The concepts of self-replicating geoengineering robots and biomechanical ecosystems are far from novel ideas in the realms of science fiction. Nor is the concept that such a system may either go out of control (self-replicating "grey goo" is a nightmare scenario that has cropped up many times) or, at the very least, naturally evolve their own selective responses and "break free" of their original masters. Heck, I even know of a speculative evolution project that has a very similar setup: a moon within our own ecosystem with a metal-and-hydrocarbon ecosystem that has emerged from a geoengineering project gone haywire, most likely of extraterrestrial (or extra-solar) origin. But, to its credit, Petrolea explores these ideas in greater depth and with more nuance than most instances I've encountered before.

So we have Titan, Jovian moon and extraterrestrial oil factory – an ideal place to analyse the ethics of extractive capitalism and the fossil fuel industry, now saved from their own form of extinction by the discovery of a seemingly inexhaustible supply within "easy" reach. Except no "machine" or "factory" can be this complex without some level of intelligence, and in this case that is being provided by a form of biological programming; robots imbued with Darwinian instincts that have driven a form of natural selection to create an entire ecosystem of robotic critters that can convert an otherwise desolate moon into a thriving biosphere. Our protagonists find themselves on either side of common conflict, chiefly whether the exploitative nature of humanity is at risk of destroying this unique habitat, which then (as is the norm) spirals into a survival narrative once the moon fights back.

Woven throughout this are some decent attempts at moralising and plenty of clever spec-evo ideas around how such an ecosystem might work and the kinds of lifeforms that might populate it. I also thoroughly enjoyed that our programmer is able to "hack" the animals around them, and thought that the twist around alien "tripwires" (more like a combination of firewall and antivirus) was nicely done. It's fun seeing a similar tale as something like The Martian play out in a world where the wildlife can be programmed to kill itself and become an oxygen still or protein formatter, or even a house.

However, whilst the romantic subplot did at least put an end to the incessant infighting between the two main characters, it also felt a little weird and unnecessary. Plus, the story really just stops. We go from a revelation about great "spore" arsenals, seemingly ready to invade the rest of the solar system and protected by ranks of militarised "dragons", one of the more formidable local lifeforms, to a jump cut where those issues are overcome off-page, our survivors have all linked back up, and are possibly considering going to war with the Terran governments to protect what they now see as either their home, or at the very least, their property. It's a bit confusing and not overly satisfying. It also leaves a lot of questions around the original intent of "Petrolea"; who the "makers" in this scenario actually were (and what became of them); and how they have managed to seemingly "domesticate" an entire biosphere? It's not so bad it ruins everything else, but I'd have loved a story twice as long, twice as detailed, and with a substantially more, well, substantial ending.

Also, I don't think I've ever read a novel in serialisation format before. I'm not sure I love it, but I don't hate it either, and it certainly helps draw out a shorter format story like this into something that feels a little more substantial.