In Texas an alert survivalist had reached his shelter in time, where he clutched his shotgun and wondered what to do about the fake snowfall that covered the ground up above. But the nanobots had traced his scent, and while some dissolved into sub-microscopic forms which could penetrate the shelter air filters, others built up into units which had the ability to force entrance into the physical structure.
All carbon-based life, except green plants which practised photosynthesis, would be wiped out within a few hours. The nanobots had been programmed to leave the plants alone, for now. More selective work would be done later.
Up in orbit an alert vibrated at Commander Mondar. The indigenes had launched a missile which scans indicated was probably armed with a fission warhead. She twitched her crest in surprise. She had not thought them evolved even that much.
"Keltan," she ordered, "stop that. Let's not take chances."
Armaments director Keltan hissed and entered the necessary commands into her console. An energy ball launched at near-light speed on an intercept course and less than a second later the missile exploded harmlessly far below.
Commander Mondar buzzed angrily at Keltan, "I didn't tell you to blow it up. I said 'stop it'."
Keltan's crest crumpled in shame. "Yes, Commander. I am instructed."
Mondar was vexed with herself. As an elder it was her responsibility to instruct clearly, and to ensure that the youth understood properly.
"So that you understand, Keltan, my concern is the effect of the blast upon the programming of the nanobots. It can be unpredictable. Therefore it would have been better to simply disintegrate the missile."
"Understood, Commander. I am instructed."
Talik listened absently to the exchange; he had more important duties to engage his attention. The initial purification had gone according to plan, but the ocean depths were more complex than preliminary surveys had indicated. He considered the options, and then computed and transmitted the necessary changes to the submarine nanobots. Within a few minutes he noted a satisfactory response.
The planet was purified. The only life remaining was plant life, and of course the nanobots which now saturated the entire globe. Talik requested a thorough final scan to confirm complete purification, and in a short while he had the yellow light of the all clear. He hummed in satisfaction and punched in the termination command to be broadcast to the nanobots.
"Planet purification complete, Commander," he reported.
"Good job, Controller," Mondar hummed back.
On Talik's main screen an error light lit.
It seemed that not all of the nanobots had terminated themselves; there were a few remaining in the indigenes' Northern hemisphere, in the northern part of the largest continent.
Talik's crest twitched and flexed, reflecting his irritation with incompetent sub-programmers. He punched in the secondary termination command and transmitted it, and when the stubborn nanobot survivors ignored this as well, sent out the failsafe 'interrupt all functions'. He hissed quietly as the number of wild nanobots reported on his screen dropped to zero.
"A small problem with termination, Commander, but I've dealt with it."
"Very good, Controller. Move to phase Two," Mondar responded.
"I am instructed, Commander."
"What exactly was the problem, Controller?" Mondar enquired in afterthought.
"An initial failure to respond to termin -" Talik broke off, and his crest retracted entirely as an icy concern chilled his brain.
On his console the detected number of wild nanobots had just flicked up from zero to one, and, even as he watched, it rose to three, to seventy, and then rapidly into large numbers.
"Commander, we have a problem," he buzzed in alarm.
As a precaution against the geometrically increasing number of uncontrolled nanobots on Regon III, Commander Mondar had withdrawn the ship somewhat, to a higher orbit.
"Could we not have programmed new nanobots to terminate these wild ones?" she asked Talik.
"Yes, sir, but look at this reading: their mutability response is off the scale. The cleanup nanobot design must specify parameters for the wild 'bots they are designed to terminate. But because these wild 'bots are so mutable they would respond too quickly; they would re-engineer their own design to beyond the parameters of the cleanup bots. So we could send down cleanup 'bots, but it would do no good."
"Then why not send down the universal termination set? They're intended for just this situation. I know we'd have to rebuild the entire planetary biosphere after the UTS have cleaned out everything, but we have the capacity to do that if we must."
Talik called up another report to his screen and gestured at it.
Commander Mondar studied it, and even her crest folded down as she turned to Talik.
"The protected termination node has somehow been communicated from the UTS to the wild bots? I thought that was impossible?"
"So did I, sir," Talik buzzed in quiet despair. The Commander hadn't yet realised the full implications of what they'd done.
"Well, at least they're confined to Regon III. We have the fallback option of Regon IV," the Commander offered hopefully.
Talik faced her, webbing grey with despair.
"No, sir, I'm afraid not. I'm afraid no one in this universe has any options any more."
"What do you mean?"
"The wild bots are not confined to Regon III. Nor even to this solar system. In my professional opinion."
"What? That's ridiculous!"
"No, sir. They will multiply until they fill Regon III, and overflow it. You know that, right?"
"Yes, that's elementary."
"You remember how evolution works, sir?"
"Of course I do, I'm neither ignorant nor a fool," Mondar buzzed harshly.
"Sir, we know that evolution works over a long time with lower radiation levels among planetary populations. What happens when a population of innumerable trillions expands into direct solar radiation to stimulate mutation? When that population also has the capacity to actively direct its own evolution? How long do we have until the nanobots fill this solar system, and then - "
Commander Mondar blanched.
"We must warn our people back home!"
"Yes sir. If we can get back to Mirda in time."