Eighty-one years ago today, on February 18, 1930, planet Pluto was discovered by 24-year-old Clyde Tombaugh, whose keen vision picked out a tiny object that moved from one position to another on two photographic plates taken six days apart the previous month.
Employed as a junior astronomer, Tombaugh, who at the time had only a high school education, had been working at the Lowell Observatory for a little over a year, taking large photographic images of various regions in the sky suspected to harbor the yet-undiscovered planet, then comparing plates of the same region taken within a few days of one another with a machine known as a blink comparator. The goal was to find an object that moved in respect to the numerous background stars on the plates, in an effort to find a predicted planet beyond Neptune.
As research for the book I am writing about Pluto, I am reading an account of the discovery written by Tombaugh himself in his 1980 publication Out of the Darkness: The Planet Pluto. The book was co-written by British astronomy writer Patrick Moore, who provided the chapters detailing the history of planet discovery beginning with William Herschel’s finding of Uranus.
Reading Tombaugh’s first hand account of his life at the Lowell Observatory and the process that led to the discovery of Pluto is fascinating. Very quickly, it becomes clear that the status of Pluto was not unquestioned until 1992, 1999, or 2006. In fact, the status of Pluto was questioned from almost the day of its discovery. Unable to resolve it into a disk even with their most powerful telescopes, astronomers at Lowell wondered whether Tombaugh had really found the moon of a larger planet. They understood almost immediately that Pluto was not the gas giant predicted by Percival Lowell, the observatory’s founder, who had conducted the search until he died in 1916. Tombaugh also notes arguments by some astronomers of the day who believed Pluto to be a large comet or asteroid, though he rejects both notions.
We commonly hear supporters of Pluto’s demotion argue that Pluto was believed universally to be a planet at the time of its discovery and that the 2006 demotion is based on new, better understanding of the solar system. Yet this clearly was not the case. Pluto was classed as a planet partly because of the strong insistence of the Lowell Observatory staff as a means of redeeming the reputation of their institution, which had lost credibility due to Percival Lowell’s determination to prove the existence of intelligent life on Mars.
Of course, this does not mean Pluto is not a planet. Similarly, those who argue that if Pluto were discovered today, it would never be considered a planet to begin with are also incorrect. Surprisingly, the degree of uncertainty and the amount of unknowns surrounding mysterious Pluto have not changed much in 81 years! The arguments from 1930 are eerily similar to those today, and this is true for both sides of the debate. It is therefore a better guess that had Pluto been discovered today, it’s classification would be determined largely by the discoverer and the institution where the discovery was made.
A little known fact about Eris, which was discovered in 2005, is that it was found by a team of three astronomers. While one member of that team, Mike Brown, actively opposes planet status for Eris and Pluto, another, Dr. David Rabinowitz, signed Dr. Alan Stern’s petition rejecting the IAU planet definition. Even the discoverers of Eris do not agree on what the object is.
Tombaugh, who died in 1997 three weeks before his 91st birthday, reports a fascinating statement by Dr. Harlow Shapley of the Harvard College Observatory, an astronomer famous for his part in the 1920 debate on the question of whether the universe contains just the Milky Way or numerous galaxies. Shapley ended up being wrong in his view that the entire universe is the Milky Way, but he showed unusual insight and forethought in his characterization of Pluto, questioning whether Pluto was the first in a new class of solar system objects and wondering whether similar bodies remained undiscovered in the outer solar system. He made these statements in 1930, only months after Pluto’s discovery!
The reality, therefore, is little has changed in this eight-decade debate. Astronomers on both sides essentially use the same arguments today as they did in 1930. There is no more scientific consensus today on just what Pluto is than there was then. Admittedly, we have learned more about Pluto’s size and composition, discovered three moons, learned that there never were perturbations in the orbits of Uranus and Neptune to begin with (the reason a planet beyond Neptune was sought), and most importantly, launched a spacecraft set to rendezvous with Pluto in only four more years.
Then, for the first time, Pluto will be forced to reveal its many secrets. The new data will tell us a lot about Pluto, but ultimately, that data will still be subject to interpretation. It likely won’t change the mind of Mike Brown, who says that the only way he could be persuaded to view Pluto as a planet is if New Horizons finds a giant billboard on the surface saying, “I’m a planet!” In other words, no matter how much we learn about this enigmatic world, those facts will still be filtered through subjective, limited, human minds, in some cases, minds that have been firmly made up in advance.
On a personal note, to coincide with my book and with this 81st anniversary of Pluto’s discovery, I have decided, based on the recommendation of good friends, to move this blog to a more professional blogging site. LiveJournal is wonderful, but it does not have many of the features that Blogger does. When I wrote my first entry on September 1, 2006, it was intended as a one-time thing, not as an ongoing blog. Obviously, that has changed as the fight for Pluto continues.
I have copied and pasted all blog entries from that first one into the new site, http://laurelsplutoblog.blogspot.com/ . Unfortunately, I was unable to figure out how to move the comments associated with each entry under the names of those who made them. However, all entries and responding comments will remain on the LiveJournal site. Since this site has been heavily publicized and is familiar to many readers, I will continue to post entries here as well, and http://laurele.livejournal.com/ will remain active as a duplicate site, and new entries will be posted there too. If any “techies” know how to link two sites so that visiting one automatically directs readers to another, please let me know, as I would love to link the two sites this way but have no clue how one might do this.
Special thanks to Stephanie Joy Smith for the suggestion of moving to Blogger. I hope readers enjoy this new site and that it facilitates better two-way communication.
Happy 81st anniversary of discovery to once and always planet Pluto! Time to celebrate!
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