Pluto

• Nitrogen
• Carbon monoxide
• Methane

Pluto is a dwarf planet and the most prominent object in the Kuiper belt. It is named after the Roman god of the underworld. The astronomical symbol of Pluto.

Pluto is smaller than Earth's moon (it has about one- third of the volume of the Moon ) and moves on to an even more elliptic path around the Sun than Mercury. From its discovery on 18 February 1930 to the redefinition of the term "planet" on 24 August 2006 by the International Astronomical Union ( IAU ), he was considered the ninth and outermost planet of the solar system. As a result, Pluto was provided by the IAU with the minor planet number 134340 so that its full official name now ( 134340 ) Pluto. Furthermore, according to the newly defined classes of Pluto Plutoiden and Plutinos were named.

In January 2006, a space probe was sent to Pluto New Horizons for the first time. It is planned to have fly by the probe in July 2015 9600 kilometers of Pluto and 27,000 kilometers on its moon Charon.

• 2.1 Physical structure
• 2.2 atmosphere

• 3.1 Charon
• Nix and Hydra 3.2
• 3.3 Kerberos
• 3.4 Styx

• 4.1 Ground-based research
• 4.2 Exploration with space probes

Orbit and rotation

Train

Pluto 247.68 years needed for a solar orbit. Compared to the planet 's orbit of Pluto clearly eccentric, with a numerical eccentricity of 0.2488. That is, the distance from the sun is up to 24.88 per cent less than or greater than the semi-major axis.

The sonnenfernste point of the orbit of Pluto, the aphelion, is 49.305 AE while the sun next point, the perihelion, with 29.658 AU closer to the Sun than the very little excentric Neptune. The last time Pluto went through this area, in which he is closer to the Sun than the orbit of Neptune, dated 7 February 1979 to 11 February 1999. Perihelion This happened Pluto in 1989. His aphelion it will reach in 2113. Here, the sun radiation is only about 0.563 W / m². On Earth, it is 2430 times as high. For an observer on Pluto, the apparent diameter of the sun is only about 1/50 of the Sun's apparent diameter, which we are accustomed to on earth would be. The sun would look for our observer like an extremely bright star, the times as bright as the full moon illuminates the Earth Pluto 164.

Due to the large distance from the Earth, the apparent brightness between opposition and conjunction differs by only 0.1 mag. However, the eccentric path changed the apparent brightness between 13.65 and 16.3 may like what difference corresponds to 2.65 like.

It is striking that Pluto, twice running around the sun in the time in which Neptune moves three times around the sun. One therefore speaks of a 3:2 orbital resonance.

Pluto was considered due to its small size and its pronounced eccentric, long 17 ° to the ecliptic strongly inclined track time - up to the discovery of many other similar objects - as an escaped moon of Neptune. The great Neptune's moon Triton said to have been captured by Neptune, while the original moon system have significantly disrupted: Pluto was thus catapulted out of the Neptune system and the significant orbital eccentricity of Neptune moon Nereid had arisen. For the capture of Triton speaks its declining sense of circulation.

The discovery of numerous other transneptunischer objects at the edge of the solar system has been proven that Pluto one of the largest and certainly the brightest representative of the Kuiper belt is an accumulation of thousands of asteroids and comet nuclei in a disk-shaped region past the orbit of Neptune. Triton said to have been ahead of his supposed capture a member of this belt.

Many of the Kuiper belt objects like Pluto are in a 3:2 orbital resonance with Neptune, and are referred to as Plutinos. Using methods of celestial mechanics, one can show that their typically very eccentric orbits are stable over millions of years.

Rotation

Pluto rotates in 6,387 days once around its own axis. The equatorial plane is inclined at 122.53 ° relative to the orbital plane, thus rotates Pluto decline. Its axis of rotation is thus even more inclined than that of Uranus, but in contrast to Uranus and Venus the reason is generally seen as the cause of Pluto's fairly large rotation period, because the intrinsic rotation of the dwarf planet is by tidal forces to the orbital motion of its very large moon Charon bound. Thus, Pluto and Charon are the only known body in the solar system with a rotary double bonded.

Construction

Physical structure

About Pluto itself, little is known, as there are no close-ups of him. With a diameter of just 2310 km, it is significantly smaller than the seven largest moons in the solar system. Its mean density of about 2 g / cm ³ speaks for a composition of about 70 % rock and 30 % water ice.

Pluto is probably very similar to the bigger and even colder Triton in construction. He is of the same density, has a very thin atmosphere of nitrogen, is also of a more reddish color, probably has ice caps and toward the equator prevail darker areas before. Its surface is of Saturn's moon Iapetus after taking all other bodies of the solar system, the greatest contrasts. This explains the pronounced brightness variations that were already measured from 1985 to 1990 at eclipses by its large moon Charon.

The outer layers are thought of loose rock having a high percentage of ice. Inside Pluto probably has a rocky core surrounded ice mantle, which accounts for about 70 % of the total mass.

In July 2005, for the first time are measured separately, the thermal emission of Pluto and its large moon, and close. It has been shown that the surface of Pluto with -230 ° C to 10 ° C cooler than it would correspond to a pure radiative equilibrium. The reason for this is the formation of the atmosphere, through the sublimation latent heat of evaporation occurs.

Atmosphere

Pluto's very thin atmosphere composed mostly of nitrogen, the second largest part of some carbon monoxide and about 0.5 % methane. After measurements on the James Clerk Maxwell Telescope, the atmosphere in the year 2011 3000 km of high and cold in their contained carbon monoxide -220 ° C. Previously it was thought the atmosphere would be 100 km high. Your pressure at Pluto's surface is, according to the U.S. space agency NASA about 0.3 Pascal and according to the European Southern Observatory ( ESO) 1.5 Pascal. The assumption that the atmosphere after the passage of the sun nearer track region would freeze out soon, could not yet be confirmed. Even a slight expansion of the gas envelope is derived from the comparison of spectroscopic measurements from 1988 and 2002.

As the ESO announced on 2 March 2009, prevails on Pluto mostly caused by methane in the atmosphere, temperature inversion, whereby the temperature increases by 3 degrees to 15 degrees per kilometer height. In the lower atmosphere, the temperature is -180 ° C and in the upper atmosphere -170 ° C, whereas it is only about -220 ° C at the bottom. It is believed that evaporative cooling contributes to this low value of the bottom temperature of methane, which passes from the solid to the gaseous state.

Monde

Pluto has five known moons. Their orbits are almost circular and coplanar to each other. They are located in Pluto's equatorial plane, but not in its orbital plane.

Charon

Pluto's companion Charon largest has a diameter of 1207 kilometers and is compared to Pluto very large. The Pluto-Charon system was formerly known because of this unusual size ratio of approximately 2:1 as a double planet. Due to the mass ratio of good 8:1 and a sufficient distance is the common center of gravity, the barycenter of the system, outside of the main body. Charon and Pluto Thus, orbiting each other.

The semi-major axis of the orbit of Charon, which is the mean orbital radius of its center of mass from the common center of gravity, measures 19,405 km. According to the mass fraction of Pluto whose analog distance to the center of mass is inversely proportional good one-eighth of it, or about 2360 km. Thus, the distance of the surface of Pluto to the barycenter with around 1,200 kilometers, about the size of his body radius. The satellite orbit of Charon is almost circular and is probably exactly in Pluto's equatorial plane. In comparison, the Earth and the Moon have a mass ratio of 81:1, and the common Earth-Moon gravity is located 4700 km away from the Erdzentrums or about 1650 kilometers below the earth's surface.

Also Charon shows - typical for a moon - synchronous rotation with a period equal to its orbital period. The mutually synchronous rotation of the satellite and its main body is sometimes called dumbbell rotation and has been proven in the solar system only between Pluto and Charon. The bodies have their own rotation due to tidal forces against each other so far slowed down, that both also rotate during one revolution around each other exactly once on its axis. Therefore contact each other always to the same page. Among pairs of approximately equal size asteroid is such a synchronous rotation probably fairly common.

The collision hypothesis appears to explain the origin of such a relatively large moon on current knowledge, analogous to the formation of the Moon the most plausible.

Nix and Hydra

The diameters of the moons Nix and Hydra could previously only be estimated due to their measured brightness. Depending on the assumed albedo values ​​between about 40 and 160 km arise. They circulate Pluto on nearly circular orbits and in a common orbital plane of Charon at a distance of about 65,000 or 50,000 kilometers. Their orbital periods are to that of the big moon nearly resonant; While Charon orbits Pluto twelve times, Pluto is from Hydra orbits in the same period almost exactly twice and Nix about three times. In contrast to the reddish Pluto the small satellites seem to have the same neutral gray color as Charon.

The two satellites were discovered by observations with the Hubble Space Telescope in 2005; This divided the NASA on October 31, 2005. By re- Hubble observations in February 2006, the discovery was confirmed. They first wore the provisional names S/2005 P1 and S/2005 P2 until they (IAU ) received in June 2006 by the International Astronomical Union, the name Hydra and Nix.

After the discovery of the small satellites of the formation of Charon is now discussed along with these two amplified by a collision with another of Pluto pluto large Kuiper Belt object. For a common origin of all Pluto moons speak the coplanar orbits with the nearly resonant orbital periods and the uniformly colored surfaces. Wherein a capture a different color would be expected more.

Pluto and its moons are exposed in the Kuiper Belt a continuous bombardment of mini meteorites that knock out dust and ice particles from the surfaces. While the gravity of Pluto and Charon ensures that all pieces of debris fall back to the heavenly bodies, the attraction of the newly discovered moons it is not enough. Therefore, the scientists suspect that the small moons in astronomical time periods by more strikes lose so much material that this will gradually form a dust ring around Pluto.

The discovery of additional moons Pluto was unexpected because until then no celestial bodies with more than one satellite was observed beyond Neptune, but a second moon was already a month later, also at ( 136 108 ) Haumea found. Since Pluto and Charon with some justification, as a double ( dwarf ) can be interpreted planet, can you see Nix and Hydra as first evidence for circumbinary satellites with stable orbits in a binary system.

Kerberos

Kerberos has an estimated size from 14 to 40 km. He is the second smallest known moon of Pluto. The moon had been discovered on a June 28, 2011 with the " Hubble 's Wide Field Camera 3" photo taken and was confirmed on further recordings of 3 and 18 July 2011. In earlier images of the heavenly bodies was not visible because they were taken with a shorter exposure time. On July 20, 2011, NASA announced its discovery still known under the provisional name " S/2011 ( 134340 ) 1" or " P4". The Trabant (the fourth Pluto Moon) was discovered using the Hubble Space Telescope in the search for any existing planetary rings. The International Astronomical Union gave the moon in July 2013 the name " Kerberos " after the hellhound Cerberus from Greek mythology.

Styx

Styx has an irregular shape and its size is estimated at 10 to 25 km. Its orbit passes between Charon and Nix on 42000 km ( ± 2,000 km). A year after the discovery of the fourth moon Pluto was a research team on July 11, 2012, discovered using the Hubble Space Telescope fifth lunar known. This was given the provisional designation " S/2012 ( 134340 ) 1" or " P5 ". The International Astronomical Union gave the moon in July 2013 the name " Styx " after the river Styx, the world of the living from the dead separates in Greek mythology.

Research

Ground-based research

The history of discovery of Pluto is somewhat similar to that of Neptune good 83 years before it finds. Both celestial bodies were computationally predicted and then looked at the derived from it track positions due to perturbations of neighboring planets. The hypothetical ninth planet was blamed for small path deviations of the planets Neptune and Uranus.

Pluto was discovered on February 18, 1930 by the Lowell Observatory in Flagstaff, Arizona by comparisons of some images of the sky at the blink comparator after about 25 years of search, but not exactly at the predicted position. The young discoverer Clyde Tombaugh had only recently been hired for photographic search of the legendary Trans Neptune. The Mars researchers Percival Lowell had been looking for since 1905, even after such a celestial body and the Lowell Observatory financed on a mountain near Flagstaff. As it turned out later, was already to be seen on two of the photographic plates, the Lowell from 1915, made ​​Pluto. Since Lowell but was looking for a much brighter object out to him this discovery had escaped.

The discovery was announced to the extremely interested public on 13 March 1930 the 149th anniversary of the discovery of Uranus by William Herschel in 1781, and the 75th birthday of Percival Lowell, who died in 1916.

Now they were looking for a suitable name. The privilege of naming was at the Lowell Observatory. There pretty soon met a large amount of proposals. The name of the ruler of the underworld for these celestial bodies so far from the sun was suggested by Venetia Burney, an eleven year old girl from Oxford, which was very interested in classical mythology. From the report of the discovery and name search in the " Times " they learned from their grandfather, Falconer Madan, in the morning after the discovery announcement. He was a retired librarian of the Bodleian Library, and found its proposal so well that he Herbert Hall Turner, a fellow astronomer and professor of astronomy at Oxford University told them. About this he came by telegram on March 15 at the Lowell Observatory, where he was adopted in May of the same year. According to the rules of the IAU naming it had to be done according to mythological aspects.

Venetia's great-uncle Henry Madan, science master at Eton College, had already suggested the names Phobos and Deimos for the moons of Mars. The suggested name for this ninth planet Pluto came in 1919 remind you of the French astronomer P. Reynaud, but it could for the first time in 1930 no one. In choosing this name may have also played a role that the astronomical symbol of the initials of Lowell was put together. Previously it was suggested by his widow already Percival Lowell and even Constance ( her own name ). After the planet Pluto and Mickey Mouse 's house Pluto was called, in August 1930, his first appearance.

1941 was named in continuation of the begun with the chemical elements uranium and neptunium series, the 94th and then last known element after the last planet at this time as plutonium.

From the observed apparent brightness of Pluto (15 mag) and a plausible assumption for its albedo, its reflectance, it was concluded that the new celestial bodies have about Earth's size. On the other hand, it was also first in large telescopes impossible to measure its diameter directly micrometrically. Therefore, soon appeared to doubt whether he gravitational effect could be responsible for the perturbations.

So the investigation after disturbing " Planet X " continued soon - as the search for a "Trans- Pluto " - among other things by Clyde Tombaugh himself had with the development of powerful telescopes diameter and mass of Pluto are continuously revised downwards, first in 1950 by measurements of the observatory on Mount Palomar half Earth's size. Soon we joked that Pluto will probably soon disappear completely in extrapolation of the measured values ​​. Unconventional theories have been postulated: Pluto is great in reality, but you can only see a small bright spot on the surface. The astronomer Fred Whipple calculated the first time an accurate orbit. These photographic plates could be used, on which Pluto was traced back to the year 1908. The discovery of the moon Charon in 1978 would then allow an accurate mass measurements of the gravitational dynamics of the system. From 1985 to 1990, there was mutual occultations between the two, with which the diameter of Pluto could be finally determined in 2390 km.

Recent measurements with adaptive optics, with the Hubble Space Telescope and at coverages of stars have revealed values ​​of about 2280-2320 kilometers. More accurate data can only be expected from the space probe New Horizons, which will fly past Pluto in 2015.

Because of its brightness Pluto was discovered more than 60 years earlier than others, very dark, Trans Neptune. About the time of its established path deviations of Neptune and Uranus is now believed that they were faked by a small, unavoidable measurement error. In addition, the mass of Neptune was misjudged before the flyby of Voyager 2. After the accurate mass of Neptune is known to the orbits of the outer planets can be well explained. There is no need to propose a further additional planetary X.

Combinations of images from the Hubble Space Telescope reveal that Pluto's northern hemisphere in the years 2002 and 2003 has become brighter and the dwarf planet looks reddish in total.

Exploration with space probes

NASA since the early 1990s, was already planning under the name Pluto Fast Flyby, later, Pluto Kuiper Express, a mission to Pluto. This should be done under the direction of the Southwest Research Institute. It was underlined that a mission should start as soon as possible to reach Pluto before its thin atmosphere freezes out. This is due to that its orbit is highly elliptical, he removed since the passage of his sun next path point in 1989, again by the sun. Only in the year 2247 Pluto will again be in greatest perihelion. But the first concepts that mission failed due to technical difficulties and a lack of funding.

2001, the New Horizons mission was started. Your launch took place on 19 January 2006. Planned flight duration of the probe of New Horizons is about 9.5 years. The flyby of Pluto and Charon to be held on 14 July 2015. The observations of the Pluto -Charon system start about 150 days before the closest approach. About 120 days before the flyby, the first pictures are expected. 90 days prior to the arrival of the recordings of the probe will exceed the resolution of the Hubble Space Telescope. It should

• Global maps of the dwarf planet and its moon,
• Per pixel resolution won high resolution photos of up to 25 m,
• Measured the temperature distribution and
• The atmosphere of Pluto are studied.

The plan is to watch the world go in 9600 kilometers distance to Pluto and Charon at 27,000 kilometers distance the probe. However, these are only objective parameters that can be changed during the flight easily. Two weeks after the closest approach observations are completed. Then, the probe begins during the passage of the collected data to transmit to the ground. Since the transmission rate over this distance is very small, a few months will pass before all data has arrived on Earth.

Debate on planet status and withdrawing

The debate over whether Pluto ever deserved the name "planet" began when it was realized also its smaller size except its highly elliptical and highly inclined orbit. After 1992 QB1 with the third trans-Neptunian object was found in September 1992 after Pluto and Charon, astronomers discovered a year later, in four days also four other Plutinos. Thus, the debate raised by Pluto's status. The proposal by Brian Marsden of the MPC in 1998 to give Pluto a double status, and it additionally classified as asteroid with the outstanding number 10000 to thereby prevent an ever- changing planet discoveries by number was not approved.

Over time, hundreds of other Kuiper Belt objects have been discovered, including some of pluto similar size. Such outstanding discoveries, especially as ( 136199 ) Eris were often referred to by the media as the " tenth planet ". With the first scientific definition of a planet and none of these objects has been confirmed as such along with Pluto. The new class of dwarf planets was set out by the IAU in 2006 for such bodies defined. However, after this decision the controversy among astronomers in terms of Pluto as the ninth planet for decades usual continues.

The definition adopted by the words, by which a body only is a planet if its mass exceeds the total mass of all other bodies in its rail sector, considering that Pluto has not cleared its railway sector to the extent of other bodies. As the largest object of the Plutinos he is more consistent with the role of Hilda asteroids, the largest member of the Hilda group. Hilda and at least 56 more objects a bit outside the main belt asteroids between Mars and Jupiter move analogous in a 2:3 ratio to in this case, longer circulation time of the neighboring giant planets.

On the 26th General Assembly of the International Astronomical Union in August 2006 in Prague before a slightly different definition without that amendment was proposed. A planet would therefore already a celestial body whose mass is sufficient for its self-gravity to a hydrostatic equilibrium shape ( " nearly round ", ie approximately spheroidal shape ) to accept, and which is located on an orbit around a star, even but no rating moon or a planet is. Thus, not only would have been Pluto a planet, but also Ceres, Charon and Eris. Charon was added through an addition to, after which it is to be a double planet, when the common center of gravity is outside of the main body. At the same time the definition of a new class of planets called " plutons " was suggested, were among the planets need to orbit the star for more than 200 years and had listened to the then Pluto. However, this proposal for the planet definition could not prevail on the General Assembly, so that on 24 August 2006 by a vote it was decided to deprive Pluto the planet status and allocated to the newly defined class of dwarf planets. The class of plutons was indeed defined ( as a class for which Pluto is the prototype ), but was initially nameless, since the name plutons as well as other name suggestions were discarded. In June 2008, this unnamed subclass of the dwarf planet by the IAU has been called " Plutoiden ", including not only the namesake of Pluto Eris yet also counts.

Since September 2006, Pluto has the minor planet number ( 134340 ). Such a unique number is assigned when an asteroid's orbit or dwarf planet is known accurately enough by a sufficient number of observations to locate him in a later visibility based on the ephemeris obtained by its orbital elements again. Pluto's orbit is indeed quite well known, but he had not yet received a minor planet number, as it was previously assigned to the planets of the solar system. A list of dwarf planets is in preparation, but the dwarf planets are expected to be conducted in two lists, the previous asteroids and dwarf planets of the new list.

The Senate of Illinois, the U.S. State of origin of the Pluto - discoverer Clyde Tombaugh, has " decided " in 2009 that Pluto was still a planet.

Visibility

Since Pluto was September 5, 1989 at perihelion, he removed since then on its elliptical orbit of the sun. Therefore take place successive oppositions at ever greater distance and with more and slightly lower brightness of the dwarf planet.