'Who is it?' whispered someone, to a chorus of shushes. Floyd raised his hands in a gesture of ignorance – and, he hoped, innocence.

'... know you are aboard Leonov... may not have much time... aiming my suit antenna where I think...' The signal vanished for agonizing seconds, then came back much clearer, though not appreciably louder.

'... relay this information to Earth. Tsien destroyed three hours ago. I'm only survivor. Using my suit radio – no idea if it has enough range, but it's the only chance. Please listen carefully. THERE IS LIFE ON EUROPA. I repeat: THERE IS LIFE ON EUROPA.'

The signal faded again. A stunned silence followed that no one attempted to interrupt. While he was waiting, Floyd searched his memory furiously. He could riot recognize the voice – it might have been that of any Western-educated Chinese. Probably it was someone he had met at a scientific conference, but unless the speaker identified himself he would never know.

'... soon after local midnight. We were pumping steadily and the tanks were almost half full. Dr Lee and I went out to check the pipe insulation. Tsien stands – stood – about thirty metres from the edge of the Grand Canal. Pipes go directly from it and down through the ice. Very thin – not safe to walk on. The warm upwelling...'

Again a long silence. Floyd wondered if the speaker was moving, and had been momentarily cut off by some obstruction.

'... no problem – five kilowatts of lighting strung up on the ship. Like a Christmas tree – beautiful, shining right through the ice. Glorious colours. Lee saw it first – a huge dark mass rising up from the depths. At first we thought it was a school of fish – too large for a single organism – then it started to break through the ice.

'Dr Floyd, I hope you can hear me. This is Professor Chang – we met in '02 – Boston IAU conference.'

Instantly, incongruously, Floyd's thoughts were a billion kilometres away. He vaguely remembered that reception, after the closing session of the International Astronomical Union Congress – the last one that the Chinese had attended before the Second Cultural Revolution. And now he recalled Chang very distinctly – a small, humorous astronomer and exobiologist with a good fund of jokes. He wasn't joking now.

'... like huge strands of wet seaweed, crawling along the ground. Lee ran back to the ship to get a camera – I stayed to watch, reporting over the radio. The thing moved so slowly I could easily outrun it. I was much more excited than alarmed. Thought I knew what kind of creature it was – I've seen pictures of the kelp forests off California – but I was quite wrong.

'I could tell it was in trouble. It couldn't possibly survive at a temperature a hundred and fifty below its normal environment. It was freezing solid as it moved forward – bits were breaking off like glass – but it was still advancing toward the ship, a black tidal wave, slowing down all the time.

'I was still so surprised that I couldn't think straight and I couldn't imagine what it was trying to do...'

'Is there any way we can call him back?' Floyd whispered urgently.

'No – it's too late. Europa will soon be behind Jupiter. We'll have to wait until it comes out of eclipse.'

'... climbing up the ship, building a kind of ice tunnel as it advanced. Perhaps this was insulating it from the cold – the way termites protect themselves from the sunlight with their little corridors of mud.

'... tons of ice on the ship. The radio antennas broke off first. Then I could see the landing legs beginning to buckle – all in slow motion, like a dream.

'Not until the ship started to topple did I realize what the thing was trying to do – and then it was too late. We could have saved ourselves – if we'd only switched off those lights.

'Perhaps it's a phototrope, its biological cycle triggered by the sunlight that filters through the icc, Or it could have been attracted like a moth to a candle. Our floodlights must have been more brilliant than anything that Europa has ever known.

'Then the ship crashed. I saw the hull split, a cloud of snowflakes form as moisture condensed. All the lights went out, except for one, swinging back and forth on a cable a couple of metres above the ground.

'I don't know what happened immediately after that. The next thing I remember, I was standing under the light, beside the wreck of the ship, with a fine powdering of fresh snow all around me. I could see my footsteps in it very clearly. I must have run there; perhaps only a minute or two had elapsed.

'The plant – I still thought of it as a plant – was motionless. I wondered if it had been damaged by the impact; large sections – as thick as a man's arm – had splintered off, like broken twigs.

'Then the main trunk started to move again. It pulled away from the hull, and began to crawl toward me. That was when I knew for certain that the thing was light-sensitive: I was standing immediately under the thousand watt lamp, which had stopped swinging now.

'Imagine an oak tree – better still, a banyan with its multiple trunks and roots – flattened out by gravity and trying to creep along the ground. It got to within five metres of the light, then started to spread out until it had made a perfect circle around me. Presumably that was the limit of its tolerance – the point at which photo-attraction turned to repulsion. After that, nothing happened for several minutes. I wondered if it was dead – frozen solid at last.

'Then I saw that large buds were forming on many of the branches. It was like watching a time-lapse film of flowers opening. In fact I thought they were flowers – each about as big as a man's head.

'Delicate, beautifully coloured membranes started to unfold. Even then, it occurred to me that no one – no thing – could ever have seen these colours before; they had no existence until we brought our lights – our fatal lights – to this world.

'Tendrils, stamens, waving feebly... I walked over to the living wall that surrounded me, so that I could see exactly what was happening. Neither then, nor at any other time, had I felt the slightest fear of the creature. I was certain that it was not malevolent – if indeed it was conscious at all.

'There were scores of the big flowers, in various stages of unfolding. Now they reminded me of butterflies, just emerging from the chrysalis – wings crumpled, still feeble – I was getting closer and closer to the truth.

'But they were freezing – dying as quickly as they formed. Then, one after another, they dropped off from the parent buds. For a few moments they flopped around like fish stranded on dry land – at last I realized exactly what they were. Those membranes weren't petals – they were fins, or their equivalent. This was the free-swimming, larval stage of the creature. Probably it spends much of its life rooted on the seabed, then sends these mobile offspring in search of new territory. Just like the corals of Earth's oceans.

'I knelt down to get a closer look at one of the little creatures. The beautiful colours were fading now to a drab brown. Some of the petal-fins had snapped off, becoming brittle shards as they froze. But it was still moving feebly, and as I approached it tried to avoid me. I wondered how it sensed my presence.

'Then I noticed that the stamens – as I'd called them – all carried bright blue dots at their tips. They looked like tiny star sapphires – or the blue eyes along the mantle of a scallop – aware of light, but unable to form true images. As I watched, the vivid blue faded, the sapphires became dull, ordinary stones.

'Dr Floyd – or anyone else, who is listening – I haven't much more time; Jupiter will soon block my signal. But I've almost finished.

'I knew then what I had to do. The cable to that thousand watt lamp was hanging almost to the ground. I gave it a few tugs, and the light went out in a shower of sparks.