Why Scientists Want Pluto Reclassified As A Planet, And Many Other 'Dwarf Planets' Added To List

In 2006, the International Astronomical Union decided Pluto will no longer be recognised as a planet. Now, some researchers have claimed that IAU's definition of a planet is not scientific.

New Delhi: In 2006, the International Astronomical Union (IAU) — which names astronomical objects — had passed a resolution that decided Pluto will no longer be recognised as a planet, but will be called a 'dwarf planet'. Several planetary scientists have since called out the decision, and claimed that they still consider Pluto a planet. 

An international team of scientists now wants Pluto to be reclassified as a planet, NBC News reported. They also want dozens of similar bodies in the solar system and those found around distant stars to be classified as planets again, the report said.

Pluto had been considered the ninth planet since its discovery in 1930. However, in August 2006, the IAU decided that a planet must be spherical, orbit the Sun, must have sufficient mass for its self-gravity to overcome rigid body forces, and should have cleared the neighborhood around its orbit, according to Resolution B5, which states the definition of a planet in the Solar System. 

Therefore, a dwarf planet is a celestial body that has all the characteristics of a planet, except the fact that it has not cleared the neighborhood around its orbit, according to the resolution. Pluto is round and orbits the Sun, and thus meets two of the requirements necessary to be classified as a planet. 

However, Pluto did not qualify under the new definition because it shares its orbit with objects called "plutinos". 

Why Has The Debate About Pluto's Status Revived?

Now, a new study published in the journal Icarus claims that IAU's definition of a planet was based on astrology, which is a type of folklore and not science.

The authors noted in the study that the IAU definition has now been rejected emphatically by many planetary scientists because of four reasons. The fourth reason is that the resolution represents to the public that taxonomy can be decided by voting, which undermines their understanding of the scientific process, and may undermine their trust in the scientific endeavour. 

The researchers noted in the study that Pluto must be classified as a planet under the definition used by scientists since the 16th century, which states that planets are geologically active bodies in space.

Philip Metzger, the lead author of the study, and a planetary physicist at the University of Central Florida, said that there are probably more than 150 planets in our solar system, according to the NBC report.

NASA's New Horizon probe, which flew by Pluto in 2015, made some interesting revelations, which revived the debate about Pluto's status, according to planetary geologist Paul Byrne. 

The researchers said that the IAU definition contradicted the century-long definition of a planet. 

The IAU created a new definition of a planet in 2006 because by then, objects similar to Pluto, such as Eris and Makemake, had been found. 

Quoting Metzger, the report said that most planetary scientists disregard the IAU's definition of a planet because it is an astrological concept, and that they are continuing to call Pluto, and Titan and Triton, along with some other moons, by the term, planet. He said: "Basically, we are ignoring the IAU."

What Other Scientists Say About Pluto's Status?

Doctor Alan Stern, a planetary scientist who leads NASA's New Horizons mission, said at the "I Heart Pluto Festival 2021", a virtual program staged by Lowell Observatory in Arizona, that the IAU's use of a vote made science seem arbitrary and political, undermining trust in science itself, according to a Forbes article. The Lowell Observatory is the very sight of Pluto's discovery on February 18, 1930, by astronomer Clyde Tombaugh.

Stern said that the IAU'S definition was created by non-experts, or astronomers who study stars galaxies and black holes. He thinks that the definition of a planet is poorly worded and that IAU botched it.

He noted that the solar system is so full of asteroids that no celestial body has "cleared the neighborhood" around its orbit.

He said that Pluto easily qualifies as a planet, as do all "dwarf planets". 

For a long time, Stern has called IAU's as unscientific, and that it was made primarily to keep the number of "official" planets at a manageable number.

At a robotics event in Colorado in 2019, former NASA chief Jim Bridenstine said that in his view, Pluto is a planet, and once can write that the NASA administrator declared Pluto a planet once, according to a space.com article.

He said Pluto is a planet and that he is sticking to it. It's the way he learnt it, and he is committed to it, he added.