The Science Behind the “Cú Chulainn Was a Comet” Theory [Cosmic Cú Chulainn Part 2]

[Note: Read part 1 if you haven’t already! >> “Was the Irish Hero Cú Chulainn Actually a Comet?“]

Scientists can all agree on this much:

Something happened in the year 536 CE. 

Correction: 

Something or some things (plural).

Because the tree-rings don’t lie. 

Years that are exceptionally cold and/or low in rainfall result in tree-rings that are narrower than their chronological neighbors. 

And when you analyze the rings of thousands of trees from different time periods stretching back to 5400 BCE, as professor Mike Baillie famously did, patterns inevitably emerge.

And the BIG events stick out. 

One such event, according to Baillie’s tree-ring chronology, occurred in 536 CE.

Now, there are two schools of thought around what caused this so-called “Volcanic winter of 536.” 

Take a wild guess at what the first one is.

Ding. Ding. Ding. Michael Flatley.

Just kidding!

A volcano. 

Or, technically, the simultaneous eruptions of (at least) three volcanoes.

And while we don’t know exactly where these volcanoes are or were (more on that soon), sulfate deposits and a layer of tephra (volcanic ash) found in polar ice cores dated to 536 CE confirm that there was a big ole volcanic eruption that year.

Even scientists like Dallas Abbott who adhere to the second school of thought around the origins of the 536 event (i.e., that a comet was to blame) concede that volcanism played some sort of role. 

To quote Abbott:

“There was, I think, a small volcanic effect,” (source: NBC).

For Abbott, the more interesting stuff to come out of the polar ice dated to 536 CE wasn’t the sulfates or the volcanic dust (volcanism is pretty common on planet Earth, after all), it was the fossilized remains of tropical marine microorganisms.

Specifically, diatoms and silicoflagellates, for all you marine microorganism fans out there.

But wait a minute, what the heck were tropical microorganisms doing in the polar ice?

And here we break back down into our two opposing schools of thought…

Volcano or Comet: Which Caused the “Nuclear” Winter of 536?

One school argues that the aforementioned microorganisms were blasted up into the atmosphere courtesy of an underwater volcano and/or multiple underwater volcanoes, which were so powerful they vaporized seawater.

In addition to explaining the origin of the tropical surf in the polar turf (sorry, had to), the undersea volcanism theory also explains why the precise locations of those volcanoes remain so elusive.

We’re not looking for a Krakatoa here—unless, of course, it was Krakatoa that caused the 536 CE because I have heard that theory before but it doesn’t really account for how the fishermen’s stew—uh, fishermen’s microorganism mist?—found its way to Greenland’s ice sheet.

The other explanation for the presence of our fossilized friends in the ice is, of course, that a comet, or a chunk of a comet, smashed into the ocean, vaporizing seawater and sending up a plume of superheated…everything. 

Bolstering the impact hypothesis are claims that tin and nickel spherules of an extraterrestrial origin have been discovered in these ice core samples as well. 

Now, if the word “spherules” is setting off alarm bells that’s because you, like me, are probably a space-nerd and have been following along with physicist Avi Loeb’s story about how he’s allegedly recovered debris of an extrasolar origin from the ocean floor. 

Rather than insert myself haphazardly into the dialogue surrounding this breakthrough/controversy, I’m gonna circumvent it by saying:

There doesn’t seem to be a ton of evidence for a BIG, direct-hit comet or meteor in 536 CE. 

There’d be even more space stuff (that’s a scientific term) in the ice cores if that had been the case.

The pro-comet crowd circumvents this issue in one of two ways. 

One, by pointing out that a comet could have grazed the earth, meaning it came close enough to screw up the atmosphere with its dust trail but remained far away enough that there was no true impact.

Or two, by pointing to research out of Cardiff University that concluded even a collision with a comet of only half a kilometer in size could have global consequences.

A “Little” Comet Could Have Done the Job

No, it wouldn’t take a city-sized celestial object to cause a “global nuclear winter effect.” A mere skyscraper-sized object could do the cataclysmic job.

And if you’re thinking to yourself, “Hey, actually, a half a kilometer is pretty big,” consider the following:

• A) The nucleus of Halley’s Comet is estimated to be 15 kilometers at its longest and carries an atmosphere, or coma, that is around 100,000 kilometers across, and
• B) the ocean covers 361 million square kilometers of the earth’s surface.

So in the scheme of things, a hypothetical half-a-kilometer chunk of Halley’s Comet that fell to earth would be a drop in the ocean.

Only…it’d be traveling at around 3,600 kilometers per hour (or 2,237 miles per hour), which apparently isn’t even that fast for a comet, but it’s fast enough that upon impact it would throw up a plume that could darken skies the world over.

The underlying science is there—even though the evidence in this particular case is a bit lacking and Occam’s Razor tells us to peg the “volcanic winter of 536” on volcanism.

But what keeps pulling me back in (in regards to the cosmic Cu Chullain theory) is the 530 CE fly-by of Halley’s Comet. I mean, the comet had been in the cosmic neighborhood just a few years before the 536 event!

What’s more, Halley’s Comet is what’s known as a “rubble pile”—a celestial body made of a bunch of smaller pieces that are loosely held together.

And sometimes those pieces come apart.

In fact, Earth has a long history of being bombarded with material that’s been ejected from Halley’s Comet. We pass through it every year during the Eta Aquariids, an annual meteor shower that peaks during early May.

Now, surely, if an unusually huge chunk of comet had come crashing to earth in the spring of 536 CE, people would have noticed.

And someone would have written about it.

That’s what we’ll be exploring next, in Part 3.

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P.S. Hope you had a great Lughnasa!

Get the low-down on the August 1st feast over at the IrishMyths YouTube channel.

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Want to learn about the darker side of Irish mythology? Check out…

Samhain in Your Pocket

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Irish Monsters in Your Pocket

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Neon Druid: An Anthology of Urban Celtic Fantasy

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More the listenin’ type?

I recommend the audiobook Celtic Mythology: Tales of Gods, Goddesses, and Heroes by Philip Freeman (narrated by Gerard Doyle). Use my link to get 3 free months of Audible Premium Plus and you can listen to the full 7.5-hour audiobook for free.