Phobos and Deimos

The planet Mars has two small satellites - Phobos and Deimos. Deimos circulates in an orbit distant from the planet by about 23 thousand km, and Phobos moves at a distance of only about 9 thousand km from Mars.

The planet Mars has two small satellites - Phobos and Deimos

The whole history of studying Phobos and Deimos is full of amazing events and fascinating riddles. Judge for yourself: the first mention of the presence of two small moons of Phobos and Deimos in Mars appeared not in scientific works, but in the pages of the famous "Gulliver's Travels" written by Jonathan Swift in the early 18th century. In the course of events Gulliver is on the flying island of Laputa. And local astronomers tell him that they managed to open two small companions circling around Mars. In fact, Phobos and Deimos were discovered by A. Hall only a century and a half after the novel was published, during the great confrontation of Mars in 1877, and they were discovered under extremely favorable atmospheric conditions after persistent, long-term observations, at the limit of the instrument's capabilities and the human eye!

However, Swift predicted not only the existence of Phobos and Deimos, but also that the radius of the orbit of the nearest satellite of Mars is equal to three diameters of the planet, and the outer - to five. Three diameters are about 20 thousand kilometers. Approximately at this distance is the orbit of Deimos. True, not an internal satellite, as claimed by Swift, but external - but still the coincidence is impressive!

Comparing the results of observations conducted in different years, astronomers came to the conclusion that the nearest satellite of Mars, Phobos, experiences inhibition, due to which it gradually approaches the surface of the planet. The phenomenon looked mysterious. In any case, no observed effects of celestial mechanics could be explained. One thing remained: to assume that the braking of Phobos is connected with the aerodynamic resistance of the Martian atmosphere. However, calculations have shown that the gas envelope of Mars at an altitude of 6,000 km is capable of providing adequate resistance only provided that the average density of the Phobos material is small. More precisely, it is implausibly small! Then it arose! the original idea: so small density of Phobos can be explained by its... hollowness! But we do not know the natural processes that could lead to the formation of empty inside the celestial bodies. The idea arose that Phobos, and possibly Deimos, were artificial satellites of Mars, created millions of years ago by intelligent beings, either inhabiting Mars at the time or flying from somewhere from outer space.

When a new, more powerful method of exploring the planets - automatic space stations - was available to Mars researchers, everything fell into place. On the satellite images it is clearly visible that Phobos and Deimos are huge blocks of irregular shape and, of course, of natural origin. If we compare the results of astronomical observations with what the space stations reported, a 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 along almost circular orbits, located in the plane of the equator of the planet, in the direction of its diurnal rotation. Deimos completes one full turn in 30 hours 18 minutes, and Phobos - for 7 hours 39 meters. Considering that the duration of the Martian day is slightly more than 24 hours 30 minutes, it is not difficult to imagine that Phobos is noticeably ahead of the daily rotation of the planet. Located on the surface of Mars, we would observe how Phobos and Deimos with their large semiaxes are always directed toward the center of Mars.

Flight of the automatic station "Viking-1" for the first time allowed 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 managed to determine the perturbation of the trajectory of its movement, caused by the attraction of Phobos. Having such data, it is not worth the effort to calculate the mass of the disturbing body. And knowing its dimensions, you can calculate the average density. For Phobos, it was close to 2 g/cm3. It is quite normal density, about the same as for a number of stony meteorites.

Of great interest are photographs of Phobos and Deimos. They were received by 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 the lunar craters are clearly visible. The largest crater on Phobos reaches in a diameter of 10 km. It is curious that at the time when the problem of low density of Phobos was discussed, it was suggested that this phenomenon is not explained by hollowness, but is the result of the processing of its surface by meteorites, as a result of which the Phobos substance acquired a strong porosity.

In addition to craters, Phobos' photographs show almost parallel furrows up to several hundred meters wide stretching for long distances. The origin of these mysterious bands remains unclear. Perhaps this is the result of a powerful impact of a large meteorite that "shook" Phobos and caused the formation of numerous cracks. Perhaps mysterious furrows arose from the tidal effect of Mars. In favor of this is the fact that on Deimos, located at a much greater distance from Mars, such details were not found. After all, it is known that gravitational influences weaken in proportion to the square of the distance.

As for the origin of Phobos and Deimos, it is possible that these are bodies of an asteroid type captured by Mars. Maybe they were formed even earlier than the planet itself. In any case, their further study is of interest for clarifying the regularities of the formation of the solar system.

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