Additional Data:

Diameter:	2.376 km
Average distance to the sun:	5.906.400.000 km
The mass of 1 kg weighs on Pluto:	133 g
One year on Pluto lasts:	247 years 343 days
One day on Pluto lasts:	6 days 9 hours
Temperature on the surface:	-240 °C
Orbital velocity:	4,67 km/s
Orbital inclination:	17,1418°
Orbital excentricity:	0,2488
Weight:	0,045 earth masses
Density:	1,854 kg/m³
Gravitational accelleration:	0,62 m/s²
Escape velocity:	1,21 km/s
Tilt of the rotational axis:	122,53 °
Number of moons:	5
Number of rings:	0

 

Pluto was discovered in 1930 by American astronomer Clyde Tombaugh. Pluto was a chance discovery, but it was not immediately recognized as such. After deviations in the orbit of Uranus led to the discovery of Neptune in 1846, deviations were also found afterwards that were not so easy to explain. The suspicion quickly arose that these deviations from the orbit could also be explained by the gravitational pull of another celestial body, so the search began again. Clyde Tombaugh worked at the Lowell Observatory in the United States in 1930 and participated in the search for this new planet. In doing so, he took photographs on glass plates that showed the region in which, according to the calculations, the new planet should be located. On February 18, 1930, he discovered on two glass plates, which had been exposed a week apart, that one of the points of light had moved on. Pluto was discovered! However, it soon turned out that Pluto was much too small to exert the desired effect on Uranus. It was later concluded that an uneven distribution of mass in Neptune was responsible for Uranus' orbital deviations, making Pluto an accidental discovery.

Following the naming scheme for planets, Pluto was named after the Roman god of the underworld. Based on its density, Pluto is thought to consist of 70% rock and 30% water ice. In addition, there is a layer of frozen nitrogen on the surface with traces of methane and carbon dioxide. Temperatures of -230 °C prevail on its surface. Pluto also has a thin atmosphere, which is created by small amounts of nitrogen becoming gaseous as it gets a little closer to the Sun. Most planets have an approximately circular orbit, but Pluto has a relatively eccentric one that is also inclined 17° to the ecliptic. In addition, its orbit temporarily overlaps with that of Neptune. Its year is so long that it has not yet been a full year of Pluto since its discovery.

Pluto is orbited by five moons. Charon is particularly striking. It was named after the mythological ferryman who takes the dead to the underworld. It is half the size of Pluto. Both celestial bodies orbit a common center of gravity, which lies between them but closer to Pluto.

Pluto was the only one not to be visited during the Voyager missions. Since Voyager 2 flew past Neptune in 1989, a separate mission was planned to explore Pluto. After a long preparation, the New Horizons probe was launched in 2006. However, it took until July 2015 for it to reach Pluto and its moons. She flew past him at a speed of 14.5 km/s, collecting as much data as possible. Due to the low data transfer rate at this distance from Earth, it took 15 months for all the results to arrive. In addition to many research instruments, the probe also transported 30 g of the ashes of Clyde Tombaugh, who had discovered Pluto 85 years earlier. Since the probe cannot decelerate, it will now fly further and further until it too will leave the Sun's sphere of influence around 2043.

At the beginning of the 21st century, no one had seriously addressed the question of what exactly a planet is. Until then, a planet was a large body orbiting the sun. In addition to the nine planets, there were also asteroids between Mars and Jupiter and far out in the Kuiper Belt and in the Oort Cloud. Pluto struggled to fit into this definition because it was very small and in a very unusual orbit. The discovery of similar celestial bodies, such as Eris, Haumea and Makemake, led the International Astronomical Union (IAU) to make a decision in 2006 and introduce new definitions.

A planet is so large and heavy that it forms itself into a sphere, and it has picked up or removed all competing bodies in its orbit around the sun.

A dwarf planet is so large and heavy that it forms itself into a sphere, but in its orbit, it has not been able to absorb or remove all competing bodies.

Small bodies in the solar system (asteroids and comets) are now defined as not being alone in their orbit and not being heavy enough to form into a sphere.

	Spherical Shape	Free Orbit	Nuclear fusion
Star	yes	yes	yes
Planet	yes	yes	no
Dwarf Planet	yes	no	no
Small Body	no	no	no