the satellite. Pressure solar radiation can also cause a noticeable effect (Vinogradova and Radzievsky, 1965).
This point of view had to be abandoned after space probes transmitted images of the Martian moons to earth. In 1969, the same year when people landed on the Moon, the American automatic interplanetary station Mariner 7 transmitted to Earth a photograph in which Phobos accidentally appeared, and it was clearly visible against the background of the disk of Mars. Moreover, there was a noticeable shadow in the photo
Phobos on the surface of Mars, and this shadow was not round, but elongated!
More than two years later, Phobos and Deimos were specially photographed by the Mariner 9 station. Not only were television films received from good resolution, but also the first results of observations using an infrared radiometer and an ultraviolet spectrometer. Mariner 9 approached the satellites at a distance of 5,000 km, so the images showed objects with a diameter of several hundred meters.
Indeed, it turned out that the shape of Phobos and Deimos is extremely far from the correct sphere. Both satellites look like oblong potatoes. Phobos has dimensions of 28*20*18 km. Deimos is smaller, its dimensions are 16*12*10 km. Telemetric space technology has made it possible to clarify the dimensions of these celestial bodies, which will no longer undergo significant changes. According to the latest data, the semi-major axis of Phobos is 13.5 km, and that of Deimos is 7.5 km, while the minor axis is 9.4 and 5.5 km, respectively. They consist of the same dark rock, similar to the substance of some meteorites and asteroids. The surface of the satellites of Mars turned out to be extremely rugged: they are almost all dotted with ridges and meteorite craters, obviously of impact origin. Probably, the fall of meteorites onto a surface unprotected by the atmosphere, which lasted extremely for a long time, could lead to such wrinkledness.
Nomenclature for the names of craters on Phobos and Deimos
The largest crater on Phobos is called Stickney(in honor of astronomer Hall's wife Angelina Stickney-Hall). Its dimensions are comparable to the size of the satellite itself. The impact that led to the appearance of such a crater must have literally shaken Phobos. The same event likely caused the formation of a system of mysterious parallel grooves near the Stickney crater. They can be traced over distances of up to 30 km in length and have a width of 100-200 m with a depth of 10-20 m.
Another feature of Phobos's topography is of interest. It's about about some mysterious furrows, as if made by a plowman, unknown, but very careful. Moreover, although they cover more than half of the satellite’s surface, all such “ridges” are concentrated only in one area of Phobos in its northern part.
The furrows stretch for tens of kilometers, their width in different areas varies from 100 to 200 m, the depth also varies in various places. How were these grooves formed? Some scientists blamed the gravity of Mars, which could distort the face of the satellite with such wrinkles. But it is known that in the initial era of its existence, Phobos was further from its central body than it is now. Only about one billion years ago, gradually approaching Mars, did it begin to really feel its tidal force. Therefore, the grooves could not have appeared earlier, and this contradicts data according to which the age of the grooves is much older, perhaps 3 billion years. In addition, the gravitational influence of Mars on Phobos continues today, which means that very fresh grooves should exist on its surface, but they are not there.
Other scientists believed that the grooves were made on the surface of the satellite by rock fragments ejected from some as yet unknown large crater. But not all scientists agreed with this. Some experts consider another hypothesis more plausible, according to which at first there was a single large proto-moon of Mars.
Then this “parent” of both “brothers” - Phobos and Deimos - split into two current satellites, and the furrows are traces of such a cataclysm.
Analysis of photographs sent to Earth by the orbital compartment of Viking 2, in which the surfaces of the satellites of Mars are colored dark colors, showed that such coloring is most often characteristic of rocks containing a lot of carbonaceous substances. But in those relatively close regions of the solar system where the orbit of Mars lies from its
satellites, carbonaceous substances are not formed in abundant quantities. This means Phobos and Deimos are most likely “aliens” and not “natives”. If they really formed somewhere in a relatively distant corner of the solar system, then by the time they were captured by the gravitational field of the Red Planet, they, apparently, were a single body, which then split into several fragments. Some of these fragments fell on the surface of Mars, some went into space, and two fragments became satellites of the planet.
However, we should also listen to opponents who reject the emergence of the satellites of Mars by capturing a previously independent body and breaking it apart.
The leading cosmogonist, Academician O.Yu. Schmidt, at one time developed a hypothesis for the formation of the Solar System, according to which the planets arose through the accretion (sticking together) of solid and gaseous particles that originally made up a protoplanetary cloud. Soviet followers of O.Yu. Schmidt believe that the satellites of the planets were formed in a similar way. A significant confirmation of their correctness is the detailed mathematical model, showing exactly how such processes can occur. These researchers consider the capture of especially large celestial bodies by planets to be a very unlikely event.
The craters on Phobos and Deimos are almost equal in size to the satellites themselves. This means that the collisions were catastrophic events for them. The shape of the satellites is very irregular: it cannot be called anything other than clastic. Therefore, Phobos and Deimos, in principle, can be fragments of a once existing larger body. It was even possible to estimate the approximate dimensions of this body. If its radius reached approximately 400 km, then the “bombardment” of meteorites would not lead to its destruction, and bodies would be circling around Mars today, not ten to fifteen, but hundreds of kilometers in size.
There is another hypothesis related to the asteroid belt. It is possible that in ancient times some asteroid flew into the atmosphere of Mars, was slowed down by it and turned into its satellite. However, the Martian atmosphere would have to be very dense for this to happen.
Proponents of contradictory hypotheses for the origin of Mars' satellites have weighty arguments, and it is only a matter of time to decide which of them is right.
One of the most important discoveries space age is confirmation of the existence of the solar wind. These are powerful streams of charged particles emitted by the Sun. They rush at supersonic speed outer space, falling on everything that comes their way. And only those celestial bodies, which, like our Earth, have a fairly strong magnetic field that serves as a strong shield from such magnetic flux, are not fully exposed to the solar wind.
Soviet interplanetary stations “Mars-2” and “Mars-3” launched in 1971-1972. conducted observations of how the solar wind interacts with the Red Planet. The stations sent information to Earth, according to which the solar wind does not reach the surface of Mars, but encounters an obstacle and begins to flow around the planet from all sides. This flow began either closer to Mars or further from it (depending on the strength of the “attacking” particles and the resistance of the “defending” magnetic field planet), but on average the distance from the center of the planet was about
4800 km. Further studies showed that in a certain region of near-Martian space the accumulation of ions is more than ten times less than in others. And the energy spectrum of these charged particles is completely different.
The strange area did not stay in one place. When her movements were examined, it turned out that she was moving along with Deimos, all the time hiding behind his back at a distance of about 20,000 km. Soviet astrophysicist A.V. Bogdanov suggested that, obviously, there is a strong release of gases from the surface of Mars that interact with the space surrounding it. When Deimos passes directly between Mars and the Sun, the area where the solar wind collides with the Martian magnetosphere moves away from the planet, as if the "defending" side, having received reinforcements, can drive off the "attackers", and the size of the Martian magnetosphere becomes significantly larger. But until now it was believed that small bodies of our solar system, such as, for example, asteroids or small satellites of planets like Deimos, were powerless to influence the powerful flow of solar wind.
Another oddity that researchers of Mars’ satellites noticed: large craters, the diameter of which exceeds 500 m, are found on Deimos about as often as on Phobos. But there are very few small craters with which Phobos is simply strewn, there are very few on Deimos. The fact is that the surface of Deimos is strewn with finely crushed stones and dust, and small craters are filled to the edges, so the surface of Deimos looks smoother. The question arises: why doesn’t anyone, figuratively speaking, fill up the pits on Phobos? There is a hypothesis that Phobos and Deimos are subject to powerful meteorite bombardment - after all, they do not have an atmosphere that would serve as a reliable shield. When a meteorite body hits the surface of Phobos, the resulting dust and small stones mostly fly away from its surface: the strong gravity of the relatively nearby Mars “takes” them away from the satellite.
But Deimos is located much further from the planet, so meteorite stones and dust thrown out when falling on its surface largely hang in Deimos’ orbit. Returning to its previous point in the orbit, the “Horror” gradually again collects fragments and dust, they settle on its surface and bury many fresh craters above them, and primarily those that are smaller.
The upper, loose layer of the Moon, Mars, and its satellites, that part of their surface that corresponds to soil on Earth, is called regolith. It can now be considered established that the regolith of the Martian moons is similar to what is observed on our “earthly” Moon. In fact, the presence of regolith on Phobos and Deimos surprised scientists at first. After all, the second escape velocity, upon reaching which any object goes into interplanetary space, on such small celestial bodies is only about 10 m/s. Therefore, when a meteorite hits, any cobblestone here becomes a “space projectile.”
Detailed photographs of Deimos have made it possible to discover as yet inexplicable fact: It turns out that some crater ridges and approximately ten-meter stone blocks scattered across the surface of Deimos are decorated with a long train. These plumes look like a rather long strip, formed as if by fine-grained material thrown out from the depths. There is something similar on Mars, but it seems that these stripes look a little different there. In any case, specialists again have something to puzzle over...
In 1945, astronomer B.P. Sharpless became convinced that Phobos had a secular acceleration in its motion around Mars. And this meant that the satellite was moving faster and faster in a very, very gentle spiral, gradually slowing down and getting closer
approaching the surface of the planet. Sharpless's calculations showed that if nothing changes, then in just 15 million years Phobos will fall to Mars and die.
But then the space age came, and humanity began to closer problems astronomy. About braking processes artificial satellites in the Earth's atmosphere became known to the broad masses. Well, since Mars also has an atmosphere, although it is very rarefied, can it not, through its friction, cause a secular acceleration of Phobos? In 1959, I.S. Shklovsky
carried out the corresponding calculations and came to a conclusion that caused ferment both in the minds of scientists and in the minds of the general public. The secular acceleration that we observe in rarefied conditions upper atmosphere Mars, can only be explained if we assume that Phobos has a very low density, so low that it would not allow the satellite to fall into pieces if it were hollow. As befits a scientist, I.S. Shklovsky did not make any categorical statements; he himself considered the question he posed to be a “very radical and not entirely ordinary” assumption.
In 1973, Leningrad scientist V.A. Shor and his colleagues at the Institute of Theoretical Astronomy of the USSR Academy of Sciences completed the processing of over five thousand comprehensive data collected over almost a century since the discovery of Phobos and Deimos. It turned out that Phobos is still accelerating. True, much weaker than Sharpless thought.
And since there is acceleration, we can predict the fate of Phobos: in no more than 100 million years it will get so close to Mars, cross the disastrous Roche limit and be torn apart by tidal forces. Some of the debris from the satellite will fall on Mars, and some will probably appear to our descendants in the form of a beautiful ring, similar to the one for which Saturn is now famous.
As for Deimos, no one has any doubts: it does not have secular acceleration.
Both satellites experience strong tidal influence from Mars, so they always face the same side towards it. Phobos and Deimos move in almost circular orbits lying in the plane of the planet's equator.
Does Mars have any other satellites that are hitherto unknown? This question was posed by J.P. Kuiper, director of the Lunar and Planetary Observatory at Arizona State University. In order to answer this question, he developed a special photographic technique that allows him to capture even very faintly luminous objects. All his research did not lead to the discovery of a new satellite of Mars.
Then the search for the unknown satellite of Mars was carried out by J.B. Polak, an employee of the NASA Ames Research Center in California. His research was also unsuccessful. So we can still assume that only Fear and Horror accompany the heavenly incarnation of the god of war.
Some researchers believe that the satellites of Mars came to him “not of their own free will,” but were captured from the asteroid belt. As you can see, the god of war is not dangerous for the Earth, but is harsh with his entourage.
The Phobos-Grunt space mission is being prepared in Russia - a repeat attempt after Phobos-2 to land a spacecraft on the surface of a Martian satellite, study its rocks and - something that was previously unthinkable - deliver the extracted samples to Earth. The estimated time for the entire operation is 2005-2008.
Material used:
1. Encyclopedia “Astronomy. Comprehension of the Universe, mysteries of stars and galaxies,
space and life."
2. Physics of the planet Mars. V.I.Moroz.
3. Satellites of Mars. Edited by P. Seidelman (Director Nautical Naval Office. U.S.
The planet Mars has two satellites: Phobos(Greek fear) and Deimos(Greek: horror).
Phobos and Deimos are the satellites of Mars. They are not round because, being so small, the force of gravity is too weak to compress them into a more round shape. Perhaps they are asteroids captured by the gravitational field of Mars.
Both satellites rotate around their axes with the same period as around Mars, so they always face the same side towards the planet.
The tidal influence of Mars gradually slows down the movement of Phobos, lowering its orbit, which will eventually lead to its fall onto Mars. Deimos, on the contrary, is moving away from Mars.
Both satellites have a shape approaching a triaxial ellipsoid. Phobos (26.6×22.2×18.6 km) is slightly larger than Deimos (15×12.2×10.4 km).
The similarity of Deimos and Phobos with one of the types of asteroids gave rise to the hypothesis that they were former asteroids, whose orbits were distorted by the gravitational field of Jupiter in such a way that they began to pass near Mars and were captured by it. However, the fairly regular shape of the orbits of the satellites of Mars and the position of their orbital planes, almost coinciding with the Martian plane, casts doubt on this version.
Another assumption about the origin of Phobos and Deimos is the disintegration of the satellite of Mars into two parts.
Both satellites experience strong tidal influence from Mars, so they always face the same side towards it. Phobos and Deimos move in almost circular orbits lying in the plane of the planet's equator. Some researchers believe that the satellites of Mars did not come to it of their own free will, but were captured from the asteroid belt. As you can see, the god of war is not dangerous to the Earth, but is harsh with his entourage.
Orbits of Mars satellites
Deimos and Phobos are composed of rocky rocks; there is a significant layer of regolith on the surface of the satellites. The surface of Deimos appears much smoother due to the fact that most of the craters are covered with fine-grained material. Obviously, on Phobos, which is closer to the planet and more massive, the substance ejected during meteorite impacts either caused repeated impacts on the surface or fell on Mars, while on Deimos it remained in orbit around the satellite for a long time, gradually settling and hiding uneven terrain.
Features of the orbital motion of Phobos
Phobos is the closest satellite to Mars. Its orbit is located at a distance of 2.77 Mars radii from the center of the planet. The satellite Phobos orbits in the plane of the equator of Mars in an almost circular orbit. Phobos rotates around its axis with the same period as around Mars, so it always faces the same side towards the planet.
The rotation period of Phobos is 7 hours 39 minutes 14 seconds. This is faster than the rotation of Mars around its axis (24 hours 37 minutes 22.7 seconds). As a result, in the Martian sky, Phobos rises in the west and sets in the east. In one Martian day, called a sol, the satellite Phobos manages to make three revolutions around the planet.
Phobos is forty times closer to the surface of Mars than the Moon is to Earth. The orbit of Phobos is inside the Roche limit and the satellite closest to Mars is not torn apart only due to its internal strength. The tidal influence of the red planet gradually slows down the movement of Phobos and in the future will lead to its destruction and fall to Mars.
Phobos orbits Mars at a distance of 9,400 km from the center of the planet, and its speed of revolution is so high that it completes one revolution in a third of a Martian day (7 hours 39 minutes), overtaking the daily rotation of the planet. In one day, Phobos manages to make three full revolutions and also go through an arc of 78 degrees. Because of this, Phobos rises in the west and sinks below the horizon in the east. Deimos behaves more familiar to us. Its distance from the center of the planet is more than 23 thousand km, and it takes almost a day more to complete one revolution than Phobos.
The strong tidal friction resulting from Phobos's proximity to Mars reduces the energy of its motion, and the satellite slowly approaches the surface of the planet, eventually falling onto it if by that time the gravitational field of Mars does not tear it to pieces (the planet's gravity will tear this the satellite will fall into pieces in 50 million years or 100 - it will fall on the planet). Until more accurate data on the satellites of Mars were obtained, scientists tried to determine the mass of Phobos, erroneously assuming that the reason for the slowdown was its braking in the Martian atmosphere. However, the first results discouraged astronomers: it turned out that, despite its large size, the satellite was very light. The famous astrophysicist Joseph Samuilovich Shklovsky even put forward a hypothesis according to which the satellites of Mars... are empty inside and, therefore, are of artificial origin.
This point of view had to be abandoned after space probes transmitted images of the Martian moons to earth. Both satellites look like oblong potatoes. Phobos has dimensions of 27 22 18.6 km. Deimos is smaller, measuring 16 12 10 km. The period of rotation of the satellite around Mars is 30 hours 21 minutes. The orbital period of Deimos is slightly longer than the rotation period of Mars, so although Deimos “normally” rises in the east and sets in the west, it moves extremely slowly across the Martian sky. They consist of the same dark rock, similar to the substance of some meteorites and asteroids. Their surface is pitted with meteorite craters. The largest crater on Phobos is called Stinky. Its dimensions are comparable to the size of the satellite itself. The impact that led to the appearance of such a crater must have literally shaken Phobos. The same event likely caused the formation of a system of mysterious parallel grooves near Stinky Crater. They can be traced over distances of up to 30 km in length and have a width of 100-200 m with a depth of 10-20 m.
Characteristics and mysteries of the surface of Phobos
Phobos has an irregular shape, approaching a triaxial ellipsoid. The dimensions of Phobos are 26.6 x 22.2 x 18.6 km. The surface of Phobos is extremely dotted with ridges and craters of various sizes, obviously of impact origin.
The largest crater on the surface of Phobos, Stickney, has a diameter of about 9 kilometers. If the blow that gave birth to it had been a little stronger, Phobos would probably have split into pieces. Systems of faults and cracks are associated with the Stickney crater, which is located in the north of the satellite. These strange grooves, tens of meters deep, stretch across the surface of Phobos for a distance of several kilometers.
After the discovery of the mysterious notches, sensational hypotheses were put forward about their artificial origin. However, further research showed that the origin of the grooves on Phobos is well explained by natural factors. For example, one hypothesis blamed the tidal influence of Mars for distorting the face of its closest satellite with wrinkles.
Another hypothesis saw in the grooves traces of a long-standing split of the once single satellite into two parts - Phobos and Deimos. According to the third hypothesis, the grooves were made on the surface of the satellite by rock fragments ejected from a large crater as a result of the collision of Phobos with a large asteroid.
On August 20 and September 9, 1975, the Viking 1 and Viking 2 spacecraft were launched in the United States of America, designed to explore Mars and its satellites - Phobos and Deimos. After a long flight along the Earth-Mars route, they entered areocentric (near-Mars) orbits on June 19 and August 7, 1976, respectively.
By using special devices located on the orbital blocks of spacecraft, a heat map of the Martian surface and a map of the water vapor content in the planet’s atmosphere were compiled. It was found that the polar caps of Mars consist mainly of water ice, on which carbon dioxide condenses during the harsh Martian winter.
Astronomers were especially interested in large-scale photographs of the surface of Mars and its satellites. What are the Martian moons? What are they like up close? Back in 1972, the first photograph of Phobos, taken by Mariner 9, went around the world. The satellites of Mars turned out to be huge shapeless blocks - they look like asteroids. The Vikings explored Phobos and Deimos in great detail. First of all, their sizes were clarified. At Phobos they are 26.2x20x18.6 km, at Deimos - 15.6x14x10.2 km.
The surface of the satellites is too uneven - covered with many craters, which are undoubtedly the result of meteorite impacts. The number of craters and their size distribution are quite comparable to the saturation of craters on the lunar surface. At the same time, the number of craters on Phobos and Deimos per unit area is approximately 100 times greater than on Mars. Since the satellites are located in the same region of the solar system as the planet itself, we can conclude that there is very high erosion (destruction rocks), a deist who lived on Mars for a long time.
A big surprise for astronomers was the difference in the surface structure of Phobos and Deimos. On Phobos, cracks up to 200 m wide and up to 20 m deep are clearly visible, and the largest crack, adjacent to the Stickney crater, is 700 m wide and 90 m deep! There is every reason to believe that both the Stickney crater and these cracks were formed as a result of a catastrophic event - the impact of a large meteorite, which almost led to the complete destruction of Phobos.
The surfaces of the Martian satellites are covered with a layer of dust. This, of course, is the result of prolonged meteorite bombardment. But on Deimos the layer of dust and regolith is much thicker than on Phobos, and craters with a diameter of less than 50 m are apparently completely covered with dust. Perhaps this explains the fact that there are a lot of small craters on Phobos, while on Deimos they are almost completely absent. Probably due to the large amount of dust, all the details on Deimos have smoothed contours, as if the image of the satellite was out of focus.
Both satellites are very dark in color. They owe their blackness to dust, which is perhaps blacker than soot and reflects very little light. Their albedo (surface reflectivity) is less than 5%. Therefore, the satellites of Mars can be classified as the darkest celestial bodies in the Solar System. While astronomers did not know this, it seemed to them that Phobos and Deimos were simply very small, sort of artificial... Phobos and Deimos rotate so that their major axes are always oriented towards Mars. And as a consequence of this, they always face their planet with one side, just as our Moon “looks” at the Earth with the same hemisphere.
Under the influence of tidal friction, the Martian satellites move in spiral orbits and very slowly approach Mars. Phobos is approaching faster than Deimos and must die first. Most likely, when the satellite enters the danger zone (reaches the so-called Roche limit, equal to approximately two and a half radii of the planet), it will be torn apart by the gravitational forces of Mars into many small parts. Then a thin ring, reminiscent of the famous ring of Saturn, can form from the substance of the former satellite near Mars.
Phobos and Deimos are two satellites of the Red Planet that were discovered by Asaph Hall in 1877. These are very tiny satellites. The diameter of Phobos is 22 km, and Deimos is even smaller - about 13 km. Both satellites always face the same side towards Mars, since they rotate around their axis with the same period as around Mars.
Deimos and Phobos are very similar to each other. These are lifeless pieces of stone, most likely former. Flying near Mars, they were captured by the planet’s gravitational field and remained with it forever. But both satellites have too regular orbits, so some scientists are not sure of the correctness of the theory of the asteroid origin of Phobos and Deimos. They are inclined to assume that at first Mars had only one satellite, which was split into two (and possibly more) pieces by a meteorite impact.
Phobos satellite
Phobos is named after the ancient Greek god of fear Phobos - the son of the god of war Ares and the goddess of love Aphrodite. It rotates very quickly around Mars - three times faster than the planet itself rotates on its axis. During a Martian day, Phobos flies around three times.
As already mentioned, the satellite always faces the planet with one side. The forces of gravity have a great influence on Phobos, gradually slowing down the speed of its movement. Scientists believe that after 7.6 million years (according to other sources, after 11 million years), the satellite will collapse under the gravitational influence of Mars.
The entire surface of Phobos is dissected by craters and deep grooves. These grooves appear due to the fact that the force of gravity from Mars rips off the satellite large stones, which “cut” the surface of Phobos and fall from it.
Generally speaking, the satellite has not yet been torn to shreds only because of its high strength, and also because its orbit is inside the Roche limit. The Roche limit is the radius of the satellite's orbit, rotating on which the tidal forces of the planet are equal to the self-gravitational forces of the satellite.
Deimos satellite
The satellite received its name in honor of the ancient Greek god of horror Deimos, one of the followers of the god of war Ares. Its orbit is further than that of Phobos, so it orbits Mars longer. It completes a full revolution around the planet in 5.3 Martian days (on Mars a day lasts 24.5 Earth hours) - 130 hours. Like Earth's Deimos, it appears in the east (if you observe it from the surface of Mars), and sets in the west. And it is also always facing the planet with the same side.
In the 20th century it was believed that Deimos is the smallest satellite in all solar system. Its dimensions are really small: 15x12x10 km. It is smoother than Phobos. The craters on its surface are covered with a large layer of dust. Scientists suggest that after a collision with a meteorite, a large number of substance that remained in outer space for a long time. And every time Deimos passed through this “cloud” of dust, it collected it on its surface. Dust, settling on the satellite, hid the craters. Therefore, we see an almost smooth ball, but this, of course, is not so. Only two objects on Deimos have proper names- these are the large craters Voltaire and Swift. They are named after the famous writers who predicted the presence of satellites on Mars long before their official discovery in 1877.
The planet Mars has two small satellites - Phobos and Deimos. Deimos orbits at a distance of about 23 thousand km from the planet, while Phobos moves at a distance of only about 9 thousand km from Mars.
The entire history of the study of Phobos and Deimos is full of amazing events and fascinating mysteries. Judge for yourself: the first mention of the presence of two small satellites on Mars, Phobos and Deimos, did not appear in scientific works, and on the pages of the famous "Gulliver's Travels", written by Jonathan Swift at the beginning of the 18th century. As events unfold, Gulliver finds himself on the floating island of Laputa. And the locals tell him that they managed to discover two small satellites orbiting Mars. In fact, Phobos and Deimos were discovered by A. Hall only a century and a half after the publication of the novel, during the great confrontation of Mars in 1877. And they were discovered under exceptionally favorable atmospheric conditions after persistent multi-day observations, at the limit of the capabilities of the instrument and the human eye!
However, Swift predicted not only the existence of Phobos and Deimos, but also that the orbital radius of the closest satellite of Mars is equal to three diameters of the planet, and the outer one - five. Three diameters are about 20 thousand kilometers. The orbit of Deimos is approximately at this distance. True, not an internal satellite, as Swift claimed, but an external one - but still the coincidence is impressive!
Comparing the results of observations carried out in different years, astronomers have come to the conclusion that the closest satellite of Mars, Phobos, is experiencing braking, due to which it is gradually approaching the surface of the planet. The phenomenon looked mysterious. In any case, the observed braking could not be explained by any effects of celestial mechanics. There was only one thing left: to assume that the braking of Phobos is associated with the aerodynamic resistance of the Martian atmosphere. However, as calculations have shown, the gaseous shell of Mars at an altitude of 6 thousand km is capable of providing the appropriate resistance only if the average density of the Phobos substance is low. More precisely, incredibly small! That's when it arose! original idea: such a low density of Phobos can be explained by its... hollowness! But we don't know natural processes, which could lead to the formation of empty celestial bodies inside. The thought suggested itself that Phobos, and possibly Deimos, were from Mars, created millions of years ago intelligent beings, either inhabiting Mars at that time, or arriving from somewhere from outer space.
When Mars researchers had a new, more powerful way to explore the planets - automatic space stations - at their disposal, everything fell into place. On satellite images it is clearly visible that Phobos and Deimos are huge blocks irregular shape and of course, natural origin. If we compare the results of astronomical observations with what the space stations reported, the following picture emerges. Phobos and Deimos are small celestial bodies. The size of Phobos is 27 by 21, Deimos is 15 by 12 km. They move in almost circular orbits located in the equatorial plane of the planet, in the direction of its daily rotation. Deimos completes one full revolution in 30 hours 18 minutes, and Phobos - in 7 hours 39 minutes. Considering that the length of the Martian day is slightly more than 24 hours 30 minutes, it is not difficult to realize that Phobos is noticeably ahead of the daily rotation of the planet. Being on the surface of Mars, we would observe how Phobos and Deimos with their semi-major axes are always directed towards the center of Mars.
The flight of the Viking-1 automatic station made it possible for the first time to estimate the mass of Phobos. When the orbital compartment of this station flew at a distance of 100 kilometers from the satellite of Mars, American scientists were able to determine the disturbance in the trajectory of its movement caused by the attraction of Phobos. Having such data, calculating the mass of the disturbing body is no longer worth the effort. And knowing its dimensions, you can calculate the average density. For Phobos it turned out to be close to 2 g/cm 3 . Quite normal density, approximately the same as that of a number of stone meteorites.
Photographs of Phobos and Deimos are of great interest. They were received space stations from a distance of only a few tens of kilometers. On the surface of Phobos and Deimos, a large number of craters similar to are clearly visible. The largest crater on Phobos is 10 km across. It is curious that at the time when the problem of the low density of Phobos was discussed, it was suggested that this phenomenon was not explained by hollowness, but was the result of processing of its surface, as a result of which the substance of Phobos acquired strong porosity.
In addition to the craters, photographs of Phobos show almost parallel grooves up to several hundred meters wide, stretching over long distances. The origin of these mysterious stripes remains unclear. Perhaps this is the result of a powerful impact from a large meteorite, which “shocked” Phobos and caused the formation of numerous cracks. Perhaps the mysterious grooves arose due to the tidal influence of Mars. This is supported by the fact that on Deimos, located at a much greater distance from Mars, such details were not found. After all, it is known that they weaken in proportion to the square of the distance.
As for the origin of Phobos and Deimos, it is possible that these are asteroid-type bodies captured by Mars. Perhaps they formed even earlier than the planet itself. In any case, their further study is of interest to clarify the patterns of formation.