Mars has two moons, they are called Phobos and Deimos. Both were discovered in 1877 by the American astronomer Asaph 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... From Deimos to Mars, the distance 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 equal to 0.071. This indicates weak reflection of 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, after 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-axis of the orbit is 9377 km. Experts say that Phobos' orbit has a downward trend (tidal braking). 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 Iosif Samuilovich Shklovsky in 1958. Studying orbital motion 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 found 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 space 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 rocks 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 density of the latter is high and is equal to 1.471 g / cc. see The two largest craters are named Swift and Voltaire. They are named after famous writers who assumed that Mars had 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 full eclipse... It appears as a small black dot crossing the solar disk. This spectacle was photographed 2 times by the 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 theory about a binary asteroid. This is when 2 asteroids revolve around a common barycenter. Once in the range 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). All of them look very attractive and convincing, but no one knows the real truth.
Vladislav Ivanov
It seems that scientists have figured out the mystery of the origin of Phobos and Deimos - two natural satellites Mars. For 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 a 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.
To understand this helped computer simulations of how the orbits of the debris from this collision changed. 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 entire planet's surface; 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 2 thousand km in size.
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 predominates - 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. This means that Mars is gradually slowing down such satellites, because each of them causes tidal humps on the planet,
and with each revolution they spin it, while 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 near 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 it is 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 (perhaps 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 alleged 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 gone cracks due to the tidal effect of Mars. Scientists hope to learn about its composition with the help of the upcoming Japanese mission Martian Moons Explorer.
Developments
NASA rover "Curiosity" first filmed the movement of two Martian satellites - Phobos and Deimosby making a series consecutive photographs from the surface of the Red Planet.
For the first time, such a phenomenon as an eclipse of one of the "moons" of another, was recorded using photographic telephoto lens apparatus, and the image is so clear that even the craters of the satellites can be discerned.
In a 30-second interval, the robot made 41 photoswhen the larger of the satellites - Phobos - passed in front of Deimos, completely blocking it out. This phenomenon has been observed August 1... Researchers from Jet engine laboratories NASA stitched together all of the images in the correct sequence to create a video.
This video will allow scientists to learn more about the satellites of our neighbor Mars, including getting more details about their orbits... As a result, it will be possible to learn more about the influence of Phobos on the solid surface of the planet. Also, scientists plan to figure out exactly how and how systematically the orbit of another satellite, Deimos, is changing.
The two satellites of Mars were in view of the rover's camera shortly after it was turned on for data transmission. Thus, observations allowed spend the minimum amount of power of the rover.
NASA Mars Science Laboratory uses the rover "Curiosity" and his 10 scientific tools to explore the history of the Red Planet in the Galais crater, where conditions are most favorable for such a project, according to scientists. As is known, "Curiosity" has been on the surface of Mars for a whole year.
Satellites of Mars
Mars has everything 2 satellites: Phobos (translated from Greek "fear") and Deimos ("horror"). They revolve around the Red Planet, like the Moon, around the Earth, therefore they are turned towards the surface only one side.
Deimos
Outwardly, these satellites are very look like asteroidsThey are not round like the Moon, but just like our satellite, they are covered with many craters. There is a version that these satellites were once captured by the gravity of Mars when they flew by.
Phobos
The presence of two satellites on Mars predicted more Johannes Kepler at the beginning of the 17th century, but then the scientist was guided by a strange logic: the further the planet is from the Sun, the more satellites it has.
He also wrote about the satellites of Mars Swift in his famous novel "Gulliver's Travels" in the middle of the 18th century, describing their sizes and orbits, unaware that the real picture is not much different from the fantasy.
Phobos' orbit gradually becomes getting closer to the surface of Mars, and the orbit of Deimos is vice versa, moving away from the planet... There is a high probability that someday Phobos will fall to Mars.
Phobos diameter is less than 1 percent from the diameter of the Earth's satellite - the Moon, and its orbit is much closer to the surface of Mars than the orbit of the Moon to the surface of the Earth.
The diameter of the largest moon of Mars Phobos in total 22 kilometers, and its distance from the surface of the planet is only 6 thousand kilometers.
If you look at Phobos from the surface of Mars, its size will be approximately twice smaller size full moonthat we see from Earth.
Earth's satellite The moon cannot be compared to the Martian satellites. The diameter of the moon is 3476.4 kilometers, when as the average distance between two objects - 384.5 thousand kilometers.
Phobos is likely to be destroyed by the tidal forces of Mars in the next 100 million years. Credit: HiRISE, MRO, LPL (U. Arizona), NASA.
Mars and Earth have several things in common. Like Earth, Mars is a planet terrestrial group (i.e. this planet is composed of silicate rocks and minerals). It also has polar ice caps, a tilted axis, and in the past probably had oceans filled with liquid water. In addition, Mars and Earth are the only terrestrial planets that have natural satellites.
In fact, Mars has two moons - these are Phobos and Deimos (they are named after the Greek gods of terror and terror, respectively). Deimos is smaller than the Moon, and its orbit is located at a greater distance from the planet. This satellite has the characteristics of an asteroid, which can be an argument in determining the place of its origin.
Deimos was discovered in 1877 by the American astronomer Asaph Hall, who purposefully searched for the Martian moons while at the US Naval Observatory (USNO). The name of the satellite was given by Henry Madan shortly after its discovery.
Since Deimos is not a round body, its average radius is between 6 and 6.38 km. (3.73-3.96 miles) or about 15 × 12.2 × 11 kilometers (9.32 × 7.58 × 6.835 miles), making it almost half the size of Phobos. Due to the small mass - about 1.4762 * 10 15 kilograms, the surface gravity of Deimos is weak (the acceleration of gravity is only 0.0039 m / s 2).
The orbit of Deimos is close to circular, the perihelion is 23455.5 km, and the apogee is 23470.9 km, so the average distance is about 23463.2 km. With an average orbital speed of 1.3513 km / s, for one revolution around Mars, Deimos spends 30 hours, 18 minutes and 43.2 seconds.
Both Deimos and Phobos are composed of silicate rocks rich in carbon, which makes them similar to asteroids from the main belt. Although the moon's surface is covered with craters, it is significantly smoother than the surface of Phobos.
Only two geological features on Deimos have got their own names: the craters of Voltaire and Swift, named after famous publicists in the 17th and 18th centuries who speculated about the existence of two Martian moons before they were discovered.
Researchers believe that the moon of Mars Phobos may someday turn into a ring around the Red Planet. Credit & Copyright: Celestia. The origin of the satellites of Mars is still uncertain, but there are a number of hypotheses among researchers. The most widely held theory is that the satellites of the Red Planet are objects ejected from the asteroid belt by Jupiter's gravity and captured by Mars.
However, this theory remains controversial, as it is unlikely that Mars would be able to slow bodies of this size enough to reach their current orbits. A modified version of this hypothesis is that Phobos and Deimos were once a binary asteroid that was then captured by Mars.
According to other popular hypotheses, satellites were formed in their present orbits as a result of accretion processes, or, possibly, in the distant past, Mars was surrounded by many large asteroids that were thrown into its orbit after colliding with planetesimals. Over time, most of them fell to the surface.
Mars, Earth's red neighbor, is often the focus of astronomers' attention. Its proximity makes it an achievable target for space travel and exploration. Today it is one of the most studied planets in the solar system.
For a long time, the satellites of the Red Planet remained hidden from view. According to the stories, the astronomer Asaf Hall, who tried in vain to find them, wanted to give up everything, and continued to work only at the insistence of his wife. The next night, after resuming the search, he discovered the Mars satellite Deimos, and a few days later - and Phobos.
Assumptions
As you know, the Red Planet is named after the Roman god of war. To match her Phobos and Deimos, satellites of Mars, received the names of his sons. "Fear" and "horror", which in translation mean the names of these cosmic bodies, did not generate the corresponding emotions among scientists. Rather, they caused confusion. The measurement results showed too little weight of objects at a rather impressive size. There was even an opinion that the satellites are hollow inside, which means that they are of artificial origin. Such assumptions were refuted after the appearance of the first images of Phobos and Deimos from spacecraft.
The smallest
Both satellites of Mars turned out to be rather small space objects. The slightly elongated ellipsoidal shape characteristic of them is clearly visible in the images. The data obtained made it possible to assign the title of the smallest such objects in the entire solar system to the satellites of the Red Planet.
Phobos is a satellite of Mars, slightly exceeding its "brother" in its parameters. It is also located closer to the planet. Both objects, like the Moon, are always facing Mars with the same side. It is extremely difficult to see them from Earth - this can only be done with the help of a powerful telescope. The reason for this state of affairs lies in the composition of the satellites: it is dominated by carbon mixed with ice. Deimos and Phobos reflect a very small percentage of light rays, and as a result, they appear as very dim objects. The same composition, which strongly distinguishes satellites from Mars, suggests that Phobos and Deimos were once asteroids captured by the Red Planet over time.
The closest satellite of the planet Mars
Phobos, as already mentioned, is the larger of a pair of "close" Red Planet. The distance that separates it from Mars is estimated at 6 thousand kilometers, making it the closest satellite known today. This situation has certain consequences: Phobos is a satellite of Mars, which in about 50 million years will fall on the planet, or will be torn to pieces and turn into a ring of asteroids. This version of the fate of the cosmic body is evidenced by its gradual decline to the surface of Mars. The distance between the two objects is reduced by 1.8 m every hundred years.
Phobos orbits Mars in 7 hours and 39 minutes. The speed allows the satellite to overtake the daily rotation of the Red Planet. As a result, Phobos for an observer on Mars moves, appearing over the horizon in the west and setting in the east.
Consequences of a collision
A characteristic feature of both satellites is the surface covered with craters. On Phobos there is the largest of them, named after the wife of the discoverer of satellites. The diameter of Stickney crater is 10 km. For comparison: Phobos itself has dimensions of 26.8 × 22.4 × 18.4 km. Presumably, the crater was the result of a strong impact when a space object fell on the surface of Phobos or a collision.
There are mysterious grooves or cracks near the crater. They represent a system of parallel grooves. Furrows extend for 100-200 km with a depth of 10-20 km, the distance between adjacent ones reaches 30 km. The reason for their occurrence is not completely clear. The most consistent with all the data obtained is the version that the grooves were formed after the material that exploded on the Red Planet fell onto the satellite of Mars. Scientists, however, are in no hurry to call this hypothesis the only correct one: research continues.
Second son of the god of war
Deimos is a satellite of Mars with parameters 15x12x11 km. It is located farther than Phobos and makes one revolution around the Red Planet in over 30 hours. Deimos is located 23 thousand kilometers from the center of Mars.
For the first time, scientists were able to consider Deimos after receiving a photograph taken spacecraft "Viking-1" in 1977. An image taken by its successor, called Viking 2, showed that Mars' smaller moon also lacks a smooth surface. True, unlike Phobos, it is decorated not with furrows, but with massive boulders, the sizes of which are estimated to range from 10 to 30 km.
Versions
Today there is no consensus on the origin of Deimos and Phobos. Most astronomers are of the view expressed above that they were once asteroids. The existing data on their composition speaks in favor of this hypothesis: by this parameter, the satellites are related to asteroids associated with Jupiter. Presumably, the gas giant, with its gravitational force, influenced the orbits of two cosmic bodies in such a way that they approached Mars and were captured by it.
Some scientists, however, adhere to an alternative point of view. They talk about the contradiction of the existing hypothesis to the laws of physics and put forward their theory. According to her, Phobos and Deimos never belonged to asteroids. They were parts of the only satellite of Mars, torn to pieces by the gravity of the Red Planet. The most massive and largest part was pulled closer to the surface and received the name Phobos, while the less impressive and light began to orbit in a distant orbit and turned into Deimos. According to astronomers who adhere to this version, evidence of it can be obtained after a more detailed study of the composition of the soil on the two moons of Mars.
Astronomers' plans
Satellites are a great place to watch Mars. Astronomers plan to organize on them something like a base, from which, with the help of robots, more detailed map Mars. It is easier to get almost any information about the planet from a satellite. Of course, the greatest hopes in this sense are pinned on Deimos, who does not face such a sad fate as Phobos.
Both satellites orbiting the Red Planet have far from all told people about themselves, like Mars itself. However, the relatively close location to the Earth gives hope for the early satisfaction of the curiosity of scientists. However, one cannot vouch for this with all certainty: space is capable of offering a hundred more questions for every answer it finds.