Pluto, the icy body in the outer reaches of the solar system, was considered the ninth planet in the system from the time it was discovered in 1930 up until 2006, when it was controversially reclassified as a dwarf planet by the International Astronomical Union (IAU) – the global authority for naming and designating celestial objects.
The IAU has since been at the receiving end by many scientists and astronomers who disagree with the union’s decision and have fiercely advocated for Pluto’s planetary status to be reinstated.
The contentious decision was based on the definition of a planet, which many scientists argue has been inconsistently applied in the case of Pluto.
In a scientific paper published in the journal Icarus in September last year, a group of scientists, led by the study’s main author Philip Metzger – a planetary scientist at the University of Central Florida – maintain that the IAU’s definition of a planet is not in the interest of science and, hence, should be revisited.
“What we’re doing is fact-checking,” Metzger, was quoted by NBC News as having said.
“There are 120 examples I found of scientists in the recently published literature violating the IAU definition, calling something a planet even though the IAU definition says it’s not a planet,” he said.
“The reason planetary scientists do this is because the IAU definition is not useful for science,” Metzger added.
Pluto’s planetary status came into question in 2005 when astronomers at the California Institute of Astronomy (Caltech) – a private doctorate-granting research university in Pasadena, California – discovered a Pluto-like celestial object in the distant solar system.
The object, which came to be known as Eres, was touted as a new addition to the planetary line-up at the time, but when more such objects were discovered in the Kuiper-belt neighborhood, the astronomical community was in a quandary over the definition of a planet.
Several definitions were considered and reconsidered before IAU called a press conference in Prague, in 2006, to give a new meaning to the term “planet,” thereby stripping Pluto of its planetary status and downgrading it to a “dwarf planet.”
The new resolution stated that in order for a solar system object in to qualify as a planet, it needed to meet three conditions:
- It has to orbit the sun
- It has to be rounded by its own gravity, for which it has to be large enough to allow its gravitation pull to shape it into a sphere
- It has to be pretty much the only object in its orbit, meaning it has to be gravitationally dominant-enough to have evicted most objects in its orbital vicinity.
While Pluto meets the first two criteria hands down, it falls short of qualifying as a planet when it comes to the third condition, because its orbit is littered with other icy bodies exerting their own gravitational forces.
Although thirteen years have passed since that eventful September day when Pluto ceased to be a planet and became a “dwarf planet,” the debate over the controversial definition and Pluto’s standing in the planetary hierarchy still rages on in the astronomical community.
NASA’s principal investigator for New Horizons mission to Pluto, Alan Stern, and other like-minded scientists have rubbished the revised definition, saying that it is flawed and needs to be reversed.
Writing in The Washington Post in May 2018, Stern and co-author of the article, David Grinspoon – an American astrobiologist and senior scientist at the Planetary Science Institute in Tucson, Arizona – stated that the IAU’s definition of a planet was “deeply flawed.”
“The process for redefining planet was deeply flawed and widely criticized even by those who accepted the outcome,” wrote Stern and Grinspoon.
“For one thing, it defines a planet as an object orbiting around our sun — thereby disqualifying the planets around other stars, ignoring the exoplanet revolution, and decreeing that essentially all the planets in the universe are not, in fact, planets,” they said.
“To add insult to injury, they amended their convoluted definition with the vindictive and linguistically paradoxical statement that “a dwarf planet is not a planet.” This seemingly served no purpose but to satisfy those motivated by a desire — for whatever reason — to ensure that Pluto was “demoted” by the new definition,” they wrote.
In fact, Stern was scheduled to debate Ron Ekers – former IAU president (2003 to 2006) – at the Powell Auditorium at the Cosmos Club on the definition of a planet and Pluto’s classification in our solar system in Washington, DC, on Monday.
Kuiper Belt is the ring-shaped accumulation of matter made up gas, dust, planetesimals, asteroids, or collision debris – also known as the circumstellar disk – in the far reaches of the solar system.
It is home to three known dwarf planets, including Pluto, Haumea, and Makemake, in addition to other icy objects.
Ultima Thule is the latest Kuiper Belt object (KBO), which NASA’s New Horizons spacecraft flew by as recently as New Year’s Day this year.
When it was thirty-three minutes past midnight in New York; when the ball had already dropped in Times Square to usher in 2019; when parties were in full swing across the city; history was made four billion miles out in space.
Technically, history happened in the blink of an eye, as NASA spacecraft New Horizons zipped past the tiny KBO at a lusty speed of 32,280 miles per hour – that’s 9 miles in a second, to put things in perspective.
However, confirmation of the historic flyby came only after an agonizing wait of six hours and eight minutes – that’s how long it took the radio signal from the robotic craft to travel through the void of space before it was plucked from the air by a NASA deep space radio dish in Madrid.
Coming back to the Pluto debate, Stern and Grinspoon summed it up extremely well when they wrote:
“The word “planet” predates and transcends science. Language is malleable and responsive to culture. Words are not defined by voting. Neither is scientific paradigm.”