THE SOUTHWORTH PLANETARIUM
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Founded January 1970
2021-2022: LXXXIII
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THE DAILY ASTRONOMER
Monday, February 14, 2022
Is Pluto About to Become a Planet Again?
Perhaps a Pointless Preface
We'll preface today's article by acknowledging that some people will insist that the article title is about three ballfields off base. They'll assert that Pluto has always been and will always continue to be a planet despite the lofty pronouncements of the International Astronomical Union. The International Astronomical Union, or IAU to its friends, is , these Pluto defenders assert, that global cabal of sinister intelligences that is vainly attempting to exert autonomous control over all of physical reality with its name-calling efforts. Others, of course, would argue that the IAU, founded only in 1919, has hardly been invested with such divine powers. Instead, it is akin to an innocuous accounting agency assigned with the daunting and tedious task of sorting p's from q's in a Universe that is expanding exponentially in our collective consciousness. Besides, one should become too toffee-nosed about names. You could confer "golf ball" status on Mercury, but good luck taking a nine-iron to it. Remember also that Shakespearean tenet about the Rose. Refer to it as "donkey's hindquarters" and wouldn't it smell as sweet? (Perhaps nobody would dare to find out.) However, the Pluto defenders retort -and I promise this is almost over- Pluto was designated a planet as soon as it was discovered in 1930 and there was no compelling reason to strip it of this coveted status. Au contraire, the IAU defenders it was -and still is- smaller than the planets. With a diameter of 2,360 km, it is even significantly smaller than Mercury, whose diameter is 4,879.4 km. It is also inclined at a 17 degree angle to the ecliptic, a far steeper inclination than the other planets. It also doesn't fit neatly into the solar system arrangement of four rocky bodies in front, four gas giant planets in the back, and, besides, it is meandering through a debris field of cometary nuclei and wasn't even able to incorporate any of this deep frozen flotsam into itself. Then again, unlike Uranus and Neptune, which were discovered by a naturalized Brit, a born Brit and a Frenchman,* Pluto was found by an American!** To add stinging insult to grievous injury, Pluto's demotion was decided in a European country!
So it goes.
A Heaping Teaspoon of History
Clyde Tombaugh (see second footnote) discovered Pluto in 1930 after an exhaustive year-long search with a blink comparitor. This device enables an observer to examine photos of the same swath of sky taken a few weeks apart. Because planets move relative to the starfield, any planet within a given starfield would appear to "jump" slightly from one frame to the next. Even though Pluto is so distant that such shifts are slight even over such a time frame, its position alteration was sufficient so as to produce a noticeable jump. Tombaugh embarked on this search while working at the Lowell Observatory, founded by that wealthy astronomical enthusiast Percival Lowell (1855-1916), who originally built his namesake observatory in 1894 to observe Martians. (We'll reserve that tale for another day.) Unaccountable perturbations in Neptune's orbit*** prompted a global search for a planet beyond it, hence the search that led to Pluto's discovery. Although it was designated a planet soon after its discovery, Pluto was soon found to have been too small to have been responsible for the unaccountable perturbations. All the same, it retained its planetary status until 2006, when, toward the end of the IAU's triennial General Assembly meeting in Prague, a group of 424 astronomers voted to alter the definition of planet and, consequently, demote Pluto. To be classified as a planet, a body has to revolve around the Sun, be rounded and also to have cleared its debris field. On this last requirement, Pluto was said to have failed. (As Pluto defenders point out, most of the other planets fail, as well, including Jupiter with its swarm of Trojan asteroids.) A lot of hearts were shattered that August of 2006, including mine. As CalTech researcher Mike Brown said after the vote, "Pluto is dead."
Well.
Ironically, while that small astronomical contingent was debating Pluto's fate in Prague, the New Horizons craft was already en route to what was then called the ninth planet. This ultra-super sonic craft was launched in 2005 and flew by Pluto in 2015. During this rapid reconnaissance mission, the New Horizons probe discovered evidence of geological activity on Pluto, a wholly unexpected finding. This discovery has led many planetary scientists, most of whom were chagrined at Pluto's demotion, to declare that its planet designation should be reinstated. They cite a 16th century definition of a planet as any body that is "geologically active." By that definition, Pluto, the asteroid Ceres, and many moons such as Titan, Enceladus and Io would earn the coveted planetary status.
As University of Central Florida planetary physicist Philip Metzger boldly said, "We think there's probably 150 planets in our solar system!" Metzger went on to say that the IAU, perhaps worried about having to assign planet designations on many of the bodies found beyond Pluto, set the number in snow-cold iron as eight.
Metzger explained that most planetary scientists now ignore the IAU definition because, by describing planets as special and rare, the organization is behaving "astrologically." Hot damn, ladies and gentlemen, if you want to watch astronomers turn a bright shade of vermillion, snort flame and then pound their pocket protectors into broadswords, just accuse them of behaving astrologically.
Of course, he has a point. Imagine how much our perceptions of the solar system would be enhanced if we described it as harboring 150 planets instead of just eight. Suddenly, our little niche around Sol would seem all the more dynamic, as dynamic as the Universe, itself. 150 planets! (Can you even begin to imagine the mnemonics?)
The IAU General Assembly is convening its next meeting this August in Korea. Will Pluto's planetary status be then reinstated? Will the planet number then rise from a paltry eight to a plethora of 150? Oh, but, of course!
*German-British astronomer William Herschel (1738-1822) inadvertently discovered Uranus in 1781. British astronomer John Couch Adams (1819-1892) and French astronomer Urbain Leverrier (1811-1877) independently discovered Neptune
**American astronomer Clyde Tombaugh (1906-1997) discovered Pluto in 1930. Now, heavens above, as far as the nationalist sentiment is concerned, one could sift through all the amber waves and not find anyone as quintessentially American as Clyde Tombaugh. Originally a farmer, he was driven westward by the Dust Bowl disaster to pursue his passion for astronomy and ended up as a young staffer with the Lowell Observatory. He literally leapt out of the "Grapes of Wrath" and landed broadsides onto a Rockwellian cover of the Saturday Evening Post. Although in later life he certainly could have given himself airs of Olympian aloofness, he was, by all accounts, ingratiatingly humble and remained unassumingly Earthbound throughout.
***Perturbations are "nudges" induced on planets by other planets and massive bodies. We recall that all massive objects exert a gravitational influence over every other massive object, the extent of which depends directly on the object's mass and inversely on the square of its separation distance. Astronomers had taken into account perturbations induced by the solar system objects then known. However, they had also observed perturbations that none of the known bodies could have induced, hence the search for the ninth planet.
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