‘I know.’ Stef sighed the way her father did. ‘It gets so wearying.’

He laughed. ‘OK, Kalinski, quit showing off. Look, putting it on is easy, the suit will seal itself up around you and adapt to fit. Just slip your shoes off . . .’

The astonishing thing was, once she was in the suit and out through a heavy-duty airlock, she really didn’t notice the suit, not visually anyhow. The suit contained some kind of immersive VR system, so when she looked down it was as if she was standing beside Lex, in their everyday clothes, on a ground of pitted rock, under Mercury’s black sky. The sun, more than twice the size it was as seen from Earth, cast long shadows across a moonlike plain. Experimentally she bent down; she felt a little stiff, and couldn’t fold quite as she was used to. She touched her toes, though, and picked up a loose bit of rock.

‘How’s the suit?’

‘Fine.’ She explored the rock; her fingers, in her vision, didn’t quite close around it. ‘It feels kind of . . . soapy.’ She threw the rock with a skimming motion. The rock whizzed away, falling, not as fast as it would on Earth, faster than on the moon. It made no sound when it fell; that wasn’t part of the sim.

‘Let’s walk.’ Lex strode easily across the surface of Mercury, his shadow long beside him. His voice sounded as if it was coming from him, not from plugs in her ears. ‘The suit will stop you from coming to any harm.’

‘I know it will.’ It was only older people who needed reassuring about stuff like that; people of Stef’s age just assumed technology would work. She followed him, watching where she was stepping. In this crater basin the surface was smoother than she had expected, with dust overlying a rocky surface pitted by lesser impacts. She moved easily enough, but felt a little heavy, as if she was over-muscled, like she’d beefed up in a gym. The suit must have exoskeletal multipliers.

The domes of the Yeats base were big blisters piled high with dirt, for protection from meteorite falls and from the sun’s radiation. Further out there were storage facilities, backup plants for air and water processing, dusty rovers on tracks that led off across the crater’s dirt floor. Not far from the inhabited facilities was the edge of the area of the crater floor panelled by solar cells, a glimmering reflective surface like a pool of molten silver that stretched away for kilometres.

And further out still she glimpsed some of the mountains that ringed this walled plain, like broken, eroded teeth. Out there stood bigger facilities, marked out by winking warning lights, all far enough from the inhabited domes to allow for safety margins. There was the broad, hardened pad where ships like her own ferry from orbit had come in to land, and fuel and energy stores, and a long shining needle that was the mass driver, which used sun-powered electromagnetism to hurl caches of material out of Mercury’s gravity well and across the solar system. In the shadow of the mountains themselves she saw the big gantries of the UEI’s drilling project, sinking shafts hundreds of kilometres deep through layers of lava and impact-pummelled bedrock to the edge of Mercury’s iron mantle, where the mysterious kernels were to be found.

And there too, huddling in the shadow, stood a taller gantry, a slim rocket: a strange sight for Stef, like something out of a history book. That was mankind’s newest spacecraft, the International-One, waiting to take Lex and his crew off into space.

Lex took a step and stamped on the ground, sending up little sprays of dust that sank quickly back down. ‘It’s an interesting little world.’

‘So you say.’

He laughed. ‘I mean it. It’s only superficially like the moon. Look at those drill rigs over there. Here, you only have to drill down a few hundred kilometres before you reach the mantle. You’d have to go ten times deeper into the Earth, say. You know why that is?’

‘Of course I know—’

Like her father, he didn’t always listen before lecturing her. ‘Because, we think, some big explosion on young Mercury, or maybe a big impact, blew off most of the rocky crust.’

She tried to imagine standing here when that big impact happened. Tried and failed. ‘What I want to know is, has all that got anything to do with the formation of the kernels they found here?’

Another voice replied, ‘Good question. Well, nobody knows. But I can see why you would ask it. You are Stephanie Kalinski, aren’t you?’

A woman was walking towards them from the direction of the domes, tall, a little heavy-set perhaps, yet graceful. Evidently projecting a virtual image, she appeared to be in regular clothes; she wore a trim blue jacket and trousers, almost uniform-like, but not as showy as Lex’s ISF suit. She looked about thirty, but was oddly ageless, as if heavily cosmeticised. Her accent was neutral, perhaps east coast American.

‘The name’s Stef,’ she replied automatically. ‘Not Stephanie. I know your face. I’ve seen your picture in my dad’s dossiers.’

‘Of course you have,’ Lex said, grinning. ‘Which is why I thought you two ought to meet. Dr Kalinski’s two daughters, so to speak. Because he never would have thought of bringing you together himself, right?’

‘I am Angelia,’ said the woman.

That puzzled Stef. ‘That’s the name of the starship. The Angelia.’

‘I know. I am Angelia. I know what you’re thinking. That I am a PR stunt. A model, hired by your father to personify—’

‘I don’t actually care,’ Stef said abruptly.

That surprised Lex. ‘You’ve got an impatient streak, haven’t you, Kalinski?’

‘If somebody’s being deliberately obscure, yes.’

‘I’m sorry,’ Angelia said. ‘I don’t intend to be. If your father had explained to you the mission concept—’

‘You know about me. How come?’

‘Well, I have got to know your father as we’ve worked together. And he speaks of you, Stef, a great deal. He’s very proud of you.’

‘I know,’ Stef snapped, feeling obscurely jealous.

Lex said, ‘Be nice, Kalinski. Now it’s your cue to ask, “What mission concept?” ’

‘Oh, Lex, I don’t care. It’s obvious this woman is some kind of projection.’ On impulse she bent, picked up a pebble, an impact-loosened bit of Mercury rock, and threw it at Angelia.

Angelia caught the pebble easily. ‘Not a projection. Not quite an android either.’ She looked at the rock, then popped it into her mouth and swallowed it. ‘I’m not in a suit like yours.’

‘You’re programmable matter.’

‘That’s right.’ Angelia held up her left hand, and watched as it morphed into a clutch of miniature sunflowers, which swivelled their heads to the low sun.

‘Ugh,’ Lex said. ‘Creepy.’

‘Sorry.’ She turned her hand back into a hand, and pointed up at the empty sky. ‘I’m to be fired off into interstellar space, by the microwave beam from your father’s defunct solar-power satellite, up there. I’m the payload. But there is a me in here. In fact, a million mes, in a sense. A whole sisterhood, all sentient to a degree. Stef, I’m sure your father will walk you through the mission design—’

‘But it makes no difference.’ Lex walked around Angelia, studying her. ‘Whether you’re sentient or not, I mean. You’re not human. And it’s an authentic, physical human presence that counts when it comes to touching a new world. Sending some AI like you doesn’t count. That’s why the kernel ships are the important breakthrough here, because they can carry humans. Maybe even all the way to the stars – and back, unlike poor old Dexter Cole.’

‘That’s very post-Heroic Generation thinking,’ Angelia said, and she smiled indulgently. ‘A backlash against the philosophical horrors of that age. And typical of what they teach you at the ISF academies, from what I understand. Human experience is primal, yes? In fact this modern incarnate-humanism is the reason why Stef’s father programmed me into this form, so I could attend the pre-launch ceremonies in person, so to speak. It’s expected, these days.’