She made a shooing motion. “Get to work!”

It takes three hours and the addition of fifty words to our shared vocabulary, but I am finally able to explain radiation—and its effects on biology—to Rocky.

“Thank,” he says in unusually low tones. Sad tones. “Now I know how my friends died.”

“Bad bad bad,” I say.

“Yes,” he chimes.

During the conversation, I learned the Blip-A has 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 spins very fast. 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 features on 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 100 percent. 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.