Bharat SainiLast Updated on October 26, 2018 by Bharat Saini
Pluto should be a planet again, researchers including Philips Metzger, a planetary scientist at the University of Central Florida’s Space Institute, in a new study published online in the journal Icarus on Wednesday September 5, 2018, argue that the definition of a planet should be based on its intrinsic properties as opposed to properties that can change, such as the dynamics of its orbit and Metzger observes that the reason Pluto lost its planet status in 2006 is not valid. This study was co-authored by Mark Sykes of the Planetary Science Institute; Alan Stern, American Engineer and Planetary Scientist at Southwest Research Institute; and Kirby Runyon of Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.
In 2006, the International Astronomical Union (IAU), a global group of astronomy experts, had downgraded Pluto’s status to “Dwarf planet” on having established a definition of a planet that required it to “clear” its orbit, or in other words, be the largest gravitational force in its orbit. IAU laid down three criteria for a celestial object to be Planet:
1. It must orbit the Sun,
2. It should be massive enough to acquire an approximately spherical shape and
3. It has to ‘clear its orbit’, that is, be the object that exerts the maximum gravitational pull within its orbit
IAU deemed that Pluto did not ‘clear its orbit’ that meant Pluto was out of planet status, owing to this 3rd property, if an object ventures close to a planet’s orbit, it will either collide with it and be accreted, or be ejected out. Since Neptune’s gravity influences its neighbouring planet Pluto and Pluto shares its orbit with frozen gases and objects in the Kuiper belt.
Dwarf planets need satisfy only the first two conditions.
Philip Metzger, lead author of the recent study, reported that this standard for classifying planets is not supported in the research literature. Metzger reviewed scientific literature from the past 200 years and found only one publication, from 1802, that employed the clearing-orbit requirement to classify planets. The 1802 study, he argues, was based on “since-disproven reasoning.”
Metzger believes on the basis of his study, that the IAU definition of what constitutes a planet needs to be rethought, “It’s a sloppy definition,” he said in a statement and added, “They didn’t say what they meant by clearing their orbit. If you take that literally, then there are no planets, because no planet clears its orbit.”
According to Metzger, Moons such as Saturn’s Titan and Jupiter’s Europa have been routinely called planets by planetary scientists since the time of Galileo, and he said, “We now have a list of well over 100 recent examples of planetary scientists using the word planet in a way that violates the IAU definition, but they are doing it because it’s functionally useful”.
Metzger explained, “Dynamics are not constant, they are constantly changing”. “So, they are not the fundamental description of a body, they are just the occupation of a body at a current era.”
Metzger recommends a planet classification based on whether it is sufficiently large so that its gravity allows it to become spherical in shape.
Metzger adds, “It turns out this is an important milestone in the evolution of a planetary body, because apparently when it happens, it initiates active geology in the body”.
Metzger notes, Pluto has an underground ocean, a multilayer atmosphere, organic compounds, evidence of ancient lakes and multiple moons.
Kirby Runyon, co-author of the study, said the IAU’s definition was erroneous since the literature review showed that clearing orbit is not a standard that is used for distinguishing asteroids from planets, as the IAU claimed when crafting the 2006 definition of planets and proposed that the offending 3rd clause be deleted. To be sure, there isn’t a novel scientific argument for Pluto’s case that hasn’t already been made. Pluto being made a planet again, according to him, would mean that “the public would again fall in love with planetary exploration.”
Kirby Runyon had also earlier in his presentation at the 48th Lunar and Planetary Science Conference at Texas in March 2017 argued that the definition of what constitutes a planet be changed. Runyon and co-authors including Alan Stern were part of the science team on the New Horizons mission to Pluto, operated for NASA by the Johns Hopkins University Applied Physics Laboratory. In the summer of 2015, the New Horizons spacecraft became the first to fly by Pluto, passing within 8,000 miles and sending back the first close-up images ever of Pluto. These factors combined to whet interest in the revivification of Pluto’s planetary status.
