Eridians are extremely susceptible to radiation, and they never even knew it existed.

The next conversation took another hour and added a few dozen more words to the vocabulary.

Eridians invented space travel quite a while ago. And with their unparalleled materials technology (xenonite) they actually made a space elevator. Basically a cable leading from Erid’s equator up to the synchronous orbit with a counterweight. They literally take elevators to get into orbit. We could do that on Earth if we knew how to make xenonite.

Thing is, they never left orbit. There was no reason to. Erid has no moon. Planets that close to a star rarely do. The gravitation tidal forces tend to rip would-be moons out of orbit. Rocky and his crew were the first Eridians to leave orbit at all.

So they never found out that Erid’s magnetic field, which extends well beyond its synchronous orbit, had been protecting them all that time.

One mystery remained.

“Why did I not die, question?” Rocky asks.

“I don’t know,” I say. “What’s different? What do you do that the rest of your crew didn’t do?”

“I fix things. My job is to repair broken things, create needed things, and keep engines running.”

Sounds like an engineer to me. “Where were you most of the time?”

“I have room in ship. Workshop.”

I’m getting an idea. “Where is workshop?”

“In back of ship near engines.”

That’s a sensible place to put your ship’s engineer. Near the engines, where things are most likely to need maintenance or repairs.

“Where does your ship store Astrophage fuel?”

He waves a hand generally around the rear of the ship. “Many many containers of Astrophage. All in back of ship. Close to engines. Easy to refuel.”

And there’s the answer.

I sigh. He’s not going to like this. The solution was so simple. They just didn’t know it. They didn’t even know the problem until it was too late.

“Astrophage stops radiation,” I say. “You were surrounded by Astrophage most of the time. Your crewmates weren’t. So the radiation got to them.”

He doesn’t respond. He needs a moment to let that sink in.

“Understand,” he says in low notes. “Thank. I now know why I not die.”

I try to imagine the desperation of his people. With a space program far behind Earth’s, no knowledge of what’s outside, and still making an interstellar ship in a bid to save their race.

No different from my situation, I guess. I just have a little more technology.

“Radiation is here too,” I say. “Stay in your workshop as much as you can.”

“Yes.”

“Bring Astrophage to this tunnel and put it on the wall.”

“Yes. You do same.”

“I don’t need to.”

“Why not, question?”