For a long time after the discovery of Pluto in the celestial horizon, astronomers did not consider it a planet. But everything changed, however, when in 2006 the International Astronomical Union (IAU) reclassified Pluto as a “dwarf planet.” This was a highly controversial decision, which was largely based on the discovery of numerous icy objects with elongated orbits similar to Pluto. Our review contains interesting facts about this distant planet.

1. Minus 225°C.

Pluto's surface is one of the coldest places in the solar system. On average, the temperature on its surface is minus 225 degrees Celsius.

2. Dwarf planet

Pluto is the only dwarf planet that was once considered an ordinary planet. Pluto became a dwarf planet only in 2006.

3. New Horizons probe

As part of NASA's New Horizons mission, a probe was launched in January 2006 and flew close to Pluto for the first time (in July 2015).

4. The diameter of the planet is 2352 km

When Pluto was first discovered, it was initially thought to be larger than Earth in size. Astronomers now know that its diameter is only 2352 km, and its surface area is less than the size of Russia.

5. A year is equal to 248 Earth years

To completely fly around the Sun in orbit (i.e. 1 year), Pluto needs 248 Earth years. To further highlight this fact, it is worth knowing that Pluto has taken another 160 years to complete its orbit around the Sun since it was first discovered.

6. Intersecting orbits

Due to Pluto's strange orbit, its orbit periodically intersects with Neptune's. This leads to the fact that Pluto at these moments is closer to Earth than Neptune.

7. Liquid water

Scientists suggest that there may be liquid water on the surface of Pluto, despite the extremely low temperature. It can be ejected to the surface by cryovolcanoes or geysers.

8. Five satellites

Pluto has five known moons: Charon, Nix, Hydra, and two recently discovered tiny moons, Kerberos and Styx. While Nyx, Hydra, Kerberos and Styx are relatively small, Charon is only half the size of Pluto. Because of Charon's size, some astronomers consider Pluto and Charon to be a double dwarf planet.

9. Less Moon

Pluto is the smallest dwarf planet in the solar system. It is smaller than the Earth's satellite the Moon and 2 times smaller than Jupiter's satellite Ganymede.

10. One day is equivalent to six

A day on Pluto is equivalent to 6 days and 9 hours on Earth, meaning it is the second slowest to spin on its axis in the solar system. The first is Venus, where a day lasts 243 Earth days.

11. Escaped from Neptune

According to some astronomers, Pluto was once one of Neptune's moons. But then he left his orbit.

12. Away from the Sun

The Sun will look like a bright star from Pluto, that's how far they are from each other. If Pluto were to approach the Sun, it would develop a “tail” and become a comet.

13. Center of mass

Charon and Pluto are gravitationally bound to each other. They always face each other because they rotate around a common center of mass located somewhere between them.

14. Unusual gravitational relationships

You might think that Charon orbits Pluto like any “normal” satellite. In reality, Pluto and Charon orbit a common point in space. In the case of the Earth and the Moon there is also such a common point, but this point is located inside the Earth. In the case of Pluto and Charon, the common point is somewhere above Pluto's surface.

15. The force of gravity is 1/12th on Earth

The force of gravity on Pluto is about 1/12th the force of gravity on Earth. This means that a person weighing 100 kilograms on Earth would weigh 8 kilograms on Pluto.

What can we say about distant planets, if people know very little about their own. So, there is, at a minimum, .

The dwarf planet Pluto is the dominant object in an unexplored and distant system of 6 small cosmic bodies located on the borders of the empire of the Sun.

After its discovery, Pluto was perceived as the most distant, ninth planet of our system. It is located on the outskirts of the known world in the Kuiper belt. Its planetary status after 76 years, by the decision of the International Astronomical Union. The Assembly of this organization adopted an addition to the definition of “planet”; it consists in the absence of other celestial bodies near its orbit, with the exception of its own satellites. Pluto does not meet this point, since there are various space objects near it. This marked the beginning of the emergence of a new category - small planets, their second name is plutoids.

History of discovery

Even at the end of the 19th century, scientists assumed the presence of an unknown planet exerting an influence on. An American professor of astronomy, creator of a large private observatory, and researcher Percival Lowell began an active search for the object in 1906.

He gave the cosmic body the name “Planet X”, but was never able to find it until the end of his days. In 1919, Californian scientists from Mount Wilson looked at photographs of the area where Pluto was located, but due to a defect, it was not seen in the photographs. The search was suspended for ten years, and in 1929 Clyde Tombaugh continued it. Taking pictures of the approximate location of the mysterious planet according to the coordinates calculated by Lowell, he worked 14 hours a day. Hundreds of asteroids and a comet were discovered, and in 1930 Pluto was discovered. The privilege of choosing the name of the planet went to Professor Lowell's associates; options were sent from everywhere. The name of the god of the dark kingdom of the dead was suggested by the young Englishwoman Venice Bernie. Most of the employees liked this option, and the planet became Pluto.

Surface and composition

Studying the planet is difficult due to its enormous distance, and there is little information about it. In its structure, it has a rocky core and a mantle of frozen nitrogen mixed with methane and carbon monoxide. The surface of Pluto has a different character, its color changes with the changing seasons. Darker areas consisting of methane ice are visible. The density of the planet - 2.03 g/cm3 - indicates the presence of 50% silicates in the internal structure. The study of Pluto is carried out based on materials received from Hubble; they noticed traces of complex hydrocarbons.

Characteristics

Astronomers' initial assumptions said that Pluto's weight was comparable to that of Earth. But by studying the gravitational effect of Charon, they found that the mass of the planet reaches 1.305x10 in 22 kg - this is only a quarter of the weight of the Earth. It is smaller in size than the Moon and six other satellites in our system. Pluto was recalculated several times, its value changed when new data was received. Now its diameter is considered to be 2390 km.

The planet is surrounded by a thin layer of atmosphere, the state of which is related to the distance to the Sun. When approaching a star, the ice melts and evaporates, forming a rarefied gas shell consisting mostly of nitrogen and partly of methane, and when moving away, these substances freeze and fall to the surface. The temperature of the object is -223 degrees Celsius. The planet is distinguished by its slow rotation around its axis; it takes 6 days and 9 hours to change the day.

Orbit

The shape of Pluto’s orbit is elongated, it is not similar to others, and its deviation from the circle is 170. Because of this, the distance of the planet to the star changes cyclically. It, ahead of Neptune, approaches 4.4 billion km, and in the other part it moves away by 7.4 billion km. The time of approaching the star lasts 20 years - then the most convenient moment for studying the planet comes. Pluto and Neptune have no points of contact; they are quite far from each other (17 AU). The planets have a resonance of 3:2, i.e. while Pluto makes two revolutions, its neighbor manages to complete three. This stable relationship lasts for millions of years. The planet travels around the Sun in 248 years. The planet moves towards the Earth, like Uranus and Venus.

Satellites

Pluto is surrounded by five small moons: Hydra, Charon, Nix, Kerberos and Styx. They are concentrated very compactly. The first was Charon, which has a diameter of 1205 km. Its mass is 8 times less than that of Pluto. Mutual eclipses of the planet and satellite were useful in calculating its diameter. The sizes of all satellites are calculated inaccurately; they have a range from 10 km, in the case of Nikta (88-98 km), to 86 km for Hydra (44-130 km). Pluto and Charon are recognized by some modern scientists as an exceptional form of connection between cosmic bodies - a double planet.

Huge heart shaped region at front center. Several craters are visible, and much of the surface appears recycled rather than ancient. Pluto. Credit: NASA

After its discovery by Clyde Tombaugh in 1930, Pluto was considered for almost a century. In 2006, it began to be classified as a "dwarf planet" due to the discovery of other trans-Neptunian objects (TNOs) of comparable size. However, this does not change its importance in our system. In addition to large TNOs, it is the largest and second most massive dwarf planet in the Solar System.

As a result, most of the research time has been devoted to this former planet. And with the successful flyby of it by the New Horizons mission in July 2016, we finally have a clear idea of ​​what Pluto looks like. As scientists became bogged down in the massive amounts of data sent back, our understanding of this world grew by leaps and bounds.

Opening:

Pluto's existence was predicted before its discovery. In the 1840s, the French mathematician Urban before Le Verrier used Newtonian mechanics to (which had not yet been discovered) based on perturbations (perturbations of the orbit). In the 19th century, widespread observations of Neptune led astronomers to believe that some planet was causing disturbances in its orbit.

In 1906, Percival Lowell, an American mathematician and astronomer who founded the Lowell Observatory in Flagstaff, Arizona in 1894, initiated a project to search for "Planet X", a possible ninth planet. Unfortunately, Lowell died in 1916 before the discovery was confirmed. But unbeknownst to him, his surveys of the sky recorded two faint images of Pluto (March 19 and April 7, 1915) that simply went unnoticed.

The first photographs of Pluto, dated January 23 and 29, 1930. Courtesy: Lowell Observatory Archives Department.

After Lowell's death, the search was not resumed until 1929, after which Lowell Observatory Westo Director Melvin Slifer was assigned the task of finding Planet X with Clyde Tombaugh. 23-year-old astronomer Clyde Tombaugh from Kansas spent the next year photographing patches of the night sky and then analyzing the photos to determine whether any objects had moved out of place.

On February 18, 1930, Tombaugh discovered a possible moving object on photographic plates taken in January of that year. After the observatory received additional photographs to confirm the object's existence, news of the discovery was telegraphed to the Harvard College Observatory on March 13, 1930. The mysterious Planet X has finally been discovered.

Naming:

After the discovery, it was announced that the Lowell Observatory was inundated with proposals for names for the new planet. , after the Roman god of the underworld, was suggested by Venetia Burney (1918-2009), then an 11-year-old schoolgirl in Oxford, England. She suggested it in a conversation with her grandfather, who recommended the name to astronomy professor Herbert Hall Turner, who informed his colleagues in the United States.

The surface of Pluto as seen by the Hubble telescope in several images in 2002 and 2003. Credit: NASA/Hubble.

The object was given an official name on March 24, 1930, and it came down to a vote between three options - Minerva, Kronos and. Every member of the Lowell Observatory voted for Pluto, and it was announced on May 1, 1930. The choice was based on the fact that the first two letters in the word Pluto - P and L - correspond to the initials.

This name quickly caught on among the general public. In 1930, Walt Disney was apparently inspired by this event when he introduced Mickey's bloodhound, Pluto, to the public. In 1941, Glenn T. Seaborg named the newly discovered element plutonium, after Pluto. This was in keeping with the tradition of naming elements after newly discovered planets - such as uranium, called , and neptunium, called .

Size, mass and orbit:

With a mass of 1.305±0.007 x 10²² kg - which is the equivalent of and - Pluto is the second-largest dwarf planet and the tenth-largest known object directly orbiting the Sun. It has a surface area of ​​1.765 x 10 7 km and a volume of 6.97 x 10 9 km.

A map of Pluto's surface, with informal names for several of the larger features of the landscape. Credit: NASA/JHUAPL.

Pluto has a moderately eccentric, inclined orbit that wobbles. This means that Pluto periodically gets closer to the Sun than Neptune, but a stable orbital resonance with Neptune prevents them from colliding.

Pluto has an orbital period of 247.68 Earth years, meaning it takes almost 250 years to complete one full revolution around the Sun. Meanwhile, the period of rotation around its axis (one day) is 6.39 Earth days. Like Uranus, Pluto rotates on its side with an axial tilt of 120° relative to the orbital plane, resulting in extreme seasonal variations. At its solstices, one quarter of the surface is in constant daylight, while the other three quarters are in constant darkness.

Composition and atmosphere:

With an average density of 1.87 g/cm³, Pluto's composition is differentiated between an icy mantle and a rocky core. The surface consists of more than 98% nitrogen ice with admixtures of methane and carbon monoxide. The surface is very varied with large differences in brightness and color. A distinctive feature is.

The theoretical internal structure of Pluto, consisting of 1) frozen nitrogen, 2) water ice, 3) rock. Credit: NASA/Pat Rawlings.

Scientists also suspect that Pluto's internal structure is differentiated, with rock settled in a dense core surrounded by a mantle of water ice. The diameter of the core is believed to be approximately 1,700 km, 70% of Pluto's diameter. Due to the decay of radioactive elements, it is possible that the thickness of the core and mantle is 100-180 km.

Pluto has a thin atmosphere of nitrogen (N2), methane (CH4) and carbon monoxide (CO), which are in equilibrium with their surface ices. However, the planet is so cold that during part of its orbit the atmosphere thickens and falls to the surface. The average temperature of the planet's surface is from 33 K (-240 ° C) at aphelion to 55 K (-218 ° C) at perihelion.

Satellites:

Pluto has five known moons. The largest and closest in Pluto's orbit is Charon. This moon was first identified in 1978 by astronomer James Christie using photographic plates from the United States Naval Observatory (USNO) in Washington, DC. with multiple orbits - Styx, Nix, Kerberos and Hydra, respectively.

Nikta and Hydra were discovered simultaneously in 2005 by a team searching for Pluto's companions using the Hubble telescope. The same team opened Kerber in 2011. The fifth and final moon, Styx, was discovered in 2012 while photographing Pluto and Charon.

An illustration comparing the scale and brightness of Pluto's moons. Credit: NASA/ESA/M.Showalter.

Charon, Styx and Kerberos are massive enough to collapse into a spheroid shape under the influence of their own gravity. Nyx and Hydra, however, have an elongated shape. The Pluto-Charon system is unusual in that it is one of the few systems in the world whose barycenter lies above the surface of the planet. In short, causing some scientists to claim that it is a "double dwarf system" instead of a dwarf planet and a satellite in its orbit.

In addition, it is also unusual in that each body has tidal locking (synchronous rotation) with each other. Charon and Pluto always face the same side to each other, and from any location on the surface of either, the other is always in the same position in the sky, or always hidden. This also means that the periods of rotation around the axis of each of them are equal to the time it takes for the entire system to turn around the common center of mass.

In 2007, Gemini Observatory observations of patches of ammonia hydrates and water crystals on Charon's surface suggested the presence of . This would seem to indicate that Pluto has a warm subsurface ocean and that the core is geologically active. The moons of Pluto are believed to have been formed by a collision between Pluto and a similar-sized celestial body in the ancient history of the Solar System. The collision ejected material that later consolidated into moons around Pluto.

Classification:

Since 1992, many celestial bodies have been discovered orbiting in the same region as Pluto, demonstrating that Pluto is part of a population. This brought its official status as a planet into question, with many questioning whether Pluto should be considered separately from its surrounding populations, like Pallas, Juno, and Pluto, which lost their planetary status after .

On July 29, 2005, the discovery was announced, which was believed to be much larger than Pluto. Originally referring to the tenth planet in the Solar System, there was no consensus on whether Eris is a planet. Moreover, others in the astronomical community consider its discovery a strong argument for reclassifying Pluto as a minor planet.

The debate came to a close on August 24, 2006, with a resolution by the International Astronomical Union (IAU) that created an official definition of the term "planet". According to the XXVI General Assembly of the IAU, a planet must meet three criteria: it must be in orbit around the Sun, it must have sufficient gravity to compress itself into a spherical shape, and it must clear its orbit of other objects.

Pluto does not satisfy the third condition because its mass is only 0.07 of the mass of all objects in its orbit. The IAU also ruled that bodies that do not meet the third criterion should be called dwarf planets. On September 13, 2006, the IAU included Pluto, Eris and its moon Dysnomia in the Minor Planet Catalog.

The IAU's decision was met with controversy, especially in the scientific community. For example, Alan Stern, the principal investigator of the New Horizons mission, and Mark Bouyer, an astronomer at Lowell Observatory, have both been outspoken about their displeasure with the reclassification. Others, such as Mike Brown, the astronomer who discovered Eris, expressed their support.

Our evolving understanding of Pluto, as represented by Hubble images from 2002-2003 (left) and New Horizons photos taken in 2015 (right). Credit: theguardian.com

On August 14-16, 2008, researchers on both sides of the issue gathered for what became known as "The Great Planet Debate" at the Johns Hopkins University Applied Physics Laboratory. Unfortunately, no scientific consensus was reached, but on June 11, 2008, the IAU announced in a press release that the term "plutoid" would henceforth be used to refer to Pluto and other similar objects.

(OPK). This led to the planning of the Pluto Kuiper Express mission, and NASA instructed the Jet Propulsion Laboratory to plan a flyby of Pluto and the Kuiper Belt.

By 2000, the program was revised due to expressed budget problems. After pressure from the scientific community, a revised mission to Pluto, called New Horizons, finally received funding from the US government in 2003. The New Horizons spacecraft successfully launched on January 19, 2006.

From September 21 to 24, 2006, the New Horizons spacecraft captured its first photographs of Pluto while testing an instrument called LORRI. These images, taken from a distance of approximately 4.2 billion km or 28.07 AU, were released on November 28, 2006, confirming the spacecraft's ability to track distant targets.

Operations for a distant rendezvous with Pluto began on January 4, 2015. From January 25 to January 31, the incoming probe took several images of Pluto, published by NASA on February 12, 2015. These photographs, taken from a distance of more than 203 million km, showed Pluto and its largest moon Charon.

Pluto and Charon, recorded by the New Horizons spacecraft from January 25 to January 31, 2015. Credit: NASA

The New Horizons spacecraft made its close approach to Pluto at 11:49:57 UTC on July 14, 2015, followed by Charon at 12:03:50 UTC. Telemetry confirming the successful flight and the “health” of the spacecraft reached Earth at 00:52:37 UTC.

During its flyby, the probe captured the clearest images of Pluto to date, and a full analysis of the data obtained will take several years. The spacecraft is currently moving at 14.52 km/s relative to the Sun and 13.77 km/s relative to Pluto.

While the New Horizons mission has shown us a lot about Pluto and will continue to do so as scientists analyze the data collected, there is still much to learn about this distant and mysterious world. With time and more missions, we will finally be able to uncover some of its deepest secrets.

An illustration of the New Horizons spacecraft near Pluto, with Charon visible in the background. Credit: NASA/JPL.

In the meantime, we offer all the information that is currently known about Pluto. We hope you find what you're looking for in the links below, and as always, enjoy your exploration!

Title of the article you read "Dwarf Planet Pluto".

General information about Pluto

© Vladimir Kalanov,
website"Knowledge is power".

Soon after the discovery of Neptune, made in September 1846 by the German astronomer Johann Halle according to the calculations of Adams and Le Verrier, the idea arose of searching for a new planet beyond the orbit of Neptune. It was assumed that the unknown planet could have an influence on the characteristics of the movement of Uranus (along with the influence of Neptune, Saturn and Jupiter).

Pluto

History of the discovery of Pluto

Back in 1848, the American mathematician and astronomer Benjamin Peirce (1809-1880) hypothesized the existence of a trans-Neptunian planet. In 1874, another American astronomer, Simon Newcomb (1835-1909), developed a new theory of the motion of Uranus, which took into account the gravity of an unknown extra-Neptunian planet.

The American astronomer, famous for his work, Percival Lowell (1855-1916), devoted 14 years of hard work to the search for this planet. He organized a large-scale search for the ninth planet of the solar system, indicated a place in the constellation Gemini where to look for an unknown planet, but his premature death did not give him the opportunity to complete the work he had started. 14 years after Lowell’s death, on March 13, 1930, American astronomer Clyde Tombaugh, working at an observatory near the city of Flagstaff (Arizona), built at one time with Lowell’s money, discovered the ninth planet. She was located exactly in the place that Percival Lowell had calculated.

We consider it our duty to note that Clyde Tombaugh, who was only 24 years old at the time of the discovery, came to this outstanding success as a result of enormous, painstaking work, working as the operator of a blink comparator - a special device that allows you to compare two photographs of the same area sky taken at different times using a photographic telescope, Clyde Tombaugh had to analyze and compare hundreds of photographic plates while sitting behind a blink comparator microscope.

On the photographic plates there were reflections of faint stars, the number of which, as they approached the strip of the Milky Way, ranged from 160 thousand to 400 thousand on each plate. What perseverance and what hard work one had to have to carefully analyze these records!

Later it turned out that Pluto could have been discovered during Lowell’s lifetime, as well as in 1919. Processing of the surviving photographic plates of the Flagstaff Observatory using modern technology showed that the image of the new planet on one of the plates was due to a defect in the photographic plate, while on the others the images were so unclear that it was simply impossible to notice them.

In the name, more precisely in the astronomical sign of the planet Pluto, certain symbolism is visible: two Latin letters P and L coincide with the initial letters of the name Persival Lowell. Although such a coincidence is probably accidental, it is perceived as a kind of historical justice. If we turn to mythology, then Pluto among the ancient Greeks was the god of the underworld, the abode of the dead. The name given to the ninth planet is not at all funny, but let’s not take it seriously, a myth is just that: a myth.

Before continuing the story about Pluto, let us immediately make a reservation that the term “planet” is no longer used in relation to this celestial body. In August 2006, the XXVI Assembly of the International Astronomical Union took place in Prague, which decided that Pluto is not a full-fledged planet of the solar system and, due to its size, is classified as dwarf planets . It must be said that among astronomers this decision was received ambiguously and, on the whole, rather restrainedly.

General information about Pluto

Pluto is the smallest and farthest planet in the solar system. Pluto has an average distance from the Sun of 5,900 million kilometers (39.9 AU). A characteristic feature of Pluto's movement is the large elongation of its circumsolar orbit and its large inclination to the ecliptic plane. Approaching one of its extreme positions in orbit (perihelion), Pluto appears for some time closer to the Sun than Neptune. In fact: the minimum distance of Neptune from the Sun is 4456 million km, and Pluto is 4425 million km. The last such period when Neptune was the most distant planet occurred in the years from 1979 to 1998.

Diagram: orbits of Neptune and Pluto

There is no need to be surprised by the long duration of this period (19 years), because the period of Pluto’s revolution around the Sun is 248 years. But the most distant point of Pluto’s orbit is 7375 million km from the Sun. At this moment, Pluto is already incomparably farther from the Sun than Neptune.

It turns out that with the appropriate location in space relative to the Sun, our Earth can be located at a distance from Pluto equal to approximately 7525 million km. At such a huge distance, exploration of the planet Pluto is very difficult. In the most powerful telescope, Pluto and its satellite appear from Earth in the form of a small star, almost merged with another, even smaller one.

True, with the help of a spacecraft launched into low-Earth orbit, scientists were able to obtain a certain amount of information about these distant celestial bodies. For example, the diameter of Pluto was determined to be 2390 km, which is almost half the diameter of Mercury (4878 km) and significantly less than the diameter of the Moon (3480 km).

The rotation period of Pluto around its own axis is 6 days and 8 hours, i.e. A day on Pluto lasts 152 Earth hours. Pluto's rotation around its axis is in the opposite direction to the direction of its orbital rotation. This is another feature of this planet.

Pluto's mass is 0.0025 of the mass of the Earth (400 times less than the mass of the Earth). The inclination of the orbital plane to the ecliptic plane is 17°2". None of the other eight planets of the Solar System has such a large inclination of the orbital plane. For example, this parameter is: for Neptune - 1°8", for Uranus - 0°8", for Saturn - 2°5", for Jupiter - 1°9".

The period of revolution around the Sun, i.e. a year on Pluto is, as we already know, 248 Earth years, i.e. almost a quarter of a millennium.

The average speed of revolution around the Sun is 4.7 km/s, or almost 17,000 km/h.

We can imagine a pilot at the controls of a jet aircraft, flying at a speed of slightly more than 1000 km/h for several hours. But it is impossible to imagine the flight of such an aircraft along the orbit of Pluto. Such a flight is unthinkable, because it would take 4,200 years to fly around the Sun in Pluto’s orbit at a speed of about 1000 km/h: after all, it would be necessary to fly about 22.2 billion km.

We present this fantastic calculation because we are talking about the most distant planet in the solar system. Space is fraught with many mysteries, and who knows whether people will be able to discover another planet. Perhaps the orbits of Neptune and Pluto are the boundaries of the solar system. And so, to give readers an idea of ​​the size of the space contained within these boundaries, we have given this simple calculation.

Atmosphere and surface of Pluto

Pluto's atmosphere was discovered in 1985 by observing its covering of stars. The presence of an atmosphere was subsequently confirmed by observations of other coatings in 1988 and 2002.

Pluto's atmosphere is very thin and consists mainly of a mixture of nitrogen (99%), carbon monoxide and methane (0.1%). The main component of the atmosphere is molecular nitrogen (N 2). It is assumed that nitrogen was formed from the substance that makes up the surface of Pluto. Currently, nitrogen is in a volatile (sublimated) state. At an average atmospheric temperature of minus 230°C, this is the natural state of aggregation of nitrogen. According to updated data, the temperature of the atmosphere (minus 180°C) is higher than the temperature of the planet’s surface (minus 230°C). Sublimation produces a cooling effect on Pluto's surface.

The atmosphere also contains molecules and ions of hydrogen, hydrocyanic acid, ethane and other substances formed as a result of photochemical processes and the influence of charged particles. It is believed that methane existed during the formation of the planet and came out of its depths.

At an altitude of 1215 km, the atmospheric pressure is about 2.3 microbars. At this altitude, the atmosphere seems to be divided into two parts. Above there is a layer of aerosol from a mixture of the substances listed above. As you move away from the Sun, the sublimation of surface ice decreases and, accordingly, the pressure drops.

Thanks to images transmitted from the Hubble telescope, scientists have an idea of ​​about 85 percent of Pluto's surface. The surface of Pluto appears as contrasting zones - from light to dark. Some dark areas can be considered formations similar to craters and depressions that appeared as a result of collisions with large asteroids.

Surface of Pluto

Pluto's surface is composed of water ice and frozen methane. The light areas of the surface are areas believed to be covered with solid nitrogen. Nitrogen status changes as long seasonal cycles occur. A change in the structure of nitrogen leads to a change in the brightness of the surface. Depending on temperature conditions, the structure of water ice also changes. As Pluto approaches the Sun, part of the ice sublimates, i.e. turns into gas and the atmosphere becomes denser. As the planet moves away from the Sun, the atmosphere partially condenses and falls out in the form of crystals, forming a kind of “snow” on the surface. This creates lighter areas of the surface.

Three views of Pluto
Surface photo based on Hubble telescope images

The homogeneous grayish spots, which were “examined” with the help of the Hubble telescope, are formed by methane. This is confirmed by spectroscopic studies performed from Earth. Methane makes up about 1% of the planet's mass.

One of the components of Pluto's surface may be carbon dioxide, the content of which is less than 1%. It is possible that the surface composition, in addition to the indicated substances, also includes other components, but so far they have not been identified.

The density of matter on Pluto averages 2.03 (g/cm³). Surface temperature - from minus 228 to minus 238 °C. The surface pressure ranges from 3 to 160 microbars. The illumination of the surface is weak: the distance from the Sun is too great. However, during the daytime the surface of Pluto is illuminated many times more than our Earth is illuminated by the Moon at night.

Much about Pluto remained unknown until 2015, when the New Horizons spacecraft flew past it.

The heterogeneity of Pluto's surface has been confirmed by much better photographs from the New Horizons probe.

The albedo of different parts of its surface varies from 10 to 70%, which makes it the second most contrasting object in the solar system after Iapetus.

Internal structure of Pluto

Pluto is a special planet, but most likely it can be classified as a terrestrial planet. According to the main hypothesis, it is believed that under the surface, consisting mainly of frozen water and methane, there is an icy mantle up to 250 km thick, consisting of ice (130 km layer), molecular nitrogen and other structures. Deeper there is a core of rocky silicates and partly ice and hydrates. According to one version, between the icy mantle and the silicate core there may be a layer of organic substances up to 100 km thick.

The ice on the surface and in the mantle was formed from water raised from the depths of the planet by heat that was released during the radioactive decay of the elements that make up the rocky formations of the core. Other speculations on this issue are that water was released from the planet's primordial fossils as a result of a collision with a large asteroid.

© Vladimir Kalanov,
"Knowledge is power"

Dear visitors!

Pluto (134340 Pluto) is the largest dwarf planet in the Solar System (along with Eris), a trans-Neptunian object (TNO) and the tenth largest celestial body orbiting the Sun (excluding satellites). Pluto was originally classified as a planet, but is now considered one of the largest objects (possibly the largest) in the Kuiper Belt.

Like most objects in the Kuiper Belt, Pluto is made mostly of rock and ice and is relatively small: its mass is five times less than the Moon's and its volume is three times less. Pluto's orbit has a large eccentricity (eccentricity of the orbit) and a large inclination relative to the ecliptic plane.

Due to the eccentricity of its orbit, Pluto approaches the Sun at a distance of 29.6 AU. e. (4.4 billion km), being closer to Neptune, it moves away by 49.3 a. e. (7.4 billion km). Pluto and its largest moon Charon are often considered a double planet because their system's barycenter lies outside both objects. The International Astronomical Union (IAU) has announced its intention to provide a formal definition for binary dwarf planets, but until then, Charon is classified as a moon of Pluto. Pluto also has three smaller moons, Nix and Hydra, which were discovered in 2005, and P4, the smallest, discovered on June 28, 2011.

From the day of its discovery in 1930 until 2006, Pluto was considered the ninth planet of the solar system. However, at the end of the 20th and beginning of the 21st centuries, many objects were discovered in the outer solar system. Notable among them are Quaoar, Sedna, and especially Eris, which is 27% more massive than Pluto. On August 24, 2006, the IAU first defined the term "planet". Pluto did not fall under this definition, and the IAU classified it in a new category of dwarf planets, along with Eris and Ceres. After the reclassification, Pluto was added to the list of minor planets and received number (English) 134340 according to the catalog of the Minor Planet Center (MPC). Some scientists continue to believe that Pluto should be reclassified back to a planet.

The chemical element plutonium was named after Pluto.

History of discovery

In the 1840s, Urbain Le Verrier, using Newtonian mechanics, predicted the position of the then-undiscovered planet Neptune based on an analysis of disturbances in the orbit of Uranus. Subsequent observations of Neptune at the end of the 19th century led astronomers to suggest that, in addition to Neptune, another planet was influencing the orbit of Uranus. In 1906, Percival Lowell, a wealthy Bostonian who had founded the Lowell Observatory in 1894, initiated an extensive project to search for the solar system's ninth planet, which he named "Planet X." By 1909, Lowell and William Henry Pickering had proposed several possible celestial coordinates for the planet. Lowell and his observatory continued searching for the planet until his death in 1916, but without success. In fact, on March 19, 1915, two faint images of Pluto were received at the Lowell Observatory, but it was not identified in them.

Mount Wilson Observatory could also lay claim to the discovery of Pluto in 1919. That year, Milton Humason, on behalf of William Pickering, was searching for the ninth planet, and an image of Pluto ended up on a photographic plate. However, the image of Pluto in one of the two photographs coincided with a small defect in the emulsion (it even seemed to be part of it), and on the other plate the image of the planet was partially superimposed on the star. Even in 1930, the image of Pluto in these archival photographs was revealed with considerable difficulty.

Due to a ten-year legal battle with Constance Lowell - the widow of Percival Lowell, who was trying to get a million dollars from the observatory as part of his legacy - the search for Planet X was not resumed. It was not until 1929 that Westo Observatory director Melvin Slipher, without much hesitation, assigned the continuation of the search to Clyde Tombaugh, a 23-year-old Kansas man who had just been accepted into the observatory after Slipher had been impressed by his astronomical drawings.

Tombaugh's task was to systematically obtain images of the night sky in the form of paired photographs with an interval of two weeks between them, then compare the pairs to find objects that had changed their position. For comparison, a blink comparator was used to quickly switch the display of the two plates, which creates the illusion of movement for any object that changed position or visibility between photographs. On February 18, 1930, after almost a year of work, Tombaugh discovered a possible moving object in photographs taken on January 23 and 29. A lower-quality photo from January 21 confirmed the movement. On March 13, 1930, after the observatory received other confirmatory photographs, news of the discovery was telegraphed to the Harvard College Observatory. For this discovery in 1931, Tombaugh was awarded the gold medal of the English Astronomical Society.

Name

Venetia Bernie is the girl who gave the planet the name Pluto. The right to name the new celestial body belonged to the Lowell Observatory. Tombaugh advised Slifer to do this as quickly as possible before they were ahead of them. Name variations began to pour in from all over the world. Constance Lowell, Lowell's widow, first suggested "Zeus", then her husband's name - "Percival", and then her own name. All such proposals were ignored.

The name "Pluto" was first suggested by Venetia Burney, an eleven-year-old schoolgirl from Oxford. Venice was interested not only in astronomy, but also in classical mythology, and decided that this name - an ancient Roman version of the name of the Greek god of the underworld - was suitable for such a probably dark and cold world. She suggested the name in a conversation with her grandfather Falconer Meydan, who worked at the Bodleian Library at Oxford University - Meydan had read about the discovery of the planet in The Times and told his granddaughter about it over breakfast. He conveyed her proposal to Professor Herbert Turner, who telegraphed his colleagues in the USA.

The object officially received its name on March 24, 1930. Each member of the Lowell Observatory could vote on a short list of three options: "Minerva" (although one of the asteroids had already been named that way), "Kronos" (this name proved unpopular, having been proposed by Thomas Jefferson Jackson See, an astronomer of disrepute), and " Pluto". The last one proposed received all the votes. The name was published on May 1, 1930. After this, Faulconer Meydan gave Venice £5 as a reward.

Pluto's astronomical symbol is a monogram of the letters P and L, which are also the initials of the name P. Lowell. The astrological symbol of Pluto resembles the symbol of Neptune (Neptune symbol.svg), with the difference that in place of the middle prong in the trident there is a circle (Pluto's astrological symbol.svg).

In Chinese, Japanese, Korean and Vietnamese, the name Pluto is translated as “Star of the Underground King” - this option was proposed in 1930 by the Japanese astronomer Hoei Nojiri. Many other languages ​​use the transliteration "Pluto" (in Russian - "Pluto"); however, some Indian languages ​​may use the name of the god Yama (for example, Yamdev in Gujarati), the guardian of hell in Buddhism and Hindu mythology.

The search for Planet X

Immediately after Pluto's discovery, its dimness, as well as its lack of a discernible planetary disk, raised doubts about its being Lowell's "Planet X". Throughout the middle of the 20th century, estimates of Pluto's mass were constantly revised downwards. The discovery of Pluto's moon Charon in 1978 made it possible to measure its mass for the first time. This mass, equal to about 0.2% of the Earth's mass, turned out to be too small to cause discrepancies in the orbit of Uranus.

Subsequent searches for an alternative Planet X, particularly those led by Robert Garrington, were unsuccessful. During the passage of Voyager 2 near Neptune in 1989, data were obtained in which the total mass of Neptune was revised downwards by 0.5%. In 1993, Myles Standish used this data to recalculate Neptune's gravitational influence on Uranus. As a result, the discrepancies in the orbit of Uranus disappeared, and with them the need for Planet X.

Today, the vast majority of astronomers agree that Lowell's Planet X does not exist. In 1915, Lowell predicted a position for Planet X that was quite close to Pluto's actual position at that time; however, the English mathematician and astronomer Ernest Brown concluded that this was a coincidence, and this point of view is now generally accepted.

Orbit

Pluto's orbit differs significantly from the orbits of the planets in the solar system. It is highly inclined relative to the ecliptic (more than 17°) and highly eccentric (elliptical). The orbits of all planets in the Solar System are close to circular and make a small angle with the plane of the ecliptic. Pluto's average distance from the Sun is 5.913 billion km, or 39.53 AU. e., but due to the large eccentricity of the orbit (0.249), this distance varies from 4.425 to 7.375 billion km (29.6-49.3 AU). Sunlight takes about five hours to reach Pluto, so it will take radio waves the same amount of time to travel from Earth to a spacecraft located near Pluto. The large eccentricity of the orbit leads to the fact that part of it passes closer to the Sun than Neptune. The last time Pluto occupied this position was from February 7, 1979 to February 11, 1999. Detailed calculations show that before this Pluto occupied this position from July 11, 1735 to September 15, 1749, and for only 14 years, while from April 30, 1483 to July 23, 1503, it was in this position for 20 years. Due to the large inclination of Pluto's orbit to the ecliptic plane, the orbits of Pluto and Neptune do not intersect. Passing perihelion, Pluto is at 10 AU. i.e. above the ecliptic plane. In addition, Pluto's orbital period is 247.69 years, and Pluto orbits two times while Neptune rotates three. As a result, Pluto and Neptune never come closer than 17 AU. e. Pluto’s orbit can be predicted several million years both back and forth, but no more. The mechanical motion of Pluto is chaotic and is described by nonlinear equations. But to notice this chaos, you need to watch it long enough. There is a characteristic time for its development, the so-called Lyapunov time, which for Pluto is 10-20 million years. If observations are made over short periods of time, the motion will appear to be regular (periodic along an elliptical orbit). In fact, the orbit shifts slightly with each period, and during Lyapunov time it shifts so much that no traces of the original orbit remain. Therefore, it is very difficult to simulate movement.

Orbits of Neptune and Pluto

View of the orbits of Pluto (in red) and Neptune (in blue) from above. Pluto periodically happens to be closer to the Sun than Neptune. The shaded portion of the orbit shows where Pluto's orbit is below the ecliptic plane. The position is given as of April 2006

Pluto is in an orbital resonance of 3:2 with Neptune - for every three revolutions of Neptune around the Sun, there are two revolutions of Pluto, the entire cycle takes 500 years. It seems that Pluto should periodically move very close to Neptune (after all, the projection of its orbit intersects with the orbit of Neptune).

The paradox is that Pluto sometimes appears closer to Uranus. The reason for this is the same resonance. In each cycle, when Pluto first passes perihelion, Neptune is 50° behind Pluto; when Pluto passes perihelion for the second time, Neptune will make one and a half revolutions around the Sun and will be at approximately the same distance as last time, but ahead of Pluto; at a time when Neptune and Pluto find themselves in line with the Sun and on one side of it, Pluto goes into aphelion.

Thus, Pluto is never closer than 17 AU. That is, to Neptune, and with Uranus, approaches up to 11 a.m. are possible. e.

The orbital resonance between Pluto and Neptune is very stable and lasts for millions of years. Even if Pluto's orbit lay in the ecliptic plane, a collision would be impossible.

The stable interdependence of the orbits argues against the hypothesis that Pluto was a satellite of Neptune and left its system. However, the question arises: if Pluto never passed close to Neptune, then where could resonance arise from a dwarf planet, much less massive than, for example, the Moon? One theory suggests that if Pluto was not initially in resonance with Neptune, then it probably came much closer to it from time to time, and these approaches over billions of years affected Pluto, changing its orbit into the one observed today.

Additional factors affecting Pluto's orbit

Perihelion argument diagram

Calculations have made it possible to establish that over millions of years the general nature of the interactions between Neptune and Pluto does not change. However, there are several more resonances and influences that affect the characteristics of their movement relative to each other and additionally stabilize Pluto’s orbit. In addition to the 3:2 orbital resonance, the following two factors are of primary importance.

Firstly, Pluto's perihelion argument (the angle between the point of intersection of its orbit with the ecliptic plane and the perihelion point) is close to 90°. It follows from this that when passing perihelion, Pluto rises as much as possible above the plane of the ecliptic, thereby preventing a collision with Neptune. This is a direct consequence of the Kozai effect, which relates the eccentricity and inclination of an orbit (in this case, the orbit of Pluto), taking into account the influence of a more massive body (here, Neptune). In this case, the amplitude of Pluto’s libration relative to Neptune is 38°, and the angular separation of Pluto’s perihelion from Neptune’s orbit will always be more than 52° (that is, 90°-38°). The moment when the angular separation is smallest repeats itself every 10,000 years.

Secondly, the longitudes of the ascending nodes of the orbits of these two bodies (the points where they intersect the ecliptic) are practically in resonance with the above vibrations. When these two longitudes coincide, that is, when a straight line can be drawn through these 2 nodes and the Sun, Pluto's perihelion will make an angle of 90° with it, and the dwarf planet will be highest above Neptune's orbit. In other words, when Pluto crosses the projection of Neptune's orbit and goes deepest beyond its line, it will move farthest away from its plane. This phenomenon is called 1:1 superresonance.

To understand the nature of libration, imagine looking at the ecliptic from a distant point where the planets are seen moving counterclockwise. After passing through the ascending node, Pluto is inside Neptune's orbit and moves faster, catching up with Neptune from behind. The strong attraction between them causes a torque applied to Pluto due to Neptune's gravity. It moves Pluto into a slightly higher orbit, where it moves a little slower in accordance with Kepler's 3rd Law. As Pluto's orbit changes, the process gradually entails a change in the periapsis and longitudes of Pluto (and, to a lesser extent, Neptune). After many such cycles, Pluto slows down so much and Neptune speeds up so much that Neptune begins to catch Pluto on the opposite side of its orbit (near the opposite node from where we started). The process is then reversed, with Pluto imparting momentum to Neptune until Pluto accelerates so much that it begins to catch up with Neptune near the original node. The full cycle is completed in approximately 20,000 years.

physical characteristics

Large plutinos compared by size, albedo and color. (Pluto is shown with Charon, Nyctus and Hydra)

Probable structure of Pluto.
1. Frozen nitrogen
2. Water ice
3. Silicates and water ice

Pluto's large distance from Earth greatly complicates its comprehensive study. New information about this dwarf planet may be obtained in 2015, when the New Horizons spacecraft is expected to arrive in the Pluto region.
[edit] Visual characteristics and structure

Pluto's magnitude averages 15.1, reaching 13.65 at perihelion. Observing Pluto requires a telescope, preferably with an aperture of at least 30 cm. Pluto appears star-shaped and blurry even in very large telescopes, since its angular diameter is only 0.11. At very high magnification, Pluto appears light brown with a faint hint of yellow. Spectroscopic analysis of Pluto shows that its surface is more than 98% nitrogen ice with traces of methane and carbon monoxide. The distance and capabilities of modern telescopes do not allow obtaining high-quality images of the surface of Pluto. Photographs taken by the Hubble Space Telescope reveal only the most general details, and even then vaguely. The best images of Pluto were obtained by compiling so-called “brightness maps”, created by observing the eclipses of Pluto by its moon Charon, which occurred in 1985-1990. Using computer processing, it was possible to capture the change in surface albedo when a planet was eclipsed by its satellite. For example, an eclipse of a brighter surface feature produces larger variations in apparent brightness than an eclipse of a darker one. Using this technique, it is possible to find out the overall average brightness of the Pluto-Charon system and track changes in brightness over time. The dark stripe below Pluto's equator, as you can see, has a rather complex color, which indicates some still unknown mechanisms for the formation of Pluto's surface.

Maps compiled from data from the Hubble telescope indicate that Pluto's surface is extremely heterogeneous. This is also evidenced by Pluto's light curve (that is, the dependence of its apparent brightness on time) and periodic changes in its infrared spectrum. The surface of Pluto facing Charon contains a fair amount of methane ice, while the opposite side contains more nitrogen and carbon monoxide ice and almost no methane ice. Thanks to this, Pluto takes second place as the most contrasting object in the solar system (after Iapetus). Data obtained using the Hubble Space Telescope suggest that Pluto's density is 1.8-2.1 g/cm2. Pluto's internal structure is probably 50-70% rock and 50-30% ice. Under the conditions of the Pluto system, water ice (the varieties ice I, ice II, ice III, ice IV and ice V, as well as frozen nitrogen, carbon monoxide and methane) can exist. Because the decay of radioactive minerals would eventually heat the ices enough for them to separated from the rocks, scientists suggest that Pluto's internal structure is differentiated - rocks in a dense core, surrounded by a mantle of ice, which in this case would be about 300 km thick. It is also possible that heating continues today, creating an ocean below the surface liquid water.

At the end of 2011, the Hubble telescope discovered complex hydrocarbons on Pluto - strong absorption lines, indicating the presence of a number of previously undetected compounds on the surface of the dwarf planet. It has also been hypothesized that simple life may exist on the planet.

Weight and dimensions

Earth and Moon compared to Pluto and Charon

Astronomers, initially believing that Pluto was Lowell's "Planet X", calculated its mass based on its supposed influence on the orbit of Neptune and Uranus. In 1955, Pluto's mass was thought to be approximately equal to that of Earth, and further calculations lowered this estimate by 1971 to approximately the mass of Mars. In 1976, Dale Cruickshank, Carl Pilcher, and David Morrison of the University of Hawaii first calculated Pluto's albedo, finding it to be consistent with that of methane ice. Based on this, it was decided that Pluto must be exceptionally bright for its size and therefore could not have a mass greater than 1% of the mass of the Earth.

The discovery of Pluto's moon Charon in 1978 made it possible to measure the mass of the Pluto system using Kepler's third law. Once Charon's gravitational influence on Pluto was calculated, estimates of the mass of the Pluto-Charon system dropped to 1.31 x 1022 kg, which is 0.24% of the Earth's mass. An accurate determination of the mass of Pluto is currently impossible, since the ratio of the masses of Pluto and Charon is unknown. It is currently believed that the masses of Pluto and Charon are in a ratio of 89:11, with a possible error of 1%. In general, the possible error in determining the main parameters of Pluto and Charon ranges from 1 to 10%.

Until 1950, it was believed that Pluto was close in diameter to Mars (that is, about 6,700 km), due to the fact that if Mars were at the same distance from the Sun, it would also have a 15th magnitude. In 1950, J. Kuiper measured the angular diameter of Pluto using a telescope with a 5-meter lens, obtaining a value of 0.23, which corresponds to a diameter of 5900 km. On the night of April 28–29, 1965, Pluto would have eclipsed a 15th magnitude star if its diameter had been equal to that determined by Kuiper. Twelve observatories monitored the brilliance of this star, but it did not weaken. Thus, it was established that the diameter of Pluto does not exceed 5500 km. In 1978, after the discovery of Charon, Pluto's diameter was estimated to be 2,600 km. Later, observations of Pluto during the eclipses of Pluto by Charon and Charon by Pluto 1985-1990. allowed us to establish that its diameter is approximately 2390 km.

Pluto (bottom right) compared with the solar system's largest moons (from left to right and top to bottom): Ganymede, Titan, Callisto, Io, Luna, Europa and Triton

With the invention of adaptive optics, it was possible to accurately determine the shape of the planet. Among the objects of the Solar System, Pluto is not only smaller in size and mass in comparison with the other planets, it is even inferior to some of their satellites. For example, Pluto's mass is only 0.2 that of the Moon. Pluto is smaller than seven natural satellites of other planets: Ganymede, Titan, Callisto, Io, the Moon, Europa and Triton. Pluto is twice the diameter and ten times more massive than Ceres, the largest object in the asteroid belt (located between the orbits of Mars and Jupiter), however, with approximately equal diameters, it is inferior in mass to the dwarf planet Eris from the open disk, discovered in 2005.

Atmosphere

Pluto's atmosphere is a thin shell of nitrogen, methane and carbon monoxide evaporating from the surface ice. From 2000 to 2010, the atmosphere expanded significantly due to the sublimation of surface ice. At the turn of the 21st century, it extended 100-135 km above the surface, and according to the results of measurements in 2009-2010. - stretches for more than 3000 km, which is about a quarter of the distance to Charon. Thermodynamic considerations dictate the following composition of this atmosphere: 99% nitrogen, slightly less than 1% carbon monoxide, 0.1% methane. As Pluto moves away from the Sun, its atmosphere gradually freezes and settles on the surface. As Pluto approaches the Sun, temperatures near its surface cause ice to sublimate and turn into gases. This creates an anti-greenhouse effect: just as sweat cools the body as it evaporates from the skin's surface, sublimation produces a cooling effect on Pluto's surface. Scientists, thanks to the Submillimeter Array, recently calculated that the surface temperature of Pluto is 43 K (-230.1 °C), which is 10 K lower than expected. Pluto's upper atmosphere is 50° warmer than the surface, at -170°C. Pluto's atmosphere was discovered in 1985 by observing its covering of stars. The presence of an atmosphere was subsequently confirmed by intensive observations of other occultations in 1988. When an object does not have an atmosphere, the occultation of the star occurs quite abruptly, but in the case of Pluto, the star darkens gradually. As determined by the light absorption coefficient, the atmospheric pressure on Pluto during these observations was only 0.15 Pa, which is only 1/700,000 of that on Earth. In 2002, another occultation of a star by Pluto was observed and analyzed by teams led by Bruno Sicardi of the Paris Observatory, James L. Eliot of MIT, and Jay Pasachoff of Williamstown College (Massachusetts). Atmospheric pressure was estimated at the time of measurements to be 0.3 Pa, despite the fact that Pluto was further from the Sun than in 1988 and thus should have been colder and had a thinner atmosphere. One explanation for the discrepancy is that in 1987, Pluto's south pole emerged from its shadow for the first time in 120 years, allowing additional nitrogen to evaporate from the polar caps. It will now take decades for this gas to condense from the atmosphere. In October 2006, Dale Cruikshank of NASA Research Center (a new scientist on the New Horizons mission) and his colleagues announced the discovery of ethane on the surface of Pluto during spectroscopy. Ethane is derived from photolysis or radiolysis (that is, chemical transformation by exposure to sunlight and charged particles) of frozen methane on the surface of Pluto; it is released, apparently, into the atmosphere.

The temperature of Pluto's atmosphere is significantly higher than the temperature of its surface and is equal to -180 °C.

Satellites

Pluto with Charon, Hubble photo

Pluto and three of its four known moons. Pluto and Charon are two bright objects in the center, to the right are two faint spots - Nikta and Hydra

Pluto has four natural moons: Charon, discovered in 1978 by astronomer James Christie, and two small moons, Nix and Hydra, discovered in 2005. The last satellite was discovered by the Hubble telescope; a message about the discovery was published on July 20, 2011 on the telescope’s website. It was temporarily named S/2011 P 1 (P4); its dimensions range from 13 to 34 km.

Pluto's moons are located further away from the planet than other known satellite systems. Pluto's moons can orbit at 53% (or 69% if the motion is retrograde) of the radius of the Hill sphere, the stable zone of Pluto's gravitational influence. For comparison, Neptune's almost distant moon Psamatha orbits at 40% of the radius of Hill's sphere for Neptune. In the case of Pluto, only the inner 3% of the zone is occupied by satellites. In Pluto researchers' terminology, its moon system is described as "very compact and largely empty." Around the beginning of September 2009, astrophysicists developed software that made it possible to analyze archival images of Pluto taken by the Hubble telescope and establish the presence of 14 more space objects located near Pluto’s orbit. The diameters of cosmic bodies vary between 45-100 km.

Studies of the Pluto system by the Hubble telescope have made it possible to determine the maximum size of possible satellites. With 90% confidence, we can say that Pluto has no satellites larger than 12 km in diameter (maximum 37 km with an albedo of 0.041) beyond 5? from the disk of this dwarf planet. This assumes a Charon-like albedo of 0.38. With 50% confidence, we can say that the maximum size for such satellites is 8 km.

Charon

Charon was discovered in 1978. It was named after Charon, the carrier of the souls of the dead across the Styx. Its diameter, according to modern estimates, is 1205 km - slightly more than half the diameter of Pluto, and the mass ratio is 1:8. For comparison, the ratio of the masses of the Moon and the Earth is 1:81.

Observations of the occultation of the star by Charon on April 7, 1980 allowed us to estimate the radius of Charon: 585-625 km. By the mid-1980s. Using ground-based methods, primarily using speckle interferometry, it was possible to fairly accurately estimate the radius of Charon’s orbit; subsequent observations of the Hubble orbital telescope did not change that estimate very much, establishing that it was within 19,628-19,644 km.

Between February 1985 and October 1990, extremely rare events were observed: alternating eclipses of Pluto by Charon and Charon by Pluto. They occur when the ascending or descending node of Charon's orbit is between Pluto and the Sun, and this happens approximately every 124 years. Since Charon's orbital period is just under a week, eclipses repeated every three days, and a large series of these events occurred over five years. These eclipses made it possible to create "brightness maps" and obtain good estimates of Pluto's radius (1150-1200 km).

The barycenter of the Pluto-Charon system is located outside the surface of Pluto, so some astronomers consider Pluto and Charon to be a double planet (a double planetary system - this type of interaction is extremely rare in the Solar System; asteroid 617 Patroclus can be considered a smaller version of such a system). This system is also unusual among other tidally influenced planets: both Charon and Pluto always face the same side toward each other. That is, on one side of Pluto, facing Charon, Charon is visible as a stationary object, but on the other side of the planet, Charon is never visible at all. Features of the spectrum of reflected light lead to the conclusion that Charon is covered with water ice, and not methane-nitrogen ice, like Pluto. In 2007, observations from the Gemini Observatory revealed the presence of ammonia hydrates and water crystals on Charon, which in turn suggests the presence of cryogeysers on Charon.

According to draft Resolution 5 of the XXVI General Assembly of the IAU (2006), Charon (along with Ceres and object 2003 UB313) was supposed to be given the status of a planet. The notes to the draft resolution indicated that in this case Pluto-Charon would be considered a double planet. However, the final version of the resolution contained a different solution: the concept of a dwarf planet was introduced. Pluto, Ceres and object 2003 UB313 were assigned to this new class of objects. Charon was not included among the dwarf planets.

Hydra and Nikta

The surface of the Hydra as imagined by an artist. Pluto with Charon (right) and Nix (bright dot on the left)

Schematic representation of the Pluto system. P1 - Hydra, P2 - Nikta

Pluto's two moons were photographed by astronomers working with the Hubble Space Telescope on May 15, 2005, and were provisionally designated S/2005 P 1 and S/2005 P 2. On June 21, 2006, the IAU officially named the new moons Nix (or Pluto II, the inner of the two moons) and Hydra (Pluto III, the outer moon). These two small satellites orbit in orbits that are 2-3 times further than Charon's orbit: Hydra is located at a distance of about 65,000 km from Pluto, Nix - approximately 50,000 km. They orbit in almost the same plane as Charon and have nearly circular orbits. They are in resonance with Charon 4:1 (Hydra) and 6:1 (Nyx) in their average angular velocity in orbit. Observations of Nikto and Hydra in order to determine their individual characteristics are currently ongoing. Hydra is sometimes brighter than Nikta. This may indicate that it is larger or that certain areas of its surface reflect sunlight better. The sizes of both satellites were estimated based on their albedo. The spectral similarity of the satellites to Charon suggests an albedo of 35%. An assessment of these results suggests that the diameter of Nyx is 46 km, and Hydra is 61 km. Upper limits for their diameters can be estimated, taking into account the 4% albedo of the darkest objects in the Kuiper Belt, to be 137 ± 11 km and 167 ± 10 km, respectively. The mass of each satellite is approximately 0.3% of the mass of Charon and 0.03% of the mass of Pluto. The discovery of two small moons suggests that Pluto may have a ring system. Collisions of small bodies can create a lot of debris that forms rings. Optical data from the Advanced Survey Camera on the Hubble Telescope indicate the absence of rings. If a ring system exists, it is either insignificant, like the rings of Jupiter, or only about 1000 km wide.

Kuiper Belt

Diagram of known objects in the Kuiper belt and the four outer planets of the solar system

The origin of Pluto and its features have long been a mystery. In 1936, English astronomer Raymond Lyttleton hypothesized that it was a runaway moon of Neptune, knocked out of orbit by Neptune's largest moon, Triton. This assumption has been heavily criticized: as stated above, Pluto never comes close to Neptune. Beginning in 1992, astronomers began to discover more and more small icy objects beyond Neptune's orbit that were similar to Pluto not only in orbit, but also in size and composition. This part of the outer solar system was named after Gerard Kuiper, one of the astronomers who, pondering the nature of trans-Neptunian objects, suggested that this region was the source of short-period comets. Astronomers now believe that Pluto is just a large object in the Kuiper belt. Pluto has all the features of other objects in the Kuiper Belt, such as comets - the solar wind blows icy dust particles off Pluto's surface, just like comets. If Pluto were as close to the Sun as Earth, it would develop a comet-like tail. Although Pluto is considered the largest belt object discovered to date, Neptune's moon Triton, which is slightly larger than Pluto, shares many of its geological, atmospheric, compositional and other properties, and is considered an object captured from the belt. Eris, equal in size to Pluto, is not considered a belt object. Most likely, it belongs to the objects that make up the so-called scattered disk. A considerable number of belt objects, like Pluto, have a 3:2 orbital resonance with Neptune. Such objects are called “plutino”.

NASA's Pluto Research

Pluto's remoteness and low mass make it difficult to study using spacecraft. Voyager 1 could have visited Pluto, but preference was given to a flyby near Saturn's moon Titan, as a result of which the flight path turned out to be incompatible with a flyby near Pluto. And Voyager 2 did not have the opportunity to approach Pluto at all. No serious attempts were made to explore Pluto until the last decade of the 20th century. In August 1992, JPL scientist Robert Stehle called Pluto discoverer Clyde Tombaugh asking for permission to visit his planet. "I told him, 'You're welcome,'" Tombaugh later recalled, "but you have a long, cold journey ahead of you." Despite the momentum, NASA canceled the Pluto Kuiper Express mission to Pluto and the Kuiper Belt in 2000, citing increased costs and launch vehicle delays. After intense political debate, a revised mission to Pluto, called New Horizons, received funding from the US government in 2003. The New Horizons mission successfully launched on January 19, 2006. Mission leader Alan Stern confirmed rumors that some of the ashes left over from the cremation of Clyde Tombaugh, who died in 1997, were placed on the ship. At the beginning of 2007, the device performed a gravity assist maneuver near Jupiter, which gave it additional acceleration. The device's closest approach to Pluto will occur on July 14, 2015. Scientific observations of Pluto will begin 5 months earlier and will continue for at least a month from arrival.

First image of Pluto from New Horizons

New Horizons took the first photo of Pluto back in late September 2006, in order to test the LORRI (Long Range Reconnaissance Imager) camera. The images, taken from a distance of approximately 4.2 billion km, confirm the craft's ability to track distant targets, which is important for maneuvering towards Pluto and other objects in the Kuiper Belt.

On board New Horizons there is a wide variety of scientific equipment, spectroscopes and imaging instruments - both for long-distance communication with Earth and for “probing” the surfaces of Pluto and Charon in order to create relief maps. The device will conduct a spectrographic study of the surfaces of Pluto and Charon, which will allow us to characterize the global geology and morphology, map the details of their surfaces and analyze the atmosphere of Pluto, and take detailed photographs of the surface.

The discovery of the Nix and Hydra satellites could mean unexpected problems for the flight. Debris from collisions of objects in the Kuiper belt with satellites at the relatively low speed required to disperse them can create a ring of dust around Pluto. If New Horizons gets caught in such a ring, it will either suffer serious damage and be unable to transmit information to Earth, or it will crash altogether. However, the existence of such a ring is just a theory.

Pluto as a planet

On the plates sent by the Pioneer 10 and Pioneer 11 probes in the early 1970s, Pluto is also mentioned as a planet in the solar system. These anodized aluminum plates, sent with devices into deep space with the hope that they will be discovered by representatives of extraterrestrial civilizations, should give them an idea of ​​​​the nine planets of the solar system. Voyager 1 and Voyager 2, which sent a similar message in the same 1970s, also carried with them information about Pluto as the ninth planet of the solar system. What's interesting: the Disney cartoon character Pluto, who first appeared on screens in 1930, was named after this planet.

In 1943, Glenn Seaborg named the newly created element plutonium after Pluto, following the tradition of naming newly discovered elements after newly discovered planets: uranium after Uranus, neptunium after Neptune, cerium after the supposed minor planet Ceres, and palladium after the minor planet planet Pallas.

2000s debate

Comparative sizes of the largest TNOs and the Earth.
Images of objects - links to articles.

Quaoar was discovered in 2002, with a diameter of approximately 1,280 km - about half the diameter of Pluto. In 2004, Sedna was discovered with upper limits for a diameter of 1800 km, while Pluto's diameter is 2320 km. Just as Ceres lost its status as a planet after the discovery of other asteroids, so, ultimately, the status of Pluto had to be revised in the light of the discovery of other similar objects in the Kuiper belt.

On July 29, 2005, the discovery of a new trans-Neptunian object was announced, which was named Eris. Until recently, it was believed that it is somewhat larger than Pluto. It was the largest object discovered beyond Neptune's orbit since Neptune's moon Triton in 1846. Eris's discoverers and the press initially called it the "tenth planet", although there was no consensus on the matter at the time. Other members of the astronomical community considered the discovery of Eris the strongest argument in favor of reclassifying Pluto as a minor planet. The last distinguishing feature of Pluto was its large satellite Charon and its atmosphere. These features are likely not unique to Pluto: several other trans-Neptunian objects have moons, and spectral analysis of Eris suggests a similar surface composition to Pluto, making it likely that it has a similar atmosphere. Eris also has a satellite, Dysnomia, discovered in September 2005. Museum and planetarium directors, since the discovery of objects in the Kuiper belt, have sometimes created controversial situations by excluding Pluto from planetary models of the solar system. For example, in the Hayden Planetarium, opened after reconstruction in 2000 in New York, on Central Park West, the solar system was represented as consisting of 8 planets. These disagreements were widely reported in the press.