We rounded a corner, and there it was: one thin river – a creek, really, if we’re being accurate. It was not in any particular hurry, and would barely have reached my knees if I’d stepped into it. Its surface glinted a mercurial grey in the light of our headlamps. Its meandering pace created a pleasant chatter along the stones it had worn smooth. The irony did not escape me – I’d ached for respite from the aquatic clamour on Opera, yet here, the sound of water was the most welcome thing imaginable.

There was something missing, though, and I could feel our collective mood dip just a touch as we individually registered it. The river had no plants, no moss, no encouraging stripes of scum. Nothing swam beneath its ripples or tiptoed toward the bank in search of a drink. Perhaps the number of living organisms on Votum numbered just four, I thought, and only temporary residents at that.

Chikondi opened his toolkit and knelt down beside the river. He retrieved a field microscope. He dipped it into the water.

We crowded patiently behind him.

The little viewscreen switched on, and the image projected was white, pure white, the same colour as the base of the sample chamber. Chikondi gently rocked the microscope, encouraging other bits of the sample to slide into view. We saw a lump of rock, a shred of silt. That was all right. Finding nothing was all right. There was still so much to learn, even in the absence of—

Out of the bottom left corner, a shape emerged. A jellied blob with tiny structures at its heart, drifting into frame.

We vibrated with noiseless excitement. It was a cell – just one. Simple and superb.

There was a pause, a subtle shudder. The cell split into two.

I can’t say that I cheered. I roared. I thundered.

‘There it goes!’ Jack cried.

‘Oh, my God,’ Elena said, grinning from ear to ear.

‘There it goes!’ Jack punched his fists at nothing, the energy within him demanding an exit.

Chikondi simply laughed. He laughed and laughed, filling the gap left by inadequate words.

Jack’s imaginary money was well placed on caves. We found one tucked into a canyon wall, a low-hanging doorway leading to another realm. We had to crawl on our knees to get through the front passageway, sometimes splashing through the flow, but beyond that, the water had carved a magnificent inner chamber. Lei’s River, as we named it, joins two subterranean waterways there, and at their nexus is a glassy pool, chest deep and uncannily serene. Dazzling twists of crystals hang overhead, festooning the ceiling and walls like antique lace. The air in there is warm, thanks to steam vents running beneath the rock, and thoroughly sequestered from the harsh sun’s reach. It is the perfect place for life to develop, and, less importantly, for us to work.

As the only macroscopic life forms on Votum (thus far, anyway), we had no compunctions about setting up a field lab within the cave itself. There are no critters to knock it over, no weather to damage it. Everything we brought was sterilised, of course. We tread lightly in this sanctuary. But it is also a place I’ve come to inhabit fully. For the moment, the cave is home. I think, to answer the question I asked myself on Opera, a home can only exist in a moment. Something both found and made. Always temporary, in the grand scheme of things, but vital all the same.

One day I looked up from my worktable, where I’d been labelling rock samples to take back to the Merian. Chikondi was sitting by the pool, like always, watching his tablet intently and humming along with his headphones. He was running some sort of test on the bacterial samples he’d collected; any attempt to ask him what he was up to was answered with a vague mumble that indicated he was in the middle of puzzling something out and would fill us in when the idea was fully formed. Elena and Jack were standing beside a glittering twist of crystal, deep in a congenial argument about something to do with salinity. I admit that I wasn’t paying attention to the particulars. I was too busy watching the three of them and myself, each firmly in our elements. The cave is a reflection of us, in its way. Rock, water, and life, all of which need tools to examine them. All of which mean nothing if no one is there to observe.

‘We can’t go back,’ I said.

Elena and Jack looked at me. Chikondi did as well, though it took my comment a half-second longer to register with him.

I knew what I’d said was ridiculous, but the urge to say it had been growing inside me for weeks, and the rest came spilling out after. ‘Lawki 5 made it back to Earth, at least. That means everybody else is long since back. And if the Moon’s been abandoned, and if there are no functioning satellites, that means nobody is launching anything. We’re not the last of the Lawki program out here. We’re . . . we’re the last. Of anyone.’

Nobody looked as if my words were revelatory. They’d all been thinking this, too. Jack sighed. ‘We don’t have the equipment to do a long-term study here. Or on Mirabilis, or wherever.’

Chikondi nodded regretfully. ‘And the longer we stay,’ he said in a measured tone, ‘the more disruptive we are. Our visits are limited for a reason. We can’t have an influence.’ This was OCA ethics, word for word.

‘I know,’ I said. ‘I don’t disagree with any of that. I never have.’

Elena looked me in the eye. ‘Then what are you saying?’

I took a deep breath. ‘The interstellar engine has enough fuel to get back to Earth. Fourteen light-years, with a bit of wiggle room.’ I paused, choosing my words, trying to speak slow. ‘Thing is, that would also get us to Tivael.’

My words hung in the still air of the cave. Everybody understood what I was saying. Tivael was one of OCA’s earliest candidates for the Lawki program, but given its distance from Earth – over thirty light-years, or sixty years in transit – it was ruled out due to the limits of technology and the logistics of time.

From Zhenyi, however, Tivael was only thirteen light-years away. And I knew, as we all did, that there are three habitable planets in orbit around it. Going by the atmospheric data, life’s a near certainty on each of them. In particular, there’s one with an awful lot of greenhouse gases in the mix. Could be volcanic activity. Could be the natural state of things.

Could be something else.

Jack paced. ‘We . . .’ He stopped and thought. Like me, he was treading carefully. ‘Okay.’ He stuck his thumbs behind his toolbelt. ‘You’re saying that if we’re the last astronauts – the last at all – then we should prolong our mission, so that this kind of work will continue in the interim while Earth gets back on its feet.’

‘Yes.’

He gave a single nod. ‘What’s your evidence that OCA is gone, and that they’re not planning to rebuild?’ The question was delivered objectively, professorially. He was challenging my suggestion, as he rightly should.

‘I have none.’

‘What’s your evidence that there are no other humans in space besides us, right now?’

‘I have none.’

‘And why Tivael?’

‘Because we can,’ I said. I gestured around. ‘Why here?’

Chikondi nodded at that, but his attention was split, one eye still on his tablet as data compiled.

Jack continued. ‘So, you’re saying that even though we have no idea what’s going on back home, and can only speculate as to the current state of Earth’s spaceflight capabilities, in order to further the . . . the spirit of the mission we were sent here for, we should break the mission parameters entirely.’