Greg Egan - Incandescence

«Some of the isotope ratios look marginal,» she noted. «Nothing we've seen here says that the meteor could not have come from this system, but the data we've got from this planet so far isn't as close a match as I'd expect.»

Rakesh laughed. «So maybe the Aloof have a sense of humor after all? They put us into orbit around this desert world, knowing there was a sibling with oceans and forests a few million kilometers away?»

«Let's see if there are any siblings at all.»

In fact, they knew from the Amalgam's catalog that there ought to be at least three, and Parantham's search quickly found them all. One was a «baked» gas giant, a ball of methane and hydrogen more than a hundred times heavier than the world below them, orbiting at less than half the distance from the sun. It possessed two rocky satellites, both far too small to hold atmospheres. The second and third gas giants lay in tilted, highly eccentric orbits, further from the sun. One had four significant moons, the other three, but none of these satellites looked promising either as hosts for life, or as geochemically plausible parent worlds for the meteor.

«This is still our best bet, then,» Parantham said.

«Assuming we're even in the right system,» Rakesh added.

«I wouldn't give up on that yet. If nothing obvious comes from the mapping sweep, we'll have to think about looking for microfossils.»

«Yes.» Rakesh's spirit sank; the promise was getting heavier by the hour. Here they were in the galaxy's vibrant core, and Parantham was talking about scouring a planet's worth of rocks for cavities that might once have been microbes. Still, if that was it — if this world was a bacterial graveyard, and the Aloof had invited them here merely to pay their last respects — once he'd done his duty they might yet reward him with the chance to see something more.

He toyed with an image of the four planetary orbits. No two of the ellipses shared the same plane, and the planets' axes were all over the place. That was what came of living in such crowded conditions: a neighboring star must have passed by and wreaked gravitational havoc. Rakesh ran dynamical models, testing the stability of the present arrangement, trying to get a sense of how long it might have persisted. The outer two gas giants were slowly nudging each other's orbits into a resonant configuration in which one world would complete exactly three trips around the sun to the other's two, but the process hadn't yet reached that stable endpoint. This and other signs that the system was still settling down after a profound disturbance suggested that the event had taken place between one and two hundred million years before. The same encounter might well have altered conditions on the world below them, though the geology still offered no indication that there had ever been running water.

«Metal!» Parantham announced.

«What?»

She pointed to the console. «The mapping probe just saw a glint of unoxidised, elemental metal. Mostly iron, with a number of impurities.»

Rakesh reviewed the data. High on a plateau in the tallest of the planet's mountain ranges, a metallic patch a few square meters in area had registered on radar, along with other wavelengths. Its detailed structure had not been resolved, but its chemical state alone was significant. In theory, rare geological processes could be responsible for such a deposit, but the surrounding rocks bore no witness to the necessary conditions.

They let the mapping probe continue its sweep of the planet, so as not to miss any further surprises, but they had the workshop build and launch a second probe tailored to investigate the strange glint more closely.

Rakesh said, «There was nothing in the structure or genome of the microbes we saw in the meteor that suggested they could metabolize metallic ores.»

«Viva diversity,» Parantham replied. «A microbial world is still a whole ecosystem. If this is biological, who knows what other niches there are that we haven't yet spotted?»

The second probe swept low over the plateau, and sent back high resolution images. The metal formed a blotchy but weirdly symmetrical patina on the rock, concentrated in six roughly elliptical lobes arranged in pairs around a central axis. It was hard to see how any underlying ore body that might have been metallized by microbes could have taken such a shape, though perhaps microbial colonies could self-organize into this pattern for some other reason. Spectroscopy revealed no organic matter, but that didn't rule anything out; a similarly remote view of the Aloof's DNA-infested meteor would have portrayed it as equally sterile.

They waited two full planetary days before taking the next step, allowing the mapping probe to image the entire surface. They passed the time arguing about the possibilities, cooking, eating, occasionally sleeping. Rakesh felt a strange mixture of urgent curiosity and an equally strong desire to prolong the unfolding process of discovery. Was this how it had been, to live in the Age of Exploration? Every world had held surprises then, when the ancestors of the Amalgam had still been slowly reaching out to find each other. Back in the disk, every planet he'd set foot upon had been visited by a hundred billion people before him, its every feature catalogued in more detail than he could hope to match with firsthand observations in a thousand years.

The mapping probe found no more elemental metal, and no other chemical anomalies at all. To the limits of the probe's resolution and sensitivity, every other structure and substance on the planet's surface could be accounted for by geological effects.

Rakesh knew exactly what he wanted to do next, but he was unsure where his obligations lay. «What are the rules about landing on a world like this? Just because we can't find a trace of life doesn't mean there aren't a billion software citizens buried in a processor somewhere.» The disk contained thousands of planets where all evidence of biological ancestry had been carefully wiped from the surface, out of a desire to avoid attracting attention. They were all catalogued now, and their inhabitants left in peace, but the earliest of the explorers who'd chanced upon such places had sometimes triggered substantial animosity.

«If the Aloof don't want us setting foot here, I'm sure they'll intervene,» Parantham replied. «If this planet has custodians who are distinct from our hosts, it's the people who brought us here who have a duty to ensure that we cause no offense. As long as we act in good faith, it's their responsibility.»

«I can't argue with that,» Rakesh conceded, «but it still doesn't feel right. Act at will and then see if you're restrained or rebuked, like a child?»

Parantham said, «They chose their relationship with us. If they want to open up a dialogue, if they want to educate us, they can do that any time. Until then, what choice do we have? We can't intuit every cultural sensitivity from first principles. So long as we do no harm, if we blunder in where we're not wanted it's up to someone with local knowledge to give us a civics lesson.»

«If you go back far enough in history,» Rakesh countered, «I can think of some civics lessons I'd rather not have.»

They argued for hours, but finally settled on a compromise. They would send down a small collection of probes to investigate the anomalous metal. They would not literally set foot on the surface, but telepresence would still grant them most of the same advantages.

Rakesh switched his senses to his avatar as it plummeted through the stratosphere, curled up inside the heat shield that protected the whole exploratory package. There was no light source within the ceramic cocoon, but when he shifted his vision to infrared the differential heating of the shield provided enough contrast for him to make out his immediate surroundings. Parantham's avatar was coiled snugly behind the laboratory/rover, his jelly-baby twin. Both of them were about a millimeter tall, and shorn of unnecessary extras, leaving torsos, pudgy arms and legs, and heads without mouths or noses. The lab's machinery would do all the smelling, and their real bodies could do all the talking.