- Mercury is the planet closest to the Sun, the smallest and fastest. The average speed of the planet's orbit is 48 km/s.
- Equatorial diameter of Mercury 4878 km. Smaller in size than Jupiter's moon Ganymede and Saturn's moon Titan.
- The mass of Mercury is 3.3 1023 kg, which is 0.055 Earth masses. In terms of mass, Mercury exceeds the satellites of the giant planets Ganymede and Titan.
- The average density of Mercury is 5.43 g/cm³(slightly less than the density of the Earth). This density indicates an increased content of metals in its depths.
- Surface temperature from -185°C to 430°C.
- It makes a complete revolution around the Sun in 88 (87.97 Earth days) in an elongated orbit, sometimes moving away from the Sun by 70 million km, while the shortest distance to the Sun is 46 million km.
- Mercury makes a full revolution around its axis in 58.65 days. The average time interval between the two upper culminations of the Sun on this planet is 176 days. Interestingly, when it is near perihelion (closest distance from the Sun), the Sun for an observer on the surface of the planet can move in the opposite direction for 8 days.
- The periods of rotation around its axis are related to rotation around the Sun as 3:2. That is, in one Mercury year the planet manages to rotate around its axis by one and a half revolutions.
- Distance from Mercury to Earth varies from 82 to 217 million km. Over the course of several days, when observed from Earth, Mercury changes its position relative to the Sun from the west (morning visibility) to the east (evening visibility).
- It was only in 2009 that scientists compiled the first complete map of Mercury, using images from Mariner 10 and Messenger.
The distance from Mercury to the Sun is 58 million km.
A year on Mercury lasts 88 days, during which time it completes a full revolution around the Sun. But a “day” on Mercury lasts almost two - it rotates very slowly.
The surface of Mercury is covered like the moon, and consists of very rarefied helium.
Primary data about Mercury
Greek astronomers initially called the planet Stilbon (“Brilliant”), and closer to the turn of the new era, the name was assigned to it in honor of the Greek and Roman god - the patron of magic and, the messenger of the Olympian gods and the guide of the souls of the dead to the other world.
At the same time, no traces were noticed, except for many kilometers of scarps - ledges that were formed as a result of shifts of some sections of the surface relative to others.
However, the cause of scarps may not be volcanoes at all. Its proximity to the hot Sun, the planet's slow rotation and the almost complete absence of an atmosphere mean that Mercury experiences the most dramatic temperature changes in the Solar System, reaching 600°C.
So, at midnight the surface cools to -180°, and at noon it heats up to +500°. It is difficult to find ones that can withstand such changes for a long time.
However, the resemblance to the Moon is incomplete. Large craters are much less common on Mercury than on the Moon. The largest of them is 625 km across and named after the German composer Ludwig van Beethoven.
There are no signs of erosion of the surface layers, which means that in the entire history of Mercury it has never had a dense atmosphere.
The brightest point on the planet's surface is Kuiper Crater, 60 km in diameter. This may be due to the fact that it was formed quite recently and is not covered with layers of crushed rocks.
The commensurability of the length of the day and year on Mercury is exceptional for solar system and leads to unique phenomena. Mercury's orbit is quite elongated, and according to Kepler, in those areas that are closer to the Sun, the planet moves faster.
And the rotation of Mercury around its axis has a constant speed, and therefore either “lags behind” or “leads” the moments of passage.
As a result, the Sun stops in the sky of Mercury and begins to move in the opposite direction - from west to east. This effect is sometimes called the "Joshua effect" - after the biblical figure who stopped the movement of the Sun in order to end the battle before sunset.
>> Rotation of Mercury
Peculiarities rotation of Mercury around the Sun: speed, period, how much time the planet spends in orbit in the solar system, length of the day and year with photo.
Of all the planets, motion and period rotation of Mercury is the most unusual. The fact is that the process of axial rotations itself occurs slowly. If Mercury's axis of rotation takes 175.97 days, then it takes 88 days to orbit the Sun. That is, a day lasts 1.999 times more than a year. The equatorial speed indicator is 10.892 km/h. This results in sunny days where 58.647 days are spent per revolution.
If you were to visit the planet, you could watch the Sun rise halfway and stay at one point throughout the day. This happens 4 days before the moment of perihelion due to the fact that the orbital speed exceeds the angular speed, and the star starts moving backwards.
Mercury's rotation around the Sun
Let's take a closer look at Mercury's rotation around the Sun. During one of the Mercury years, the average solar motion reaches two degrees per day in a westerly direction, causing the day to be three times longer than the rotation. Traffic will vary depending on the year. And at the moment of aphelion it will slow down and give 3 degrees per day. But the Sun will also slow down and stop its shift to the west, move to the east and return to the west again. The tilt of Mercury's rotation axis is demonstrated below.
It is worth understanding that at the moment the solar speed changes, the star will increase in its observed size and then decrease.
The peculiarities and speed of rotation of the planet were not known until 1965. Then it was believed that everything depended on the planetary tides to the Sun. The breakthrough was made by Soviet researchers who, in 1962, managed to bounce radio signals off the surface of Mercury. Later, the Americans used Arecibo and confirmed the results, as well as the rotation period, which reached 58.647 days.
So, what is the planet Mercury and what is so special about it that makes it different from other planets? Probably, first of all, it’s worth listing the most obvious things that can be easily gleaned from different sources, but without which it will be difficult for a person to get the overall picture.
On this moment(after Pluto was demoted to dwarf planets) Mercury is the smallest of the eight planets in our solar system. Also, the planet is at the closest distance from the Sun, and therefore rotates around our star much faster than the other planets. Apparently, it was precisely the latter quality that served as the reason to name her in honor of the fastest-footed messenger of the Gods named Mercury, an extraordinary character from legends and myths Ancient Rome with phenomenal speed.
By the way, it was the ancient Greek and Roman astronomers who more than once called Mercury both the “morning” and “evening” star, although for the most part they knew that both names correspond to the same cosmic object. Even then, the ancient Greek scientist Heraclitus pointed out that Mercury and Venus rotate around the Sun, and not around.
Mercury today
Today, scientists know that due to Mercury's close proximity to the Sun, temperatures on its surface can reach up to 450 degrees Celsius. But the lack of an atmosphere on this planet does not allow Mercury to retain heat and on the shadow side the surface temperature can drop sharply to 170 degrees Celsius. The maximum temperature difference between daytime and nighttime on Mercury turned out to be the highest in the Solar System - more than 600 degrees Celsius.
Mercury is slightly larger in size than the Moon, but much heavier than ours. natural satellite.
Despite the fact that the planet has been known to people since time immemorial, the first image of Mercury was obtained only in 1974, when the Mariner 10 spacecraft transmitted the first images in which it was possible to make out some features of the relief. After this, a long-term active phase began to study this cosmic body, and several decades later, in March 2011, a spacecraft called Messenger reached the orbit of Mercury. after which, finally, humanity received answers to many questions.
The atmosphere of Mercury is so thin that it practically does not exist, and the volume is about 10 to the fifteenth power less than the dense layers of the Earth's atmosphere. Moreover, the vacuum in the atmosphere of this planet is much closer to a true vacuum if we compare it with any other vacuum created on Earth using technical means.
There are two explanations for the lack of atmosphere on Mercury. Firstly, this is the density of the planet. It is believed that with a density of only 38% of the Earth's density, Mercury is simply not able to preserve most atmosphere. Secondly, the proximity of Mercury to the Sun. Such a close distance to our star makes the planet most susceptible to the influence of solar winds, which remove the last remnants of what can be called an atmosphere.
However, no matter how scarce the atmosphere on this planet is, it still exists. According to the space agency NASA, in its own way chemical composition it consists of 42% oxygen (O2), 29% sodium, 22% hydrogen (H2), 6% helium, 0.5% potassium. The remaining insignificant part consists of molecules of argon, carbon dioxide, water, nitrogen, xenon, krypton, neon, calcium (Ca, Ca +) and magnesium.
It is believed that the rarefaction of the atmosphere is due to the presence of extreme temperatures on the surface of the planet. The lowest temperature can be about -180 °C, and the highest approximately 430 °C. As mentioned above, Mercury has the largest range of surface temperatures of any planet in the Solar System. The extreme maxima present on the side facing the Sun are precisely the result of an insufficient atmospheric layer that is not able to absorb solar radiation. By the way, the extreme cold on the shadow side of the planet is due to the same thing. The lack of a significant atmosphere prevents the planet from holding solar radiation and the heat very quickly leaves the surface, freely escaping into outer space.
Until 1974, the surface of Mercury remained largely a mystery. Observations on this cosmic body from Earth were very difficult due to the planet's proximity to the Sun. It was possible to see Mercury only before dawn or immediately after sunset, but on Earth at this time the line of visibility is significantly limited by the too dense layers of our planet’s atmosphere.
But in 1974, after a magnificent three-time flyby of the surface of Mercury by the Mariner 10 spacecraft, the first fairly clear photographs of the surface were obtained. Surprisingly, despite significant time constraints, the Mariner 10 mission photographed almost half of the entire surface of the planet. As a result of analyzing observational data, scientists were able to identify three significant features of the surface of Mercury.
The first feature is the huge number of impact craters that gradually formed on the surface over billions of years. The so-called Caloris basin is the largest of the craters, with a diameter of 1,550 km.
The second feature is the presence of plains between the craters. It is believed that these smooth surface areas were created by the movement of lava flows across the planet in the past.
And finally, the third feature is the rocks, scattered across the entire surface and reaching from several tens to several thousand kilometers in length and from one hundred meters to two kilometers in height.
Scientists especially emphasize the contradiction of the first two features. The presence of lava fields indicates that in the historical past of the planet there was once an active volcanic activity. However, the number and age of craters, on the contrary, indicate that Mercury was geologically passive for a very long time.
But the third one is no less interesting. distinguishing feature surface of Mercury. It turned out that the hills are formed by the activity of the planet’s core, which results in the so-called “bulging” of the crust. Similar bulges on Earth are usually associated with the displacement of tectonic plates, while the loss of stability of Mercury's crust occurs due to the contraction of its core, which is gradually compressed. The processes occurring at the core of the planet lead to compression of the planet itself. Recent calculations by scientists indicate that the diameter of Mercury has decreased by more than 1.5 kilometers.
Structure of Mercury
Mercury is made up of three distinct layers: the crust, the mantle, and the core. The average thickness of the planet's crust, according to various estimates, ranges from 100 to 300 kilometers. The presence of the previously mentioned bulges on the surface, whose shape resembles those of the earth, indicates that, despite being sufficiently hard, the crust itself is very fragile.
The approximate thickness of Mercury's mantle is about 600 kilometers, which suggests that it is relatively thin. Scientists believe that it was not always so thin and that in the past there was a collision of the planet with a huge planetesmial, which led to the loss of significant mass of the mantle.
The core of Mercury has become the subject of much research. It is believed to be 3,600 kilometers in diameter and has some unique properties. The most interesting property is its density. Considering that the planetary diameter of Mercury is 4878 kilometers (it is smaller than the satellite Titan, whose diameter is 5125 kilometers, and the satellite Ganymede with a diameter of 5270 kilometers), the density of the planet itself is 5540 kg/m3 with a mass of 3.3 x 1023 kilograms.
So far, there is only one theory that has attempted to explain this feature of the planet's core, and has cast doubt on whether Mercury's core is actually solid. Having measured the characteristics of the bounce of radio waves from the surface of the planet, a group of planetary scientists came to the conclusion that the planet’s core is actually liquid and this explains a lot.
Mercury's orbit and rotation
Mercury is much closer to the Sun than any other planet in our system and, accordingly, it requires the most a short time for orbital rotation. A year on Mercury is only about 88 Earth days.
An important feature of Mercury's orbit is its high eccentricity compared to other planets. Additionally, of all the planetary orbits, Mercury's orbit is the least circular.
This eccentricity, along with the lack of a significant atmosphere, explains why Mercury's surface experiences the widest range of temperature extremes in the Solar System. Simply put, Mercury's surface heats up much more when the planet is at perihelion than at aphelion, because the difference in distance between these points is too great.
The orbit of Mercury itself is an excellent example of one of the leading processes of modern physics. We are talking about a process called precession, which explains the shift in Mercury's orbit relative to the Sun over time.
Despite the fact that Newtonian mechanics (i.e. classical physics) predicts the rates of this precession in great detail, the exact values have never been determined. This became a real problem for astronomers in the late nineteenth and early twentieth centuries. Many concepts have been formulated to explain the differences between theoretical interpretations and actual observations. According to one theory, it was even suggested that there is an unknown planet whose orbit is closer to the Sun than that of Mercury.
However, the most plausible explanation was found after Einstein's general theory of relativity was published. Based on this theory, scientists were finally able to describe the orbital precession of Mercury with sufficient accuracy.
Thus, for a long time it was believed that Mercury's spin-orbit resonance (the number of revolutions in its orbit) was 1:1, but it was eventually proven that it was actually 3:2. It is thanks to this resonance that a phenomenon is possible on the planet that is impossible on Earth. If an observer were on Mercury, he would be able to see that the Sun rises to the highest point in the sky, and then “turns on” the reverse stroke and descends in the same direction from which it rose.
- Mercury has been known to mankind since ancient times. Although the exact date of its discovery is unknown, the first mention of the planet is believed to have appeared around 3000 BC. among the Sumerians.
- A year on Mercury is 88 Earth days long, but a Mercury day is 176 Earth days long. Mercury is almost completely blocked by tidal forces from the Sun, but over time the planet slowly rotates around its axis.
- Mercury orbits the Sun so quickly that some early civilizations believed it was actually two different stars, one appearing in the morning and the other in the evening.
- With a diameter of 4.879 km, Mercury is the smallest planet in the solar system and is also one of the five planets that can be seen in the night sky with the naked eye.
- After Earth, Mercury is the second densest planet in the solar system. Despite its small size, Mercury is very dense, as it consists mainly of heavy metals and stone. This allows us to classify it as a terrestrial planet.
- Astronomers did not realize that Mercury was a planet until 1543, when Copernicus created a heliocentric model of the solar system, in which the planets revolve around the sun.
- The gravitational forces of the planet are 38% of the gravitational forces of the Earth. This means that Mercury is unable to retain the atmosphere it has, and what remains is blown away by the solar wind. However, these same solar winds attract gas particles and dust from micrometeorites to Mercury and form radioactive decay, which in some way forms an atmosphere.
- Mercury has no moons or rings due to its low gravity and lack of atmosphere.
- There was a theory that between the orbits of Mercury and the Sun there was an undiscovered planet Vulcan, but its presence was never proven.
- Mercury's orbit is an ellipse, not a circle. It has the most eccentric orbit in the solar system.
- Mercury has only the second highest temperature among the planets in the solar system. The first place is taken
A group of astrophysicists from the University of Paris Diderot has proposed a hypothesis that explains why Mercury rotates around the Sun in a completely different way than it should. From their point of view, “childhood trauma” is to blame for this - the collision of this small planet with large asteroids at the dawn of the formation of the Solar system.
The smallest planet in the solar system, Mercury (and it became such when Pluto was deprived of the proud title of planet in 2006) is also the most... wrong. Of course, this was to be expected from a celestial body with a similar name, since, as we remember, the messenger of the gods, Mercury, has always been distinguished by strange, and at times even simply asocial behavior. However, some of the “twists” of this planet simply amaze scientists. And not all of them can be explained from the point of view of astrophysics.
For example, calculations and observational data have been saying for quite a long time that a day on Mercury should be equal to a year. Let me remind you that this planet, closest to the Sun, makes its revolution around the luminary in 87.97 Earth days. And it completes a revolution around its axis, as astrophysicists believed, in about the same amount of time. That is why many thought that Mercury constantly faces the Sun with the same side.
As a matter of fact, this state of affairs did not surprise anyone - after all, with such closeness to the Sun, it cannot be otherwise (and the maximum distance from Mercury to the luminary is 57.91 million kilometers), if we assume that its orbit is the same as for all other planets. A huge star, through tidal force, taking away angular momentum, slows down the rotation of a small planet around its own axis, which is why a day on Mercury is equal to a year.
It should be noted that this misconception was due to the fact that the most favorable conditions for observing Mercury are repeated after a period approximately equal to six times the rotation period of this celestial body (352 days). Because of this, it turned out that approximately the same section of the surface of Mercury was observed at different times. The true state of affairs was revealed only in the mid-1960s, when radar of the planet was carried out.
And this is where surprises began to fall - it turned out that in fact, Mercury rotates around its axis by one and a half revolutions (and not one) per year. And in two orbits around the Sun, the planet makes exactly three revolutions around its axis. In addition, Mercury’s orbit is very non-standard - precession, that is, a phenomenon in which the angular momentum of a body changes its direction in space under the influence of an external force, the perihelion (the closest point of the orbit to the Sun) of Mercury is 5600 arc seconds per century. Although, according to calculations of the influence of all other celestial bodies per planet, it should be no more than 5557 arcseconds per century.
That is, someone adds a shift of as much as three seconds in a hundred years. But who is unclear, because Mercury has no satellites (although scientists suspected the existence of a hypothetical planet Vulcan nearby, but it was never discovered). That is, there is no such body that would “pull” the unfortunate “messenger of the gods” into such a non-standard orbit. But why doesn’t it fly around the Sun as it should?
Previously, astrophysicists believed that the liquid iron core of the planet was to blame for this - the currents that periodically arise in it due to the fact that the planet moves unevenly around the star, “knocks” Mercury off the “true path” (and the speed of the orbital movement of the “messenger of the gods” is constantly changing, with the fact that the speed of rotation around its axis is always constant - as a result, it may seem to an observer on the surface of the planet that at times the Sun in the sky of Mercury stops and begins to move in the opposite direction - from west to east). However, recently a group of astrophysicists led by Mark Wieczorek from the University of Paris Diderot proposed another, very original hypothesis that explains the modern orbit of Mercury.
According to French astrophysicists, the asteroid that did this “dirty deed” should have left a crater with a diameter of 250 to 450 kilometers, no less. And there are such marks on Mercury - according to Messenger images, there are about 40 craters on its surface with similar sizes. And there are about fourteen more, the dimensions of which even exceed the calculated limits of Wieczorek - among the indicated “pits” there are also those whose diameter is 650 and even 1100 kilometers.
Next, scientists determined where the asteroid that knocked Mercury out of orbit should have hit. According to their calculations, the “marks” from these aliens should have been closer to the poles (after all, when Mercury rotated in a “normal orbit,” it was the circumpolar zones that were open to such attacks). And so astrophysicists once again carefully studied images of the surface of Mercury obtained by the Mariner and Messenger space probes.
The result met all expectations - according to the photographs, there were practically no large craters on the equator and adjacent areas (this, by the way, confirmed that Mercury once rotated in a “normal” orbit around the Sun). But the largest number of traces of collisions between the “messenger of the gods” and asteroids were located precisely in the circumpolar regions. And, accordingly, the largest craters were also there.