Phobos and Deimos are artificial satellite. "Fear" and "Terror" of the red planet. The origin of the satellites of Mars
Mars has two moons, they are called Phobos and Deimos. Both were discovered in 1877 by the American astronomer Asaf Hall. The discovery was made at the United States Naval Observatory in Washington DC. The astronomer saw Deimos on August 12 at 7 hours 48 minutes GMT, and he discovered Phobos on August 18 at 9 hours 14 minutes GMT. Thus, the red planet has officially acquired satellites.
Phobos is translated from ancient Greek as "fear", and Deimos as "horror". Why were these cosmic bodies named so? By analogy with the god of war Mars. According to ancient Greek mythology, he had two sons - Deimos and Phobos. They accompanied his father everywhere and instilled terror and fear in the hearts of people. And so astronomers decided to translate ancient myths into reality. Thus, they paid tribute to Ancient Greece.
The satellites are small in size. Each of them rotates in its own orbit, while Phobos is in a closer orbit to Mars, and Deimos is in a distant one. The orbits of these cosmic bodies are almost round. The distance from Phobos to Mars is 6 thousand km. It is much closer to any other known planetary moon in Solar system... The distance from Deimos to Mars is 23,460 km.
The satellites of Mars are always turned to it by the same side, as they rotate around their axes with the same period as around the red planet. These objects have an irregular shape, that is, different from round. They look like dark rocky formations and resemble asteroids.
Phobos
The dimensions of this Martian moon are 27 km × 22 km × 18 km, and the mass is 1.0659 × 10 16 kg. With such a small mass, the satellite could not take a rounded shape under the influence of its own gravity. Accordingly, there is no atmosphere, and the force of gravity is extremely low. This space body has an albedo of 0.071. This indicates a weak reflection. sunlight from the surface.
The porous surface has a low density. It is assumed that the satellite contains a large amount of ice. There are many craters on it. The largest of them is called Stickney in honor of Asaf Hol's wife Angelina Stickney. Its diameter is more than 9 km, and the crater occupies a significant proportion of the satellite's area.
There are parallel grooves on the surface near Stickney. Their depth reaches 30 m, and their width is 100-200 m. It is assumed that these are crater chains formed at different periods of time. The cause of their occurrence was the impact of meteorites, as a result of which the rocks of the satellite were thrown into space.
The orbital period around Mars is 7 hours 30 minutes. The half-orbital axis is 9377 km. Experts say that Phobos' orbit has a downward trend (tidal drag). Every 100 years, the satellite approaches the surface of the red planet by 1.8 meters. After 43 million years, this Martian moon will fall on the main cosmic body, but before that it will collapse into many pieces.
An interesting hypothesis was put forward by the Soviet astrophysicist Joseph Samuilovich Shklovsky in 1958. Studying the orbital motion of Phobos, he assumed that the satellite was empty inside. That is, this space object is of artificial origin. According to calculations, it was a hollow iron ball with a wall thickness of no more than 6 cm.
However, later errors were discovered in Shklovsky's calculations. And accurate measurements of the orbit were carried out in 1969. Spacecraft have measured the density of Phobos. It is equal to 1,887 g / cc. The satellite is a natural space debris and there is nothing artificial in it. At the same time, it contains voids (approximately 30%), and it is not a solid piece of rock.
Deimos
As already mentioned, the satellites of Mars are 2 cosmic bodies, and the farthest of them in relation to the red planet is Deimos. Its dimensions are 15 km × 12.2 km × 11 km, and its mass is 1.4762 × 10 15 kg. The average radius is 6.2 km. This satellite makes a complete revolution around Mars in 30 hours and 17 minutes. The half-axis of the orbit is 23463 km. Deimos' orbit is slowly increasing, and the red planet will lose its second moon in the distant future.
The satellite is highly nonspherical in shape. It consists of a rock rich in carbonaceous material. There are few craters on the surface. This is explained by the partial filling of the impact dents with regolith. The latter has a high density and is equal to 1.471 g / cc. see The two largest craters are named Swift and Voltaire. They are named so in honor of famous writers who assumed that Mars has two moons long before their discovery.
If you stand on Mars, you can see Deimos, which regularly passes in front of the Sun. But it is so small that it cannot cause a total eclipse. It appears as a small black dot crossing the solar disk. This spectacle was photographed 2 times by landing modules operating on the red planet. The albedo of this satellite is 0.068.
The origin of the satellites of Mars
It is unknown how the satellites of Mars came to be. There are many hypotheses, and they are all extremely contradictory. The main hypotheses state that Deimos and Phobos became satellites as a result of asteroid capture or accretion. During asteroid capture, the asteroid enters the orbit of a large planetary body and becomes its satellite. Accretion is understood as the accumulation of particles in a massive object by means of gravitational attraction. There is also an assumption that 2 asteroids entered the Martian orbit from the asteroid belt.
In addition, there is a binary asteroid theory. This is when 2 asteroids revolve around a common barycenter. Once in the zone of action of Mars, they were torn apart by tidal forces, and each of them began to revolve around the red planet in its own orbit. There are other scientific assumptions related to theories of planet formation (planetesimal hypotheses). They all look very attractive and convincing, but no one knows the real truth.
Vladislav Ivanov
MOSCOW, July 21 - RIA Novosti. The Hubble Orbiting Observatory accidentally obtained a series of high-quality photographs of Phobos orbiting Mars, which NASA specialists used to prepare a time-lapse video, according to the space telescope's website.
Today, two small irregular satellites revolve around Mars - Phobos and Deimos with a diameter of 22 and 12 kilometers, only 10 and 23 thousand kilometers away from the surface of the red planet. Today, many scientists believe that both of these moons are not planets, but asteroids captured by the pull of Mars in the distant past.
Planetologists: the destruction of Phobos will turn Mars into the "Lord of the rings"Phobos will collapse under the influence of tidal forces in the next 20-40 million years and its remains will form a ring similar in density and appearance to those possessed by Saturn, while the only "lord of the rings" in the solar system.Interestingly, Phobos is approaching Mars and will be destroyed and turned into a giant dust ring in 20-40 million years, while Deimos, on the contrary, is moving away from it and in the distant future it will "escape" from the red planet.
Now scientists can hardly explain why this is happening, and how Deimos and Phobos could have ended up in their current orbits. Astronomers recently suggested that in the past, Mars may have had three moons, one of which has already fallen to its surface.
The Soviet missions Phobos-1 and Phobos-2, as well as the Russian mission Phobos-Grunt, could solve the riddle of the formation of Phobos and Deimos. All of them either did not reach the moons of Mars, or mysteriously failed when they approached Phobos. The reputation of the "damned moon" was recently strengthened by the American probe MAVEN, which narrowly escaped a collision with Phobos in early March this year.
"Hubble", fortunately for mankind, is far from Mars, which allows it "with impunity" to follow its natural satellites and study the mysteries of their birth.
In May last year, scientists used it to study individual regions on the surface of Mars, photographing the red planet at the moment when it approached the Earth as close as possible over the past few years. Together with photographs of Mars, they accidentally received pictures of Phobos emerging from behind the "back" of Mars and starting its next seven-hour flight around the red planet.
These photographs, which Hubble received over 20 minutes, were used by scientists to prepare a video of Phobos' flyby around Mars. These photographs and videos have no serious scientific value, but they allow us to see how the moon of a planet far from us revolves around its "big sister".
Satellites of Mars
© Vladimir Kalanov,
site"Knowledge is power".
Phobos (left) and Deimos (right) are two famous moons of Mars
As already mentioned, Mars has two natural satellites called Phobos and Deimos. The main characteristics of the satellites are shown in the table:
| Satellite | Specifications | Quantitative indicators |
| Phobos | Opening time | 08/12/1877 |
| Dimensions (edit) | 27x21x19 km | |
| Period of circulation | 7 hours 39 minutes | |
| Distance to Mars | 9400 km | |
| Medium density | 2 g / cm³ | |
| Deimos | Opening time | 08/10/1877 |
| Dimensions (edit) | 15x12x11 km | |
| Period of circulation | 30 hours 17 minutes | |
| Distance to Mars | 23400 km | |
| Medium density | 1.7 g / cm³ | |
The small satellites of Mars are irregularly shaped celestial bodies, very similar to asteroids. The largest size of Phobos is 27 km, and Deimos is 15 km. the orbits of both satellites are tilted approximately 2 ° to the plane of the Martian equator. Phobos is removed from Mars by an average of 9400 km and has a very short orbital period - 7 hours 39 minutes, i.e. during a Martian day, it orbits the planet three times. Deimos is 23400 km from Mars, and it takes 30 hours 17 minutes to fly around Mars, i.e. longer than a Martian day lasts. Like the Moon turned to the Earth on one side, both satellites of Mars are always turned to it by 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 the probable collision of Phobos with some large celestial body. No craters with a diameter of more than 2.3 km have been found on Deimos. Based on the density of craters, their age is determined at 3 billion years.
Images of Deimos (left) and Phobos (right). The huge Stickney crater is visible on Phobos.
Hypotheses of 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, in the past asteroids, were captured gravitational field Mars and for several billion years have been its satellites. According to the second hypothesis, the satellites of Mars were once part of its mass, which broke away as a result of a collision with some large celestial body. This hypothesis seems to be more logical because the orbits of the satellites are low, in shape approaching a regular circle, and their planes almost completely coincide with the plane of the orbit of Mars (the inclination is only 2 °).
American astronomer B. Sharpless in 1945 discovered the so-called secular acceleration in the motion of Phobos. This means that Phobos is moving in a gentle spiral, gradually approaching the surface of Mars. In approximately the same way, in spiral orbits, artificial satellites of the Earth move. In the upper layers of the earth's atmosphere, the satellite decelerates and descends, and approaching the Earth accelerates the satellite's motion. The atmosphere of Mars is so rarefied that at the altitude of Phobos' orbit, its effect on the satellite is practically absent. However, there is a secular acceleration.
The famous Soviet astrophysicist I.S. Shklovsky in 1959 decided to calculate under what conditions deceleration in the upper layers of the atmosphere of Mars can lead to the movement of the satellite in a gentle spiral. The design altitude was taken as 6,000 km. the result is sensational: Phobos can fly along a gentle spiral if it is ... hollow, i.e. empty inside, like artificial earth satellites. It turns out that Phobos is also an artificial celestial body made by some intelligent beings ?!
But the sensation did not work, 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 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 about the same way as it happens on Earth from. The attraction of the moon leads to the fact that the earth's crust rises and falls twice a day almost half a meter following the movement of the moon. Although the mass of Phobos is small, but it is so close to the surface of Mars that it creates tidal waves (they are called tidal humps) are much smaller than those that arise on Earth from the motion of the Moon, but still sufficient to influence the motion of Phobos. The tidal wave on Earth, due to friction and stress in the earth's crust, does not keep up with the Moon and lags behind its motion by about a quarter of the Earth's circumference. Something similar happens on Mars. Phobos is inhibited by the attraction of tidal humps. Deimos has not seen the secular acceleration. How sensitive is the inhibition of Phobos by tidal humps? According to calculations, if such a movement continues, then Phobos may fall to the surface of Mars in ... 15 million years. Whether such alarming predictions are correct will be shown by future research and calculations. Launches of Soviet automatic stations Phobos-1 and Phobos-2, carried out in 1988-1989 to study the motion of the satellites of Mars, ended in failure.
It seems that scientists have figured out the mystery of the origin of Phobos and Deimos - two natural satellites of Mars. For many years, the shape of both satellites, reminiscent of potatoes, has persuaded scientists to believe that both current satellites of Mars are just asteroids captured by the planet in the distant past. However, this hypothesis could not explain the fact that the orbits of the satellites are circular and lie close to the equatorial plane of the planet.
An alternative explanation, suggesting that these moons, 22 and 12 km in size, were each born as a result of the impact of some body on Mars, also raised a number of questions, for example, why, as a result of the collision, Mars was left with two small satellites, and not with one moon, as happened in the case of the Earth.
In an article published in the journal Nature geoscience, scientists led by Pascal Rosenblatt of the Royal Observatory of Belgium gave a convincing answer to a question that has worried scientists for decades, and came to the conclusion,
that these blocks really owe their birth to a powerful blow.
Computer simulations of how the orbits of the debris changed from this collision helped to understand this. The created animation illustrates how events developed around Mars after the catastrophic impact:
The so-called North Polar Basin is the largest basin in the northern hemisphere of Mars. It occupies about 40% of the surface of the entire planet; it is assumed to have an impact origin and, apparently, was formed as a result of a catastrophic collision of Mars with a giant body billions of years ago. The shape and size of the pool make it possible to assume that it was formed as a result of a body impact,
most likely, protoplanets with a size of 2 thousand km.
Modeling showed that as a result of this impact, 10 20 kg of debris were thrown into space, forming a ring, the total mass of which could be 10 thousand times the total mass of Phobos and Deimos. Calculations show that the formation of satellites inside the disk of debris occurs close to the inner edge of the disk, where the concentration of debris is maximum, their speeds are high, which means that collisions are frequent. However, the formation of satellites is impossible within a certain area where the gravitational influence of the planet prevails - the so-called Roche limit. This is the radius of the satellite's circular orbit, on which the planet's tidal forces are still balanced by the satellite's self-gravity (in the case of Mars, 3 planetary radii).
Therefore, the most ancient satellites should form at the leading edge of the disk slightly beyond the Roche limit. However, in the case of Mars, this is too close for the orbits of these satellites to remain stable on geological time scales. The fact is that Mars has a low speed of its own rotation (only 24.7 hours), therefore all satellites rotating within the so-called synchronous radius (~ 6 radii of Mars) rotate faster than the planet itself. And this means that Mars gradually slows down such satellites, because each of them causes tidal humps on the planet,
and with each revolution they spin it, and the satellites themselves slowly lose their orbital momentum and go out of orbit.
This is what happens today with Phobos - it is known that the satellite is located at a distance of 2.76 radius of Mars, makes a complete revolution in just 8 hours
and most importantly - it is gradually approaching the planet at a speed of 2 cm per year!
Forecasts for him are disappointing - calculations show that in the next 20-40 million years, Phobos, finding itself in an orbit of 2 radii of Mars, will be torn apart by tidal forces and itself will create a ring of debris that will fall out in the vicinity of the planet's equator. In the case of the Earth, apparently, everything happened exactly the opposite. The first satellites were formed after a similar impact, also at a distance of three radii. However, due to the fact that the early Earth rotated on its axis five times faster than now, it did not de-orbit, but threw the only Moon further away from itself.
Having traced the evolution of Phobos and Deimos in time, scientists have established that both satellites most likely formed near a synchronous radius (6 R), however, to explain the appearance of the North Polar Basin, a third body was missing - a large, rather close moon (several hundred kilometers in diameter).
Actually, this moon, with its gravity, gave rise to Phobos and Deimos, blinding them from the debris in two resonant orbits.
Having done its "job", the large third large moon (possibly Mars had other satellites, but they all left orbit) fell onto the planet, losing its orbital momentum and forming the mentioned pool.
The existence of this third moon in the distant past of Mars is a key finding in the work of scientists. Calculations show that as a result of the supposed megacollision, half of the debris comes from the planetary material, half from the impactor material. Currently, Phobos has already gone inside the Roche limit and scientists see that its surface has cracked due to the tidal effect of Mars. Scientists hope to find out about its composition with the help of the upcoming Japanese mission Martian Moons Explorer.
Comparative sizes
The planet Mars has the moons Deimos and Phobos, which are believed to be captured asteroids. Phobos and Deimos were discovered in 1877 by Asaph Hall and were subsequently named after the Greek gods. It is possible that Mars may have satellites less than 50-100 meters in size in its orbit and a dust ring between Phobos and Deimos, but so far none of this has been discovered.
Asaph Hall, the astronomer who discovered the moons of Mars, originally discovered Deimos on August 12, 1877 around 7:48 UTC, and Phobos on August 18, 1877, at the United States Naval Observatory in Washington, DC, at approximately 9:14 GMT. At the time, he was busy deliberately looking for Martian moons. The telescope with which the moons were discovered - 66 cm refractor. In 1893 it was re-assembled and put into a new dome, where it remains to this day.
Companions in mythology
Image of Deimos obtained spacecraft MRO in 2008
The Greek god Phobos - fear and the Greek god Deimos - horror, accompanied the father of Ares, the god of war, into battle. Ares, it was known to the Romans as Mars.
Many believe that Asaph Hall named the satellites of Mars, but the names of the satellites were suggested by Henry Madan and are taken from Greek mythology.
Visibility of satellites from Mars
When viewed from the surface of Mars, the satellites are clearly visible. To see them, you need to be near the equator of the planet, from this position Phobos will be about a third of the size of the full Earth Moon. Its angular dimension is 8 by 12 arc minutes. It looks smaller when the observer is farther from the equator of Mars, and is completely invisible (always behind the horizon) in the region of the polar caps of Mars.
A snapshot of the Curiosity rover on August 1, 2013. The image shows the satellites of Mars: Phobos and Deimos in one frame!
Deimos is more like bright star or a planet, for a Martian observer it is slightly larger, brighter than Venus in the Earth's sky and has an angular diameter of about 2 minutes. The angular diameter of the Sun on Mars is about 21 arc minutes. Thus, there are no full-fledged solar eclipses on Mars, as on Earth, the satellites are too small to completely cover the solar disk. On the other hand, partial solar eclipses of Phobos (one might even say: transit along the solar disk) are very common and occur almost every night.
Structure
The largest of the so-called Monoliths on Phobos rises about 85 meters above the surrounding landscape
Based on data on mass, density and composition, the structure of the satellites is fully consistent with small asteroids. Except that due to the low density of Phobos, the latter is most likely almost a pile of stones held together by the weak gravity of the satellite. Their surface is covered with a 100 m layer of regolith and heavily “strewn” with craters.
Interesting facts about Phobos and Deimos
The motions of satellites are very different from those of our own moon. Phobos rises in the West and sets in the East, completing 1 revolution in just 7 hours and 40 minutes, while Deimos, being in close proximity to the synchronous orbit, also rises in the east, but very slowly. Despite a 30-hour orbit, Deimos' journey across the sky of Mars takes 2.7 days to enter the West. The inclination of the orbits of Phobos and Deimos to the equator of Mars is about 1 degree. The mass of these tiny moons is very small: 10 and 2 × 10 * 15 kilograms, respectively.
Influence of Mars
Natural satellites of Mars are tidally blocked by the planet's gravity (like our Moon) and are always facing it on one side. Since Phobos orbits Mars faster than the planet itself, tidal forces are slowly but steadily reducing the radius of its orbit.
At some point, in the future, when it gets close enough to Mars and tidal forces will tear Phobos apart. Several craters on the surface of Mars, located near the equator, indicate that the planet may have had many other small satellites that met the fate awaiting Phobos, and that the Martian crust had time to shift between these events. Deimos is located far enough from the planet, and its orbit is slowly increasing all the time, as is the case with our own moon.
Information about the satellites of Mars
| Name | Dimensions (km) | Weight (kg) | Semi-major axis of the orbit (km) | Period of circulation(h) | Travel speed in km / s |
| Phobos | 22.2 km (27 × 21.6 × 18.8) km | 10.8 × 10 15 | 9,377 km | 7.66 | 6,2 |
| Deimos | 12.6 km (10 × 12 × 16) km | 2 × 10 15 | 23,460 km | 30.35 | 3,94 |
Origin
The origin of the Martian moons remains controversial. The surface of the moons has much in common with carbon C-type asteroids, and the spectrum, albedo and density are very similar to C- or D-type asteroids. Based on their similarities, the dominant hypothesis today is that both moons could have been captured from the main asteroid belt.
Both satellites have almost circular orbits lying almost exactly in the equatorial plane of Mars, and, therefore, the theory, their capture requires that they initially move in a very elongated orbit, which then, due to the resistance of the atmosphere and the planet's tidal forces, took on its current form. However, it is not clear how the capture of Deimos occurred. Capturing also requires energy dissipation (when moving to another orbit) and the present atmosphere of Mars is too thin to capture an object like Phobos by atmospheric deceleration. Astronomer Jeffrey Landis noted that the capture could have occurred if the original body was a double asteroid, which then split as a result of the planet's tidal forces.
Phobos can be a second generation object, i.e. it could have already formed in the orbit of the planet, after the very formation of Mars, and not be formed simultaneously with the planet.
Alternative hypothesis of education
Another satellite formation hypothesis claims that Mars was once surrounded by many bodies, the size of current satellites, that were thrown into its orbit as a result of a collision with a large planetesimal. The high porosity of Phobos (density 1.88 g / cm3 and voids, which make up 25 to 35 percent of the volume) are not in favor of asteroid origin.
Infrared observations of Phobos indicate that it mainly contains phyllosilicates, which are well known on the surface of Mars. Its spectra differ from all classes of chondrites - meteorites of asteroid origin. Based on these data, Phobos was formed from material that was thrown into the planet's orbit when Mars collided with an asteroid or other large body.
Solar eclipses on Mars
Solar eclipse on Mars, starring Phobos
Another variant of the eclipse