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.