Will Pluto ever regain its status as a planet? Does it matter?

 

The general public was furious. Textbooks needed revision. On August 24, 2006, scientists at the International Astronomical Union (IAU) decided to reclassify Pluto, reducing its status from a planet to a dwarf planet. This decision was widely viewed as a demotion and has had a lasting impact on our understanding of the solar system. 

The whole Pluto controversy is based on the problems with the definition of a "planet." According to the International Astronomical Union, a planet is a celestial entity that 

1)  orbits the sun,    

2)  appears almost spherical    

3)  has largely cleared its orbital vicinity of debris. 

However, opinions on even this collection of measures differ. Despite their massive size, few asteroids have been removed from Earth's and even Jupiter's orbits. Ceres is one example of a small, circular globe that orbits the sun but is not regarded as a planet.

A lot of confusion indeed

The purported downgrade of Pluto from planetary classification presents more significant questions regarding the definition of any object in the solar system, or perhaps in space in general. It demonstrates how science isn't always able to classify objects into neat categories. Because it is not clear how to evaluate the many non-circular objects that round our sun if the definition of a planet is expanded once more. This might potentially cast doubt on the asteroid belt—the vast swath of tiny asteroids that lies between Mars and Jupiter. Or what would happen if a planet were to mysteriously fragment?

Nevertheless, many people are still confused about the controversy surrounding Pluto and the reasons behind its removal from the planetary orbit, even after the argument began nearly 20 years ago. However, the evolution of the solar system from nine planets to eight (at least according to the IAU definition) took a long time and illustrates one of science's greatest assets: the capacity to modify concepts that appear unchanging in the face of new information.

Peculiarity of Pluto

When astronomer Clyde Tombaugh of the Lowell Observatory in Arizona studied photographic plates of the sky on several nights, he saw a tiny dot that floated back and forth against the backdrop of stars. This led to the discovery and classification of Pluto as a planet in 1930 (note the IAU was created in 1919). However, the newest possibility in the solar system was immediately seen as a peculiarity. For 20 of its 248-year journey, it actually approaches the sun closer than Neptune due to its extremely eccentric, or non-circular, orbit. In addition, it is inclined toward the ecliptic, the plane that the other planets in the solar system revolve.

The first object in the Kuiper Belt was identified by scientists in 1992 as 1992 QB1, a small body orbiting beyond Neptune's orbit and out in Pluto's neighborhood. Soon, a large number of these objects were discovered, and they revealed a belt of tiny, frozen worlds like the asteroid belt between Mars and Jupiter. Though first believed to be even larger than Pluto, the faraway body Eris was discovered by astronomers in July 2005, upending Pluto's reign as the ruler of this region.

Confusion all around

The following queries required to be posed to researchers: Did this imply that Eris was a planet as well if Pluto was? What about the smaller things in the asteroid belt or all those other icy objects out in the Kuiper belt? What was the precise threshold for designating a body as a planet? A phrase that had appeared clear-cut and uncomplicated was now revealed to be strangely equivocal.

Following a heated discussion, numerous new definitions for planets were put forth.

Astronomers were no closer to finding a solution a year later, and the problem cast a shadowy pall over the 2006 IAU General Assembly meeting in Prague. Four proposals were put forth throughout the eight days of intense debate that the researchers had to sit through at the meeting. A contentious proposition proposed increasing the number of planets in the solar system to 12, incorporating the largest asteroid, Ceres, and Pluto's moon, Charon. 

By the end of the Prague conference, three new categories for solar system objects were decided upon by the 424 astronomers. Only the planets Mercury through Neptune would be regarded as planets after that. From then on, Pluto and its relatives, which were spherical objects that orbited alongside other objects, were referred regarded as dwarf planets. Small solar system bodies would be the name given to all other objects in orbit around the sun.  

The planet discussion underwent a major sea change as the New Horizon spacecraft flew across Pluto, revealing a world far more active than anyone had previously thought. Big mountains, beaten craters, and evidence of liquid moving across the surface all indicate that the world has experienced significant geological change since it formed. Based solely on this, some, like Stern, have argued that Pluto ought to be classified as a planet because it is a dynamic location that is not so static that the only things that perturb its surface are micrometeorites.

Observations of Charon, the moon of Pluto, reveal a very dynamic planet with a red cap on its pole that seems to change color in response to the gradual seasonal changes that occur so far out in the solar system. Notably, Mercury and Venus, two well-known planets, do not have as many moons as Pluto. (Most asteroids and dwarf planets have moons as well, which further complicates the definition of a planet.)

There are always new classification schemes emerging. As per a suggestion from 2017, a planet is characterized as "a round object in space that's smaller than a star." This would reclassify Pluto as a planet, but it would also reclassify the moon of Earth and many other moons in the solar system, bringing the total number of planets recognized by the scientific community to 110. A year later, Alan Stern, a leader of NASA's New Horizons mission coauthored an editorial piece in The Washington Post with planetary scientist David Grinspoon, claiming that astronomers ought to reevaluate their theories since the IAU's definition was "flawed" and "hurriedly drawn." 

Will Pluto ever regain its planetary status?

So far, these requests have been ignored, and it doesn't appear probable that the IAU will take up the issue again anytime soon. As of now, it is thought that Pluto was misclassified when it was first discovered; it was never on the same footing as the other eight worlds. So Pluto is still not a planet. It was never, in fact. Scientists think that we have misinterpreted it for fifty years. Maybe we are wiser now. Nostalgia for Pluto indeed makes for a weak planet argument, but that's all there is to it. Probably we should move on to reality now.

Does it really matter?

This abundance of planet-forming possibilities suggests that every solar system might be a different ecosystem. Although it is generally true that stars can create planets through the collapse of gas and dust in their surroundings, the specific dynamics involved in planet formation are much more intricate. Are several stars involved, for instance? What is the amount of dust that is available? Is a supernova or a black hole stealing the essential gas and dust that planets require to expand?

All of this suggests that in order to account for the variety of ways that a globe could emerge, our definition of a planet might need to change. Planets might be associated with specific zones or creation conditions. It appears that the only certainty is that planethood and the controversy surrounding Pluto will remain hotly contested for some time to come as data continue to be gathered.

But when modern-day kids (who were not born when Pluto was a planet) raise a question about the necessity of the definition of a planet, it is very difficult to give an answer, and one generally avoids such a situation by saying that it's complicated!!

Prabir Rudra