Endeavour pulls out of Earth orbit with 26 souls on board. First destination: Alpha Centauri. For the scientists the month of travel is a relatively quiet time: most of the advance work has been done, and apart from the day-to-day lab maintenance there's little of importance. For the crew it's rather busier: this is further from home than humans have ever been before, and there's no way to call for help. Billy runs simulations of the complex Alpha/Proxima Centauri system.
A light year out, the ship's telescope is pointed at the target, and the system can be seen in rather more detail than from Earth. Alpha Centauri A has two planets, one small rockball and one large chthonian (big enough to hold an atmosphere, but it's been stripped by ion pressure from the star). Proxima has one small rockball and an asteroid belt. But Alpha Centauri B, as well as a couple of small worlds close in, has a gas giant around 160 Earth masses in an eccentric orbit about 0.9 AU out, and one of its many moons is showing signs of oxygen.
From 200 AU out, the ship's spinal-mount telescope can resolve definite signs of life, and something that from its distribution across the surface might even be cities! It's a cold world, though, with mean surface temperatures around -40C; the only liquid water is what's exposed by tidal stress as it orbits the gas giant, and it rapidly freezes. It's also tidally locked, meaning the local day matches its 18-day orbit round the gas giant.
Interestingly, the two moons immediately closer in to the gas giant are also substantial, though not big enough to retain atmospheres of their own. At conjunction, the outer one would be closer than Earth's own Moon.
Endeavour drops off stellar-observation satellites on its run in-system, and there's some discussion about naming. Borshevsky favours heroes from Russian opera, and Billy suggests Exploration Service board members for the many small useless moonlets, but eventual consensus is to use the names of astronauts and others who died trying to leave Earth's atmosphere. So with deference to Borshevsky the life-bearing world is named Volkov, with the two substantial inner moons becoming Dobrovolski and Patsayev.
Endeavour takes up orbit round the gas giant, and observation continues. There's an interesting life form on Volkov, roughly human-sized, though it rather resembles a six-legged starfish in overall plan. It doesn't seem to be using any sort of visible tools or technology; and judging by the amount of plant life, the ``cities'' are either ruined or based entirely on biotechnology.
It ranges between the equator and about fifty degrees north or south; the ``cities'' are scattered across the same range. Much further north, about eighty degrees and on the side of the world facing away from the gas giant, is a plateau about ten miles wide, with a mile-high tetrahedal mountain in the middle of it (rather weathered); this is certainly not a geological accident.
Working on the assumption that it was built by intelligent life, rather than being a giant alien beehive-equivalent, names like ``Precursors'' and ``Great Old Ones'' are discussed, but there's no immediate consensus.
The first expedition to the surface goes down in the lander Nina, led by Borshevsky and carrying mostly bioscientists, including Liu - heading for an area without any of the large creatures. Everyone's wearing insulating covers over their pressure suits, and while Borshevsky gives a prepared speech to the cameras the other scientists spread out in a sample-gathering frenzy.
The presence of the gas giant in the sky, eight times the size of the sun and permanently in the same place, is distracting, and without shifting shadows only reminders from the ship get the team to stop working and return. They don't have any trouble on the surface; a small predator, about three or four inches across, has a try at getting through someone's boot, but when flicked away doesn't return. The local macrolife seems to be fairly clearly divided into plants and animals, though one of the plants uproots itself and scuttles away when not directly observed.
Billy tries to persuade Borshevsky, from orbit, that this expedition is a waste of time and the tetrahedral mountain repays immediate study. He doesn't have much success.
Once the expedition has returned, the analysis begins. The local life is using structurally-recognisable nucleic acids, but they're compounds other than DNA and RNA; if Earth life were to try to eat them, or vice versa, there wouldn't be much nutritional value, and there might be a risk of nausea.
The ship's sensors catch a flash of light from the next moon in, Dobrovolski, and the big telescope is focussed on it. There seems to be a geodesic structure on the surface, some three miles across, facing outwards from the gas giant; more probing reveals another on Patsayev. It's at background temperature, but is quite certainly artificial, and on the next ship's day Pinta is taken to have a closer look.
Looking at the micrometeoroid wear suggests that this structure has been in place for at least twenty million years; it's been built with thick plates and braces, and doesn't seem to have suffered structural damage. Its triangular framework is about a mile high at the centre, and supports a mesh of thick metallic plates. The framework is open at ground level, and several struts are missing, making an entryway some five metres wide. Outside are various worn features that might be wheel ruts.
The crew takes an exo-spider across the rough terrain; there's some light inside, but the headlights help a lot. There are various tracks in the dust, preserved by the framework; one consists of a series of parallel lines, like the track left by a rake. Another looks like a wire-mesh wheel like those used on the first lunar rovers. Everything gets documented.
At the centre of the dome is a series of upright cuboids, about eight feet tall, three feet wide, and one foot thick. On both flat sides, letters are incised several inches deep. There's very little meteoroid damage or dust intrusion (and what there is seems to be even along the row).
The first slab lists, in a vertical column on the right, prime numbers, as patterns of dots. In a parallel column are the same numbers in what seems to be a base-16 representation. Further in there's a periodic table (whoever wrote it apparently regarded chlorine and silicon as more important than the other elements). The rest of the messages are more complex, though two things stand out: something long and complex about incident radiation, atmospheric gases, and a planet's climate, and a pair of maps.
One of the maps is clearly of this solar system: next to the symbol for Volkov is a glyph of one of the six-legged starfish. The other is more of an enigma: it clearly associates Alpha Centauri B with the starfish, and another star with a latticework of triangles. But it's not at all clear what that other star is: it's labelled as 27 somethings away, but there's no immediate clue as to the size of those units or how the map should be orientated.
Billy sets up seismographic probes to look at the valley in which this structure was built (to initial inspection it's a fairly normal lunar surface consisting of loose dust over rock). First results suggest that it's a fairly thick slab of rock, but all in one piece, unusual for something between a pair of hill ranges. More detailed surveying suggests that the whole floor of the valley has been re-formed, perhaps melted; the upper levels are slightly more depleted of volatiles than the lower.
This isn't beyond the reach of current technology: Billy's first reaction is that a solar mirror would be the right tool for the job. But it would be a substantial undertaking, particularly given the complex orbital pattern of Dobrovolski, and it doesn't appear to add any especially great stability to the setup; the moon's been tectonically dead for much longer than this has been here.
The dome itself is a metal-heavy composite; it's not a particularly consistent alloy, but there's aluminium and magnesium in there. It's probably not constructed entirely from local materials.
Looking at the orbital periods of the three large moons, there's no obviously significant ratio between them. Billy points out that with enough searching there's bound to be something.
Something that seems to be a star map shows up on the slabs, but it's odd; the three-dimensional projection is hard to work out, and there's a jagged line across it, jumping from star to star apparently at random (certainly not by anything like a direct route).
Jim catalogues the tracks. They're generally in a rough ring just inside the dome area; they all seem to lead inwards. Some show definite traces of bipedal locomotion; others, hexapedal.
Min-Jee confirms that the XNA of the Volkov creatures has been sequenced; knowing how DNA works was obviously a good start.
Patsayev, the third large moon, is surveyed; there's another site there, similarly in a valley, and facing away from the gas giant. The setup isn't identical, but it's very similar.
Struck by a sudden sense of paranoia - after all, there's a lot of general grot orbiting the gas giant, what if a larger rock had fallen on the dome? - Billy scans the mountaintops surrounding the valley, but there's no sign of anything odd. If there is a defence system here, it didn't react to the shuttle.
Landing at Patsayev reveals an identical dome, with a similar setup of footprints inside it; Jim leaves some of his own. Looking at the erosion of the others, they all appear to have been made at roughly the same time.
The contents of slabs are identical. Really identical. Including the micrometeoroid scratches.
Marking the corner of one of them with a hand tool, then going back to Patsayev, reveals that it's now marked in the same way. It's not warm or emitting anything unexpected.
Jim: ``You know how Billy said they like to make their point? They're quite fond of understatement.''
The next experiment uses a seismic thumper, rerigged onto one of the slabs, and a sensor at the other site. The vibrations propagate. Instantly, rather than with the four seconds or so of light-speed delay.
Tapping out codes, and listening, reveals no signal coming out that's not being put in. There's a slight increase in gravitational noise, very roughly correlated with input, and counting that there seems to be more energy being emitted overall than is being supplied.
Jim wonders whether there might be a slab inside the tetrahedral mountain on Volkov. There's no detectable gravitational noise, but it's harder to spot near the massive moon.
The crew sends a shuttle down to the mountain, and Billy applies more seismic probes. This one does show very eroded signs of tool marks, or at least things that might be heavily-eroded scars of drilling and dynamiting. The valley floor shows no signs of having been melted.
More probes get a rough picture of the inside of the mountain: there are vertical chambers up the middle, with a division about two-thirds of the way up, and a horizontal passage leading out from that point.
The rock is igneous, presumably ex-volcanic, so these might be lava tubes. But it's ten to a hundred million years since they cooled.
Getting to the entrance is tricky: while the shuttles can hover, the drive field makes it tricky to let people on and off. Eventually a shuttle lands on the summit and drops off an exo-spider with a long rope; the driver rappels it down the steep face, then locks it in place with more anchor cables next to the entrance.
The entrance is choked with frozen rubble, clearing which takes some hours. It's a cylindrical passage about two metres in diameter; about three metres in, there's a ring that might have been some sort of anchorage point for a door, though it's decayed enough that there's no way of telling. There's only the one ring; this doesn't seem to have been an airlock.
The passage continues, still cylindrical. High on one side there's a long thin rust stain, possibly from an iron or steel thing that was once fastened to the wall.
At the end of the passage, a larger cylinder some twenty metres across stretches up into the darkness. There's a railing dividing a narrow outer catwalk from the central area, which contains a huge brass gear (some ten metres across). In the centre is a pendulum, oscillating very slightly and very slowly - perhaps from trivial earth tremors.
There are two sets of dials, offset slightly round the chamber from the entrance point. They're pointing in various directions, though the two sets are consistent with each other, and arranged in rings, between half a metre and two metres above the floor.
There are other gears, one of which moves perceptibly (though still very slowly); some examination shows quite a bit of play: they've been turning for a very long time (and their tooth surfaces are quite shiny). There are piles of swarf under the relevant spots. Billy reckons on metallurgical grounds that this has been running for between one and ten million years.
There are vertical shafts passing through holes in the floor of the pit, but not obvious way of getting down; there are also helical rust stains on the walls, leading upwards.
A plaque on the far side lets the team link some of the dials to local astronomical events, and thus years; the elapsed time it's showing is around eight million (Earth) years. It'll roll back to zero in another fifty-odd.
Min-Jee squeezes through one of the holes in the floor, working her way round the rod. There's mineral oil vapour coming up from below, but still no sign of light sources. The vertical rod continues to descend through the smaller chamber she emerges into, passing through a fluid surface; it's all a bit slippery, and her boot ends up going into the oil, but this is just another way of getting a sample.
There's no obvious tide-mark, but it seems as though this might be an energy storage system of some sort.