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.

Ministry of Education of Ukraine

Secondary school No. 13, Nikopol

Abstract on astronomy

on the topic of:

“Phobos and Deimos - satellites of Mars”

Completed:

Vasilenko A. (11-B)

“...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 Mars' density to be 22 times that of Jupiter (which now seems an absurdly high value), then the inner satellite should 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. François 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 this planet Mars have two of its moons, 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 nearby

Mercury and Venus." However, before the genuine, and not “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 the 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 research into other possible reasons for the secular acceleration of Phobos. One of them may be tides caused in the Martian crust by the gravity of the satellite. Solar radiation pressure 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 with good resolution obtained, 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 for an extremely long time, could lead to such furrowing.

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.

The moons of Mars were discovered in 1877. during the great controversy by American astronomer Asaph Hall. They were called Phobos (translated from Greek Fear) and Deimos (Horror), since in ancient myths the god of war was always accompanied by his children with fear and horror. The satellites are very small in size and have an irregular shape. Phobos (translated from Greek Fear) and Deimos (Horror) - two small satellites of Mars were discovered by the American astronomer Hall during the great confrontation of 1877. The dimensions of Phobos are 28x20x18 km, and Deimos is 16x12x10 km. The Mariner 7 spacecraft accidentally photographed Phobos against the backdrop of Mars in 1969, and the Mariner 9 spacecraft transmitted many images of both satellites, which show that the surfaces of the satellites are uneven, abundantly covered with craters. Several close approaches to the satellites were made by the Viking and Phobos 2 spacecraft. The best photographs of Phobos show relief details measuring 5 meters in size.

The orbits of the satellites are circular: Phobos orbits Mars at a distance from the center of the planet of 9400 km with a period of 7 hours. 39 min. Deimos is located at a distance of 23,500 km, and its orbital period is 30 hours. 18 min. The period of rotation around the axis of each of the satellites coincides with the period of revolution around Mars. The major axes of satellites are always directed towards the center of the planet. Phobos rises in the west and sets in the east 3 times per Martian day. The average density of Phobos is less than 2 g/cm 3 , and the acceleration of free fall is 0.5 cm/s 2 . A person would weigh several tens of grams on Phobos, so it would be easy to jump into space from Phobos. The largest crater on Phobos has a diameter of 8 km, comparable to the smallest diameter of the satellite. On Deimos, the largest depression has a diameter of 2 km.

The surfaces of the satellites are dotted with small craters in much the same way as the Moon. Despite the general similarity, the abundance of finely crushed material covering the surfaces of the satellites, Phobos looks more “torn”, and Deimos has a smoother, dust-covered surface. Mysterious grooves have been discovered on Phobos, crossing almost the entire satellite. The furrows are 100-200 m wide and stretch for tens of kilometers. Their depth is from 20 to 90 meters. There are several hypotheses explaining the origin of these grooves, but so far there is no sufficiently convincing explanation, as well as an explanation of the origin of the satellites themselves. Most likely these are captured asteroids.

In 1945, American astronomer B. Sharpless discovered a secular acceleration in the orbital motion of Phobos. This meant that Phobos, strictly speaking, was moving in a very gentle spiral, gradually approaching the surface of Mars. If this continues, then in 15 million years—a very short period from a cosmogonic point of view (1/300 of the age of Mars)—Phobos will fall on Mars.

However, only 14 years later did they pay attention to this. By that time, celestial bodies had appeared that moved in exactly the same way. These were artificial satellites of the Earth. Braking in the earth's atmosphere caused them to decrease, and approaching the center of the Earth caused their movement to accelerate. In 1959, Soviet astrophysicist I. S. Shklovsky calculated that the effect of atmospheric friction on Phobos could cause the observed effect only if Phobos was hollow. The second hypothesis explaining the acceleration of Phobos by tidal interaction was put forward by geophysicist N.N. Parian.

The presence of a secular acceleration of Phobos has been repeatedly disputed due to the low accuracy of the first observations, and only time will give a final answer to this question. However, it is interesting that no secular acceleration was detected for Deimos.

American astronomer Asaph Hall was born on October 15, 1829. In 1877, he made his most important discovery: during the closest approach of Earth and Mars, he discovered two satellites of the latter - Deimos and Phobos.

In honor of the scientist, we found several interesting facts about the objects he discovered.

1. Deimos and Phobos always face the same side towards Mars. This is due to the fact that they are so-called synchronous satellites: the period of revolution of each of them coincides with the corresponding period of revolution around Mars. In this regard, Deimos and Phobos are similar to the Moon, the far side of which is also never visible from the surface of the Earth.

2. One day Deimos will fall to Mars, scientists believe. This is due to the fact that the movement of this satellite slows down due to the tidal influence of the planet. It has been proven that every hundred years Phobos becomes 9 cm closer to Mars, and in about 11 million years it will collapse on its surface. However, thanks to the same processes, Phobos may simply collapse in 7.6 million years.

3. Unlike the Moon and other satellites of the Solar System, Deimos and Phobos have a distinctly irregular shape, and in appearance they look more like a pair of cobblestones. More strictly speaking, their shape is close to a triaxial ellipsoid.

4. The sizes of Deimos and Phobos are very small. For comparison, the radius of the Moon is 158 times the radius of Phobos and approximately 290 times the radius of Deimos. The latter, until the 21st century, was considered the tiniest satellite of the solar system. The same applies to the distance from the “host”: the Moon is located at a distance of 384 thousand km from the Earth, Deimos and Phobos are 23 and 9 thousand km from Mars, respectively.

5. The names of the satellites were not chosen by chance: in ancient Greek mythology, Phobos (“fear”) and Deimos (“horror”) were gods who accompanied the god of war Ares in battles. In Roman mythology, Mars took the place of Ares. Thus, Phobos and Deimos were also satellites of Mars in ancient beliefs.

6. There is practically no attraction on Phobos, or rather, there is practically no gravity on the “Martian” side. This is caused primarily by the proximity of the satellite to the surface of Mars and the strong gravity from the planet. In other parts of the satellite, the gravitational force varies.

7. The issue of the appearance of the satellites of Mars remains the subject of heated debate to this day. The unusual shape of Deimos and Phobos and some other features make popular the version of Mars capturing two asteroids and turning them into satellites. However, the difference in their structure from the objects of the group of asteroids of which they could be part speaks against this version. According to one hypothesis, Deimos and Phobos may be parts of a once split apart single satellite.

8. Some similarity of Deimos and Phobos with asteroids, as well as their close location to the surface of Mars, will help conquerors of interplanetary space in the future colonization of space. It is on Martian satellites that they will probably test means of asteroid colonization after Mars itself has been relatively developed.

9. Even before the official discovery in 1877, there were speculations about two satellites of Mars. An interesting theory was put forward by Johannes Kepler in 1610: looking at the Moon and Jupiter, of which four satellites were known at that time, Kepler suggested that the number of satellites of planets increases exponentially with distance from the Sun. Thus, Mars must have had two. Writers Voltaire and Jonathan Swift also spoke about two companions. By the way, the only two objects on Deimos (the Swift and Voltaire craters) that have their own names are named after them.

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 gravitational force from Mars tears large rocks from the satellite, 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 Deimos was believed to be the smallest moon in the entire 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 amount of material broke off from the satellite, which 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 their own names - 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.