The Long Mars

The ground rose up as they neared the lip, hard-packed under the dust, to become a circular barrier maybe fifty feet tall, Sally saw as she crested it, a wall that ran right around the rim of the hole in the ground. This was a big feature, it was obvious now they were standing on top of it, a hole a full half-mile across encircled by this smooth wall. Away from this highest point, which was a broad ridge so Sally had no fear of falling, the lip fell away smoothly, fu

Willis cautiously knelt down, tied a fine rope to a handheld sensor pod, and lowered it into the pit, paying out the rope, clumsy with his gloved hands. ‘Yeah, this pit is indeed just about twenty miles deep; the radar confirms it. And pretty much the same radius all the way to the bottom. It’s a cylinder.’

Frank said, ‘Surely no meteor could create a pit as deep and orderly as this. A bigger impactor doesn’t drill a deeper hole, it just melts more rock, and you get a wider, shallower crater.’

‘Hmm,’ Willis said. ‘I can imagine how it could be done. A string of small impactors coming down one after the other. Deepening the hole before it had a chance to infill.’

Frank pulled a face, looking dubious. ‘Maybe. If this is artificial I can think of easier ways to build it. Like with a massive heat weapon. Like we saw used in war, back on world – what was it?’

‘About a million,’ Willis said. ‘The Martian Arecibo.’

‘But,’ Sally said, ‘that’s a long way from here, stepwise. We’ve seen no evidence of cross-stepwise transfer of technologies, or even life forms, here on Mars.’

‘True. But convergence of technology types isn’t impossible,’ Willis said. ‘We have directed-energy weapons, and we’re not even from Mars.’

Sally shook her head. ‘We’ve got nothing but guesses. Why would anybody build this, though?’

Willis was monitoring the results coming back from his sensor pod. ‘I can make a guess at that. This pit is deep. The Martian atmosphere’s scale height is only around five miles. At twenty miles deep, you’d expect the air pressure to be around fifty times its value on the surface. Up here you have a typical Martian-surface atmosphere, a scrape of carbon dioxide at about one per cent Earth’s sea-level pressure. At the bottom of this pit, and my instruments are confirming it, that’s up to about fifty per cent.’

Frank whistled. ‘That’s better than on the Gap Mars.’

‘Right. Which is about as hospitable as we’ve found it, anywhere across three million stepwise copies. That’s why they built this pit, Sally. As a refuge.’

‘From what?’

Willis said, ‘From the collapse of the air. Maybe there was something like a volcano summer here – a deep one, a long one—’

Frank said, ‘Long enough for some breed of Martians to come up with a space programme.’

‘Right. But, like all summers, eventually it came to an end. The heat leaked out, the snow started falling at the poles, the oceans froze over and receded. The usual story.’

Sally thought she saw it now. ‘This pit is a refuge.’

‘Yeah. And it couldn’t be simpler. The pit would keep its air, water, even if civilization fell.’

Frank said, ‘And the elevator?’

‘Maybe they moved the root station here, before the end, from Pavonis or wherever else. Kind of romantic, but very long-term thinking. They lived in a hole in the ground to make sure they saved their air and water, but they kept their ladder to the planets.’

Sally peered into the pit. ‘So what’s down there now?’

‘Life,’ said Willis. ‘I can tell that much. There’s oxygen, methane – the atmosphere is unstable, chemically. So something must be photosynthesizing away, pumping all that oxygen into the air.’ He glanced around, at the way the slanting morning sunlight caught only the upper surface of the pit walls. ‘No, not photosynthesis. Not primarily anyhow – not enough direct light, in the depths. Maybe it’s like the deep-sea organisms on Earth, out of sight of sunlight, feeding on seeps of minerals and energy from underground. We’re close enough to the Tharsis volcanoes for that to work; the big magma pockets under those babies must leak a lot of heat.’

Sally asked, ‘So this is the last refuge of their civilization. Where’s the city lights, car exhausts, radio chatter?’

‘None of that, I’m afraid. There is one splash of metal.’

Frank looked startled. ‘Metal?’

‘An irregular form. Down on the floor of the pit.’

Sally said wistfully, ‘All this makes me think of Rectangles.’

Willis wasn’t interested, but Frank glanced at her. ‘Where?’

‘A Long Earth world I discovered with Lobsang and Joshua. We called it Rectangles, for the traces of foundation ruins we found on the ground. Another site with relics of a vanished civilization.’

‘Right. And a cache of high-tech weapons.’

She looked at Frank in surprise. ‘How did you know that? Oh. Jansson told you.’

‘We spoke a lot. Especially when she was in her last days, during Yellowstone. Told me a lot about her life. Her time with you—’

‘We’ll have to go down,’ Willis said, cutting across their talk. ‘Into the hole.’

Sally took a breath. ‘I was afraid you’d say that.’

‘In the spirit of noble exploration, I suppose,’ Frank said.

‘No. So that I can get up close and personal with that cable. And get a look at the root station.’

‘OK,’ Sally said dubiously. ‘Suppose, hypothetically, we agree we’re going to do this. How? We don’t have twenty miles of rope – do we, Frank?’

‘No. Anyhow we’d need a lot more, for doubling up, fail-safes.’

‘We don’t have winches, or jet packs—’

‘We fly down,’ Willis said. ‘We take one of the gliders, and fly down.’ He looked at them both. ‘You’re going to say no, aren’t you? Look. You can see how wide this pit is. A half-mile across – plenty of room for a spiral flight, down and back up.’

‘The air at the base is a hell of a lot thicker than the design optimum, Willis,’ Frank protested.

‘You know as well as I do that fifty per cent bar is still within the performance envelope. And besides, there’s a lot of heat seeping out of this hole in the ground. We can ride back up using the thermals; that will help.

‘Here’s the plan. Two of us will ride one glider down, leaving the other glider on the surface as backup, together with one pilot. We can offload stores before the flight. There are obvious fallback strategies, if anything goes wrong. Maybe we could even climb back up, out of this pit. The gravity is a baby.’

Frank said, ‘Why not send down a drone plane?’

‘Not equipped to take samples.’

‘But—’

‘End of discussion,’ Willis said. ‘We came here for that damn space elevator. We ain’t going home without a piece of it. Got that? OK. Let’s get down to specifics.’

They argued about how to split the crew. They agreed that one should stay on the surface, two descend. Which one, which two?

In fact the logic was clear. Willis was always going to go into the pit. Sally was the least good pilot, but as the youngest and fittest she had the best chance of climbing out of that hole in the ground if things got bad enough. Frank, meanwhile, the best pilot, was the obvious choice for the reserve on the surface.

Willis and Sally it would be, then.

Willis fretted through the day that Frank insisted they took in offloading Thor, the glider to be used for the descent, testing through its systems one more time, checking over their pressure suits and other gear, working out communications protocols and the like. And if Willis was restless, Frank was visibly unhappy, whether because the stunt was so obviously dangerous or because he was the guy left behind to mind the store, Sally wasn’t sure.