Pluto at 95

 

Happy International Pluto Day! Ninety-five years ago today, on February 18, 1930, 24-year-old Clyde Tombaugh discovered Planet Pluto while blinking between photographic plates of the sky taken on two separate nights in January of that year.

The goal was to find anything that moved against the background stars between nights. That object would not be a star but a planet within our solar system.

The announcement of Pluto’s discovery was not made until a month later, on March 13, 1930 by the Lowell Observatory, which chose this date because it was the birthday of its late founder Percival Lowell as well as the anniversary of the discovery of Uranus in 1781.

Incredibly, Tombaugh was not even credited in initial announcements of the discovery. He was described as a “junior astronomer” and not named, as the observatory wanted to focus the credit on Percival Lowell, who had predicted the existence of a planet beyond Neptune but had not actually found it.

Ironically, given that Lowell died despairing about never having discovered the planet, Pluto does appear on what are called “precovery” images he took around 1905 and 1906. It is not unusual for scientists to search earlier images after the discovery of a celestial object to determine whether that object appeared in a photo but remained unrecognized.

That was the case with Lowell and Pluto. He had photographed Pluto, but he didn’t recognize it for what it was, likely because he was looking for a giant planet like Uranus or Neptune rather than a small one, which Pluto turned out to be.

Celebrated annually at the Lowell Observatory to this day with an I Heart Pluto festival, Pluto’s discovery remains in many ways a triumph of underdogs. Tombaugh had only a high school diploma when he made the discovery. While searching for the planet, he was told by a professional astronomer that he was wasting his time, that if there were any more planets to be found, they would already have been found.

When Lowell Observatory director Vesto Slipher published an article about the discovery in Science News-Letter, he credited Lowell without even mentioning Tombaugh. Similarly, in the same publication, Harvard astronomer Harlow Shapley and Yale astronomer Frank Schlesinger wrote, “to Professor Lowell…belongs the credit.”

A certain elitism among astronomers of the time led them to have trouble accepting that a “kid” without an advanced degree had discovered a planet. Citizen science was not yet a “thing,” and the notion that an ordinary person could make the type of discovery for which those with PhDs worked hard for many years appeared to make those scholars uncomfortable.

After falling into obscurity for decades as the planet the least was known about, Pluto began to regain popularity during the 1960s and 1970s. Its largest moon, Charon, really a binary partner, was found in 1978.

Tombaugh himself described feeling like an outsider, someone who did not quite measure up to others in his field. This is evident from his sense of genuine surprise at his burgeoning popularity following the 50th anniversary celebrations of Pluto’s discovery, in 1980.  Biographer David Levy quotes Tombaugh’s ironic reaction. “I misjudged the attitude of astronomers. I thought I was a nobody. I thought they had contempt for me”

For almost a century, Pluto and its discoverer have shared this underdog quality, from some, a sense that they weren’t good enough and didn’t measure up, but from others, the sense of being a folk hero and a rock star.  Both were seriously underestimated—Tombaugh as a professional astronomer and Pluto as a planet.

Pluto may be smaller than most solar system planets and have an eccentric orbit, but those things do not preclude it from being a planet. They just make it a different type of planet. In the last 30 years, exoplanets have been found with orbits around their stars that are far more eccentric than Pluto’s path around the Sun. Some of these exoplanets are giant, Jupiter-like worlds.

New Horizons surprised scientists and ordinary people worldwide, who had expected to see a dead world but instead were treated to images of one that is geologically active and has some planetary processes seen elsewhere in the solar system only on Earth and Mars.

Yet even now, misinformation about Pluto is rampant. An article about the I Heart Pluto celebration stated that Pluto’s “reclassification” was done because objects larger than Pluto were discovered in the outer solar system. This is not true and is based on information that was proven wrong close to 15 years ago.

Eris was initially thought to be larger than Pluto, but a team of astronomers led by Bruno Sicardy observed it occult (pass in front of) a star in 2010 and found Eris to be marginally smaller than Pluto yet slightly more massive. It is disappointing that so many years later, the initial error about Eris being larger is still being spread in the mainstream media.

With time, Tombaugh has been recognized and fully credited for his discovery. Similarly, as time passes, I believe Pluto will be recognized for and credited as the planet it is. It may be different from the solar system’s four terrestrials and four jovians, but it is far from the only planet of its kind. And it is only a matter of time before similar small planets are discovered orbiting other stars.

Meanwhile, the same persistence and perseverance that led to Pluto’s discovery will motivate those of us who fight for its rightful recognition as a planet. Dwarf planets are planets too!

I Heart Pluto Festival at Lowell Observatory This Weekend

 

Lowell Observatory’s annual I Heart Pluto festival is back, celebrating the 95^th anniversary of Pluto’s discovery on February 18, 1930.

This year’s celebration, held in Flagstaff, Arizona, features a Pluto Pub Crawl with Pluto-themed drinks and talks with Lowell astronomers; various science talks including a keynote Night of Discovery featuring Alan Stern, David Levy, and Adam Nimoy, son of Star Trek actor Leonard Nimoy; various festival activities, and a children’s choir performance of “Ode to Pluto,” the song by Mark Burrows that I sing at my annual birthday party.

There will even be a “Shakespeare on Pluto” performance, a comedy with music celebrating both Shakespeare and space exploration.

For more on these events, which take place tonight and this weekend, visit Lowell’s I Heart Pluto page.

Even if you can’t make it to Flagstaff, this is the time to celebrate Pluto’s discovery 95 years ago and learn more about this small but amazing planet.

I hope some of the talks will be recorded and put online and will keep everyone informed if and when this happens.

Presentation Recordings of February 2024 Planet Characterization Workshop

 

Documents from and recordings of all presentations at the Lunar and Planetary Institute's Planet Characterization Conference, held in February 2024, are available for reading and viewing here.

My presentation on February 21 was one of several under the heading, "The Impact of Taxonomy on Public Perception of Science and Our Universe: Advantages and Pitfalls. All the presentations are worth watching. Mine is titled, "Impact of the IAU Planet Definition on Public Perception of Science." Under this same grouping is John Vester's "A Linguistic Planetary Definition."

Some of the presentations were done in person at the conference while others were done virtually. For each one, clicking on "Presentation" will show their Power Point slides while clicking on "Recording" will show their work on a YouTube video.

Enjoy! The fight for Planet Pluto continues...

Winter Solstice

 

“It is the secret of the world that all things subsist and do not die, but retire a little from sight and afterwards, return again.” ― Ralph Waldo Emerson

Sometimes described as “the most wonderful time of the year,” December has its own special magic. While some religions celebrate miracles occurring at this time, the Winter Solstice, a scientific event, brings miracles and magic as well.

In an endless cycle of birth, growth, death, and rebirth, the Winter Solstice marks the beginning of rebirth. The darkness stops growing. The Sun symbolically “dies” and is “reborn”; one solar cycle—year—ends, and a new one starts.

Life that appears dead is merely dormant. In a few months, the growing light will penetrate the frozen Earth, enabling the resting seeds to germinate and begin a new cycle.

Winter Solstice is one of my most favorite times of year. It is a time of celebration and joy, but it is also a time when we slow down and think about the deeper things that connect all people and all life on this planet. In the darkest, coldest time, we come together to make our own warmth and our own light.

None of us can make it through this most difficult season alone. Kindness, love, and empathy are things we all need to survive the season. We donate coats, gloves, toys, and food so others will be warm, entertained, and well-fed.

The Winter Solstice reminds us that we are all vulnerable. We may believe differently, have differing political views, but we all need each other. Money and social status won’t keep us warm if we’re stranded outside in freezing temperatures or a blizzard.

Giving and receiving empathy enables us to survive the cold and dark together with joy and hope.

For many, 2024 has been a difficult year. At times, it can take effort to find reason to hope. It can feel like for every step forward, we take two steps back. Those of us fighting for Pluto, dwarf planets, and a better planet definition have now been at it for more than 18 years.

When we support one another and give comfort to one another, we transform a season of cold and dark to one of warmth and light. When we recognize that the darkness is a time not of death but of dormancy in preparation for new life, we realize that hope is the way of the world. Nothing stays dead forever. As Emerson notes above, all living things retreat from our view, from our awareness, for a while, but in one form or another, they always return, just as new sprouts, new leaves, new greenery, and new growth emerge in the spring.

In this difficult time, let us be one another’s light and warmth, with the knowledge that rebirth follows death, and life will always return.

I wish everyone a beautiful season and a Happy, Healthy, Hopeful 2025.

“Out of darkness comes the dawning,

Out of winter comes the spring!

We sing and welcome back the Light,

Celebrate the year’s turning.”

18 Years Later, Proposed Change to IAU Planet Definition is Not the Answer

 

It isn’t, as the Celestron website one-sidedly states on its page about observing Pluto, a “fun holiday to celebrate.” What today is is the anniversary of a terrible day for science and knowledge, a day in which a very political vote was taken, which has done tremendous harm to science education and communication over the last 18 years.

“It” is the 18^th anniversary of the highly controversial vote by four percent of the IAU on a very flawed planet definition that excluded Pluto and all small planets that do not “clear their orbits,’ or, in other words, gravitationally dominate their orbits.

That definition is problematic because it puts primacy on a celestial object’s location rather than on its intrinsic properties. This runs contrary to the use of taxonomy and definitions in science. It was also a violation of the IAU’s own bylaws, which require a resolution to be put to the appropriate IAU committee before being put to the floor of a General Assembly. This was not done with the resolution adopted by the IAU in 2006.

The passage of 18 years without this travesty being corrected is a disservice to science and to all who are interested in it. During this time, New Horizons revealed Pluto to the world as a geologically active world with some complex processes seen elsewhere in the solar system only on Earth and Mars, yet the IAU and supporters of its definition have completely ignored this new information and doubled down on the “orbit clearing” requirement.

A baby born when the IAU vote took place is now old enough to vote. This means an entire generation has grown up with confusion and misinformation, as the media continue to present the IAU view as gospel truth rather than what it really is—one side in an ongoing debate.

And this year, scientist Jean Luc Margot, who was once a student of Mike Brown, the astronomer who unprofessionally brags that he “killed” Pluto, has proposed to remedy only part of the IAU definition to include exoplanets.

By stating that planets must orbit the Sun rather than a star, the IAU definition precludes any exoplanets from being classed as planets.

The problem with Margot’s proposal, which was presented at this year’s IAU General Assembly but not put to a vote, is that it goes out of its way to preserve orbit clearing, or as more accurately stated, gravitational dominance, as a criterion for planethood.

The proposal establishes a minimum mass for planet status that includes Mercury but does not include Pluto or Ceres.

The paper uses circular reasoning to justify this. It states, “Dynamical dominance looms large in planetary taxonomy because both Ceres and Pluto lost their status as planets once they were found to belong to a belt of small bodies.”

This is circular reasoning because it essentially says, Ceres and Pluto lost their status as planets not because of any change they underwent but because the IAU created a requirement of dynamical dominance that excluded them.

Contrary to media reports and this article, Pluto and Ceres never lost their status as planets. Instead, what happened is that the IAU stopped considering them planets. That doesn’t mean they stopped being planets or that we have to stop viewing them as planets. This is an important distinction.

Pluto and Ceres are far more than objects in belts. They are significantly different from the overwhelming majority of the objects in those belts because they are rounded by their own gravity, a state known as hydrostatic equilibrium. This is crucial because it is the threshold when active geology begins, making these objects significantly different than tiny, shapeless asteroids and comets, which are shaped only by their chemical bonds.

Classifying these objects merely as inhabitants of belts completely ignores their unique characteristics, shared with the terrestrial planets, and blurs the distinction between them and the majority of objects in these belts.

And again, it amounts to putting an object’s location above its intrinsic properties, which is a major problem.

It also precludes any rogue planets, which do not orbit any star but float freely in space, from being considered planets. Many of these objects have been found over the last 18 years. If they aren’t planets, then what are they?

If rogue planets were planets when they orbited their parent stars but stopped being planets when they were ejected from those orbits, then we again have the fallacy that an object’s location is put above its intrinsic properties. The same object can be a planet in one location but not a planet in another location.

The same is true for binary planet systems like Pluto-Charon, as neither object in such a binary “clears its orbit.” As for gravitational dominance in a binary system, that would require one of the companions to be significantly more massive than the other one, which is not the case for Pluto-Charon.

Adherents of the geophysical definition, which does not require orbit clearing or dynamical dominance for planethood, do not discount orbital dynamics or think they aren’t important. There is no reason why, in accordance with a study published in 2000, we cannot distinguish dynamically dominant planets from non-dynamically dominant planets via the use of subcategories.

With the geophysical definition, some planets are gravitationally dominant while some are not. This and its importance are acknowledged by placing these two types of planets in different subcategories. Dwarf planets are simply a subclass of planets that are not gravitationally dominant. This does not mean they aren’t planets at all, just that they are a different subclass of planets.

In fact, the IAU itself had a resolution in 2006 establishing dwarf planets as a subclass of planets. This resolution was voted down in a vote of 186-183, in a group with a membership of 10,000.

So dynamical dominance, to which Margot gives such priority, has this status due to 186 people out of 10,000, a difference of just three votes among the 424 IAU members present at that time.

This belies Margot’s claim that “A dispassionate analysis of the features of solar system bodies yielded a distinct group of eight bodies that have been historically referred to as planets.”

It isn’t a dispassionate analysis that yields this. It is a vote of 186-183 on a particular day in 2006, nine years before the New Horizons Pluto flyby.

Margot’s paper doesn’t miss the chance to push the fallacy that opposition to making gravitational dominance a criterion for planethood is based on emotion. In a highly patronizing and demeaning statement, it says, “Readers who are chagrined that smaller bodies are not recognized as planets should take comfort in the fact that these bodies are no less worthy of exploration.”

Readers and others who oppose keeping dynamical dominance as a criterion for planethood are not “chagrined.” We dissent and do so because we reject this premise and prefer the geophysical definition, which, while not discounting an object’s location, does not put primacy on that as a requirement for planethood.

In other words, our objection is scientific, not emotional.

Margot’s proposal was not put to a vote at this year’s IAU General Assembly but that could be done at its next one in 2027.

At the same time, most planetary scientists believe the IAU is the wrong venue for planet definition. Most IAU members are not planetary scientists but other types of astronomers. It makes no sense that those who study galaxies, black holes, cosmology, etc., should decide what a planet is. That decision should be made by a different organization, a group composed of planetary scientists, and should be done not in a vote but through evolution over time as more knowledge about these worlds becomes available.

Eighteen years is a long time for a bad definition to stick around, but at the same time, the passage of time does not make that definition any more “official” or “legitimate.” Those of us who oppose the IAU definition and recognize its harm to planetary science and public education will continue to fight it and advocate for a better definition. We will never give up, and we will never accept what we know is wrong. And in the long term, I strongly believe, we will prevail.

 

Why is Pluto not a planet? Planetary scientists say it is. Here’s why the IAU got it wrong

I Saw PLUTO From the CITY