Zahlen, bitte! 136199 Eris: The reason why Pluto is no longer a planet
When Eris was discovered in 2005, astronomers were under pressure: did they discover the 10th planet or is Pluto too small for its status?
When Eris was discovered in 2005, astronomers were in a quandary: the celestial body appeared to be larger than Pluto. Either it was announced that a tenth planet had now been discovered, or the already controversial planetary status of Pluto had to be reconsidered. NASA did the first, the International Astronomical Union (IAU) – did the second after months of expert debate –.
On October 21, 2003, the Samuel Oschin Telescope at the Palomar Observatory near San Diego in California took three images about 90 minutes apart. Filtered out by the automatic search system, a moving object was noticed in these images during personal inspections at the beginning of 2005.
Videos by heise
Minor planet with an unusual orbit
The minor planet, which was later named Eris, was discovered on January 8, 2005 and the discoverers Mike Brown, Chad Trujillo and David Rabinowitz actually wanted to continue observing the orbit before announcing the discovery. However, since they realized that others could download the data from the institute's website, they went public on July 29, 2005, so that other astronomers could not beat them to it.
Eris has a diameter of 2326 kilometers and moves in a very eccentric orbit against the ecliptic (the orbit of the sun) with an orbital inclination of about 44 degrees. It is about 97 astronomical units away at aphelion (the farthest point from the sun) and 38.5 astronomical units away at perihelion (the closest point to the sun). For comparison: Pluto's aphelion is at 49 AU, its perihelion at 29.7 AU. (An astronomical unit is the distance from the Earth to the Sun: 1 AU = 149,597,870,700 meters, or about 150 million kilometers). With an albedo of 0.96, it is also considered one of the brightest objects in the solar system.
Researchers assume that the composition of Eris consists of 65 to 75 percent rock and 25 to 35 percent ice. The Eris day is almost like on Earth: the dwarf planet revolves around itself once in just under 26 hours. The Eris year is again biblical: due to the great distance, it does not take 12 months, but 557 years to complete one orbit around the sun.
(Image:Â CC BY-SA 3.0, Litefantastic)
Provisionally named after a TV series warrior
The provisional name outed the team of astronomers led by Dr. Michael Brown from the California Institute of Technology as nerds. They tentatively christened the planetoid "Xena", named after the main character from the series "Xena - The Warrior Princess", played by the New Zealand actress Lucy Lawless. The name was chosen, says Brown, "because we always wanted to name something after Xena."
However, the International Astronomical Union (IAU), based in Paris, is responsible for the official naming. However, the 9,000 astronomers from all over the world at the time had other concerns about the object than its nerdy name: "Xena" was too big. According to initial calculations, the celestial body surpassed Pluto, which was the ninth planet at the time.
The planetary status of Pluto, which was discovered in 1930, had been disputed for decades, and the discovery of the new celestial body intensified the debate, which had already gathered momentum with the discovery of the objects Quaoar and Sednar in previous years.
Xena, whose technical designation in 2003 was UB313, broke the mold: either the astronauts had discovered the 10th planet in the solar system, or the planetary status of Pluto had to be reconsidered. With a diameter of 2377 kilometers, Pluto is five times smaller than the Earth, and even the Earth's moon is a third larger. In addition, there were two candidates, Ceres and Pluto's moon Charon, which also had planetary properties like Pluto itself.
(Image:Â CC BY-SA 3.0, Orionist)
Reclassification of the planet definition
As the new celestial body was possibly larger than Pluto, and the ever more precise observation of the sky makes further discoveries of this kind more likely, the IAU had no choice but to clarify the planet definition and make Pluto a dwarf planet. On August 24, 2006, at the IAU General Assembly in Prague, a new definition of planets was adopted under Resolution 5A and a distinction was made between planets and dwarf planets.
According to the new definition, a planet is
- a celestial body that (a) is in orbit around the sun
- which has sufficient mass to assume hydrostatic equilibrium (an almost round shape), and
- which "cleared the neighborhood" around its orbit, i.e. incorporated surrounding matter such as asteroids.
The new point 3 did not apply to Pluto, so it slipped into the new class of dwarf planets. Pluto's fate was sealed in Resolution 6A: Since then, Pluto has officially been named (134340) Pluto – From planet number 9 to asteroid number 134340: this angered many astronomy nerds.
Astronomical dispute over redefinition
The planet redefinition was also controversial. Alan Stern, head of the Horizons Pluto mission, accused the IAU of having adopted an unscientific definition, as even large planets did not "clear their orbits". He claimed: "If Neptune had cleared its zone, Pluto would not be there".
This in turn annoyed other scientists. Astronomer Robin Cathpole from the Institute of Astronomy in Cambridge, UK, summed up the problem: "By the end of the century we would have had 100 planets, and I think people would have said, 'My goodness, what a mess they decided to make in 2006'."
Empfohlener redaktioneller Inhalt
Mit Ihrer Zustimmung wird hier ein externes YouTube-Video (Google Ireland Limited) geladen.
Ich bin damit einverstanden, dass mir externe Inhalte angezeigt werden. Damit können personenbezogene Daten an Drittplattformen (Google Ireland Limited) übermittelt werden. Mehr dazu in unserer Datenschutzerklärung.
Curious: At the end of the ten-day meeting, only 424 delegates out of a total of 2500 were still present for the vote –. One or two may have stayed away because they did not want to be involved in the planetary demission of Pluto.
Once this had been clarified, the IAU was able to take care of the name of the new celestial body, as nerd fiction is not a permitted category for a planet name. And the astronomers proved to have a sense of humor with the naming; after all, in Greek mythology, "Eris" is the goddess of discord and strife. In view of the heated discussions, the name was very appropriate. Even the discoverers were pleased: Dr. Michael Brown declared that the name was "too perfect" to "resist".
Eris also has a moon, estimated to be between 100 and 700 kilometers in diameter, orbiting it at an average distance of about 37500 kilometers. It was christened Dymonia, the daughter of Eris in mythology.
As a consolation, the IAU decided in 2008 that the trans-Neptunian dwarf planets (i.e. minor planets beyond Neptune) should be called plutoids. And in general, the demotion has not harmed the fascination with Pluto: the New Horizons Pluto mission was a complete success. Nevertheless, or perhaps precisely because of this, the voices calling for Pluto to be relegated to planetary status have not stopped.
And Eris? According to the latest research, the controversial dwarf planet appears to be an interesting celestial body with volcanic activity, similar to Pluto. Even water and thus an important component for life would be possible in Eris.
(mawi)
