Pluto (left) and its moon Charon (photo taken using the Hubble Space Telescope).

After complex mathematical processing on a computer, based on the initial image (inset above), scientists were able to construct a photometric model of the surface of the planet Pluto.

The satellite telescope, named after the American astronomer Hubble, made the first observations of Pluto, the most distant (ninth in order from the Sun) of the major planets in the Solar System. This tiny, cold planet, orbiting at a distance 40 times greater from the Sun than Earth, has long remained completely unexplored.

In one of the articles last year (see "Science and Life" No. 1, 1997) we said that spacecraft were not sent to Pluto, and almost nothing could be discerned on it using ground-based telescopes. And that now, it seems, the chance to explore the atmosphere of this planet is lost. Because Pluto, which has a highly elongated orbit, will move away from the Sun in the next hundred years. The planet's atmosphere will soon solidify and fall onto its surface in the form of snow. Only in two hundred years will Pluto again be at its closest distance from the Sun and will be in an advantageous position for observations from Earth.

The existence of the planet Pluto, as we know, was first theoretically predicted by the American astronomer P. Lovell in 1915. 15 years after this, the planet was discovered by amateur astronomer K. Tombaugh. He discovered in photographs taken by the Flagstaff Observatory (USA) a 15th magnitude star moving among the other stars. And I realized that this was the ninth major planet of the solar system. For several decades it was not known that Pluto had a satellite. It was discovered almost by accident in 1978 by an American astronomer. Looking through photographic images of the planet, he noticed that in the photographs a faint star, such as is obtained when photographing Pluto, looks slightly elongated. Astronomers double-checked this discovery several times and made sure that Pluto has a satellite. He was named Charon.

It was only recently that the Hubble Space Telescope obtained an image for the first time in which both Pluto and Charon were clearly visible.

We now know that the diameter of Pluto is 2320 kilometers, and that of its satellite is 1270 kilometers. A truly unique couple. Nowhere else in the solar system is it found that a planet is only twice the size of its satellite. It would be quite fair to call Pluto a double planet.

After several shooting sessions using the Hubble telescope, astronomers have accumulated enough information to build the first, of course, very approximate map of the surface of the mysterious planet. Using complex mathematical processing, they created a terrain model with the location of all any noticeable light and dark formations. The map is not very impressive, but if you imagine that it can be compared to trying to see something on a tennis ball carried 125 kilometers away...

Almost nothing can be said about the nature of Pluto and its satellite, except that Charon is somewhat bluer in color than Pluto. This may mean that they were not formed from a single cloud, but were later somehow brought together by circumstances unknown to us. In order to expand our knowledge of the solar system's most distant planet, additional observations with a space telescope are needed. We'll wait for them.

Until 2006, Pluto, whose moon is Charon, was considered the ninth planet of the solar system. In connection with the discovery of many similar objects in the Kuiper belt, 2.5 thousand astronomers at the 26th Assembly of the International Astronomical Union classified Pluto as a dwarf planet.

The Mystery of the Ninth Planet

Observation of Neptune and analysis of its orbit showed that it alone cannot have such a strong impact on the movement of the seventh planet - Uranus. In 1906, the American philanthropist and amateur astronomer Percival Lowell launched the Planet X project to search for the ninth “inhabitant” of the solar system. Various combinations of circumstances (a defect in the emulsion of a photographic plate, a coincidence of the image with the image of a star) allowed the mysterious planet to elude the optical instruments of astronomers until 1930.

Finally, an employee of the Lowell Observatory, 23-year-old K. Tombaugh, managed to obtain the necessary photographs and identify the movement of the desired object. Of the three options for the name of the planet - Minerva, Kronos and Pluto - the last one was chosen, proposed by the English schoolgirl Venice Burney.

Size matters

Calculating the exact physical parameters of the planet, due to its extremely large distance (on average 39.4 AU, or 5.85 billion km), is fraught with certain difficulties. The estimated orbit of Pluto has an inclination to the ecliptic of 17˚, which is unusual for planets. Over the past century, repeated attempts have been made to clarify the mass of the planet, and with each calculation the value turned out to be smaller and smaller. In 1978, Pluto's first satellite, Charon, was discovered. This made it possible to fairly accurately calculate the mass of the planet. It became clear that with the obtained value (0.2% of the mass of the Earth), the “lightweights” Pluto and Charon (this is a satellite) cannot have a serious impact on Uranus. What planet is still missing from this gravitational equation? The search for “Object X” resumed again with the same zeal, but did not bring any results.

To the relief of many, information transmitted to Earth by the Voyager 2 unmanned spacecraft in 1989, and updated calculations performed by NASA four years later, explained all the discrepancies in the movement of Uranus.

Ice world

Pluto can only be seen through a telescope as a 15th magnitude object. The period of revolution around the Sun is 248 years, around its axis (reverse rotation) - 6.4 days. Spectral analysis of the planet shows that its surface is 98% icy nitrogen. Minor traces of carbon monoxide and methane are present. The curve of apparent brightness versus time indicates the heterogeneous structure of Pluto's surface. The average density of matter on the planet is 2 g/cm 3 . Pluto's core (50 to 70% of its total volume), consisting of rocks, is surrounded by ice. It is possible - due to internal heating due to the decay of radioactive minerals - the existence of a liquid layer.

According to updated data, the equatorial diameter of the planet is 2380 km. Pluto is five times lighter in mass than the Moon. To date, five natural satellites are known. The last one - Styx - opened in 2012. The largest satellite is Charon. Not everything is so simple with him, but more on that below.

The cosmic body got its name from the ancient Greek mythical boatman who transported the souls of the dead across the waters of the Styx. Charon is the planet's satellite, the first to be discovered (D. Christie, USA, 06/22/1978). It is sometimes called Pluto 1.

The diameter of Charon is 1220 km. The mass is six times less than the mass of Pluto. The distance between the centers of cosmic bodies is 19.6 thousand km. The satellite Charon runs through its orbit in 6.4 days, which coincides with the period of revolution of the planet around its axis (a similar picture is observed for the Earth and the Moon). The average density of matter on Charon is 1.73 g/cm 3 . The surface of the satellite is covered with a layer of water ice. Spectral studies indicate the presence of ammonia hydrates, indicating geological activity on Charon today.

Charon still hides many mysteries! Whose satellite this is is clear, but is it a satellite?! The fact is that the center of mass of the Pluto-Charon system (barycenter) lies outside the planet.

Double planet?

No double planets, even dwarf ones, have yet been discovered in the Solar System. There are double asteroids. The most famous of them is Antiope (Main Belt). There are also trans-Neptunian (cubiwano) binary objects - Sila-Nunam. The only cosmic bodies in the vicinity of the Sun that can claim the status of a double planet are Pluto and Charon.

At the 26th IAU Assembly, a proposal was made to assign Charon the status of a dwarf planet. Automatically, the Pluto-Charon union would be recognized as a binary system. Then the resolution did not receive the support of the majority of forum participants, although it is possible that the issue may be reconsidered in the future.

New Horizons

In the spring of 2015, after a nine-year flight, NASA's unmanned spacecraft New Horizons began its mission. Among the main tasks is the study of the Pluto-Charon system, namely:

• surface mapping, construction of temperature diagrams;
• geological and morphological (texture and relief) surveys;
• determination of the composition of the atmosphere or its traces (object - satellite Charon).

The device approached Pluto at a minimum distance of 12.5 thousand km on July 14. The program was implemented over 9 days, during which more than 50 GB of information was sent to Earth. It took a little over a year to transfer the data. What did New Horizons reveal to us?

The alleged geological activity of Pluto has been fully confirmed. The transmitted images show that there are very few meteorite craters on the surface of the planet (compared to Charon). This indicates periodic renewal of the outer layers of the planet as a result of tectonic processes.

Pluto's atmosphere turned out to be more rarefied than scientists expected - the pressure does not exceed a hundred thousandth of the earth's. Presumably, it is in the air envelope of the planet that tholins are formed - polymerized simple hydrocarbons, and then, condensing, they fall to the surface, giving it a bright color.

Mordor and the Tolins

Charon also presented many surprises. The hemisphere facing Pluto is cut by a dense network of abysses. The depth of some exceeds 7.5 km. The entire surface is covered with a layer of dirty water ice.

The northern polar cap of the satellite is of great interest. Unlike many cosmic bodies, on Charon it is dark red. According to astronomer W. Gandhi (Lowell Observatory, USA), the color of the pole can be given by the same organic copolymers - tholins, which through complex physical and chemical processes form a thin layer on the surface.

The same area, called Mordor, was discovered on another satellite of Pluto - Nix.

In the solar system there are planets so small that they are called dwarfs. This includes Pluto. But even small planets have satellites. Her largest companion is Charon. But he is not the only one of his kind. There are others too. They, of course, are not so great, but they are also of great importance.

In this article we will look at the features of Pluto and find out what Charon, the satellite of this planet, is. Let's also talk about the other, smaller satellites.

Planet Pluto

Until 2006, Pluto stood on a par with the main planets of the solar system and was a full-fledged unit.

Now it was given the name dwarf planet, after which they began to believe that it is the largest object in the dark disk-shaped zone.

One day, it became clear to scientists that Pluto is not a unique object in its environment, like all the other planets located in the Solar System. And that more than one such object can be discovered if you explore the space beyond the orbit belonging to Neptune. And soon a certain body was indeed discovered, called Eris. This was which can be compared with Pluto. After this discovery, it became clear that the world, in fact, lacks the definition of a planet. And in 2006, a definition was approved that included three positions. According to him, those that correspond to only two positions out of three are called Pluto.

It got its name from an eleven-year-old girl who decided that the name of the god of the underworld was suitable for a distant, probably cold and dark planet, and told her grandfather about it. And the grandfather already conveyed his granddaughter’s wish to the observatory, where it was finally approved.

In 2006, a spacecraft called New Horizons was launched towards the planet Pluto. It was the month of January. This device flew up to the planet at a distance of twelve thousand kilometers and accumulated a large amount of information about it. All this data is gradually transferred to scientists. This is due to the too slow transmission of information over such long distances.

Features of the planet

Pluto has the shape of a perfect sphere. This discovery came as a surprise, as did the discovery of various landforms on the surface.

Moreover, there are extended areas on the planet that are completely devoid of impact craters. It is also known that Pluto's glaciers are unevenly distributed across its surface, but it is still not clear why.

The satellite Charon, like other small satellites, is quite far removed from the Earth. Therefore, they have not been studied very well. There is an assumption that the surface of this planet has a rocky base, which is covered with water ice, as well as frozen methane and nitrogen. It is the products resulting from the photodissociation of methane that color the planet red.

Rotating in its orbit, which is far from the shape of a circle, Pluto can either get very close to the Sun, or, conversely, move away to a great distance. As it approaches, an atmosphere is formed around the planet, which consists of methane and nitrogen. The further the planet moves away from the Sun, the smaller the atmosphere becomes, and eventually only a small haze remains, which, when viewed with the naked eye, has a red tint. This happens because the glaciers freeze again.

Moons of Pluto. Charon and the planet's small satellites

Pluto has five natural satellites. The largest satellite, Charon, was discovered in 1978. Two smaller moons, named Nikta and Hydra, were spotted in 2005.

Kerber was next. Its discovery occurred thanks to the Hubble telescope in 2011. And finally, in 2012, scientists discovered the presence of a fifth satellite of Pluto, which was named Styx. All the names of the satellites in one way or another refer to the underworld of Greek mythology.

Charon is a satellite of the planet Pluto

Charon got its name in honor of the carrier of the souls of dead people from the myths of Ancient Greece. It was discovered by US astrophysicist James Christie. This happened at the Naval Observatory in 1978.

This satellite is very large. Its size is equal to half the size of Pluto itself. The distance separating him from the planet he is accompanying is almost twenty thousand kilometers. This is approximately the same as from London to Sydney.

Charon is a satellite of Pluto, which many scientists have come to consider as a small component of a binary system of planets. It was even given the name Pluto 1. The rotation periods of Pluto and Charon are the same. Thanks to this phenomenon, they always face each other with the same side. This phenomenon even got its own name - tidal lock.

Surface and composition of the satellite

The satellite Charon differs in its composition from Pluto. Unlike the planet, it is covered not by nitrogen, but by water ice. This is due to the fact that its surface temperature is 220 degrees Celsius below zero. But also the reasons for this composition include the fact that Charon is not so massive as to retain volatile compounds. The color of the satellite is more neutral, grayish. According to the existing theory, Charon was formed from fragments of Pluto itself that found themselves in orbit. Also, many scientists believe that Charon is connected.

Satellite Nikta

Charon is the largest but there are others. One of them is Nikta. The discovery of this satellite was made public in 2005, on October 31. He owes his name to the goddess of eternal night.

The orbit in which the satellite is located is circular. There is no information yet about the exact dimensions of Nikta, but it is presumably smaller than Hydra. This is indicated by the darker color of the surface.

Hydra

If you carefully examine the existing images, you can see that Hydra is located in the same plane as the satellite Charon. The distance between Pluto and Hydra is approximately 65 thousand kilometers. There is no data on the exact size of this satellite. Scientists only assume that its diameter ranges from 52 to 160 kilometers.

Hydra's surface is brighter than Nyx's. By about 25%. This suggests that its reflectivity is higher, which means its dimensions are larger. The satellite received its name in honor of a monster from Greek mythology with a hundred heads.

Kerberos and Styx

Pluto's fourth satellite is named Kerberos, also named after the mythical character of the underworld. Before the discovery of the fifth satellite, it was considered the smallest. Its estimated diameter is 13-34 kilometers.

The discovery of Kerberos was made thanks to the Hubble Space Telescope. The orbit in which the fourth satellite rotates is located between the orbits of Nix and Hydra. It orbits the planet in thirty-one days.

The smallest size is the fifth satellite Styx. Presumably its diameter is between 10 and 25 kilometers. This satellite rotates in an orbit located between the orbits of Charon and Nix. Its resonance with Charon is a ratio of one to three. It owes its name to the river, which in the myths of Ancient Greece separates two worlds - the living and the dead. It was also discovered by Hubble in June 2012.

This article covered many issues. We found out which planet Charon is a satellite of, what are its features, size and composition. Now to the question: “Charon is a satellite of which planet?” - you will confidently answer: “Pluto.” By the way, one of the theories for the emergence of satellites around Pluto says that they were all formed as a result of the collision of this planet with some large object from the Kuiper belt. Unfortunately, today almost nothing more can be learned about these amazing objects. After all, Pluto is not only too far from Earth, but also does not have very good reflectivity.

Forgotten by everyone Pluto and Charon

He bears the name of the ruler of the underworld and makes his way in the dark depths of space. The Sun itself is barely visible there - a small light circle rolling over the horizon. Until recently, it was called the ninth, most distant planet of the solar system. Now it has been demoted and is considered a dwarf planet, along with hundreds of its fellows. Despite all the efforts of astronomers, it still remains the “great unknown.” After all, it is too far from Earth and too small to be observed using ground-based telescopes. So far, the information we have about Pluto is scanty and unreliable.

Pluto and its moon Charon

Astronomers cannot even guarantee that they know exactly the size of this planet and its density. According to their calculations, the density of Pluto and its moon, Charon, is approximately twice the density of water. In this case, these celestial bodies are likely composed of ice and rocks. For everything else we have to rely on hypotheses. What is the internal structure of Pluto? Isn't there a whole ocean of liquid water hidden under its icy surface, like on Jupiter's moon Europa? Pluto is a very unusual planet. Truly, it has always kept itself apart from the eight other large planets of the solar system, to which it recently belonged.

Immediately after the discovery of Pluto, astronomers began to ask questions. Where did he come from? Did it arise from the same protoplanetary cloud as the other planets of the solar system? Or maybe he accidentally hit her? After all, if all the other large planets revolve around the Sun in approximately the same plane in a circular or slightly elongated orbit, then Pluto moves in an elliptical orbit, inclined at an angle of almost 17° relative to the plane of motion of the other planets. Periodically, it crosses the orbit of Neptune and appears either further from the Sun or closer to it than Neptune.

Pluto owes its discovery to its color. It is much brighter than other trans-Neptunian objects, which only began to be discovered in the 1990s, six decades after Pluto was discovered. At first, astronomers believed that this planet was not inferior in size to Mars. It wasn't until the late 1980s, by watching Pluto's moon Charon cover its surface, that scientists were able to more accurately estimate Pluto's size. Its diameter, according to their calculations, was 2390 kilometers. Observations made with the Hubble telescope forced this figure to be corrected, but did not bring the desired accuracy: 2280–2330 kilometers.

In 1975, it was possible to establish why Pluto is painted in light colors. American astronomers Dale Cruikshank, David Morrison and Carl Pilcher discovered traces of methane ice in its infrared spectrum. At least part of Pluto's surface is covered with it. Later observations made with the Hubble Telescope revealed significant reserves of frozen nitrogen on this planet, as well as water ice and frozen carbon monoxide. This suggested that there are ice volcanoes on the surface of Pluto that emit liquid nitrogen outward.

The photographs taken by the Hubble Telescope, although very blurry, revealed another feature of Pluto. Its surface was not at all uniformly light; there were also dark spots that stood out especially against the light background. What are these spots? Maybe some organic compounds? The area of ​​the south pole, for example, is painted in very bright colors. It is likely covered in frozen nitrogen mixed with methane ice. The equatorial regions, on the contrary, appear as dark spots. The further north you go, the weaker the dark color becomes, giving way to grayish colors.

Based on computer models, astronomers suggest that Pluto has a solid, rocky core that is heated by natural radioactivity and is surrounded by a mantle. The content of rocks and possibly metals is estimated in these models at 65–70%, and ice and liquid materials such as water at 30–35%.

In June 1988, by observing Pluto engulf the star, astronomers concluded that it had an atmosphere. An interesting observation was made. Starlight does not seem to penetrate to the planet's surface. This may be hampered by thick cloud cover. In 2005, the Hubble telescope helped determine the temperature on the surface of Pluto: –230 °C. This is about ten degrees lower than was evident from previous calculations. Obviously, some processes occurring in the atmosphere contribute to the sharp cooling of Pluto.

What does its atmosphere even consist of? From observations of comets, it is known that near the Sun, ice from their surface begins to evaporate, bypassing the liquid phase. It is likely that sublimation of the ice cover also occurs on Pluto. Therefore, its atmosphere must contain the same gases - nitrogen, methane and carbon monoxide - that cover its surface in the form of ice.

By the way, the temperature of Pluto’s air shell is about 40 degrees higher than its surface. This effect is due to the fact that its atmosphere contains methane. This greenhouse gas absorbs sunlight, causing the atmosphere to warm up.

In 2011, British astronomers who observed Pluto using the Maxwell Telescope built in Hawaii found that the thickness of the gas shell surrounding Pluto reaches 3,000 kilometers. This is 30 times more than previously thought. Thus, almost a quarter of the gap separating the two planets, Pluto and Charon, is occupied by this air envelope. For comparison, the outer layer of the Earth's atmosphere - the exosphere - ends approximately 10 thousand kilometers from the planet. Perhaps the solar wind drives away this gaseous shell, much like the tail of a comet. What if Pluto, and even Charon, are... comets, only very large ones?

Pluto and Charon form a double planetary system. They are quite close in size; their masses have a ratio of 1:8. For comparison, the Earth weighs 81 times more than the Moon. The distance between them is only 17 radii of Pluto, and therefore the common center of mass of this system is not located in the depths of Pluto, but in the space separating both planets - and this has consequences. If the Moon orbits the Earth, then Pluto and Charon jointly orbit around a common center of mass that lies between them. So the waltzers, holding hands, spin around a certain point in space that separates them.

How did this unusual couple form? Astronomers suggest that a catastrophe once occurred on the outskirts of the solar system. Here two protoplanets of approximately the same size collided. They moved at a relatively low speed, but still collapsed after this impact. Two new planets were formed from the scattered debris: most of the blocks went to form Pluto, and the rest to Charon. At first, Pluto rotated very quickly, but Charon gradually slowed down its rotation.

However, it is not yet possible to test this hypothesis even with the help of computer models, because we still do not know much about Pluto and Charon. NASA's interplanetary probe New Horizons can tell a lot of interesting things about these planets. It will arrive at Pluto in 2015. This expedition, astronomers believe, will rediscover for us the world of the “space dungeon”, lost on the outskirts of the solar system.

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Satellite Charon is almost half the size of Pluto. This small moon is so large that Pluto and Charon are sometimes called a double dwarf planetary system. The distance between them is 19,640 km (12,200 miles).

Satellite Charon - a distant guest

This new photograph of the region of Pluto's largest moon, Charon, reveals a unique feature: numerous depressions, which can be seen in the enlarged portion of the image on the right side.

The Hubble Space Telescope also photographed Pluto in 1994, when Pluto was at a distance of about 30 AU. from the earth. These photographs showed that Charon is grayer than Pluto (which has a red tint), indicating that they have different surface compositions and structures.
A high-resolution image of Charon taken from the Long Range Reconnaissance Imager on NASA's New Horizons spacecraft at its closest approach to the surface on July 14, 2015, with an enlarged color image from the Ralph/Multispectral Visual Imaging Camera (MVIC) superimposed.

A full revolution of Charon around Pluto takes 6.4 Earth days, and one revolution of Pluto (1 day on Pluto) takes 6.4 Earth days. Charon neither rises nor descends in the system's orbit. Pluto always stands on the same side of Charon - this is called tidal capture. Compared to most planets and moons, the Pluto-Charon system is tilted on its side, as is Uranus. Pluto's orbit is retrograde: it rotates in the opposite direction, from east to west (Uranus and Venus also have retrograde orbits).

Pluto's Moon Charon: Discovery

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But the moons of Jupiter were discovered much earlier. Galileo also discovered