Ice caps of Dune

And if there's ice, why isn't there at least SOME water around it?

I've spent way too much time thinking about this.

Yes, there’s plenty of sandworms, Duncans, and known-universe-spanning politics to obsess over, but something about these polar caps kept me up at night.

I can get behind having ice caps on a planet that’s primarily desert, but what keeps nagging at me is the lack of a wet, temperate zone between the freezing cold and the sizzling hot.

Why does Arrakis cosplay as a Song of Ice and Sand?

So I did some digging. I went through the Core Canon, the Dune Encyclopedia, and the Expanded Universe, and I think I found the in-universe answer(s).
(Even if actual science might not support it.)

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SPOILER WARNING: CONTENT FROM ALL DUNE BOOKS

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A ball of sand with some ice

While the original book has plenty of references to the north pole of Dune, I was shocked to discover that it’s never mentioned again in any of Frank Herbert's sequels. Not once.

Was it something he wanted to sweep under the rug? Maybe it just wasn’t relevant. Who knows?

The first time we get to see the ice is thanks to the Baron Harkonnen, who, of course, has an ornate globe with "polar caps [of] finest cloudmilk diamonds " in his study.

"I invite you to observe," the basso voice rumbled. "Observe closely, Piter, and you, too, Feyd-Rautha, my darling: from sixty degrees north to seventy degrees south—these exquisite ripples. Their coloring: does it not remind you of sweet caramels? And nowhere do you see blue of lakes or rivers or seas. And these lovely polar caps—so small. Could anyone mistake this place? Arrakis! Truly unique. A superb setting for a unique victory."
— Dune [1965]

And while you might not have a fancy globe, if you keep reading your copy of Dune past the appendices, you’ll eventually get to the map of the northern hemisphere and some cartographic notes.

From these we know that the ice sits in a "Polar Sink: 500 m. below Bled level."

Take a moment to imagine that: a massive bowl filled with what little ice Arrakis has to offer.

Wait, here’s a picture:

Lore-accurate Polar Sink in Dune: Spice Wars

And from the same notes, we also know that you can boldly walk with rhythm here because, despite a lack of open water, the humidity alone is too much for Shai-Hulud.

Wormline: indicating farthest north points where worms have been recorded. (Moisture, not cold, is determining factor.)
— Cartographic notes, Dune [1965]

So, coming back to my original question: if there’s a polar cap (even if it’s tiny), then why isn’t there any water around the ice?

Here’s why there isn’t any water around the ice

On Earth, our polar ice doesn't just abruptly stop - moving from north to south, we have tundra, taiga, temperate forests, and so on.

But Arrakis is different in at least three major ways.

1. Wormsign

The main difference, of course, is the sandworm.

Canonically, we know from Leto II (specifically from his ancestral memories) that the sandworm is not native to Arrakis. The planet now known as Dune was once similar to Earth, but then…

"The sandtrout," he repeated, "was introduced here from some other place. This was a wet planet then. They proliferated beyond the capability of existing ecosystems to deal with them. Sandtrout encysted the available free water, made this a desert planet . . . and they did it to survive. In a planet sufficiently dry, they could move to their sandworm phase."
— Children of Dune [1976]

The “haploid phase of the planet's giant sandworm” is indeed so prolific, pervasive, and thirsty that Fremen “had always known to plant predator fish in their water cisterns” to prevent the sandtrout from drinking all their water.

To put it bluntly, while large amounts of water can be deadly for sandworms, sandtrout suck up any water they can find.

Here’s Jessica and Yueh being puzzled by the effects of these creatures:

“But the mystery, Wellington, the real mystery is the wells that’ve been drilled up here in the sinks and basins. Have you read about those?”

“First a trickle, then nothing,” he said.

“But, Wellington, that’s the mystery. The water was there. It dries up. And never again is there water. Yet another hole nearby produces the same result: a trickle that stops. Has no one ever been curious about this?”
— Dune [1965]

Sandtrout will drink all the water - but it seems they can’t chew on ice.

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🔒 In the full article:

• How Arrakis’ orbit factors into things

• Why the ice isn’t used for irrigation

• Who has the coolest mansion (pun intended)

• What’s going on at the South Pole

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