Pluto’s status still up for debate

Ever since the International Astronomical Union demoted Pluto from the status of a planet, the war over the strange world at the edges of our solar system has continued unabated. Now a group of scientists who worked on the New Horizons flyby of Pluto mission has developed an alternate definition of a planet that would restore Pluto’s status that was taken from it in 2006, according to Spaceflight Insider.

The IAU defined a planet as meeting the following criteria:

The object must be in orbit around the sun.

The object must be massive enough to be rounded by its own gravity.

It must have cleared its neighborhood of other objects.

Pluto failed to meet the third criterion, since it orbits near the Kuiper Belt where a large number of celestial objects reside, some of them bigger than the former ninth planet from the sun. Hence Pluto has been reclassified as a “dwarf planet.”

The New Horizon scientists have come up with a definition of a planet that is based on geophysics rather than astronomy, according to Spaceflight Insider. To be a planet, a celestial body has to be a round object that is smaller than a star. The idea is that a planet’s definition should be based on its inherent properties and not its interaction with other objects.

One problem with this definition is that it not only restores Pluto to the status of a planet but also elevates quite a few moons, an asteroid or two, and a host of Kuiper Belt objects to planet status, as well. If the new definition is accepted, then the solar system’s count of planets rises from eight or nine to hundreds.

Ever since Clyde Tombaugh discovered Pluto in 1930, generations of school children were taught that it was the ninth planet from the sun. Starting at the beginning of the 21st century, scientists such as Mike Brown, the discoverer of the Kuiper Belt object Eris, and celebrity astrophysicist Neil deGrasse Tyson began to campaign for Pluto’s demotion. The deed was done at the 2006 meeting of the IAU by resolution.

Not every scientist accepts the new definition. Alan Stern, the principal investigator of the New Horizons mission, points out that about 5 percent of astronomers voted for the resolution and are therefore not representative of the scientific community. He also believes that the definition offered by the IAU is arbitrary and would rule out other accepted planets, even Earth, if strictly enforced.

The controversy heated up even more starting in July 2015 when the New Horizons space probe flew by Pluto and began returning hundreds of images and instrument readings. Far from being a dead world of ice and rock, Pluto proved to be a strange place with nitrogen ice glaciers and water-ice mountains wracked with geological and geophysical processes that scientists are still studying and trying to understand. The upshot was that if a place as exciting and as dynamic as Pluto is not a planet, then what is?

The controversy over what to call Pluto is not going to go away anytime soon. Part of the reason is that the positions the two warring camps have taken are as based on emotion and ego as they are on science. Pluto was a planet for 76 years before a small group of scientists decided it was not. Indeed, the state House of New Mexico, where Tombaugh lived and worked, passed a resolution declaring Pluto a planet regardless of what the IAU says. The state Senate in Illinois, where Tombaugh was born, has passed a similar resolution.

The other part of the problem is that the universe is too strange and unusual a place for the objects within it to be placed in neat classifications. Thus Pluto will always be a planet to some and a dwarf planet for others, even in the long distant future when human beings will voyage to that distant world and see its strange landscapes with their own eyes.

Whittington, who writes frequently about space and politics, has just published a political study of space exploration titled, “Why is It So Hard to Go Back to the Moon?” He blogs at Curmudgeons Corner.