Why is Pluto now called a dwarf planet?
Pluto is now classified as a dwarf planet because of a decision made by the International Astronomical Union (IAU) in 2006. The IAU established three criteria for a celestial body to be considered a planet: it must orbit around the Sun, it must have sufficient mass to assume a nearly round shape, and it must have cleared its orbit of other debris.
While Pluto meets the first two criteria, it fails to satisfy the third criterion. Its orbit overlaps with that of Neptune, and it shares its orbital space with a number of other objects in the Kuiper Belt, a region beyond Neptune containing many icy bodies. As a result, Pluto was reclassified as a dwarf planet, along with other similar objects that also do not meet the third criterion.
Pluto is now called a dwarf planet due to the redefinition of the term "planet." In 2006, the International Astronomical Union (IAU) established new guidelines for what constitutes a planet. According to the IAU definition, a planet must meet three criteria:
1. It must orbit the Sun.
2. It must be spherical in shape, or in hydrostatic equilibrium (meaning its gravity has pulled it into a round shape).
3. It must have cleared its orbit of other debris.
While Pluto meets the first two criteria, it fails to meet the third. Its orbit around the Sun is not clear of other objects, mainly due to the presence of countless other icy bodies known as Kuiper Belt objects in its vicinity. Therefore, Pluto was reclassified as a dwarf planet, which is a distinct category of celestial bodies that meet the first two criteria but fail to meet the third.
Pluto is now referred to as a dwarf planet because it does not meet the criteria to be classified as a full-fledged planet. The International Astronomical Union (IAU) redefined the definition of a planet in 2006, and Pluto no longer met the updated criteria.
To understand why Pluto is now called a dwarf planet, we can look at the criteria set by the IAU. According to the new definition, a celestial body must meet three conditions to be considered a planet:
1. It must orbit the Sun: Pluto does meet this criterion as it orbits the Sun, so it satisfies this requirement.
2. It must be spherical in shape: Planets are large enough for gravity to pull them into a round or nearly round shape. Pluto meets this criterion, so it satisfies this requirement as well.
3. It must have "cleared the neighborhood" of its orbit: This is where Pluto falls short. To qualify as a planet, a celestial body must have enough gravitational influence to dominate its orbit and clear out any other debris or smaller objects. Pluto shares its orbit with many other similar-sized objects, known as Trans-Neptunian Objects (TNOs). Due to this, Pluto has not cleared its neighborhood and is considered a dwarf planet.
Based on these criteria, the IAU classified Pluto as a dwarf planet rather than a full-sized planet. However, it's important to note that this decision has been subject to ongoing debate and discussion in the scientific community.