‘Is no more real than you. You are just as I remember, at least,’ she said. ‘Right down to that odd brooch on your lapel. Which is just like the chunk of carved concrete, the plaque, you were careful to ship aboard the Tatania, isn’t it? I always wondered what the significance of that was.’

He didn’t rise to the bait. ‘My goal with this virtual presentation has been to emphasise our shared past. How much we have in common.’

‘Well, you’ve done that. But that’s as far as it goes. You’re just as you were then,’ she went on. ‘Whereas – look at me. Withered.’

‘You have done well to survive a dozen years here, after all the traumas of your earlier life, and the inadequacy of medicine and health care in this new reality, despite all my own proselytising—’

‘You mean, selling the data you stole from the memory of the Tatania. Lex never forgave you for that, you know.’

‘I know,’ he said indifferently. ‘And now it’s too late to apologise.’

‘Good old Lex. At least he died well – eighty years old and throwing himself into the site of that tanker crash on the moon, on Luna. The Brikanti built a statue to him.’

Earthshine laughed. ‘Good for General McGregor. He’d have loved that. And of the others?’

‘Jiang has stayed with me, at the Academy. Sadly he’s still not accepted more widely, in Brikanti society. You can’t overcome centuries of xenophobia with a cultured smile – not here, at least. Two of the surviving crew of the Tatania work with me there also. They married, in fact, Marie Golvin and Rajeev Kapur.’

‘I did hear. I sent a gift … And what of Beth, and her child?’

‘Mardina. Growing now, ten years old. Doing fine. Beth’s forty-eight now, and Mardina makes her feel her age, I think. They’re living independently, but I keep an eye on them. Beth’s estranged from Ari Guthfrithson – the father. Beth does make enemies and then clings to them, if you know what I mean.’

‘I do know.’

Penny was puzzled by that response. ‘Why would she have a grudge against you?’

‘Because of something I told her. It was just as we fled the inner solar system in the Tatania – just as the light wavefront from the kernel detonations overtook us, in fact.’

‘I don’t understand. What did you tell her?’

‘My name. Or one of them.’ He said no more, and looked at her steadily.

‘All right. Then is that why you asked me here? As a way to get through to Beth? Funnily enough, Ari asked me to do the same thing for him. What am I, a UN mediator?’

‘Partly that, yes, for Beth’s sake. And partly because I want you to understand what it is I am doing here, Penny. At least begin to see what it is I am exploring.’

‘Why me?’

He laughed. ‘You are the only specialist in kernel physics in this universe.’

‘Ah. And you have a kernel test laboratory up on the higher ground to the north, don’t you?’

‘Also you are one of a handful of survivors who lived through the history change.’ He grinned. ‘The “jonbar hinge”. I enjoyed your little joke, in the name of your Academy. And of course you endured an earlier jonbar hinge in your own life.’

She always had to remember, she told herself, that everything that Earthshine did was about advancing his own agenda, not hers; she was a tool here, a pawn. But he did know a hell of a lot about her. She said carefully, ‘What exactly do you want of me, Earthshine? The truth now.’

‘There may come a time when we will have to flee this place. As we fled Earth – our Earth.’

She frowned. ‘Why? What would make that necessary?’

‘And if that comes,’ he said patiently, ‘I want you to ensure that Beth is ready, with Mardina, that they come away with me.’

‘That’s what you’re proposing to purchase from me, in return for a few dribbles of information. A promise. Is that the deal?’

He smiled. ‘If you want to put it like that. Of course your own life might be saved too. Call that a sweetener.’

She sighed. ‘What are you up to, Earthshine, you old monster?’

He grinned. ‘I’m trying to talk to the Martians. Come. I’ll show you.’

They stood together over the pond.

‘As I said, most of what you see here is a virtual representation. Not real. But this, I assure you, is real. Samples of life from the deep rocks of Mars, retrieved with great care, brought to this place in conditions of high pressure, heat, salinity, anoxia – lethal for you and me, balmy for these bugs, our cousins.’

‘Cousins?’

‘Oh, yes. Individually they are simple bacteria – simple in that they lack proper cell structures, nuclei. Together they make up something that is not simple at all. But they are creatures of carbon chemistry as we are; their proteins are based on a suite of amino acids that overlaps but is not identical to our own; they have a genetic system based on a variant of our own DNA coding. Some of this, actually, was discovered by the Chinese on our own Mars. They always kept the analysis secret, at least from the UN nations.’

‘But not from you.’

He just smiled.

‘Umm. So, we’re related to these creatures. Just like on Per Ardua. The evidence the first explorers brought back indicated that the life forms there were also based on an Earthlike biochemistry.’

‘Yes, but that relationship is more remote. Penny, I am sure you understand this. We can’t say on which world our kind of life originated – on Earth, Mars, Per Ardua, somewhere else entirely. It was probably spontaneous. On a world like the primitive Earth, the flow of energy – lightning, sunlight – in a primordial atmosphere of methane, ammonia, water, would create complex hydrocarbon compounds like formaldehyde, sugars, polymers. The food of life. Then comes a process of self-organisation, of complexification and combination … A spontaneous emergence of life.

‘And all the while the young worlds are pounded by huge falls of rock and ice from space, the relics of the formation of the planets themselves. Chunks of the surface are blasted into space and wander between the worlds: natural spacecraft, that carry life between the planets of a solar system – and, though much more rarely, across the interstellar gulf. This is called panspermia. If life began on Earth, it may have seeded Mars many times over – but Per Ardua, say, perhaps only once.’

‘Which is why Arduan life was a more remote relation.’

‘That’s it. Or, of course, it could have been the other way round. It seems that we’re living in the middle of a panspermia bubble, a complex of stars bearing life forms that all branch back to some originating event.’

She looked down at the purplish water. ‘A nice idea. But on some worlds life flourished better than on others. On Earth, rather than Mars—’

‘Well, it depends what you mean by “flourished”, Penny. On Earth, the biosphere, the realm of life, extends from the top of the lower atmosphere down through land and oceans, and into the deep subsurface rocks, kilometres deep, until the temperature is too high for biochemical molecules to survive. But even on Earth it is thought that there is more biomass, more life as measured in sheer tonnes, in the deep rocks than on land and air and in the oceans. And on Mars, as this small world cooled too quickly, and much of the water was lost, and then the air—’

‘It was only underground that life could survive.’

‘Yes. Microbes, living on mineral seeps and a trickle of water and the flow of heat from the interior – even on radiation from natural sources. The dark energy biosphere, some called it. Time moves slowly in those deeps, and the energy sources are minimal compared to the flow of cheap power from the sun at the surface. The bugs themselves are small – their very genomes are small. Reproduction is a rare event; the microbes of Mars, and Earth’s deeps, specialise rather in self-repair. Individual microbes, Penny, that can survive for millions of years.’