prompter: If we assume that Pluto is a planet, how many planets there are in the solar system?

assistant: If we assume that Pluto is a planet, there would be nine planets in the solar system. Before 2006, Pluto was considered the ninth planet in our solar system. However, the International Astronomical Union (IAU) redefined the definition of a planet in August 2006 and reclassified Pluto as a "dwarf planet," leaving eight planets in our solar system. However, there is still some debate among astronomers and the public about whether Pluto should be considered a planet, so some people may still consider it the ninth planet.

assistant: If we assume that Pluto is a planet, then together with Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune, it would be the ninth planet.

prompter: What criteria do scientists use to determine whether an object is classified as a planet or not?

assistant: In 2006, the International Astronomical Union (IAU) established three criteria for an object to be classified as a planet:

1.The object must be in orbit around the Sun: This means that the object must not be a moon or satellite of another planet, but must instead orbit the Sun directly.

2.The object must have sufficient mass to form a nearly round shape: This means that the object must be large enough to have become spherical due to its own gravity. The minimum size required for an object to achieve this shape is not precisely defined, but it is typically thought to be about 500 kilometers (310 miles) in diameter.

3.The object must have "cleared its orbit" of other debris: This means that the object must be the dominant gravitational force in its orbit and must have "swept up" or cleared away other debris in its vicinity. Essentially, the object must have become gravitationally dominant in its orbit and be able to orbit freely without colliding with other debris.

If an object meets these three criteria, it is classified as a planet. However, if an object only meets the first two criteria, it is classified as a "dwarf planet" (like Pluto), and if it only meets the first criterion, it is classified as a "small solar system body" (like comets and asteroids). The IAU's definition of a planet is still somewhat controversial, and some scientists and members of the public have suggested alternative definitions or argued for the inclusion of additional objects as planets.

prompter: ohh, so that is the reason why pluto is not considered a planet

assistant: Scientists use a set of criteria known as the International Astronomical Union (IAU) definition of a planet to determine whether an object is classified as a planet or not. The criteria include:

    1. The object must be in orbit around the Sun.
    2. The object must have sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a nearly round shape (this is known as hydrostatic equilibrium).
    3. The object must have cleared the neighborhood around its orbit of other debris, such as asteroids or comets.

If an object meets all three of these criteria, it is classified as a planet. If it meets the first two criteria but not the third, it is classified as a dwarf planet, like Pluto.

The third criterion is often the most controversial, as it requires that a planet must be gravitationally dominant in its orbit, meaning it has cleared out any debris that might compete with it for space in its orbit. This is why Pluto was reclassified as a dwarf planet in 2006, as it orbits in a region of the Solar System with other large objects and has not cleared its orbit of debris.

It's important to note that this definition is not without controversy and has been debated by scientists and astronomers. However, it remains the official definition used by the IAU for the classification of planets.

prompter: Who decided Pluto was not a planet and do you think the decision was right?

assistant: In 2006, the International Astronomical Union (IAU) voted to reclassify Pluto as a dwarf planet, based on the criteria I mentioned earlier. The decision was made during the IAU's General Assembly in Prague, where a resolution was passed defining what constitutes a planet, and Pluto no longer met the third criterion of the definition.

Whether the decision was right or not is a matter of debate and personal opinion. Some scientists and members of the public have argued that Pluto should still be considered a planet, while others support the decision to reclassify it as a dwarf planet.

The IAU's decision was based on scientific criteria, and the organization is made up of astronomers and scientists from around the world who have expertise in the field. However, the decision has been controversial and some members of the scientific community have disagreed with it. Ultimately, the classification of Pluto as a planet or dwarf planet is a matter of scientific convention and does not change the actual properties and characteristics of the object itself.

assistant: The decision was made by 424 member astronomers of the International Astronomical Union (IAU) in August 2006, in Prague. The two options were to either keep Pluto as a planet and add a number of other small astronomical objects among the planets, or keep having an inconsistent definition for what a planet is.

I think it was the right choice, because it's good to have a consistent definition for a planet, and also excluding one planet is less trouble than adding many more.