The question is "Why is Pluto not a planet?" When I was growing up, I remember that there was nine planets in our solar system. There was a saying students memorized in school that helped them to remember the nine planets : My Very Educated Mentor Just Showed Us Nine Planets. : Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto.
In 2006, the International Astronomical Union (IAU) voted to no longer call Pluto a planet. They now call Pluto a transneptunian object. Why did they do this? Even though Pluto is spherical, has five known moons and orbits the sun in the right direction.
Pluto was discovered on March 12, 1930 by Clyde W. Tombaugh (1906-1997). It revolves around the Sun at a distance of 4.5 billions miles (at aphelion) away from the Sun and takes 248.4 years to go around it. Pluto, god of the underworld is quite an appropriate name for a planet moving in the dark outer regions of the solar system.
I believe why they changed Pluto's status from planet to transneptunian object is because Pluto does not fit into any evolutionary scenarios. But what is a planet? Its original meaning was "wandering star". Planets revolve around the Sun which Pluto does. It does not revolve around Neptune.
What about the tens of thousands of textbooks and other books that call Pluto a planet? How about the hundred of millions of students who have called Pluto a planet? Why would they take this discovery away from Clyde Tombaugh who found this ninth planet when astronomers were searching for it for some 25 years?
I will always associate Pluto with Clyde Tombaugh and the worldwide excitement of finally discovering the ninth planet.
Even though no other planet is mentioned in Scripture except Earth (Genesis 1:1). I believe God created Pluto and the other planets on the fourth day of Creation week (Genesis 1:14-19) to be "lights in the firmament of heaven to divide the day from night; and let them be for signs, and seasons, and days, and years (Genesis 1:14).