“Every Sunday my father explains to me our nine …” – stop, it’s wrong. The donkey bridge to memorize the planets of the solar system no longer ends with “nine planets” (Neptune, Pluto), but on “our night sky”. Neptune has ended since the International Astronomical Union (IAU) downgraded Pluto to a dwarf planet in 2006. Pluto’s bad luck is a new definition of the IAU: According to it, a planet must be large enough to dominate its orbit. But Pluto is influenced by Neptune and shares the orbit with other chunks, so he’s out.
There was already a lot of bad blood among astronomers about the vote. Now US planetologists are laying new argumentswhy Pluto belongs back to the pantheon of planets – and so does several other celestial bodies in the solar system, including the Earth’s moon.
To prove this, researchers working with Philip Metzger from the University of Central Florida pored over documents from the past four centuries. Galileo Galilei counted moons as “planets” as early as 1632, since he had recognized geological structures on the lunar surface that were similar to those of the earth. This orientation towards structure and characteristics such as water or an atmosphere largely prevailed in science. Until well into the 20th century, newly discovered satellites of other celestial bodies and even asteroids were called planets.
Astrology and theology have distorted the discussion about planets, so the allegation
The process of cognition was different in the broader population of Europe and America. Since the solar system was hardly a topic in schools until the 19th century, almanacs from the pen of astrologers were used. One of their assumptions is that there are few planets that move in orderly orbits. Because only then can their supposed effects on people be explained and distinguished. The multitude of newly discovered celestial bodies did not fit in there, so the astrologers quickly sorted them out. In addition to the scientific, a popular planetary science spread. The second source of inaccuracy was the theologically inspired representations. Few celestial bodies on an ideal course seem to confirm God’s work better than constantly new chunks that behave chaotically.
“Planets were no longer defined by their complexity, with an active geology and the potential for life and civilization,” complains Metzger. “Instead, they should be as simple as possible and follow idealized paths around the sun.” This popular notion finally crept into the official definition of astronomers.
However, it is unlikely that this will be corrected again. “That is now widely accepted,” says the planetologist Tilman Spohn from the International Space Science Institute in Bern. In technical terms, however, Spohn agrees with his US colleagues: “Rock moons do not differ in principle from planets in terms of their development and physics.” However, if one were to regroup moons in addition to Pluto and other dwarf planets (Saturn alone counts 82), one would suddenly be dealing with hundreds of planets in the solar system. Hardly suitable for a motto – but an impressive sign of the complexity of the cosmic neighborhood. And the work shows one more thing: Even a modern science like astronomy is probably not entirely free of influences from theology, for example, from which it believed it had long since been freed.