That's Why Pluto Is Not a Planet Anymore

Summary

This script delves into the historical and scientific debate over Pluto's planetary status. It recounts the mnemonic 'My very eager mother just served us nine pizzas' used to remember the solar system's planets, including Pluto, before its demotion. The script explores the discovery of Pluto in 1930, its size revisions, and the International Astronomical Union's 2006 definition that led to Pluto's exclusion due to not 'clearing its neighborhood.' It also touches on the controversy and alternative definitions that could reinstate Pluto as a planet, highlighting the complexities in defining celestial bodies.

Takeaways

• 📚 The mnemonic 'My very eager mother just served us nine pizzas' was used to help children remember the order of the planets before Pluto's demotion.
• 🪐 Pluto was discovered in 1930 and was initially thought to be as large as Uranus or Neptune, but its size estimates were repeatedly revised down.
• 🌌 The discovery of Ceres in 1801 led to a reevaluation of what constitutes a planet, as it was similar in size to other objects in the asteroid belt.
• 🌕 The International Astronomical Union (IAU) defined a planet in 2006 as an object that orbits the Sun, is nearly spherical, and has 'cleared the neighborhood' around its orbit.
• 🚫 Pluto failed to meet the third criterion of having 'cleared the neighborhood', as it shares its orbit with other objects in the Kuiper Belt.
• 🌟 The IAU's definition of a planet excludes objects like rogue planets not orbiting a star and places emphasis on the environment around a celestial body rather than its intrinsic properties.
• 🌙 Some scientists propose a different definition that would include Pluto as a planet, but this would also elevate other moons and celestial bodies to planet status.
• 📉 Pluto's demotion to a 'dwarf planet' sparked debate and some controversy, with a few scientists disagreeing with the IAU's ruling.
• 🔍 The script suggests that the current definition of a planet may not be perfect and hints at the possibility of revisiting the criteria in the future.
• 🐶 An amusing aside in the script mentions the myth that Pluto was named after a Disney dog, which is not true.

Q & A

What mnemonic device was traditionally used to remember the order of the planets in our solar system?

The mnemonic device used was 'My very eager mother just served us nine pizzas,' which stood for Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.

Why might students today question the number of planets mentioned in the traditional mnemonic?

Students might question the number of planets because Pluto was reclassified and is no longer considered a planet by the International Astronomical Union (IAU).

What significant change occurred in 2006 regarding Pluto's status in the solar system?

In 2006, the IAU redefined the criteria for a celestial body to be considered a planet, and as a result, Pluto was reclassified as a 'dwarf planet' rather than a full-fledged planet.

What was the historical definition of a planet from the age of Galileo to the nineteenth century?

From the age of Galileo to the nineteenth century, a planet was defined as any object orbiting the Sun.

What discovery in 1801 led to a reevaluation of the definition of a planet?

The discovery of Ceres in 1801, which was initially considered a planet but later recognized as part of the asteroid belt due to its small size and the discovery of similar objects, led to a reevaluation of the definition of a planet.

How did the discovery of Pluto's moon, Charon, affect its status as a planet?

The discovery of Charon, which is relatively large compared to Pluto, caused Pluto's orbit to wobble, which is atypical for a planet, leading some astronomers to question its planetary status.

What were the three qualifications set by the IAU in 2006 for an object to be considered a planet?

The three qualifications set by the IAU in 2006 are: 1) the object must orbit the Sun, 2) the object must be a sphere or nearly so, and 3) the object must have 'cleared the neighborhood' around its orbit, meaning there are no other objects of comparable size nearby.

Why did the discovery of Eris in 2005 pose a challenge to Pluto's status as a planet?

Eris, although slightly smaller than Pluto, was initially believed to be more massive, which added to the debate about Pluto's status as a planet and contributed to the IAU's decision to redefine what constitutes a planet.

What alternative definition of a planet has been proposed by some scientists, and what would be the consequence of adopting it?

Some scientists propose that only the second qualification (being a sphere or nearly so) should be required for an object to be considered a planet. The consequence of adopting this definition would be an increase in the number of recognized planets, including our Moon and several moons of other planets, as well as many asteroids.

What are some of the criticisms of the current definition of a planet as set by the IAU?

Some criticisms of the current definition include the exclusion of rogue planets not orbiting any star, an emphasis on the surroundings of a planet rather than the planet itself, and the potential for confusion with celestial bodies like Proxima Centauri, which fulfills all the requirements but is unquestionably a star.