The IAU and classification of planets:
Pluto: It’s Not a Planet, But Why? According to the International Astronomical Union, a planet is a celestial body that (a) orbits the Sun, (b) has enough mass for its self-gravity to overcome rigid body forces, and (c) has cleared the orbital neighborhood.
A planet must orbit the sun and fetch at least 100 kilometers (60 miles) of its orbit around the sun. In this case, Pluto’s orbit is more than 3,500 miles (5,600 kilometers) from the sun and its surface is heated by radiation, but it doesn’t have an atmosphere to protect it. Thus, Pluto is not considered a planet. It has a “dwarf planet” status, a round or spherical shape, and a volume that is greater than 300 million cubic kilometers (over 160,000,000 cubic miles).
An object must be in orbit around the sun, must be large enough to assume a round shape (thus a spherical shape), and also must have enough mass to fill its orbit and account for all its orbital motions. Pluto does not fit that description. It’s not even in its own solar system—it orbits a distant star, called the Kuiper Belt, some 3 billion miles from the sun. Moreover, Pluto was a minor planet in the Kuiper Belt before it was discovered in 1930. When it was discovered by American astronomer Clyde Tombaugh, it was the only object discovered in the Kuiper Belt. At the time, astronomers thought the Kuiper Belt was a sparse collection of small objects because it did not represent the “usual” part of the Solar System. They expected it to contain objects too small to detect with telescopes and therefore knew very little about its contents.
Pluto: It’s Not a Planet, But Why?
The general distinction between the terms “planet” and “dwarf planet” is that a planet is something bigger than a minor planet and is the fourth type of body in the Solar System. Dwarf planets are objects that are substantially smaller than a planet but are still larger than a dwarf planet.
The Moons of Pluto:
Pluto has five known moons, the largest of which, Charon, is a previously undiscovered moon of Pluto. Charon is so large that it cannot fully clear Pluto’s orbit, which is like a vast traffic jam that slows down the speed of any objects that travel on the orbits of Pluto. Charon is nearly 600 miles across, about 20% larger than Pluto’s own moon, Hydra. On July 19, 2005, astronomers discovered the first known moon of Pluto, Charon. This moon is a significant piece of the mysterious Pluto system, which was discovered in 1930 by Clyde Tombaugh. At the time of the discovery of Pluto, astronomers thought Pluto had no satellites because it did not have any atmospheric or surface features.
What else have scientists found out about Pluto since it was demoted?
In the last couple of years, astronomers have uncovered a treasure trove of information about Pluto. For example, astronomers have learned the best way to locate Pluto and its moons is by using the equipment of NASA’s New Horizons spacecraft. That spacecraft was launched in 2006 and after traveling through the solar system, the first photo was taken in January 2015.
Some Other Interesting Facts about Pluto:
Pluto has a water content of about 2%. Pluto’s orbit is believed to be tilting it onto a highly elongated elliptical orbit. According to the IAU, dwarf planets like Pluto are those that have not cleared their neighboring regions of other objects. On July 4, 2015, NASA celebrated Pluto’s dwarf planet status with a holiday-themed “launch party”. In 2003, and then in 2006, NASA proposed a mission to Pluto. In both cases, the proposal was shot down. In 2006, NASA proposed a Pluto Orbiter that would have entered into orbit around the planet but still required the approval of the IAU. In the end, they were denied.
Pluto has been categorized as a dwarf planet because it has characteristics of both a planet and a brown dwarf, as evidenced by a 2006 study that indicated Pluto had a high percentage of nitrogen and extremely high surface gravity. However, other astronomers disagree with the designation, as does the IAU, and it’s still difficult to make a definitive call.
Pluto might not be a planet anymore, but the legacy and exploration of its discovery and exploration is something we should be proud of. Like any other space mission, New Horizons provided us with new discoveries about the solar system and Earth. Even if it is not a planet anymore, it is a planet that represents everything we love about exploration. It’s not easy being a scientist, it’s not easy being an explorer, and it’s not easy being an astronaut. But despite those hardships, we should always remember that this is what science is all about: exploring, exploring, and exploring.