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Wednesday, November 3, 2021

Pluto: Ethan Siegel wrongly attributes support for geophysical planet definition to emotion


Planetary scientist Phil Metzger and other proponents of the geophysical planet definition, including Kirby Runyon, Alan Stern, Mark Sykes, William Grundy, Jim Bell, Charlene Detelich, and Michael Summers on October 22 scheduled for publication in the journal Icarus arguing that moons should be considered a subclass of planets.

In response, astrophysicist and science writer Ethan Siegel, author of the blog Starts with a Bang wrote an article that centers not on moons, but on Pluto, once more repeating the claim that Pluto can never again be classed as a planet. While this piece goes into extensive scientific detail about the formation of stars and solar systems, in the end, it falls back on the same old argument, accusing supporters of the geophysical planet definition of being motivated by emotion rather than by scientific concerns.

The article opens with a minor error, stating Pluto was discovered in 1929 when the actual discovery date is 1930. But it is when he gets to describing planetary systems and the various boundaries within them that his argument begins to fall apart.

After noting the “soot line,” the location in a solar system subject to large amounts of radiation and unable to hold onto volatiles, and the “frost line,” the location in a system where temperatures are cold enough for volatiles to condense into solid ice grains, Siegel adds a designation of his own, the “Kuiper line,” which he describes as a region beyond a system’s massive planets. In this area, he states, “these objects are composed almost exclusively of various ices and volatiles.”

He then goes on to say, “Objects beyond the Kuiper line will be made mostly of volatile ices, and all of those volatiles would likely boil away in short order if they are brought inside the frost line” and "But out beyond the final large, massive body that forms — the last one to sweep out all the other objects that share its orbit — are a large number of mostly icy bodies of various masses. These objects are composed almost exclusively of various ices and volatiles, and in our solar system they include the Kuiper belt and, beyond that, the Oort cloud."

These statements are incorrect in terms of the composition of objects like Pluto, objects large enough to be rounded by their own gravity, in the outer regions of the solar system. These objects are composed mostly of rock, not ice. Pluto is estimated to be 70% rock, and Eris, which is marginally smaller but denser, is likely even more rocky.

The claim that these objects are composed entirely of volatiles that would boil away if brought closer to the Sun is the same argument that labels Pluto a “large comet”—which it is not. Comets are much smaller than any dwarf planet and are composed largely of volatiles that do boil away on close approach to the Sun. Rock, however, does not do that. If brought closer to the Sun, Pluto would lose its atmosphere but still remain intact.

Any object brought close enough to the Sun or its parent star would develop a tail due to outgassing. Mercury has a tail, as do hot Jupiters—giant exoplanets in close orbits around their stars. Some of those hot Jupiters are on unstable orbits and will eventually fall into their stars. Forget orbit clearing; if an object cannot even maintain its own orbit without eventually spiraling to destruction, should it be considered a planet?

Of course, the IAU planet definition does not address exoplanets, so the question of hot Jupiters is never addressed. Such an object would be a planet under the geophysical definition until it is destroyed, at which point it would no longer exist.

Siegel goes on to mischaracterize Pluto, with the following: "Still, based on what we can observe in the Universe, the fact remains that Pluto is completely unremarkable, as far as objects found beyond its solar system’s ‘Kuiper line’ go. It has a perfectly normal mass, radius, composition, and formation history, and is a member of a population of objects that has very little in common with objects like terrestrial planets like Venus, ice giant planets like Neptune, and gas giant planets like Jupiter."

This description is incorrect in terms of the claim that Pluto has little in common with terrestrial planets. Pluto actually has a very similar composition and geological features and processes as the rocky planets have. These include interaction between atmosphere and surface, layered atmosphere, windswept dunes, active geology, floating glaciers, possible cryovolcanism, and a likely subsurface ocean. There are processes that occur on Pluto found elsewhere in the solar system only on Earth and Mars.

NONE of the terrestrial planets have much in common with the gas giants in terms of composition. Jupiter and Saturn are composed largely of hydrogen and helium, like the Sun. They have no solid surfaces. Uranus and Neptune have water, methane, and ammonia in addition to hydrogen and helium and small cores made up of rock and ice. The terrestrial planets have more in common with Pluto than they do with the gas and ice giants.

The real problem with Siegel’s argument comes at the end of his article. He states, "However, it’s a far worse offense to water down a previously useful definition to the point of universal uselessness than it is to exclude a subset of one’s “favorite” objects from a designation that was previously assigned to them."

What is this “previously useful definition?” Is it the IAU definition, which Siegel himself recognizes as having the “terrible flaw” of applying only to objects that orbit the Sun? He quotes Jean Luc Margot, who published a paper extending the IAU definition to exoplanets, but Margot’s position does not represent that of most planetary scientists or that of the IAU, which has chosen to remain silent on this issue for 15 years, as the number of exoplanets discovered increased from 300 plus to 4,500 plus.

While Siegel spends a lot of time on the science of star and solar system formation, the crux of his argument, as revealed here, is that planetary scientists who favor a geophysical planet definition are motivated by emotion--preference for their "favorite planet." This is absolutely false and is a common argument of those who support the IAU definition.

It is not wanting a "favorite"--Pluto--to be classed as a planet that is motivating those who support a geophysical definition but preference for a definition that puts primacy on an object's intrinsic properties over its location. This does not mean location does not matter. Location can be recognized in establishing subclasses of planets--satellite planets, rogue planets, etc. It just means location should not be the primary factor in defining what a planet is.

One could easily argue that Siegel, who responds to an article about the classification of moons by centering his article on Pluto, who repeats Mike Brown’s insistence that Pluto can “never again” be considered a planet, is the one motivated by emotion, in this case, by wanting his view to prevail and the debate to be shut down.

In short, Siegel may want Pluto to never be up for consideration as a planet again, but that does not mean there aren’t scientifically sound reasons for such consideration to occur.

Thursday, September 9, 2021

Planetary Scientist Paul Byrne makes some great arguments in favor of Pluto's planethood

 In an article published today, September 9, 2021, in the magazine Science Focus, planetary scientist Paul Byrne makes some sound, logical, scientific arguments for Pluto's classification as a planet. Read the article here:

Tuesday, August 31, 2021

Great Article by Jacqueline Hale: "Pluto is a Planet, and Nothing will Convince me Otherwise"


This article by Jacqueline Hale of Jacqueline's Space Blog does a great job discussing the weaknesses of the IAU decision and the scientific arguments for the geophysical planet definition. I encourage all Pluto supporters to read it.

Tuesday, August 24, 2021

Pluto, the IAU, and the Planet Debate: Where Do We Go From Here?

Fifteen years have passed since the debacle perpetrated by four percent of the IAU when the group violated its own bylaws and adopted a controversial planet definition that it then attempted to impose on the world.

The event was not just, as New Horizons principal investigator Alan Stern accurately described, “an embarrassment to astronomy.” It was also an embarrassment to journalism because the media chose to report that vote as a seismic change to the solar system rather than what it actually is—one position taken by one very limited group of people, rejected by an equal number of people in the field.

The anniversary, especially as one that ends with a “0” or “5,” means it’s time for the usual media reports that present the IAU definition as the only “truth,” with the usual insulting adjectives for those who reject it, referring to us as “disappointed,” “sore,” “dismayed,” etc. Those words are derogatory because they characterize dissenters as people motivated by emotion. The reality is that many, not just a few people, including most of the world’s leading planetary scientists, dissent with the IAU position and reject it in favor of the geophysical definition presented by Kirby Runyon at the 2017 Lunar and Planetary Sciences Conference or other alternative definitions that do not require orbit clearing for planethood.

A kids’ article in the Washington Post even went as far as claiming August 24 is celebrated as an “international holiday,” Pluto Demotion Day, by scientists worldwide. This could not be further from the truth. Unfortunately, after a decade and a half, the media continues to misrepresent this issue, doing a tremendous disservice to readers.

This year, Science News does a better job in discussing the milestone, quoting Kirby Runyon on the geophysical definition and doing so not just in one sentence tagged on to the end. Writer Lisa Grossman even admits she may be coming around to supporting a more inclusive rather than exclusionary definition.

Of course, there is the usual line by Mike Brown, who claims, “Fifteen years ago, we finally got it right. Pluto had been wrong all along,” and “If you dropped me in the solar system for the first time, and I looked around and saw what was there, nobody would say anything other than, ‘Wow, there are these eight — choose your word — and a lot of other little things.’ ”

Brown is wrong on both counts. There is nothing “final” about the 2006 IAU vote, which violated the organization’s own bylaws. Numerous discoveries of additional solar system planets and exoplanets have been made since then. New Horizons revealed Pluto to the world and showed it to have complex planetary processes, some seen elsewhere in the solar system only on Earth and Mars.

No one got anything “right” in 2006. Pluto was never “wrong”; instead, it represented a new subclass of planets that had just started to be discovered. Unfortunately, some could not wait for the spacecraft to reveal this and didn’t care to use its revelations to revise their flawed conclusion.

It is interesting that Brown presumes to speak for aliens who might be “dropped into the solar system” and in doing so, projects his view onto them. What any alien would see would depend on their level of technological advancement and what they are looking for.  Some might see only Jupiter and Saturn and think the system has no habitable planets. Others might focus on small planets that could serve as outposts of intelligent civilizations and specifically look for worlds like Pluto and Eris.

Anyone from an advanced civilization would clearly discern that solar system planets come in many types. Rather than see just “eight big things,” they likely would see rocky planets, gaseous planets, and smaller dwarf planets. If they looked at Pluto up close, they very likely would see its round shape, and think planet, as per what Alan Stern describes as the “Star Trek test.”

Actually, if they looked at the Pluto system up close, they would see a binary or double planet system, the only one in the solar system. Rather than orbit Pluto, the four small moons orbit the center of gravity, known as the barycenter, between Pluto and its large moon/fellow planet Charon.

Former IAU president Catherine Cesarsky is quoted stating the very unscientific argument that the solar system cannot have “too many planets” and that it would be difficult to keep changing the number of solar system planets with each new discovery.

Why is the number even important? Finding new solar system planets is exciting! And almost every textbook has a web page that can be instantly updated to reflect new discoveries.

Cesarsky didn’t have New Horizons data back in 2006, but in 2021, referring to Pluto as “a new class of solar system objects” instead of “a new class of solar system planets” has little merit. The spacecraft clearly revealed Pluto to be a planet though the first in a new subclass of planets.

Unfortunately, most science reporting in the mainstream media does not involve a lot of research. Most of the journalists who write these stories are generalists who are not well informed about their subjects and do just cursory research before writing their stories.

In the planetary science world, things are very different, as the Science News article indicates. The IAU definition there has clearly been a failure. It is seldom used by planetary scientists, and new developments have made its logic significantly more tenuous over the last decade and a half.

Take one exoplanet discovery: the L 98-59 system, a red dwarf star with as many as five Earthlike planets, just 35 light years away. Two of those five, which still need to be confirmed, orbit in a different plane than the other three and therefore cannot be detected by the transit method, which searches for the dimming of a star’s light as a planet passes in front of it. These same two are also the star’s largest planets, and one of them may be in the star’s habitable zone.

If planethood requires all objects in a system to orbit on the same plane, then what are these two objects?

The science that has been done in the last 15 years, the discoveries made, are what weaken the IAU definition the most!

Where do we go from here? Over a decade and a half, the IAU has shown complete intransigence in making clear it never wants to revisit this issue, discoveries and new science be damned.

It’s time to forget the IAU and find another path forward.

At the same time, Alan Stern and the New Horizons team have published the textbook of the generation, The Pluto System After New Horizons, which will serve as the textbook for college and graduate studies on the subject.

What we need now is the formation of a planetary science group that will distill the findings in this book and come up with K-12-level discussions of Pluto and its place in the solar system, with which it can approach textbook publishers and educators. These can and should be incorporated into the textbooks’ depictions of the solar system.

A formal organization grants a level of legitimacy that is badly needed to represent the view opposing the IAU definition. Such a group, ideally composed of both professionals and amateurs, can publish articles, newsletters, a web site, and even books that teach the controversy rather than promote one side.

Ultimately, the geophysical definition is not so much about Pluto but about a much more expansive, inclusive, exciting view of the universe, one in which there is always more to discover, more to understand, more to question.

Since the IAU vote, the world has added nearly another billion people to its population. It is time to do right by them and give all eight billion people on Earth   the opportunity to know the whole story of the solar system and worlds beyond.

Wednesday, August 18, 2021

In Memoriam: Carolyn Shoemaker, 1929–2021

In addition to being a co-discoverer of Comet Shoemaker-Levy 9, Carolyn Shoemaker signed Alan Stern's petition of more than 300 scientists rejecting the 2006 IAU planet definition.

In Memoriam: Carolyn Shoemaker, 1929–2021

Monday, March 1, 2021

BBC Future Gets It Wrong on Both Planet X and Pluto

The BBC Future article "If Planet Nine Exists, Why Has No One Seen It," published on February 16, 2021, unfortunately presents a very biased view of the ongoing planet debate. Instead of acknowledging the continuing debate over Pluto's planet status and how to define the term "planet," the article presents only the position of the International Astronomical Union as if it were a done deal, which it is not.

Just four percent of the IAU voted on the controversial 2006 demotion of Pluto, and their decision was immediately rejected in a formal petition by an equal number of professional planetary scientists. Yet nowhere is this mentioned in the article. Instead, the writer simply makes the biased statement, "the ninth planet was no more" regarding the aftermath of the IAU 2006 vote, completely ignoring the fact that the majority of planetary scientists reject that decision to this day.

In this Science Direct paper, planetary scientist Phil Metzger discusses the history of planetary classification and the fact that planetary scientists do not use the IAU definition in their peer-reviewed published papers.

Those who reject Pluto's planet status completely ignore the stunning revelations of active geology and planetary processes on Pluto by the New Horizons probe in 2015.

Nowhere does the article mention the alternative geophysical planet definition, presented by planetary scientist Kirby Runyon at the Lunar and Planetary Sciences conference in 2017 and in a 2018 article in Astronomy magazine. This definition views dwarf planets as a subclass of planets and therefore keeps Pluto, Ceres, Haumea, Makemake, and Eris in the planet list. It is the definition preferred and used by most planetary scientists.

Also problematic is the repeated quoting of Mike Brown, a controversial figure who represents just one side in this debate. Brown unprofessionally promotes himself as the man who "killed" Pluto, and it is disappointing to see the writer repeat this without question and even promote his twitter account. Brown was one of a team of three who discovered Eris, but he did not "kill" planet Pluto, and journalists should not be promoting this nonsense. Notably, the other two members of the discovery team reject the IAU planet definition in favor of the geophysical one.

Brown controversially named the hypothetical planet in question "Planet Nine" to further promote the self-serving notion that he "killed" planet Pluto. In 2018, a group of planetary scientists formally objected to this term in their publication Planetary Science Exploration Newsletter because of its inherent bias. There, they noted that the appropriate professional term for a hypothesized but undiscovered planet is "Planet X," with "X" referring to the unknown, not the number 10.

It is unfortunate that some scientists continue to mislead the public by promulgating their own biased positions as fact, without even acknowledging the existence of a debate or of other legitimate scientific positions. I urge the BBC to be more vigilant in the future when it comes to the planet definition debate to use neutral language that acknowledges the fact that this issue is not settled but remains an ongoing debate in the science community.