This planet was noticed by ancient astronomers in the XIV century BC. True, due to its proximity to the Sun and rapid movement across the sky, they took it for two celestial objects and gave different names.
"Uninteresting" planet
Only at the beginning of the 17th century, Galileo Galilei, observing a nimble celestial body through a telescope, established that the "morning star" and "evening star", faintly distinguishable in the glow of the nearby Sun, are in fact the same. The planet is very small, about the size of the moon.
The name for the new inhabitant of the solar system was no longer: the closest to the central star, mobile, hard to observe … of course, Mercury! The patron saint of thieves, merchants and travelers among the ancient Romans, also acting as a messenger of the main gods.
After its discovery, the planet did not arouse much interest either from Galileo himself or from his followers. Only at the end of the 20th century, with the development of means of astronomical observations and the launch of interplanetary probes, it again attracted the attention of scientists.
Meet Mercury
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In 1975, the American space probe Mariner-10 orbited Mercury three times, mapped 45% of its surface and carried out many scientific measurements. In 2011, another automated Messenger station became its artificial satellite.
Rotating in a close orbit, working, one might say, in the most difficult conditions, Messenger transmitted the most valuable information about the planet to Earth for four years. Alas, in such close proximity to the sun, due to quantum effects and the destructive effects of solar radiation, the most advanced devices could not last longer. In April 2015, the station went down and fell on Mercury. But the information received by the Earth was worth it.
… At first glance, the "passport" of Mercury looks completely ordinary. Its mass is 0.055 Earth, and its diameter is 0.4 Earth. The distance from Mercury to the Sun varies from 45 million kilometers at the closest point of the orbit to 70 million at the most distant. The period of revolution around the Sun (Mercurian year) is equal to 88 Earth days.
In general, an ordinary planet of the so-called terrestrial type, like Venus or Mars. But it only seems so.
Stopping Sun
A day on Mercury lasts 176 Earth days. It is the only planet in the solar system where the length of "day" and "night" is equal to the length of the year. But the most curious thing is the change in the time of day. In some places of the planet, especially on the meridians, the rising and setting of the Sun can be observed twice or even three times a day!
If you and I could be on Mercury, we would see a very strange picture. A huge, one-eighth of the celestial hemisphere, a fireball, barely appearing above the horizon, suddenly stops, freezes for several Earth days (and according to Mercury reckoning only for a couple of minutes), and then slowly “crawls away” to the same point. And only the second or third time does the luminary really rise. When the sun sets, the same thing happens.
The reason for this phenomenon is still unknown, but there is an assumption that the proximity of the Sun is to blame for everything. Its powerful gravitational field can create effects that require at least general relativity to describe.
The gravitational effect of the Sun, which bends the nearby space, may also explain the mysterious "jumps" of Mercury during its orbit. Prior to Einstein's creation of the theory of relativity, astronomers believed that the motion of Mercury was influenced by a planet even closer to the Sun and therefore no longer distinguishable in its brilliance. She was even given a name - Vulcan (the ancient Roman god of fire and blacksmithing). But modern means of observation, which are not interfered with by the blinding light, have not found any Vulcan.
Where does the magnetic field come from?
Despite the name (mercury - "mercury"), the planet is two-thirds of the much harder metal - iron. Mercury ranks second in density among the planets of the solar system (in first place is our Earth, which is much larger than Mercury in size). Due to the smallness of Mercury, its iron core should have cooled and hardened long ago. But the data from both space probes suggest that the core of Mercury is still liquid and hot.
The fact is that Mercury has a very powerful magnetic field for its scale. As is known from physics, the magnetic field is created only by moving charges, which means that powerful waves still occur in the bowels of Mercury. There may even be active volcanoes there.
And this is the main mystery of the planet. A liquid core producing a magnetic field detected by instruments - why, as it should be according to all cosmological theories, did not cool down three billion years ago?
Maybe the Sun is to blame for everything, warming up and shaking the core of the planet with its tidal waves? Or maybe the core is not purely iron, but contains impurities of lighter elements, for example, sulfur, which melts at a lower temperature. And that is why the core is kept afloat, so to speak, for several billions of extra years. Or are gravitational effects again to blame, which can only be explained by the theory of relativity?
But the most curious and intriguing theory that can explain the presence of the magnetic field of Mercury is the hypothesis of the Soviet astrophysicist Nikolai Kozyrev about the physical nature of time. Based on this hypothesis, he predicted volcanic activity on the Moon 60 years ago, which was later confirmed by observations.
Kozyrev likened time to other forces of nature. He suggested that time, like gravity, can do work and produce energy. Moreover, it is the flow of time, according to Kozyrev, that feeds the stars, and not their thermonuclear "fuel" at all. According to the calculations of the scientist, without the help of a great and inexhaustible time, all thermonuclear fusion in stars should have stopped long ago, and all planets should have cooled down and turned into solid stone-metal blocks.
Oddly enough, it is Kozyrev's theory that explains not one, but all the mysterious features of Mercury, even “small” touches and additions to his portrait, which will be discussed below. The only problem is that very few people believe in Kozyrev's theory. At least for now.
To fly there …
It is clear that many scientists have itching hands to get to the mysterious Mercury. If it were not for funding issues, the third, fourth, and fifth space probes, stuffed with the most modern equipment, would have long been sent to the planet.
Meanwhile, expeditions to Mercury could have not only scientific, but also practical interest. Where, if not on the planet closest to the most powerful source of gravity, could one study the nature of gravitational forces, so that in the future - not so distant future - it could be used for space flights? What other planet can be found valuable and rare minerals, especially radioactive elements?
At the poles of Mercury, according to Messenger, there is water (that is, not water, of course, at a temperature of -180 ° C, but ice). The surface of Mercury contains traces of meteorite bombardments. Among them, the main geographic "attraction" of the planet is the Caloris Pianitia crater with a diameter of 1550 kilometers, which was formed at the dawn of the planet's history and could tell a lot about the events that happened four billion years ago.
Finally, there is a kind of atmosphere on Mercury. More precisely, the exosphere. It consists of hydrogen, oxygen and helium, as well as very insignificant impurities of light metals - sodium, potassium and calcium. Its pressure does not exceed one trillionth of the earth's atmosphere.
But nevertheless, the exosphere is, and its presence is also hardly explained by generally accepted theories - after all, the solar wind should have “blown off” all gases into space a long time ago. Is that the radioactive substances contained in the crust feed the exosphere with their continuous decay.
But then the amount of radioactive elements in the surface layers of the planet must be very, very large! So much so that their industrial production could be of certain interest to earthlings. Not now, of course, but in, say, a hundred years, when the Earth's uranium mines are completely depleted.
Or maybe time played a role in the presence of the Mercurian exosphere, which, according to Kozyrev, is not the length of events, but an independent physical force? Who knows … Now, if only to fly there! Or at least launch another probe.
Olga STROGOVA