Moons of Mars

© Vladimir Kalanov,
website"Knowledge is power".

Phobos (left) and Deimos (right) are two known moons of Mars

As already mentioned, Mars has two natural satellites called Phobos and Deimos. The main characteristics of the satellites are given in the table:

Satellite	Characteristics	Quantitative indicators
Phobos	Opening time	08/12/1877
	Dimensions	27x21x19 km
	Circulation period	7 hours 39 minutes
	Distance to Mars	9400 km
	Average density	2 g/cm³
Deimos	Opening time	08/10/1877
	Dimensions	15x12x11 km
	Circulation period	30 hours 17 minutes
	Distance to Mars	23400 km
	Average density	1.7 g/cm³

The small satellites of Mars are celestial bodies of irregular shape, very similar to asteroids. The largest size of Phobos is 27 km, and Deimos is 15 km. The orbits of both satellites are inclined approximately 2° to the plane of the Martian equator. Phobos is on average 9400 km away from Mars and has a very short orbital period - 7 hours 39 minutes, i.e. During a Martian day, it circles the planet three times. Deimos is 23,400 km away from Mars, and it takes 30 hours and 17 minutes to fly around Mars, i.e. longer than a Martian day. Like the Moon, turned to the Earth with one side, both satellites of Mars are always turned to it with the same side. Numerous craters are visible on the rocky surface of the satellites. The largest of them, with a diameter of about 10 km, is located on Phobos. Astronomers associate the origin of such a huge crater with a probable collision of Phobos with some large celestial body. No craters larger than 2.3 km in diameter have been found on Deimos. Based on the density of the craters, their age is determined to be 3 billion years.

Images of Deimos (left) and Phobos (right). The huge crater Stickney is visible on Phobos.

Hypotheses for the origin of the satellites of Mars

There are two hypotheses about the origin of the satellites of Mars. The first is that both satellites, formerly asteroids, were captured by the gravitational field of Mars and have been its satellites for several billion years. According to the second hypothesis, the satellites of Mars were once part of its mass, broken off as a result of a collision with some large celestial body. This hypothesis seems more logical because the orbits of the satellites are low, approaching a regular circle in shape, and their planes almost completely coincide with the plane of the orbit of Mars (inclination is only 2°).

American astronomer B. Sharpless in 1945 discovered the so-called secular acceleration in the movement of Phobos. This means that Phobos is moving in a gentle spiral, gradually approaching the surface of Mars. In approximately the same way, artificial Earth satellites move in spiral orbits. In the upper layers of the earth's atmosphere, the satellite slows down and descends, and approaching the Earth accelerates the satellite's movement. The atmosphere of Mars is so thin that at the altitude of Phobos orbit its effect on the satellite is practically absent. However, secular acceleration exists.

The famous Soviet astrophysicist I.S. Shklovsky in 1959 decided to calculate under what conditions braking in the upper layers of the atmosphere of Mars could lead to the satellite moving in a gentle spiral. The calculated altitude was taken as 6000 km. the result was sensational: the flight of Phobos in a gentle spiral is possible if it is... hollow, i.e. empty inside, like the artificial satellites of the Earth. It turns out that Phobos is also an artificial celestial body, made by some intelligent beings?!

But there was no sensation, because with the help of photographs transmitted to Earth by an automatic interplanetary station Mariner 8 it was finally established that Phobos and Deimos are solid stone blocks of irregular shape. Soon the Soviet scientist N.N. Pariysky found an explanation for the secular acceleration. According to this scientist, due to the proximity of Phobos to Mars, tidal waves of soil arise on the surface of the planet in much the same way as occurs on Earth from . The gravity of the Moon leads to the fact that the earth's crust rises and falls by almost half a meter twice a day following the movement of the Moon. Although the mass of Phobos is small, it is so close to the surface of Mars that it creates tidal waves (they are called tidal humps) much smaller than those that arise on Earth from the movement of the Moon, but still sufficient to influence the movement of Phobos. The tidal wave on Earth, due to friction and tension in the earth's crust, does not keep up with the Moon and lags behind its movement by about a quarter of the Earth's circumference. Something similar is happening on Mars. Phobos is slowed down by the attraction of tidal humps. Deimos has not seen any secular acceleration. How sensitive is the braking of Phobos by tidal humps? According to calculations, if such movement continues, Phobos may fall to the surface of Mars in ... 15 million years. Future studies and calculations will show how true such alarming forecasts are. Launches of Soviet automatic stations "Phobos-1" And "Phobos-2", carried out in 1988-1989 to study the movement of the satellites of Mars, ended in failure.

Today, Mars appears to be a desolate, cold, desolate world with a barely noticeable atmosphere and no liquid water. However, numerous convincing evidence suggests that the appearance of this planet was very different in the past. It was probably covered with lakes and rivers, had a denser atmosphere fueled by continuous volcanic eruptions, and had a milder climate. In a word, this world was potentially capable of generating and maintaining a spark of life for some time. However, if it once began to develop on the Red Planet, it stopped after the very first steps. Today, the presence of macroscopic life forms on Mars is not even discussed for a number of reasons: the lack of liquid water on the surface, a sufficient atmosphere, a magnetic field capable of shielding cosmic radiation, and an ozone layer that protects from ultraviolet rays. But regarding elementary forms of life the question is still open.

Mount Olympus

When, at the turn of the 1960s and 70s, the Mariner probes reached Mars and sent back the first photographs of the planet, scientists were struck by two circumstances. First, the tallest mountain in the entire solar system was discovered on Mars, a volcano large enough to cover most of the Apennine Peninsula. Secondly, not far from the mountain, a crack opened up, cutting the Martian surface and forming a canyon the size of an entire Earth continent.

So big that you can't see it!

Reaching a diameter of 500 km and a height of 27 km, Mount Olympus is the record holder in the entire solar system. And yet, its size and its relationship to the small radius of the planet would not allow an observer on the surface of Mars to admire its silhouette from afar. It's like looking at a mountain whose slopes are located in Rome, and the top rises in Livorno. Although panoramic views of Olympus are not available, a hypothetical observer would certainly sense the presence of a giant volcano from a number of features, including the spectacular cliffs surrounding it, rising almost vertically from the base to a height of 6 km.

First observations

Olympus Mons, which cannot be observed from the surface of Mars, is quite accessible to large telescopes from Earth. The first astronomer to see it was Giovanni Virginio Schisparelli. During the 1879 confrontation, he noticed a whitish speck, which he named Nix Olympica ("Snows of Olympus"). The glow discovered by the astronomer, however, was caused not by the presence of snow, but by clouds, which on Earth often gather near the highest peaks.

Life on Mars

Many images of the surface of Mars have been obtained, which show something similar to the winding beds of dry rivers. The almost indisputable fact of the past presence of liquid water on the Martian surface is a powerful incentive to search for microscopic life forms that, by evolving, could adapt to the inhospitable natural conditions that characterize Mars today. And today, the possibility of discovering the simplest forms of life in the depths of Mars cannot be completely excluded.

"Viking" and "Beagle"

The first serious studies of Martian life forms were carried out by biological laboratories located on the twin probes Viking 1 and Viking 2 that landed on Mars in 1976. The probes were equipped with a manipulator capable of collecting soil samples, which were subjected to a series of multidirectional experiments. The landing module launched in 2003 from the Mars Express probe was intended to conduct new experiments. The European Space Agency (ESA) named the probe Beagle 2 after the brigantine on which naturalist Charles Darwin made the very discoveries that led him to develop the theory of evolution. Unfortunately, Beagle 2 died during landing.

Conflicting results

One of the most controversial Viking probe experiments aimed at searching for biological activity on Mars was Labeled Release. It consisted of “feeding” the Martian soil with organic compounds marked with radioactive carbon. The assimilation of these organic compounds by microorganisms hypothetically present in the soil would lead to the emission of carbon dioxide (CO2), containing radioactive carbon atoms. From the very beginning, the experiment resulted in the formation of a significant amount of CO2, which subsequently began to decrease and eventually disappeared. This result could hardly indicate the presence of biological activity. The initial formation of CO2 was declared to be the result of the presence in the Martian soil of a large amount of peroxides - highly reactive compounds capable of producing it. The idea arose to repeat the experiment, preheating the soil to 50°C: the heat was supposed to eliminate traces of the presence of hypothetical bacteria, leaving the peroxides intact. Carbon dioxide production, however, dropped to zero. Were the bacteria actually responsible for the CO2 production, or were the Martian peroxides particularly sensitive to heat? And today, 30 years later, there is no unambiguous interpretation of the results obtained by Viking.

Mysterious meteorite

The controversy surrounding the possible presence of life on Mars periodically resumes and even among scientists causes heated controversy. In addition to the presence of water, another source of debate was the discovery of traces of supposed fossil microbacteria in a meteorite of Martian origin.

Found in Antarctica

A meteorite, possibly of Martian origin, was discovered in 1984 in Antarctica, in an area called Alan Hills, which is why it received the designation ALH 84001. This piece of rock, weighing about 2 kg, probably turned out to be the hero of an incredible epic: approximately 17 million years ago it was “launched” from Mars by a meteorite impact, fell to Earth about 13,000 years ago and was found in 1984. Gases were discovered inside it, the composition of which is very similar to the gases of the Martian atmosphere.

But that's not all: in August 1996, Johnson Space Center researcher David McKay announced the discovery of traces of suspected bioactivity, possibly explained by the presence of fossilized Martian bacteria. The rock contains aromatic polycyclic hydrocarbons - substances that could be formed both inorganically and organically. The latter hypothesis seemed preferable to McKay's group, since crystals of magnetic iron ore and other iron compounds were also discovered - by-products of the activity of certain bacteria. In addition, fossil bacteria were evidenced by the encountered ovoid formations of a slightly elongated shape, similar to small worms.

Magnetic iron ore crystals

The question remains open. Since then, confirmations and refutations have followed each other at a frantic pace.

The next chapter of this story was written in 2001, when Imre Friedman of the University of Florida reported that, according to his observations, magnetic iron ore crystals form a chain - this would be normal if their origin was explained by bioactivity. Friedman also claimed that he saw traces of a fossil membrane enveloping this chain, as happens with terrestrial bacteria that produce magnetic iron ore.

Skeptics objected that these nanobacteria could be “ours,” introduced into the meteorite at some point, particularly during the preparation of laboratory samples for analysis. In general, nothing is clear yet. Everything leads to the fact that the dispute will continue in the coming years, at least until some probe is sent to check everything on the spot.

Moons of Mars

Two small satellites of Mars, Phobos and Deimos (“fear” and “terror”) were discovered in 1877 by the American astronomer Asaph Hall. They orbit so close to the Red Planet that it makes them difficult to detect. The size of the satellites also does not make the task easier: the diameter of Phobos is approximately 27 km, and Deimos is only 15. Many characteristics of these satellites suggest that they are tiny planets captured from the nearby Main Asteroid Belt.

On the surface of Phobos there is a striking crater with a diameter of 10 km, occupying slightly less than half the size of the entire moon. It was named Stickney in honor of Asaph Hall's wife, who apparently played a decisive role in encouraging the scientist to continue his research and ultimately discover these moons.

Looking into the details

A careful study of Phobos, carried out by the American Mars Global Surveyor probe, made it possible to find out how 50-meter stones appeared on the wall of the Stickney crater. They may have been thrown out as a result of the collision. The force of gravity on Phobos was even accurately calculated: a person weighing 68 kg would weigh only 57 g there! The probe's spectrometer also recorded that between the illuminated and shadowed sides of the satellite, the temperature varied from -4°C to -112°C. This difference suggests that the surface of Phobos is covered with fine dust, which releases heat very quickly after sunset. When observing Deimos, it is striking that its surface is much smoother and, compared to Phobos, has fewer differences: the few craters do not exceed 2.5 km in diameter.

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.

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.

Deimos and Phobos are small satellites of our neighbor, Mars, by cosmic standards. Despite their rather menacing names, they look modest compared to the rest of the celestial bodies of the Solar System. Nevertheless, the “Fear” and “Horror” that accompanies Mars in its eternal circling in orbit are of great value to researchers and are of considerable interest to astrophysicists.

Writer's prediction

Few people know that the discovery first occurred not at the observatory, but on the pages of Jonathon Swift’s famous work “Gulliver’s Adventures.” In one of the chapters, scientists from the flying island of Laputa told the main character about two bodies they discovered moving around Mars. The story of Gulliver's adventures appeared at the beginning of the eighteenth century. The scientific discovery of Phobos and Deimos took place much later - in 1877. It was performed by A. Hall during the great confrontation of the Red Planet. The discovery is worthy of commemoration for many reasons: it was made possible by exceptionally favorable weather conditions and the incredible work of a scientist who only had rather imperfect tools from the late nineteenth century.

Crumbs

Deimos and Phobos are inaccessible for study using amateur equipment due to their modest size. They are many times smaller than the Moon. The satellite Deimos is the smallest such object in the entire solar system. Phobos is somewhat larger than its “brother”, but also cannot boast of impressive size. Since the beginning of the era of astronautics, both objects have been studied using several devices: Viking-1, Mariner-9, Phobos, and Mars Express. During the research, images of satellites were obtained, as well as data on the nature of their surface and composition.

Origin

Today, the question of where Mars got its satellites is not entirely clear. One of the probable versions says that Deimos and Phobos are asteroids captured by the Red Planet. Moreover, it is assumed that they arrived from distant parts of the solar system or even formed outside its borders. Less plausible, scientists call the hypothesis of the origin of satellites from the Main One. Perhaps a certain role in the appearance of such a “retinue” on Mars was played by the giant Jupiter, which with its powerful gravitational field distorts the orbits of all asteroids flying nearby.

"Fear"

Phobos is the closest to. Like Deimos, it has an irregular shape and moves in a nearly circular orbit around Mars. Phobos is always turned to the planet with one side, in which it is similar to the Moon. The reason for this is the coincidence of the periods of rotation of the body around Mars and around its own axis.

The orbit of Phobos is very close to the Red Planet. According to scientists, the satellite is gradually decreasing under the influence of Mars (by a little less than ten centimeters per year). In the distant future it is threatened with destruction. Either Phobos will fall to Mars in about 11 million years, or a little earlier, in 7 million years, the planet will be torn apart and form a ring of debris around it.

Surface

Phobos and Deimos are satellites covered with traces of meteorite encounters. The surface of both is dotted with craters of different sizes. The largest of them is located on Phobos. The diameter of the crater is 10 km; for comparison, the size of the satellite itself is 27 by 21 km. An impact that left such a mark could easily lead to the complete destruction of this cosmic body.

The surface of Phobos has one more feature that distinguishes it from its “brother”. These are almost parallel furrows up to several hundred meters wide, occupying a vast area. Their origin remains a mystery. According to scientists, they may also be the consequences of a powerful impact or be a consequence of the gravitational influence of Mars.

"Horror"

Deimos has dimensions of 15 by 12 kilometers and circles in an orbit more distant than Phobos: the distance to the planet is approximately 23.5 thousand kilometers. “Horror” completes one revolution around Mars in 30 hours and 18 minutes, which is slightly longer than the length of a day on the planet and more than four times slower than the movement of Phobos. It takes 7 hours and 39 minutes to fly around the planet.

Deimos, unlike its “brother,” is not going to fall. Some scientists suggest that the Horror's likely fate is to overcome the gravity of Mars and fly into space.

Structure

For a long time it remained unclear what Deimos and Phobos were hiding inside. Scientists knew only about the suspiciously low density of these bodies, calculated in the process of observations from Earth. In connection with these data, the most fantastic assumptions arose about what objects accompany Mars. Phobos and Deimos in some hypotheses were listed as artificial hollow satellites created in ancient times and, possibly, by the civilization of another planet.

After studying the data obtained, it was discovered that the “retinue” of Mars is more similar to asteroids, that is, natural objects. The density of matter on the satellites was calculated to be approximately 2 g/cm 3 . A similar indicator is found in some meteorites. Today, the low density of the satellites of Mars is explained by the peculiarities of their structure: Phobos and Deimos are believed to consist of a mixture of carbon-rich rock with ice. In addition, images from spacecraft suggest that the surface of the object closest to Mars is covered with a meter-long layer of dust, similar to the regolith of the Moon.

The “retinue” of the Red Planet still holds many secrets, so astronomers are constantly developing projects for flights to it. Mars itself is also of great interest. Some projects consider it as a candidate for terraforming or a suitable location for the extraction of certain resources. Also in scientific circles, the seemingly fantastic prospect of placing research bases first on the Moon and then on Mars is being discussed quite seriously. In addition, the study of such objects can always bring information not only about themselves, but also about the Solar system, its formation and characteristics. And even about the Universe as a whole.