Page 101 of Project Hail Mary

“Yes,”he chimes.

During the conversation, I learned theBlip-Ahas no radiation protection at all. And I know why Eridians never discovered radiation. It took a while to assemble all of this information, but here is what I know:

The Eridian homeworld is the first planet in the 40 Eridani system. Humans actually spotted it a while ago, obviously not knowing there was a whole civilization there. The catalog name for it is “40 Eridani A b.” That’s a mouthful. The planet’s actual name, from the Eridians, is a collection of chords like any other Eridian word. So I’ll just call it “Erid.”

Erid is extremely close to its star—about one-fifth as far as Earth is from our sun. Their “year” is a little over forty-two Earth days long.

It’s what we call a “super-Earth,” weighing in at eight and a half times Earth’s mass. It’s about twice Earth’s diameter, and a little over double the surface gravity. Also, it spinsveryfast. Absurdly fast. Their day is only 5.1 hours long.

That’s when things started to fall into place.

Planets get magnetic fields if the conditions are right. You have to have a molten-iron core, you have to be in the magnetic field of a star, and you have to be spinning. If all three of these things are true, you get a magnetic field. Earth has one—that’s why compasses work.

Erid has all of those featureson steroids. They are larger than Earth, with a larger iron core. They are close to their star, so they have a much stronger magnetic field powering their own field, and they spin extremely fast. All told, Erid’s magnetic field is at least twenty-five times as strong as Earth’s.

Plus, their atmosphere is extremely thick. Twenty-nine times as thick.

You know what strong magnetic fields and thick atmospheres are really good at? Radiation protection.

All life on Earth evolved to deal with radiation. Our DNA has error-correction built in because we’re constantly bombarded with radiation from the sun and from space in general. Our magnetic field and atmosphere protect us somewhat, but not 100 percent.

For Erid, it’s 100percent. Radiation just doesn’t get to the ground. Light doesn’t even get to the ground—that’s why they never evolved eyes. The surface is pitch-dark. How does a biosphere exist in total darkness? I haven’t asked Rocky how that works yet, but there is plenty of life deep in Earth’s oceans where the sun doesn’t shine. So it’s definitely doable.

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.