Fisher spread his arms. ‘You tell me, Dr Jarlow. It will save time, I'm sure.’

‘All right. It took Rotor two years to get here - if it got here. That means it's been here thirteen years. If all of Rotor were solid algae and it was all dumped into the ocean and lived and grew and produced oxygen, then to get to the present level, where I estimate the oxygen content is 18 per cent and carbon dioxide is present only in traces, I would imagine it would take some thousands of years. Perhaps hundreds of years - if conditions were enormously favorable. It certainly would take more than thirteen years. And, frankly, Earth algae are adapted to Earth conditions quite precisely. On another world, the algae might not grow, or might do so very slowly, till it adapted itself. Thirteen years wouldn't change a thing.’

Fisher seemed unperturbed. ‘Ah, but there is lots of oxygen there and no carbon dioxide, so if it's not the result of Rotorian action, what is it the result of? Doesn't it strike you that we must assume there's non-Earthly life on this world?’

‘It's what I did assume,’ said Jarlow.

Wendel said, ‘It's what we have to assume immediately. Native vegetation is photosynthesizing. It doesn't mean, for one moment, that Rotorians are on the world, or that they ever even reached this system.’

Fisher looked annoyed. ‘Well, Captain,’ he said with pointed formality, ‘I have to say that neither does it mean that Rotorians aren't on the world, or that they haven't reach the system. If the planet has vegetation of its own, it just means that no terraforming was required and the Rotorians could move right in.’

‘I don't know,’ said Blankowitz. ‘I should think there would be no reasonable chance at all that vegetation evolving on a strange planet would be nourishing to human beings. I doubt that human beings could digest it, or that they could assimilate even if they could digest it. I would certainly offer high odds that it would be poisonous. And if there's plant life, there's bound to be animal life, and we don't know what that would entail.’

‘Even in that case,’ said Fisher, ‘it's still possible that the Rotorians would fence off a tract of land, kill the native life within it, and seed plants of their own. I imagine this alien planting - if you want to call it that - would expand with the years.’

‘Supposition on supposition,’ muttered Wendel.

‘In any case,’ said Fisher, ‘it's completely useless to sit here and make up scenarios, when the logical thing is to explore the world as best we can - and from as close a view as possible. Even from its surface - if that seems feasible.’

And Wu said with surprising force, ‘I completely agree.’

Blankowitz said, ‘I'm a biophysicist, and if there's life on the planet, then whatever else it may have or may not have, we must explore it.’

Wendel looked from one to the other and, reddening slightly, said, ‘I suppose we must.’

‘The closer we get,’ said Tessa Wendel, ‘and the more information we gather, the more confusing it all is. Is there any question that this is apparently a dead world? There is no illumination on the night hemisphere; there are no signs of vegetation or of any form of life.’

‘No gross signs,’ said Wu coolly, ‘but something must be happening to keep oxygen in the air. Not being a chemist, I can't think of any chemical process that would do the trick. Can anyone?’

He scarcely waited for an answer. ‘In fact,’ he went on, ‘I seriously question whether a chemist could come up with a chemical explanation. If the oxygen is there, it must be a biological process that produces it. We just don't know of anything else.’

Wendel said, ‘If we say that, then we're judging from our experience with exactly one oxygen-containing atmosphere - Earth's. Someday we may be laughed at. It may turn out that the Galaxy is littered with oxygen atmospheres that have no connection with life, and we'll be on record as having been stymied entirely because of our experience with the one planet that is a freak and has a biological source of the oxygen.’

‘No,’ said Jarlow angrily. ‘You can't get out of it that way, Captain. You can picture all sorts of scenarios, but you can't expect the laws of nature to change for your convenience. If you want to have a nonbiological source of an oxygen-containing atmosphere, you have to suggest a mechanism.’

‘But,’ said Wendel, ‘there's no sign of chlorophyll in the light reflected from the world.’

‘Why should there be?’ said Jarlow. ‘The chances are that a somewhat different molecule has been evolved under the selective pressure of light from a red dwarf star. May I make a suggestion?’

‘Please do,’ said Wendel bitterly. ‘It seems to me you do nothing else.’

‘Very well. All we can actually tell is that the land areas of the world seem to be completely denuded of life. That means nothing. Until four hundred million years ago, Earth's land areas were similarly sterile, but the planet had an oxygen atmosphere and abundant life.’

‘Sea life.’

‘Yes, Captain. There's nothing wrong with sea life. And that would include algae or the equivalent - microscopic plants that would do perfectly well as oxygen factories. The algae in Earth's seas produce 80 per cent of the oxygen that pours into the atmosphere each year. Doesn't this explain everything? It explains the oxygen atmosphere and it also explains the apparent lack of land life. It also means we can safely explore the planet by landing on the sterile land surface of the world and studying the sea with what instruments we have - leaving it for a later expedition, suitably equipped, to do the detailed work.’

‘Yes, but human beings are land animals. If Rotor had reached this system, they would surely have attempted to colonize the land areas and of such colonization there is no hint. Is it really necessary to investigate the world further?’ the Captain asked.

‘Oh yes,’ said Wu quickly. ‘We can't go back with deductions only. We need some facts. There may be surprises.’

‘Do you expect any?’ asked Wendel with a touch of anger.

‘It doesn't matter whether I do or not. Can we go back to Earth and tell them that - without looking - we were sure there would be no surprises? That would not be very sensible.’

‘It seems to me,’ said Wendel, ‘that you've changed your mind rather drastically. You were ready to return without even approaching the Neighbor Star.’

‘As I recall,’ said Wu, ‘I had my mind changed for me. In any case, under the circumstances, we must explore. I know, Captain, that there is a certain temptation to seize the opportunity to visit a few other star systems, but now that there is an apparently habitable world in view, we must come back to Earth with maximum information on something that may be far more important to our planet in a very practical sense than any amount of catalogue-type information concerning the nearer stars. Besides’ - and he pointed at the viewport with what was almost surprise on his face - ‘I want to take a closer look at that world. I have this feeling it will be completely safe.’

‘This feeling?’ said Wendel sardonically.

‘I'm allowed my intuitions, Captain.’

Merry Blankowitz said in a rather husky voice, ‘I have my intuitions, too, Captain, and I'm worried.’

Wendel looked at the young woman with sudden surprise. She said, ‘Are you weeping, Blankowitz?’

‘No, not really, Captain. I'm just very upset.’

‘Why?’

‘I've been using the ND.’

‘The neuronic detector? On that empty world? Why?’

Blankowitz said, ‘Because I came here to use it. Because that's my function.’

‘And the results are negative,’ said Wendel. ‘I'm sorry, Blankowitz, but if we visit other star systems, you'll have other chances.’

‘But that's just it, Captain. The results are not negative. I detect intelligence on the world and that's why I'm upset. It's a ridiculous result, and I don't know what's wrong.’

Jarlow said, ‘Perhaps the device isn't working. It's so new that it wouldn't be surprising if it weren't reliable.’

‘But why isn't it working? Is the neuronic detector detecting us here on the ship? Or is it simply giving a false positive? I've checked it. The shielding is in perfect order, and if I had a false positive, I ought to have it elsewhere. There are no signs of any positive responses from the gas giant, for instance, or from the Neighbor Star, or from random points in space, but every time I allow it to sweep the satellite, I get a response.’

‘You mean,’ said Wendel, ‘that on this world, where we can detect no life, you detect intelligence?’

‘It's a very minimal response. I can just barely pick it up.’

Crile Fisher said, ‘Actually, Captain, what about Jarlow's point? If there's life in the world's ocean and we don't detect it because the water's opaque, there might still be intelligent life, and perhaps Dr Blankowitz detects that .’

Wu said, ‘Fisher has a good point. After all, life in the sea - however intelligent - is not likely to have a technology. You can't have fire in the sea. Nontechnological life does not make itself very evident, but it may still be intelligent. And a species, however intelligent, is not to be feared without technology, especially if it can't leave the sea, and if we remain on land. It just makes things more interesting and makes it more necessary for us to investigate.’

Blankowitz said in annoyance, ‘You all talk so quickly and so endlessly that I don't get a chance to say anything. You're all wrong. If it were intelligent sea life, I would get a positive response only from the oceans. I get it everywhere , just about evenly. Land as well as sea. I don't understand it at all.’

‘On land as well?’ said Wendel, clearly incredulous. ‘Then there must be something wrong.’

‘But I can't find anything wrong,’ said Blankowitz. ‘That's what's so upsetting. I just don't understand this.’ Then, as though in extenuation, she added, ‘It's very feeble, of course, but it's there.’

Fisher said, ‘I think I can explain it.’ All eyes turned to him, and he grew immediately defensive. ‘Maybe I'm not a scientist,’ he said, ‘but that doesn't mean I can't see something that's pretty plain. There's intelligence in the sea, but we can't see it because the water hides it. All right, that makes sense. But there's intelligence on land, too. Well, that's hidden also. It's underground.’

‘Underground ?’ said Jarlow explosively. ‘Why should it be underground? There's nothing wrong with the air or with the temperature or with anything we can detect. What's here to hide from?’