We didn't figure it out then and I wasn't even sure that I'd made the right diagnosis, but things went on every day afterwards that left me convinced there was something else living on this hunk of rock besides Red and me. It didn't have mass, apparently, because we tried our best to touch it.
Once when it got to fooling around with the laboratory balance, Red and I encircled the balance with our arms and then squeezed together without feeling a thing.
It wasn't energy, because we tried every instrument to detect electricity, heat, light, and radio. But it was alive, because it moved. It read books and monkeyed with the lab scales.
And at last I decided that maybe it had something to do with the apparent discrepancy in the asteroid's change in mass. After that I had a great deal to work on.
Red began behaving queerly too. He swore that he was getting too small for his clothing. His shoes, he said, were almost a size too large. I was too busy to check, so I put it down as a loss in weight.
We'd spent a year on the asteroid when we were due to pass Mars. So our first anniversary was spent in checking our movements with a telescope, a camera and a chronometer. We discovered our mass—or that of Asteroid 57GM—had depreciated another 25 per cent. It now had only half the mass it was supposed to have. This was too much of an error for even a grade school student.
"I'll bet some astronomers back on earth will get redder than my hair when we get home," Red said.
I shook my head. "It hasn't anything to do with their observations," I said. "It's what is happening now to you and me. We're losing mass someway."
There was only one way to check it and that was to weigh ourselves. So I rigged up a rude sort of a balance by weighing out chunks of rock until we had a mass equal to what we should weigh, placing them on a teeter-totter arrangement I rigged up in the lab.
"It'll be close enough to learn if we've lost half our mass," I said.