Pluto

Introductory text to the dwarf planet Pluto

Pluto is a dwarf planet in the Kuiper Belt, an asteroid-rich region, behind Neptune's orbit. By 2006, Pluto was considered the ninth and outmost planet in the solar system before being denied status by the International Astronomical Union (IAU). Pluto is named after the Roman god of the underworld. Compared to the other planets, apart from the also very late discovered planets Uranus and Neptune, Pluto did not owe its name to the Romans, but to the Lowell Observatory, which first discovered the celestial body in 1930.

The sun's light takes six hours to hit Pluto. This enormous distance is one of the reasons why the mean average temperature is -230 ° C. The planetary surface is in the ratio of 7: 3 of rock and ice. Carbon monoxide, nitrogen and methane make up the atmosphere.

At 2300km in diameter, Pluto is less tall than the Earth's Moon. The picture on the left shows the size comparison between Earth and Pluto. One turn around the sun takes 248 years. At 4.72 km / s, Pluto moves slower than any of the eight planets in the solar system. However, this is not a special feature, as with increasing distance to the sun and the web speed decreases. In addition to Ceres, Eris, Haumea and Makemake, Pluto is one of the five recognized dwarf planets.

Pluto's moons

Five moons circle Pluto: Charon, Nix, Hydra, Kerberos and Styx. All names are figures borrowed from Greek mythology.

By far the largest moon Charon was discovered in 1978, the other four only in the last 10 years, since their diameters are relatively small. Between Pluto and Charon there is a so far uniquely observed special feature. Both objects orbit each other, in a double-bounded rotation. They thus show themselves permanently to the same surface side. There is only one bound rotation between Earth and Moon. We always see the same side of the moon. But if you look from the moon to the earth, you can examine - with appropriate waiting time - both planetary halves.

Planet or no planet?

Is Pluto a planet or is not it a planet? The International Astronomical Union (IAU) has published a definition to determine whether or not a celestial body is a planet. But beware, this only applies to corresponding objects in our known solar system. The definition does not refer to constellations in other planetary systems. There are basically three requirements:

A planet has to ...
 ... orbiting the sun
 ... have so much mass that the self-gravity rounds the planet
 ... cleaned his orbit from other bodies

The IAU received harsh criticism for this definition, because, strictly speaking, the Earth would also lose its status as a planet. Your orbit is not cleansed from other bodies. Thousands of more or less large objects are located in the orbital zone of the earth. For this purpose, the so-called planetary discriminant was introduced. It describes the absolute ratio of the mass of the planet and the objects in its orbital zone. If, in the orbital zone of an object, the summed mass of the smaller objects is greater than the mass of the object itself, it is a dwarf planet. Values ​​below 1 indicate a dwarf planet. Values ​​above 1 indicate a planet.

The discussion about Pluto's planetary status is far from over. The above definition is the point of view of the International Astronomical Union (IAU), whose view is not shared by all astronomers. The 'rehabilitation' of Pluto is regularly argued in professional circles. If one decides to eventually take Pluto back into the select circle of planets, that would also affect the other dwarf planets. The inclusion of Ceres and Eris would then require a more intense discussion.

The space probe 'New Horizons'

In 2006, the NASA spacecraft New Horizons started with the ambitious target Pluto, which was still considered as a planet at this time. The takeoff weight was just under half a ton, of which only 1/6 fuel. Through a successful swing-by-maneuver on the gravitational field of Jupiter, the speed of the spacecraft could be increased. Large amounts of fuel could thus be saved and are available for future missions. To date, it is the only Pluto mission. After more than nine years of flying time, the probe reached its provisional destination on July 14, 2015, as it flew past Pluto 12,000 km away.

The objectives of the mission initially defined the exact mapping of Pluto and its moon Charon, as well as the study of the atmosphere and geological structure of the dwarf planet. After New Horizons was able to accomplish these goals, the probe continues to fly through the Kuiper belt at the edge of the solar system. Should the probe remain functional, recordings can be sent back to Earth by the year 2026, possibly even longer.

Summary

Pluto is one of five dwarf planets in the solar system.

Until 2006, Pluto was considered a planet before the International Astronomical Union denied him this status.

With Styx, Kerberos, Nix, Hydra and Charon, five moons revolve around Pluto. Because of their small size, the moons were discovered only in recent years.

The constellation of Pluto and Charon is unique in the solar system. Both objects are orbiting in a double-bounded rotation.

The New Horizons spacecraft flew near Pluto on July 14, 2015, as close as any space probe has ever been.