“But what else could give us abnormally high values?”
“I’ve no idea.” He looked at me apologetically. “And we’ll never know from this distance. Seems to me that Anna’s right. We may have to get in a lot closer for a good look if we really want to find out.”
Perhaps the idea that Lanhoff and his crew were almost certainly dead was hitting Anna hard for the first time. At any rate, there was no triumph in her expression as she watched me ease us gingerly forward until we were only ten thousand kilometers from the planetoid. We went slowly, all our sensor input channels wide open. I set the control system to hold us at a constant distance from the surface of Manna.
“That’s as far as I’m willing to take us,” I said. “We’re a long way from home, and I won’t risk our only way of getting back. Any closer look will have to be done with the transfer pod. Mac, I’ve not had time to watch the inputs. Is there anything about the ship or about Manna that’s looking out of line?”
He had been muttering to himself over by a display screen. Now he frowned and pressed a sequence of control keys.
“Maybe. While you were busy I did a complete data transfer from Star Harvester’s computer to ours. Lanhoff and his crew stopped feeding in new inputs a hundred and fifteen days ago — that’s when the signals to Oberon Station cut off — but the automatic sensors kept right on recording. See, here’s the very first radioactivity reading from Manna when they arrived, and there’s one taken just a few minutes ago. Look at ’em. Identical. And now look at this. This is the thermal profile of a cross-section through Manna’s center.”
A multi-colored blob filled the screen. It was a set of concentric ellipses, color coded to run from a dark red in its center portion to a violet on the outer boundary.
“Different colors represent different temperatures.” McAndrew touched a button, and a dark ellipse appeared around the red and orange portions at the center of the image. “I’ve just put in the contour for zero degrees Celsius. See? Significant, eh?”
“See what?” said Anna. She was sitting close to McAndrew, their shoulders touching.
“The inside — inside the curve. It’s warmer than the melting-point of ice. If Manna has a water-ice core, it must be liquid. There’s a couple of kilometers of frozen surface, then that liquid interior.”
“But we’re out in the Halo,” I protested. “We’re billions of miles from a source of heat. Unless — did Lanhoff already put one of his fusion plants in there?”
“No.” McAndrew shook his head. His eyes were sparkling. “The temperature distribution inside was like this before Lanhoff arrived. You’re right, Jeanie, it looks impossible — but there it is. Manna is three hundred degrees warmer than it has any right to be.”
There was a long silence. Finally Will Bayes cleared his throat. “All right, I’ll be the dummy. How can that happen?”
McAndrew gave a little bark of excitement. “Man, if I had a definite answer to that I wouldn’t hold out on you. But I can make a good guess. There has to be a natural internal source of heat, something like uranium or thorium deep inside. That’s consistent with the high radioactivity value, too.” He turned to me. “Jeanie, you have to get us over there, so we can take a good look at the inside.”
I hesitated. “Will it be safe?” I said at last. “If it’s uranium and water — you can make a nuclear reactor from them.”
“Yes — if you try really hard. But it wouldn’t happen in nature. Be reasonable, Jeanie.”
He was looking at me expectantly, while Anna sat silent. She liked to see him putting the pressure on me for a change.
I shook my head. “If you want to go over there and explore, I won’t try to stop you. But my job is the safety of this ship. I’m staying right here.” Logic was all on my side. But even as I spoke I felt that I was giving the coward’s answer.
From a distance of fifty kilometers, Manna already filled the sky ahead, a black bulk against the star field. Star Harvester hung as a cluster of glittering spheres near one end of the planetoid. It steadily grew in size on the screen as the pod moved in, one of its television cameras sending a crisp image back to my observing post on the Hoatzin. I could see the dozen Sections and the narrow connectors between them, hollow tubes that were flexible now but electromagnetically stiffened when the drive went on.
“Approaching outermost cargo sphere,” said McAndrew. I could see him on the screen that showed the inside of the pod, and a third image showed and recorded for me the pod control settings exactly as he saw them himself.
“Everything still appears perfectly normal,” he went on. “We’ll make our entry of Star Harvester through the Control Section. What is it, Anna?”
He turned to where she was monitoring another sensor, one for which I was not receiving coverage.
“Cut in Unit Four.” I said quickly.
At my command the computers sent the image Anna and Will were watching to fill the center screen. I saw a long shaft that extended from a cargo hold of Star Harvester and drove down to penetrate the rough surface of Manna. The camera tracked its length, switching to deep radar frequencies to generate an image where the shaft plunged below the planetoid’s surface.
“Is that a drilling shaft?” I asked. “It looks as though they were getting ready to put a fusion plant in the middle of Manna.”
“Wouldn’t make sense.” McAndrew spoke in an abstracted grunt, and I saw him rubbing at the balding spot on the back of his head. “Lanhoff knew quite well that Manna has a liquid core — he had the same computer base to look at as we do. With that core he didn’t need a fusion plant at all. The interior would be warm enough already for his enzymes to thrive.”
“Was he looking for radioactive material?” I asked; but I could answer that question myself. “It wouldn’t make sense. He could locate them the same way we did, from remote measurement. So why would he drill into the core?”
“I’ll tell you why,” said Anna suddenly. “That’s the way Arne always was. Anytime he saw something that he didn’t understand he wanted to investigate — he couldn’t resist it. I’ll bet he drilled to the core to take a closer look at something he’d detected in there — something he couldn’t examine closely enough from outside.”
The pod had been creeping in nearer and nearer to the hatches on the Control Section. I suddenly realized that once the three of them went inside I would be blind.
“Mac, as soon as you get in there, turn on all the monitors and tell the computer to send the signals back to me here on the Hoatzin.” I raised my voice. “And one of you has to stay in the Control Section if you go down to the surface. D’you hear me?”
He nodded vaguely, but he was already moving toward the hatch. Anna followed him. The last thing I saw before the camera could no longer keep them in view was Will Bayes’ face as he turned to take a last worried look around the pod.
Deserted, but in perfect working order; that was the conclusion after a thorough examination of the Control Section of Star Harvester.
I had followed on the remote monitors as the other three made their inspection, step by step, and I could not fault them for lack of caution.
“We’ll not find Lanhoff and his crew here,” said McAndrew finally, when they were back in the main control room. “They must have gone down into the interior of Manna. Look at this.”