It is time to
celebrate! Today marks the 94th anniversary of Pluto’s discovery by
Clyde Tombaugh on February 18, 1930, at the Lowell
Observatory in Flagstaff, Arizona.
The observatory is celebrating with its annual I Heart Pluto event this weekend, featuring
a Pluto pub crawl, a talk by writer Diana Gabaldon, and various science talks
and demonstrations.
In honor of this anniversary, National Geographic has published an article titled, “Did Pluto Ever Stop Being a Planet: Experts Debate with citations of Philip Metzger and Mike Brown.
Phrasing the issue as a question rather than a statement is progress, as it amounts to not blatantly portraying the IAU view as objective truth. It is also an acknowledgement that the debate over planet definition and Pluto’s status continues.
There are several errors in this article. First, contrary to the writer’s claim, Brown is not responsible for the demotion of Pluto, no matter how much he wants to be. That was done by 4% of the IAU, a group of which he has never been a member.
Also, Brown is wrong in claiming that the term "planetoid" referred to small spherical objects. Planetoid has always been a synonym for asteroids/comets, objects not large enough to be rounded by their own gravity.
Brown is also wrong when he says that the pro-Pluto faction is dominated by members of the New Horizons mission. While most New Horizons scientists do view Pluto as a planet, largely due to their preference for the geophysical definition as well as their interpretation of the flyby data, they are by no means the only scientists who take this view. There are many planetary scientists and even astronomers, both amateur and professional, who are not affiliated with New Horizons but reject the IAU planet definition and view Pluto—and all dwarf planets—as a subclass of planets.
Regarding New Horizons scientists, Brown states, “When they launched, Pluto was a planet. By the time they got there, it wasn’t.”
This statement should be of concern to anyone who cares about science. Why? Because it essentially argues for science by decree of “authority.” Pluto was not hit by a large asteroid between 2006 and 2015. No portion of Pluto was lobbed off in an impact as was done to ancient Pallas and Vesta, taking the objects out of hydrostatic equilibrium. Nothing about Pluto changed from the launch of New Horizons to the 2015 flyby.
The change to which Brown is referring is the vote by four percent of the IAU in August 2006, meaning Brown is championing the idea of science by authority, something that is very unscientific.
As Jack Mitch Culberson stated on Twitter and in a presentation, what the media should have reported of the August 2006 vote is not that Pluto stopped being a planet but that the IAU stopped considering Pluto to be a planet.
Brown also makes an ad hominem attack when he says, “The pro-Pluto side tried to change the definition of a planet to be something it’s not because they were so desperate to keep Pluto a planet…”
Here he deliberately attributes an emotional motivation rather than a scientific one to the pro-Pluto side. The truth is not that pro-Pluto scientists were desperate to keep Pluto a planet but that they favored a geophysical planet definition, which is centered on an object’s intrinsic properties rather than its location.
So what if the latter results in the solar system having 200 planets? As stated
many times, there is no scientific merit to the argument that the solar system
cannot have “too many planets.” If there were, scientists would have to do
something about Jupiter and Saturn having “too many moons,” the galaxy having “too
many stars,” and the universe having “too many galaxies.”
This week, in conjunction with the anniversary of Pluto’s discovery, the Lunar and Planetary Institute in Houston, Texas, is holding a two-day workshop titled, “Planet Characterization in the Solar System and the Galaxy” on February 21-22.
The conference description notes, “The diversity of planets and planetary types has exploded since the first discoveries of exoplanets and shows no signs of abating as the total population of known planets in our system and others has grown from 9 planets to over 5,000. We will convene to describe, discuss, and debate the various planet classification schemes. We consider the needs of both astrophysics and planetary science, geophysics, ocean worlds studies, atmospheric studies, magnetospheric studies, and more, with the goal of informed scientific debate, education, and progress toward consensus classification schemes.”
Clearly, the debate over planet definition and classification is very much ongoing.
I will be attending this conference virtually and will give a brief presentation on the harm the 2006 IAU vote has done to public perception of science and scientists worldwide.
Clyde Tombaugh’s discovery of Pluto at age 24 was a triumph for science and showed the world that there is more to the scientific process than an advanced degree. It continues to inspire generations of people to look up and try to make their own discoveries. It is a victory for persistence and perseverance that merits being celebrated to this day and beyond.
