When you write an epic science fiction novel, you ask a lot of questions. If you do your job right, you answer enough of them to leave your readers satisfied without dousing the fires of curiosity. Dune walks this fine line masterfully, building mystery upon mystery with each successive book, always leaving us with just enough fuel to keep the bonfires blazing.

No matter how many times I read, research, highlight quotes, or argue with Dune fans, some mysteries remain unsolved. That’s a good thing, especially after 50 years of wild fan theories and inquisitions. Below are a few of the biggest questions Frank Herbert left unanswered after his last Dune book. Spoilers are abound for all six of the original series!

What was the point of the Golden Path?

The Golden Path is the vision Paul had about the future of mankind, and how to save our wretched little souls. The Old Imperium was rotting with corruption, people were crippled by reliance on spice, and monopolies had a stranglehold on much of the empire. The solution was revealed by prescience, but walking that path wasn’t something Paul was prepared to subject everyone to.

Paul’s son, Leto II, wasn’t so hesitant. He had the same visions, but instead of turning aside, Leto charged ahead. He merged his physical body with the little makers and became a long-lived human-sandworm hybrid known as the Tyrant. Over the next 3,500 years, Leto ruled as God Emperor over all of humanity, controlling every aspect of their lives with absolute rigidity. Remember when you were a teenager, did something dumb, and got grounded? Imagine that, for everyone, for three-and-a-half millennia. Harsh.

On the surface, the Golden Path was intended to break mankind’s reliance upon a single source for anything, whether that be a messianic figure or a substance like spice. Space travel was forbidden, giving the entire species a serious case of cabin fever. As soon as the Tyrant was killed, people ran to their ships and didn’t look back. Humans spread across the universe and learned to deal with entirely new sets of problems, without the crutches of prescience or spice to hold their timid little hands. Golden Path achieved, right?

Maybe not. A quote from Bene Gesserit Mother Superior Alma Mavis Taraza in Heretics of Dune pushes the notion that the Golden Path’s purpose wasn’t the Scattering: “Surely, the Atreides worm had planned more than the simple survival of the species.” The Scattering wasn’t the endgame. It was another brick in the road, one step forward into a future so distant, only Leto II could see it. What else did that crazy worm guy plan for, and how did the technological and societal evolution gained in the Scattering prepare us to face it? Too bad Frank didn’t write Dune 12 so we could find out.

What did humans find in the Scattering?

Leto II’s vision of the Golden Path involved a few thousand years of oppression followed by an explosive expansion. After about 1,500 years of exploring the far reaches of space, some of those people came back, and boy did they have stories to tell. Some supremely twisted stuff went on out there, probing the limits of human physiology and morality with all the delicacy of a thrown sledgehammer. Genetically engineered semi-sentient human-cat hybrids? Dogs that function as massage chairs? That crosses a few lines, even in the Dune-iverse.

Believe it or not, this wasn’t the most terrifying part of the Scattering. Returning peoples mentioned an enemy waiting for them out in space. Leto II was afraid of some force looming in mankind’s future. Part of the Golden Path’s purpose was to prepare a shield against those hunters, whoever they may be. The exact nature of the threat is never pinned down, but it was there, it had “many faces”, and it was horrible.

A few decades of fan theorizing have settled on something less dramatic than we might imagine, but it’s still oh-so Dune. Instead of aliens or secret AI machines hiding in space, the great threat came from within, from the people of the Scattering. Human ability and human experimentation reached a point where groups of people became more monster than man (Tleilaxu, this means you). We passed our own limits and didn’t pause to consider what that meant. Once again, we are our own greatest threat. Thanks for the reminder, Frank.

Who are Daniel and Marty?

These two enigmas have the honor of starring in the last chapter of the last Frank Herbert-penned Dune book. They bust out all kinds of information from a remote garden abode, talking about gholas, Face Dancers, and events that occured throughout the universe. The nature of their existence hints at something outside the scope of Dune, something the novels have barely even touched upon.

Theories have been thrown around for decades as to who or what Daniel and Marty are. Some sort of unintended side-effect of the Scattering? Ancient aliens, says that TV dude with the crazy hair? Most fans agree they are some kind of new Face Dancers. Unlike other Face Dancers, though, they can absorb people’s personalities without actually becoming that person. Their core awareness stays the same, allowing them to pick up personas like we pick up take-out menus from Chinese restaurants, giving them extraordinary insight into Other Memory, possibly even approaching that of the Tyrant’s. Scary.

The newer books written by Brian Herbert and Kevin J. Anderson tie up the Daniel and Marty mystery by revealing them to be AI machines from the The Butlerian Jihad. That’s sort of a neat thing to imagine, but probably wasn’t what Frank Herbert intended, and it really doesn’t fit the facts or spirit of Dune. In an interview, Brian admitted this nugget didn’t come from any of his father’s notes, but was something he and his co-author came up with.

Finally, there is one other theory about the mystery duo: shortly before Chapterhouse: Dune was complete, Frank Herbert’s wife of 38 years, Beverly, passed away. Daniel and Marty could be Frank and Beverly saying goodbye to the readers and setting the series’ characters loose in a universe of endless possibility. The way Daniel and Marty sit in their garden, pruning the bushes, idly chatting about the events of the book, I’d like to think it’s true.

We’re celebrating the 50th anniversary of Dune throughout 2015. View the complete article series here.