Is there Mercury, the element, on Mercury, the planet? Uranium on Uranus? Plutonium on Pluto?

Short answer: Almost certainly, but it’s hard to say how much.

Long answer:  Just like how the crust of the earth has a bunch of other metals mixed into it in small quantities, I would find it hard to believe there is no elemental mercury on planet Mercury, it’s just not as abundant as other elements like iron and silicon. For example, this table tells me that Mercury is the 66th most abundant element in the Earth’s crust, with an abundance of 0.05 parts per million. Given that everything in the solar system formed from the gravitational collapse of the same cloud of gas, I wouldn’t be surprised if that number was similar for planet Mercury, and the same argument makes sense for uranium on Uranus. Unfortunately, the composition is only well known for these planets’ atmospheres, so there’s really no way to say how much of their eponymous element they contain.

Plutonium on Pluto is tricky. It has a fairly short half life so there won’t be much. It’s only made in nature one atom at a time when cosmic rays strike uranium. We use the same process on earth to produce plutonium, and I think it’s safe to guess that there’s probably more plutonium on board New Horizon’s generator than on Pluto.


With that out of the way, why do the planets and the elements seem to share names?



By me (Image:Uranium.gif) [CC BY-SA 2.5 (], via Wikimedia Commons

How did I not notice this before?

The naming convention for uranium, Uranus, plutonium and Pluto, is a modern invention. Scientists discovered all of them in the past 300 years, and the element uranium was named after the planet Uranus, which was discovered 8 years earlier, in 1781 by William Herschel. The same thing happened with Pluto – the (now dwarf) planet Pluto was discovered in 1930, and the element was named for the planet following its discovery in 1941. In fact, nine elements are named for bodies in the solar system!

I wouldn’t be surprised if one of those unnamed elements on the bottom of the Periodic Table gets the same treatment if another dwarf planet is discovered past Pluto, though we might be running out of Roman gods to pick names from.


Vulcan - By V.odchazel (Own work) [CC BY-SA 3.0 (], via Wikimedia Commons

Vulcan, Roman god of fire, god of metalworking, and god of getting snubbed when naming planets.

However, the naming convention of Mercury – both the element and planet – is far from a coincidence, and is a historical consequence of alchemy. Alchemy was basically the proto-science of antiquity, you know, the whole ‘earth/air/wind/water’ shtick? The alchemists had a diverse body of ideas about the world, and a lot of them also involved astrology and the seven classical planets: Mercury, Venus, Mars, Jupiter, Saturn, the Sun, and the Moon. Yes, the sun and moon were both planets, because “planet” is just Greek for “wanderer,” which emphasized the fact that these were the bodies in the sky that seemed to move freely among the other, fixed stars.

So what does astrology have to do with alchemy?

It turns out there were only seven metals known in antiquity – silver, gold, iron, copper, mercury, tin, and lead – and since there were conveniently seven known bodies in the heavens, each of the metals had an associated planet. Gold, for instance, was tied to the Sun, and silver, to the moon. The planet Mercury, being closest to the sun, is the fastest moving in the night sky, so it was associated with the metal quicksilver, which today we know as elemental Mercury. It’s no coincidence that they chose this planet to be the wing-footed messenger God [1][2].


Raphael [Public domain], via Wikimedia Commons

“You know, we’ve got seven Gods, seven metals, and seven wonders. How about seven days of the week? Sunday, Moonday, Saturnday…”

In fact, that list of metals I just gave is nearly an exhaustive list of elements on the Periodic Table whose symbols don’t match their names, because the symbols are holdovers from Latin and Greek. For example, how did silver end up with a symbol of Ag, and mercury with Hg? Well, the Latin for silver is argentum, while the Latin for Mercury is hydrargyrum, which translates to ‘water-silver’ or ‘quick-silver.’

It’s neat that ‘mercury’ is the only case where the planetary naming convention for the element survived, because otherwise instead of ‘gold wedding rings’ we might be walking around with ‘solar wedding rings.’ As one last fun fact, iron was paired with Mars, God of War, which is an amusing coincidence considering the planet’s rusty surface. Had the Latin naming convention survived for iron, we would talk about humanity progressing from the “Stone Age,” to the “Bronze Age,” into the “Martian Age” and then eventually to the “Space Age,” which just seems so backwards.




asked by /u/GeneralJohnSedgwick
image credit: Wikimedia Commons




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