But I didn’t care about that dark-red color. I wanted to see a bright-yellow flash. That would be the Petrova frequency that Astrophage spit out to move around. If any of my Astrophages moved even the tiniest amount, I’d see a very obvious yellow flash.

But it never came. Nothing happened. Nothing at all. Usually, I’d see a jerky motion from at least one of them every few seconds. But now there was nothing.

“So,” I said. “You little brats have settled down, eh?”

Light. Whatever their navigation system was, it was based on light. I suspected that would be the case. What else could you use in space? There’s no sound. No smell. It would have to be light, gravity, or electromagnetism. And light’s the easiest of those three to detect. At least, as far as evolution is concerned.

For my next experiment, I taped a little white LED and a watch battery together. Of course, I wired it backward at first and the LED didn’t light up. That’s pretty much a rule in electronics: You never get diodes right on the first try. Anyway, I rewired it correctly and the LED lit up. I taped the whole contraption to the inside wall of the closet. I made sure to position it so the Astrophage on the sample slide would have a direct line of sight on it. Then I sealed everything up again.

Now, from the Astrophage’s point of view, there was a lot of black nothingness and one shining spot of white. That’s kind of what Venus might look like if you were out in space and looking directly away from the sun.

They didn’t budge. No hint of motion at all.

“Hmph,” I said.

To be fair, it wasn’t likely to work. If you were at the sun, looking away from it for the brightest splotch of light you could see, you’d probably zero in on Mercury, not Venus. Mercury is smaller than Venus, but it’s a lot closer so you’d see more light.

“Why Venus?” I mused. But then I thought of a better question. “How do you guys identify Venus?”

Why did they move randomly? My theory: By pure chance, every few seconds or so, an Astrophage thought it had spotted Venus. So it thrusted in that direction. But then the moment passed, so it stopped thrusting.

The key had to be frequencies of light. My boys didn’t wiggle at all in darkness. But it wasn’t just about the sheer volume of light, or they would have gone for the LED. It had to be something about the frequency of the light.

Planets don’t just reflect light. They also emit it. Everything emits light. The temperature of the object defines the wavelength of light emitted. Planets are no exception. So maybe Astrophage looked for Venus’s IR signature. It wouldn’t be as bright as Mercury’s, but it would be distinct—a different “color.”

A little googling told me Venus’s average temperature was 462 degrees Celsius.

I had a whole drawer full of replacement bulbs for microscopes and other lab stuff. I grabbed one and hooked it up to a variable power supply. Incandescent bulbs work by getting the filament so hot it emits visible light. That happens around 2,500 degrees Celsius. I didn’t need anything so dramatic. I just needed a measly 462 degrees. I adjusted power going through the bulb up and down, watching with an IR camera, until I got exactly the light frequency I wanted.

I moved the whole contraption into my test closet, watched the monitor with my boys on it, and turned on the artificial Venus.

Nothing. Absolutely no movement from the little jerks.

“What do you want from me?!” I demanded.

I pulled my goggles off and threw them to the ground. I drummed my fingers on the table. “If I were an astronomer, and someone showed me a blob of light, how would I know if it’s Venus?”

I answered myself. “I’d look for that IR signature! But that’s not what Astrophage does. Okay, someone shows me a blob of light and says I’m not allowed to use emitted IR to work out the temperature of the body. How else could I find out if it’s Venus?”

Spectroscopy. Look for carbon dioxide.

I raised an eyebrow as the idea came to me.

When light hits gas molecules, the electrons get all worked up. Then they calm down and re-emit the energy as light. But the frequency of the photons they emit is very specific to the molecules involved. Astronomers used this for decades to know what gases are out there far, far away. That’s what spectroscopy is all about.

Venus’s atmosphere is ninety times Earth’s pressure and almost entirely carbon dioxide. Its spectroscopy signature of CO2 would be overwhelmingly strong. Mercury had no carbon dioxide at all, so the nearest competitor would be Earth. But we had a minuscule CO2 signature compared to Venus. Maybe Astrophage used emission spectra to find Venus?

New plan!

The lab had a seemingly infinite supply of light filters. Pick a frequency, and there’s a filter for it. I looked up the spectral signature of carbon dioxide—the peak wavelengths were 4.26 microns and 18.31 microns.

I found the appropriate filters and built a little box for them. Inside I put a small white lightbulb. Now I had a box that would emit the spectral signature of carbon dioxide.

I put it in the test closet and went out to watch the monitor. Larry, Curly, and Moe hung out on their slide, just like they had all day long.

I flicked on the light box and watched for any reaction.

The Astrophage left. They didn’t just meander toward the light. They were gone. Absolutely gone.

“Um…”

I had been recording the camera input, of course. I ran it back to watch frame by frame. Between two frames they simply disappeared.

“Um!”

Good news: Astrophage were attracted to carbon dioxide’s spectral signature!

Bad news: My three irreplaceable, 10-micron-wide Astrophage had launched off somewhere—maybe at velocities approaching the speed of light—and I had no idea where they went.

“Craaaaaap.”

* * *

—

Midnight. Darkness everywhere. The army guys changed shift to two guys I didn’t know. I missed Steve.

I had aluminum foil and duct tape up over every window of the lab. I sealed the cracks around the entrances and exits with electrical tape. I turned off every piece of equipment that had a readout or LED of any kind. I put my watch in a drawer because it had glow-in-the-dark paint on the hands.

I let my eyes adjust to the total darkness. If I saw so much as a single shape that wasn’t my imagination, I sought out the light leak and put tape over it. Finally, I reached a level of darkness so intense I couldn’t see anything. Opening or closing my eyes had no effect at all.

The next step was my newly invented IR goggles.

The lab had many things, but infrared goggles were not among them. I’d considered asking Steve the army guy if he could score some. I probably could have called Stratt and she would have had the president of Peru personally deliver them or something. But this was faster.