Kuiper belt objects

Kuiper-belt objects (blue) with the sun and giant planets marked. Distances, but not sizes, are to scale.

10 April 2023

The Kuiper belt is the region of the solar system beyond Neptune ranging from 30 to 50 astronomical units (AU, an AU is some 93 million miles, or 150 million kilometers, equivalent to the distance from the Earth to the Sun.) The Kuiper belt is the region of origin for the short-period comets, i.e., those that take less than 200 years to orbit the sun. The belt is named for astronomer Gerard Kuiper.

In 1943, astronomer Kenneth Edgeworth suggested that material from the primordial solar system might exist in the region beyond Neptune and such material might occasionally wander into the inner solar system. In 1951, Gerard Kuiper made a similar postulation, but believed that such primordial trans-Neptunian material no longer existed because Pluto, which he assumed was the size of Earth, would have cleared it out. Neither Edgeworth nor Kuiper provided any evidence for the existence of such a belt of material, only postulation. As a result, the name is something of a misnomer, as neither Edgeworth nor Kuiper were firm in their suggestions. And if anyone should get credit for the idea it should be Edgeworth. As a result, the region is sometimes referred to as the Edgeworth-Kuiper belt.

Kuiper belt was coined by three astronomers in 1988. Martin Duncan, Thomas Quinn, and Scott Tremaine created a mathematical model to characterize the behavior of the short-period comets and determined that they originated in a region beyond Neptune. The name first appears in an article in the journal Science on 18 March 1988, prior to the formal publication of their paper:

Ruling out the Oort cloud, the modelers next tried a belt of low-inclination comets near Neptune’s orbit. The idea dates back to a suggestion by Gerard Kuiper in 1951 that it would only be natural to find some debris from the formation of the solar system beyond Neptune.

[…]

There are hurdles yet for the “Kuiper belt.” One is finding a means of bringing comets from the belt into Neptune-crossing orbits, which is where they were at the beginning of the simulation.

The formal article by the trio was published in the Astrophysical Journal on 15 May 1988:

In this Letter we present the key results of a set of extensive numerical simulations of gravitational scattering of comets by the giant planets, designed to determine whether the most likely source of the SP [short-period] comets is the Oort cloud or the Kuiper belt.

[…]

To summarize, the SP comets cannot be produced by planetary scattering of comets from the Oort cloud, or any other isotropic parent population. A comet belt (the "Kuiper belt”) containing a fraction of an Earth mass and located in the outer parts of the solar system is plausible on cosmogonic grounds and appears to offer the most promising source for the SP comets, although the mechanisms by which the comets are supplied to planet-crossing orbits remains unclear.

Besides the comets, the Kuiper belt is home to at least eight larger objects that qualify for the status of dwarf planet. There are two other known dwarf planets in the solar system: Ceres in the asteroid belt and Sedna (see below), which orbits at a distance beyond the Kuiper belt and is the farthest known solar system object.

Pluto (see Pluto), discovered in 1930, is the most well-known of the Kuiper-belt objects.

Quaoar was the second Kuiper-belt object to be discovered. That was on 4 June 2002 by astronomers Chad Trujillo and Mike Brown. It is named for the creator spirit of the Tongva people, an Indigenous people of Southern California. Quaoar’s moon is Weywot, named for the deity’s son.

Sedna was discovered by Brown, Trujillo, and David Rabinowitz on 14 November 2003. It is the solar system object the farthest from the sun, that we know of. Technically, it is not a Kuiper belt object as it orbits beyond the belt but too close to be in the Oort cloud, ranging from 84 to 937 AU. In Inuit mythology, Sedna is the goddess of the sea and marine animals and the ruler of the Inuit underworld. Brown and his team suggested the name for her because of the planet’s cold temperature due to its distance from the sun.

Orcus was discovered on 17 February 2004 by Brown, Trujillo, and Rabinowitz and named for one of the Etruscan and Roman gods of the underworld, and in later Roman mythology he was conflated with Pluto.

Salacia probably qualifies as a dwarf planet, but too little is known about it to be sure. It was discovered by Henry Roe, Mike Brown, and Kristina Barkume on 22 September 2004. It was officially named in 2011 after a Roman goddess of the sea, the consort of Neptune.

Haumea has a contentious discovery, with two teams claiming that honor in 2004. Brown, Rabinowitz, and Trujillo discovered the planet on 28 December 2004 on images taken on 6 May 2004 and published the discovery online on 20 July 2005. A Spanish team, led by José Luis Ortiz Moreno found the planet on images taken in March 2003 and published the discovery on 27 July 2005. It later was revealed that the Spanish team had accessed Brown’s telescope observation logs prior to his announcement. Ortiz admitted to looking at Brown’s logs but only to search for images confirming his own discovery. In its naming announcement, the International Astronomical Union (IAU), which is responsible for officially naming celestial objects, did not credit either team, but the name chosen was one suggested by Brown. Haumea is the Hawaiian goddess of childbirth and fertility.

Eris is another one credited to Brown, Trujillo, and Rabinowitz, this time on 5 January 2005. The name Eris was proposed by Brown and accepted by the IAU on 14 September 2006. Eris is the Greek goddess of discord and strife. The planet Eris has a moon, named Dysnomia, after the daughter of the goddess Eris.

Makemake is yet another discovered by Brown, this time on 31 March 2005. Makemake is the Rapa Nui creator and fertility deity. The name was suggested by Brown and adopted by the International Astronomical Union (IAU) in July 2008. Brown said of the name:

We consider the naming of objects in the Solar System very carefully. Makemake's surface is covered with large amounts of almost pure methane ice, which is scientifically fascinating, but really not easily relatable to terrestrial mythology. Suddenly, it dawned on me: the island of Rapa Nui. Why hadn't I thought of this before? I wasn't familiar with the mythology of the island so I had to look it up, and I found Makemake, the chief god, the creator of humanity, and the god of fertility. I am partial to fertility gods. Eris, Makemake, and 2003 EL61 [i.e., Haumea] were all discovered as my wife was 3-6 months pregnant with our daughter. I have the distinct memory of feeling this fertile abundance pouring out of the entire Universe. Makemake was part of that.

Gonggong was discovered on 17 July 2007 by Megan Schwamb, a graduate student of Mike Brown. It was named after a Chinese water god in an online poll run by the discovery team. The god Gonggong is often depicted as a red-headed human with a snake’s body. He is attended to by a snake-monster named Xiangliu, for whom the planet Gonggong’s moon is named.

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Sources:

Duncan, Martin, Thomas Quinn, and Scott Tremaine. “The Origin of Short Period Comets.” The Astrophysical Journal, 328, 15 May 1988, L69, L72. SAO/NASA Astrophysics Data System.

Edgeworth, Kenneth E. “The Evolution of Our Planetary System.” Journal of the British Astronomical Association, 53.6, July 1943, 181–88. SAO/NASA Astrophysics Data System.

International Astronomical Union (IAU). “Fourth Dwarf Planet Named Makemake” (Press Release IAU0806), 19 July 2008.

———. “IAU Names Dwarf Planet Eris” (Press Release IAU0605), 14 September 2006.

———. “IAU Names Fifth Dwarf Planet Haumea.” (Press Release IAU 08070), 17 September 2008.

Kerr, Richard A. “Comet Source: Close to Neptune.” Science, 239, 18 March 1988, 1372/2–1373/1. ProQuest.

Kuiper, Gerard P. “On the Origin of the Solar System.” In J.A. Hynek, ed. Astrophysics: A Topical Symposium. New York: McGraw-Hill, 1951, 357–424 at 400–403. Archive.org.

Minor Planet Center. Minor Planet Circular, 20 November 2002, 47170. (PDF)

———. Minor Planet Circular, 26 November 2004, 53177. (PDF)

———. Minor Planet Circular, 6 November 2016, 73984. (PDF)

———. Minor Planet Circular, 5 February 2020, 121135. (PDF)

Oxford English Dictionary, third edition, September 2007, s.v. Kuiper belt, n.

Image credit: WilyD, 2015. Wikimedia Commons. Licensed under a  Creative Commons Attribution-Share Alike 3.0 Unported license.

cadmium

Two blocks of cadmium, one an oblong bar and the other a cube

7 April 2023

Cadmium is a soft, silvery-white metal with atomic number 48 and symbol Cd. Its etymology is quite straightforward, coming from the Latin cadmia (zinc oxide) as it was first isolated from zinc oxide sold in German pharmacies. Cadmium is often found mixed with zinc in ores.

It was so dubbed by its discoverer, Friedrich Stromeyer in 1817:

Dieses sind die bis jetzt über dieses Metall von mir gemachten Erfahrungen. So unvollkommen dieselben auch noch sind, so trage ich hiernach doch kein Bedenken dieses Metall für ein wirklich neues und von allen übrigen wesentlich verschicdenes Metall, zu, halten. Da ich dasselbe zuerst in den Zinkoxyden aufgefunden habe, so nehme ich hiervon Anlafs es Kadmium zu nennen.

(These are the experiences I have had with this metal so far. However imperfect they may still be, I have no hesitation in considering this metal to be a really new metal that is essentially different from all the others. As I first found it in the oxides of zinc, I take the occasion to call it cadmium.)

The name quickly became established in most European languages.

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Sources:

Miśkowiec, Pawel. “Name Game: The Naming History of the Chemical Elements: Part 2—Turbulent Nineteenth Century.” Foundations of Chemistry, 8 December 2022 (online).

Oxford English Dictionary, second edition, 1989, s.v. cadmium, n., cadmia, n.

Stromeyer, Friedrich. “Ein Neu Entdecktes Metall und Analyse Eines Neuen Minerals.” Journal für Chemie und Physik. 21, 1817, 303. HathiTrust Digital Archive.

Photo credit: Heinrich Pniok, 2010. Wikimedia Commons. Licensed under a Creative Commons Attribution-NonCommercial-NonDerivative 3.0 (US) License.

brass tacks

5 April 2023

The phrase get down to brass tacks means to address the heart of an issue, to deal with the basic facts of a matter. The phrase is an Americanism, dating to the mid nineteenth century, but the underlying metaphor is unknown. There are many speculative explanations as to what the brass tacks signify, but there is no evidence to support any of them. There is, however, an earlier, shorter, version of the phrase that reads simply, down to the brass.

This earlier version is first recorded in a Louisiana newspaper editorial from 30 June 1853:

It often happens that meetings of this kind are holden [sic], at which the stereotype phrase “I move, Mr. Chairman, that Mr. — be appointed,” falls thick and fast on the President’s ears until the assessment roll is nearly exhausted, and enough delegates are appointed to crowd a Mississippi steam “down to the brass,” after which the meeting breaks up under the flattering delusion that the Parish has secured an efficient representation in the forthcoming Convention. On half of those appointed never hear of it, and the other half trust to the probabilities of some going from among so many, and the result is that no one attends.

We see it again in the Wisconsin State Journal of 21 April 1854:

There is one thing we wish the Argus to do. Come right down to the brass—to use an ordinary phrase—and say whether it considers the late legislature particularly eminent for economy and public spirit. Does it believe that it did its duty faithfully to the State?

And in another Madison, Wisconsin paper on 13 September 1856:

But, now, after all, Mr. Journal—Suppose we come right down to the brass, and admit, just to please you, all you claim, what then? Would that show that your principles were more just and correct, or that ours were less so? Does that show that your principles are too good to be discussed?

The brass tacks version appears by 21 January 1863. Here is the earliest known example, a Houston, Texas newspaper editorial titled “Brass Tacks” about inflation affecting Confederate currency:

No one we apprehend will accuse Washington of a want of patriotism, unless he have some other object than the truth in view. For doing what he did, we, with others, accuse people of selfishness, but we should  in justice add that when you come down to “brass tacks”—if we may be allowed the expression—everybody is governed by selfishness, and if the merchant, who refuses to take what is due him at 50 cents on the dollar, is selfish, the debtor who insists on doing so is just as selfish.

Perhaps the most common speculative explanation is that it is Cockney rhyming slang for “facts.” The phrase is used in Cockney rhyming slang, but that isn’t its origin. For one thing, the phrase is American in origin. For another, uses that rhyme brass tacks with facts don’t start appearing until the twentieth century. Nor does this explanation account for the earlier use of the shorter down to the brass.

Other speculative origins are plausible but lack evidence connecting them to the phrase. One is that brass tacks were placed on store counters marking out a yard so that purchases of cloth and other products could be measured. Another is that the brass refers to upholstery foundations and fasteners. Yet another is that the brass refers to coffin nails, representing the final undeniable truth.

In the end, we just don’t know how the phrase came about, and we probably never will.

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Sources:

“Brass Tacks.” Tri-Weekly Telegraph (Houston, Texas), 21 January 1863, 2/1. Readex: America’s Historical Newspapers.

Green’s Dictionary of Slang, 2023, s.v. brass tacks, n.

“Legislative Extravagance.” Wisconsin State Journal (Madison, Wisconsin), 21 April 1854, 2/1. NewspaperArchive.com.

Oxford English Dictionary, second edition, 1989, s.v. brass, n.

“’Pump’ Carpenter.” Weekly Wisconsin Patriot (Madison), 13 September 1856, 1/3. Readex: America’s Historical Newspapers.

“Something for the Whigs.” Planter’s Banner (Franklin, Louisiana), 30 June 1853, 2/3. NewspaperArchive.com.

Tréguer, Pascal. “‘Come (Right) Down to the Brass’ | ‘Come Down to Brass Tacks.’” Wordhistories.net, 5 April 2019.

———. “A Hypothesis as to the Origin of ‘to Get Down to Brass Tacks.’” Wordhistories.net, 6 April 2019.

Image credit: John Dalton, 2006. Wikimedia Commons. Licensed under a Creative Commons Attribution-Share Alike 3.0 Unported license.

asteroid / Ceres / Pallas / Juno / Vesta

The asteroid Ceres

3 April 2023

An asteroid is a small, rocky or metallic body that orbits a star. In our solar system, asteroids are concentrated in a belt between Mars and Jupiter. The name was coined by astronomer William Herschel in 1802 from Greek and Latin roots: ἀστήρ (star) + -oides / -οειδής (-oid, resembling). So, an asteroid resembles a star, and indeed, with the telescopes of the early nineteenth century, astronomers could not discern any asteroid’s disc, as they could with a planet. So, while they appeared to be point sources to nineteenth-century astronomers, like stars, asteroids moved like planets across the background of stars.

Herschel proposed the name asteroid in a 6 May 1802 paper given at the Royal Society:

With this intention, therefore, I have endeavoured to find out a leading feature in the character of these new stars; and, as planets are distinguished from the fixed stars by their visible change of situation in the zodiac, and comets by their remarkable comas, so the quality in which these objects differ considerably from the two former species, is that they resemble small stars so much as hardly to be distinguished from them, even by very good telescopes. It is owing to this very circumstance, that they have been so long concealed from our view. From this, their asteroidical appearance, if I may use that expression, therefore, I shall take my name, and call them Asteroids; reserving to myself, however, the liberty of changing that name, if another, more expressive of their nature, should occur. These bodies will hold a middle rank, between the two species that were known before; so that planets, asteroids, and comets, will in future comprehend all the primary celestial bodies that either remain with, or only occasionally visit, our solar system.

I shall now give a definition of our new astronomical term, which ought to be considerably extensive, that it may not only take in the asteroid Ceres, as well as the asteroid Pallas, but that any other asteroid which may hereafter be discovered, let its motion or situation be whatever it may, shall also be fully delineated by it. This will stand as follows.

Asteroids are celestial bodies, which move in orbits either of little or of considerable excentricity [sic] round the sun, the plane of which may be inclined to the ecliptic in any angle whatsoever. Their motion may be direct, or retrograde; and they may or may not have considerable atmospheres, very small comas, disks, or nuclei.

As mentioned, most of the asteroids in our solar system orbit between Mars and Jupiter, and the term asteroid belt has been in use since at least 1867. That term appears in Jacob Ennis’s book The Origin of the Stars, published that year:

SECTION XXXIII.

Asteroids, Meteorites, and Comets.

Asteroids.

The orbits of the asteroids are generally interlinked; that is, they are so near together that the perihelion distance of an outer asteroid is nearer the sun than the aphelion distance of an inner one. They are probably a few hundred in number, about eighty having been discovered in the last twenty years, and they are included within a belt about 150,000,000 miles broad. In view of the dimensions of the rings which formed the planets as given in the thirtieth section, we cannot suppose that a single ring occupied all the space within the asteroid belt.

Asteroid belt is the term generally used in scientific literature, but one often finds asteroid field used in the realm of science fiction. This term dates to at least 1942, when it appears in Raymond Jones’s short story Starting Point:

Jack put in a call to the nearest safety monitoring ship.

“Yes, the Asteroid Kid finally took off, and what a cockeyed curve he’s running. You better pull him out and disqualify him before he kills himself.

“The crazy kid, instead of curving up over the asteroid field, he’s smashing through the thick of them at nearly four gees. He’ll bust a gut even if he don’t hit another asteroid.”

In science fiction, asteroid fields are often depicted as a danger to space navigation, but in reality that’s not the case, at least not in our solar system. For while there are around a million asteroids that we know of, space is what astronomers call “very big,” and the distance between any two asteroids is vast. The chance of a spacecraft hitting one by accident is very low.

Of the million or so asteroids, a few dozen have common names. The first four asteroids to be discovered were Ceres, Pallas, Juno, and Vesta. These were discovered in the opening years of the nineteenth century, with many more to follow in subsequent decades.

Ceres is the largest of the asteroids and the first to be discovered, by Giuseppe Piazzi in January 1801. Named by Piazzi for the Roman goddess of agriculture, it was classified at first as a planet, but it was later downgraded to asteroid after others of its type started to be found. Today, it is officially designated as a dwarf planet by the International Astronomical Union. The name appears in English by the end of 1801, as recorded by the Hampshire Chronicle of 28 December:

Letters from Berlin state, that the celebrated astronomer Bode, has received from M. De Piazzi, of Palermo, two letters, in which he concurs with M. Bode, that the star discovered on the 13th of January last, is a planet. The German astronomers propose to call it Juno, in analogy with the names of the other Planets, but M. De Piazzi wishes it to be called Ceres Fernandia, in allusion to Sicily, the ancient dominion of Ceres, and to the reigning monarch.

The next to be discovered was Pallas, found by Heinrich Wilhelm Matthäus Olbers on 28 March 1802. In Greek mythology, Pallas was the foster-sister of Athena, and Athena accidentally killed her in mock combat. The two were closely associated, and Athena is often referred to as Pallas Athena—the Palladium was a Trojan statue of Athena that protected the city, until it was stolen by Odysseus and Diomedes, enabling Troy to be sacked. The first mention of the asteroid’s name in English that I’m aware of is by Herschel in the above quotation.

Juno would be next, discovered on 1 September 1804 by Karl Ludwig Harding. Again, the first mention of the name in English would be by Herschel, in a paper given before the Royal Society on 6 December 1804:

Mr. Bode's stars 19, 25 and 27 Ceti are marked 7m, and by comparing the asteroid, which I find is to be called Juno, with these stars, it has the appearance of a small one of the 8th magnitude.

With regard to the diameter of Juno, which name it will at present be convenient to use, leaving it still to astronomers to adopt any other they may fix upon, it is evident that, had it been half a second, I must have instantly perceived a visible disk. Such a diameter, when I saw it magnified 879,4 times, would have appeared to me under an angle of 7’ 19",7, one half of which, it will be allowed, from the experiments that have been detailed, could not have escaped my notice.

Juno, of course, is the Roman name for the goddess married to Jupiter.

The second largest asteroid would be the fourth to be discovered, this time by Olbers on 29 March 1807. Dubbed Vesta, after the Roman goddess of hearth and home, the first English mention of the name is in a translation of a letter by John Jerome Schroeter published by the Royal Society on 28 May 1807. The German original is from 12 May:

At our very first observations with magnifying powers of 150 and 300 applied to the excellent new 15-feet reflector, we found the planet Vesta without any appearance of a disc, merely as a point like a fixed star with an intense, radiating light, and exactly of the same appearance as that of any fixed star of the sixth magnitude. In the same manner we both afterwards saw this planet several times with our naked eyes, when the sky was clear, and when it was surrounded by smaller invisible stars, which precluded all possibility of mistaking it for another. This proves how very like the intense light of this planet is to that of a fixed star.

As the observations and measurements of Ceres, Pallas, and Juno, were made with the same eye-glasses but with the 13-feet reflector, we soon after compared the planet Vesta with the same glasses of 136 and 288 times magnifying power in the 13-feet reflector. In both these telescopes its image was, without the least difference, that of a fixed star of the 6th magnitude with an intense radiating light; so that this new planet may with the greatest propriety be called an asteroid.

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Sources:

Ennis, Jacob. The Origin of the Stars. New York: D. Appleton, 1867, 292. HathiTrust Digital Archive.

Herschel, William. “Experiments for Ascertaining How Far Telescopes Will Enable Us to Determine Very Small Angles, and to Distinguish the Real from Spurious Diameters of Celestial and Terrestrial Objects” (6 December 1804). Philosophical Transactions of the Royal Society, 95, 58. HathiTrust Digital Archive.

———. “Observations on the Two Lately Discovered Celestial Bodies” (6 May 1802). Philosophical Transactions of the Royal Society, 92, 228–229. Hathitrust Digital Archive.

Jones, Raymond F. “Starting Point.” Astounding Science Fiction, 28.6, February 1942, 75/2. HathiTrust Digital Archive.

“London.” Hampshire Chronicle (England), 28 December 1801, 2/3. Gale Primary Sources: British Library Newspapers.

Oxford English Dictionary, second edition, 1989, s.v. asteroid, adj. and n., Vesta, n.

Sheidlower, Jesse, ed. Historical Dictionary of Science Fiction, 8 January 2021, s.v. asteroid field, n.

Schroeter, John Jerome. “Observations and Measurements of the Planet Vesta” (28 May 1807). Philosophical Transactions of the Royal Society, 97, 245. HathiTrust Digital Archive.

Image credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA / Justin Cowart, 2015. Wikimedia Commons. Public domain image.

plutonium

A sphere of plutonium partially surrounded by tungsten-carbide blocks to reflect neutrons back into the sphere; used in 1945 at Los Alamos in experiments to test the critical mass of the element

31 March 2023

Plutonium, element 94, symbol Pu, was first produced in December 1940 at the University of California, Berkeley by a team led by chemist Glenn Seaborg. Plutonium is readily fissionable and along with Uranium-235 is used as the fuel in nuclear reactors and weapons. The element is named for the planet Pluto (now officially defined as a dwarf planet), following the pattern set by uranium and neptunium. Uranium, neptunium, and plutonium have atomic numbers 92, 93, and 94, the same order as the planets Uranus, Neptune, and Pluto.

The initial experiments with and discovery of plutonium were conducted at the University of California, Berkeley, but the discovery was not made public until World War II had ended. Further experimentation and production of plutonium was done under the Manhattan Project. The first recorded use of plutonium is by Seaborg and Arthur Wahl in a then-classified 1942 government report:

Naming the Elements

Since formulae are confusing when the symbols "93” and “94" are used, we have decided to use symbols of the conventional chemical type to designate these elements. Following McMillan, who has suggested the name neptunium (after Neptune, the first planet beyond Uranus) for element 93, we suggest plutonium (after Pluto, the second planet beyond Uranus) for element 94. The corresponding chemical symbols would be Np and Pu.

Public disclosure of the discovery of plutonium came in the wake of the atomic bombings of Hiroshima and Nagasaki. An Associated Press article from 11 August 1945 reads:

The two new elements are neptunium, No. 93, and plutonium, No. 94, which have been added to the previously known 92 varieties of matter. The two are derived from Uranium.

Production of the new elements was disclosed in a scientific review, released by the War Department, of experiments leading up to final production of the atomic bombs.

In 2001, Seaborg would recall how his team came up with the name:

At first we gave the new element no name, simply referring to it as 94. But even that revealed too much for casual conversations around the Faculty Club or the lab, so we adopted the code name of “copper” for element 94 and “silver” for 93. This code worked well enough through 1941, until some experiments required the use of some real copper, which we then referred to as “honest-to-God copper.”

A year after its discovery we finally named our new element. It was so difficult to make, from such rare materials, that we thought it would be the heaviest element ever formed. So we considered names like extremium and ultimium. Fortunately, we were spared the inevitable embarrassment that one courts when proclaiming a discovery to the ultimate in any field by deciding to follow the nomenclatural precedents of the two prior elements.

A new planet had been discovered in 1781 and, like the rest of the planets, named for a Greek or Roman deity—Uranus. A scientist who discovered a heavy new element eight years later named it after the planet: uranium. The planet Neptune was discovered in 1846, so Ed McMillan followed this precedent and named element 93 neptunium. Conveniently for us, the final planet, Pluto, had been discovered in 1930. We briefly considered the form plutium, but plutonium seemed more euphonous. Each element has a one- or two-letter abbreviation. Following the standard rules, this symbol should be Pl, but we chose Pu instead. We thought our little joke might come under criticism, but it was hardly noticed.

In The Making of the Atomic Bomb, Richard Rhodes writes of the symbolism that we “would name element 94 for Pluto, the ninth planet outward from the sun, discovered in 1930 and named for the Greek god of the underworld, a god of earth’s fertility but also the god of the dead.” Any such symbolic meaning, however, was entirely coincidental; I was unfamiliar with the god or why the planet was named for him. We were simply following the planetary precedent.

There is an earlier elemental usage of plutonium, however. Starting in 1816, naturalist Edward David Clarke used plutonium as a name for the element barium, which had already been discovered and named by Humphry Davy. Clarke’s attempt to rename the element never caught on. But one may run across this use of plutonium when engaged in historical research of early nineteenth-century chemistry.

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Sources:

Associated Press. “2 Elements Discovered by Atomic Work” (11 August 1945). Atlanta Constitution, 12 August 1945, 11-A. ProQuest Historical Newspapers.

Oxford English Dictionary, third edition, September 2006, s.v. plutonium, n.2.

Seaborg, Glenn T., with Eric Seaborg. Adventures in the Atomic Age. New York: Farrar, Straus and Giroux, 2001, 72. Archive.org.

Seaborg, Glenn T. and Arthur C. Wahl. The Chemical Properties of Elements 94 and 93. US Atomic Energy Commission, AECD-1829, 19 March 1942. HathiTrust Digital Archive. [The version at HathiTrust is a later reprint of the original, published in 1947 or later, when the report was declassified. It contains a note to a 1946 report, so it has been altered from the original in some respects, but the text quoted here would seem to have come unaltered from the original.]

Photo credit: Los Alamos National Laboratory, 1945. Wikimedia Commons. Unless otherwise indicated, this information has been authored by an employee or employees of the Los Alamos National Security, LLC (LANS), operator of the Los Alamos National Laboratory under Contract No. DE-AC52-06NA25396 with the U.S. Department of Energy. The U.S. Government has rights to use, reproduce, and distribute this information. The public may copy and use this information without charge, provided that this Notice and any statement of authorship are reproduced on all copies. Neither the Government nor LANS makes any warranty, express or implied, or assumes any liability or responsibility for the use of this information.