The Lurker
by Gregory Benford & James Benford
August 12, 2049, 8:33AM
“What the hell is that?” Sabine says.
Her husband, Dilip, frowns at the big screen. They’re approaching the quasi-satellite officially known as 2016 HO3. It’s a small asteroidal body, a rubble pile most likely, that was only discovered in 2016. It’s named Kamo’oalewa, a Hawaiian word that refers to an oscillating object. The earthlike orbit and lunar-like silicates might be explained as lunar ejecta, a piece of the Moon broken off by some past collision.
Kamo’oalewa is very small, a fast rotator, about a hundred meters in diameter. It falls into the category of quasi-satellites of Earth. It’s the smallest, closest, and most stable known quasi-satellite, which is an object in a 1:1 orbital resonance with a planet, so that the object always stays close to the planet. Outside the Hill sphere, that region where an astronomical body dominates the attraction of satellites, which for Earth is 1.5 million kilometers. So quasi-satellites cannot be considered true satellites. Instead, while their period around the Sun is the same as the planet, they seem to travel in an oblong retrograde loop around it. Kamo’oalewa roves in an odd looping orbit, varying its distance between thirty-eight to a hundred times as far from Earth as the Moon.
Sabine is using advanced multispectral telescope imagery at a range of five kilometers.
Dilip says, “Looks circular, but with odd white spokes extended radially.”
Sabine peers at the shifting view and says, “Not a crater, though. Too regular. The spokes are at . . . . . . . . . lessee . . . . . . . . . sixty degree spacing.”
Dilip comes to sit beside her. “So . . .”
“Artificial. Not natural, not human . . .”
“Didn’t the Chinese send Tianwen 2, a collector probe, out here back in—what?—the 2020s?”
“Launched in ’26. They couldn’t get it to match with the fast rotation, every half hour. So they just tried a landing on it anyway, even though it’s rotating. Never heard from again.”
“This thing though—” Sabine pauses, making the perspective calculation on her board. “It’s big. Ten meters across, easy.”
Dilip frowns. “That old Chinese craft was plenty less than that.”
“So this is . . .”
“Not theirs. And not ours at all. This answers two big questions. Clearly there is life and civilization elsewhere! It can’t have come from the solar system.”
“Look at how the shadows of that edge move, as the rotation brings it into view. The circle is higher than the dusty regolith around it. Yep, not a crater. Or a rebound from an earlier impact, or . . .”
“But the same pale dusty color as the regolith around it. So camouflaged, maybe?”
Sabine nods. “Hidden from any ordinary spectrum search, can’t see it by just looking at its reflected sunlight. So this thing is impossible to see from Earth. It’s well hidden, but can see Earth closer than anything except the Moon.”
Their craft is named Dyson after the great twentieth-century scientist. The onboard nuclear drive, lodged below a cluster of thick cylindrical propellant tanks, gets managed by the robotic crew. “Above,” relative to forward acceleration, is the tech-deck where the other crew works to keep the nuke and everything else running right, plus usual maintenance work. The big craft needs as much attention as a newborn baby.
Dyson is a nuclear thermal rocket. Fact is, chemical rockets are just not good enough. Sure, chemical rockets took us to the Moon the first time, but to do that, most of what was launched from Earth was fuel and the tanks to hold the fuel. What we needed was the spaceship equivalent of a pickup truck: a simple, rugged, and basic transportation system capable of hauling the astronauts and a big load of cargo for the Space Force to police cislunar space. And that pickup truck is the nuclear thermal rocket.
A nuclear thermal rocket is fundamentally extremely simple. A nuclear reactor produces heat. If you pass a gas over that heated reactor core, the gas heats up—and you can expand heated gas out a nozzle to produce thrust.
So a nuclear thermal rocket is actually far simpler than the nuclear generators used to produce electrical power on the Earth; most of the parts needed to generate electricity aren’t needed. A nuclear thermal rocket consists of a tank, a pump, a nuclear reactor, and a nozzle. That’s all.
In fact, space is the ideal place for nuclear power: between the trapped high-energy particles of the Van Allen belts, cosmic rays, and solar flares, space already is basically radioactive. You wouldn’t want to crash a nuclear thermal rocket on Earth, so there are operating regulations that don’t allow nuclear rockets in orbits that would decay in any time shorter than a hundred thousand years. Their natural home is in space.
Back in the 1960s, NASA had a program called NERVA (Nuclear Energy for Rocket Vehicle Applications) to develop nuclear rockets. The Russians also had their own development project. But these were mothballed. Nixon decided not to follow the Apollo missions to the Moon with a program to send humans to Mars, so the NERVA program was canceled for lack of an application—but not before over twenty different nuclear rockets were designed, developed, and tested. They just never were used in an actual flight.
Then in the 2020s nuclear rockets came back with the DRACO program. Nuclear rockets are so effective because the energy in nuclear bonds is so much greater than that in chemical bonds. For any thermal rocket, nuclear, or otherwise, the exhaust velocity is proportional to the square root of the temperature. So for more thrust per pound of fuel, you must have higher temperature exhaust. How hot can you go? Dyson uses the particle bed method and operates at 5,000 degrees Celsius, a temperature way above what chemicals burn at.
In a nuclear rocket, the energy source and the reaction mass are separate, so in principle, you can use almost anything for reaction mass: heat it to a plasma, and let it expand out back. Hydrogen can be found anywhere a spaceship might want to go in the form of water ice, so it makes an attractive propellant. You can use electrolysis to split out the hydrogen for reaction mass and save the oxygen for the crew to breathe, or if you want higher thrust but can afford lower performance, you can use the water directly. Water’s a lot easier to store, and you need big, tight tanks to hold hydrogen, and you have to keep it cold, about twenty degrees above absolute zero.
Dyson is fueled using water harvested from the Moon. That makes the hardware simpler and more robust and helps provide the thrust sometimes needed on Space Force duty. But water isn’t as good at blocking neutron radiation. So the reactor engine is at the back, below the tanks, which in turn are separated from the crew compartment to provide the best possible crew protection from stray reactor-generated radiation.
August 12, 2049, 9 PM
They coast closer to Kamo’oalewa. Space Force Huntsville, still puzzled by their detection, has observed a Chinese nuclear craft of unknown design headed toward their vicinity. It had appeared visibly on Huntsville’s system as it lifted off from the lunar south pole.
Dyson manages thrust and maneuvers, now slowly gliding toward the asteroid.
Huntsville’s flat voice comes on. “We’ve determined that the Chinese ship vectoring toward you is a new design, a nuke drive with surprisingly high acceleration. We think it may be a stripped-down freight carrier module, with a personnel compartment riding on the main thrust axis.”
Dilip says to Huntsville, “Sounds odd. What ETA?”
“Soon, a day or two. Depends on their approach strategy. Maybe a Chinese stealthsat intercepted your report,” Huntsville said after the usual several-second delay.
“Look at this closeup spectral scan,” Sabine says as she gracefully walks across their control deck in the light-g tug. They keep it at a fifth g to lessen the zero-g body effects.
She had snapped the spectral lines at high rez. Huntsville runs those through their team and in a few minutes says, “The Chinese ship is running an augmented fuel, maybe pure hydrogen. No oxygen lines we can see.”
“So they’re lugging all the mass needed to keep liquid hydrogen from leaking. Not using water like us. They’re coming out at us pretty damn quick too” Dilip says. “Must be a nuke with high specific thrust.”
“Let’s do a flyby of Kamo’oalewa now,” Sabine says.
August 13, 2049, 10 AM
Kamo’oalewa swims on their big screen as a gray rock pile. They stand off at one hundred meters and watch it spin. Spectra show that it’s mostly metals with some ceramics. It spins so fast because of the YORP effect, due to the scattering of solar radiation off its surface and the later emission of its own thermal radiation as it rotates away from the Sun.
Sabine points to their big deck screen, set to max magnification. “See? Those shifting networks in the surface.”
Dilip frowns. “So? It has a pattern on it?“
“A pattern that’s changing. Look at this, from just eight minutes ago.” Huntsville already has the patterns, sent live. The flat voice says, “This is active matter. Not passive. Crystals altering, self-organizing into a new pattern. We’ll get the AI doing pattern recognition.”
“How did it look before?” Dilip asks.
“Static. It’s reacting to us. Or to the Chinese approaching. Maybe it reacted to that Chinese mission way back in the 2020s, and that’s why they lost comm with it. Where did this thing come from? Interstellar?”
Dilip squints at the display.“And how did it get here? I see no propulsion. It looks like a big disk. I’ll ask Earthside . . .” He thumbs on the mic and says, “Operations, need back info. Ask Oracle, when did a star last pass near ours?” He’s calling on the Cislunar Highway Patrol System, which hadseemed to produce negative feelings and so had been renamed “Oracle,” without any irony.
After some delay, the reply is “Our most recent stellar visitor was . . . . . . . . . let’s see . . . . . . . . . Scholz’s Star. This infograb says it’s ‘two dwarf red stars orbiting each other, slinging by us.’ It came within 0.82 light-years from the Sun about 70,000 years ago, at about 82 kilometers a sec. Pretty fast. In their work on minor objects with long orbital periods and extreme orbital eccentricity, researchers find a significant overdensity of objects toward the constellation of Gemini that may be the result of the passage of this star. Studies of the paths of comets with exaggerated, hyperbolic orbits found that a subset appear to have trajectories that were perturbed by Scholz’s Star. It passed through the Oort Cloud. So we’ll get comets falling into the inner solar system in about 2 million years. The Scholz’s Star is a binary; primary is a red dwarf about 86 Jupiter masses. The secondary is a brown dwarf with 65 Jupiter masses. The system has a mass total of 0.15 of the Sun’s mass. The pair orbit closely at a distance of about 0.8 astronomical units (120 million kilometers, 74 million miles) with a period of roughly 4 years. The system is estimated to be between 3 and 10 billion years old. It’s speeding away; about 80 star systems are known to be closer to the Sun now.”
Sabine is skeptical. “Why send a probe here?”
Dilip replies, “The time over which our biosphere has been observable from great distances, perhaps thousands of light-years, due to oxygen in the atmosphere, is a very long time, billions of years. The first oxidation event occurred about 2.5 billion years ago! An ET civilization anywhere nearby can see there’s an ecosystem here, due to the out-of-equilibrium atmosphere. They could send interstellar probes to investigate.
“Sabine, do some trig, and—say the probe moved at a thousand kilometers a sec . . .”
“That’s damn fast for a ship.”
“But not for our beam-driven sails.”
“Those are light structures for fast interplanetary supply in emergencies. And for interstellar flybys. We’re talkin’ interstellar here . . .” Her fingers dance on her arm familiar, which winks to show it’s on the computations, based on what it’s heard, without her further instruction. “Scholz’s Star would be within a light-year of us for maybe a year, depending on its angle of approach . . . . . . . . . So could launch a few probes toward us. It would take about three centuries for them to get close enough for optical and radio observations, but still far enough away not to be easily detected.”
“You’re assuming this society around Scholz’s Star is interested in info coming back to them, centuries later. So their institutions must last that long. So their probe—that thing holding onto this co-orbital rock, because it stays near Earth and comes near Earth every year—has to last centuries. In open space with radiation, vacuum. How?”
Sabine shrugs. “For power, a good reactor.”
“How long could that last?”
“Decades easily, but even centuries, with more uranium or plutonium-239—that’s maybe bomb-grade, swift stuff indeed. Maybe they knew tech we haven’t thought of yet.”
“So this thing has been looking at Earth for . . . . . . . . . a long time.”
“It’s got to be somewhat intelligent, just to survive out here.”
Dilip covers the mic even though it’s off. “Those changing dots down there—a signal? It wants to talk?”
“Earthside has to decide what we do next.”
“Let’s use our heads, not theirs! And let’s call it ‘the Lurker.’ Maybe it’s this close in order to observe Earth.”
Sabine works the controls, gathering high-resolution data on the Lurker. She finds no hidden structures, telescopes or antennas. Then she looks down at a panel. “Space Force Earthside sends exhaust velocity readings of a Red Chinese high-thrust rocket that’s approaching our position. Big thrust.”
They maneuver closer to the Lurker, observing the probe on the asteroid’s surface and flurries of messages from Space Force command, about whether to announce the find versus media firestorms et cetera. The consensus seems to be that might lead to hasty thinking. Let’s release minimal information, if any, and take no provocative action.
Which is fine, Dilip and Sabine agree, except for the international incident bearing down on them at interplanetary speed.
They hold in place, discuss how to closely approach the asteroid.
“Should we signal it?” Dilip asks.
“Not authorized, for sure.”
“Let’s not tell them. Let’s just inch up on it. Just nearer, maybe turn on our outer spotlights to show we are aware.”
Sabine nods. “The Lurker might think that’s a signal.”
“So we’ll blink the lights, no more?”
Sabine nods and together they make it happen. The Lurker’s pattern again changes appearance, but no signal is sent back via radio, microwave or visible.
Desperately overdue, and wanting to be rested when the Chinese arrive, Dilip and Sabin signal Huntsville they are starting their sleep cycle. They instruct their onboard Watch Assist to keep a standoff distance of three hundred meters, record everything, and alert them when anything changes.
August 13, 2049, 9 PM
The Chinese craft comes in at high speed. No comm from them at all. Earthside has decided to withhold the story from the public. The Chinese–Space Force comms have gone silent, shut down. The Chinese rocket turns about and starts a powerful decelerating pulse. Hours later, the craft arrows in to rendezvous at a one kilometer standoff.
By this time, Sabine and Dilip are awake.
“There’s a Chinese voice signal, Dilip. It’s in spoken Mandarin.” It’s made into English by the AI translator, complete with grammar and pronouncement errors. This is part of that continuing Chinese attempt to force people to master Mandarin. Their campaign has failed but they keep at it. The Chinese message is just a call sign.
“Let’s reply.” Dilip opens the mic and says, “This is Dilip and Sabine Bhadra calling from the Space Force ship Freeman Dyson. What is your identification and what is your mission? What are you trying to do?”
There is no reply.
After two full minutes, Dilip closes the channel. “I guess we’re going to stay quiet.”
They observe the Chinese craft deploy a team of telepresence robots, heading toward the Lurker. Space Force Earthside says to stand back and watch. Dilip thinks otherwise. “We’d better send out our bots too.”
Space Force agrees. They begin the checklist to deploy their own telepresence robots as the Lurker starts showing visual quick shifting patterns—as if trying to deal with the intruders.
Chinese in space suits and riding an EVA craft detach from the Chinese vessel, joining their robots.
Sabine says, “The Chinese vehicle and their robots are approaching closer, and the Lurker pattern is getting a more agitated surface. I see puffs of local dust at the Lurker perimeter. They’re prying at the edge of the Lurker! Maybe dislodging some anchors? They’re trying to pull it away from the surface!”
There’s a visible flash from the Lurker and suddenly their screens go blank.
Sabine scans the console. “There’s an AI alert . . . . . . . . . There’s been an electromagnetic pulse on all measured bands and wavelengths, optical through radio. We can’t see anything. Good thing we hadn’t deployed our robots!”
Inside Dyson, they are shielded. Its external systems soon reboot and screens flicker back to life.
Dilip says, “The Chinese robots and spacecraft are drifting. And their comm carrier has gone dead. The pulse must have scrambled electronics in their spacesuits and their spacecraft. And their robots.” The Chinese taikonauts don’t seem to be moving in their vehicle.
Sabine says, “We’ve got to get them out of there! Into our ship, I suppose. Let’s launch our robots and try to open up their ship and extract them.”
Their robots deploy normally. Some attach to the Chinese EVA craft, hanging adrift in space now. Some tug drifting space suits toward Dyson and into its air lock. When it cycles, Dilip is standing by to render air. He finds that the Chinese respiration systems are still functioning, so they’re still breathing. He cracks open their faceplates. They’re still alive, but unconscious, and their suit monitors flash and buzz with obvious errors and malfunctions.
Sabine uses the autodoc to try to revive them. “Good thing we standardized these space medical systems in the thirties like the docking systems back in the twentieth. Otherwise the incompatibility would have killed these guys. Let’s see if they’ll revive in a bit.”
Dilip looks over the tools still tethered to some of the spacesuits: spades, cutters and electric pry-jaws. “Clearly they just wanted the tech. Pry it loose and take it home for study.”
Sabine nods agreement. “But this isn’t some passive space relic. It started transmitting in microwave. Maybe it’s talking to us. We’ll have to use an AI to see if it’s language. We’re gonna have to monitor this Lurker.”
After a few minutes, back on the console, Dilip says, “We’re getting a tightbeam transmission from unknown origin, looks like it’s further out, away from Earth. I’ll have the AI backtrack it and find the location—it’s from another co-orbital! The aliens sent more than one Lurker! It’s from asteroid 2023 FW13, which shares a similar orbit to Kamo’oalewa, but 9 million miles out. How many Lurkers are out here? We’ve already found a couple dozen co-orbitals. Are they all watching us?”
“Dilip, I wonder how long it has been here? Co-orbitals can be stable for very long times, so maybe we’ve been observed for a long time. Dating it will require a great deal of remote observation, but that’s a problem for the next expedition out here. Maybe this confirms the zoo hypothesis, that they don’t want to disturb us.“
“Zoo . . . . . . . . . Sabine, say it is trying to communicate; are we going to be able to understand it?”
“We’re going to have to stand off and try. And it’s going to try, too, now that it is awake. It will be faster than we will; it’s been listening to us and learning.”
“I wonder if it sent a signal out to wherever it came from?”
Sabine says, “I guess we’ll know in a few years. Space Force Command Station message coming in, says back off from the alien Lurker. They’re afraid if we linger, it’ll zap us like it did the Chinese. Maybe that’s right. Let’s get out of here, before the Lurker awakens further.”
Dyson turns away, heading for Earth orbit and the Space Force station, leaving the Lurkers to the next expedition . . . . . . . . .
***
Gregory Benford is best-known for his Galactic Center Saga novels and in 2017, The Berlin Project. His work has earned him two Nebulas and the Campbell Award, along with four Hugo awards and twelve Nebula nominations. He was a scientific adviser for Star Trek: The Next Generation, and his contributions in astrophysics and plasma physics earned him the Lord Prize in 1995 and the Asimov Prize in 2008. He is a Professor Emeritus at UC, Irvine, and an ongoing advisor to NASA, DARPA, and the CIA.
James Benford is a physicist, high-power microwave scientist, author and entrepreneur, perhaps best known for introducing novel technological concepts and conjectures related to the exploration of outer space, including laser-driven sailships, the possible use of co-orbital objects by alien probes to spy on Earth, and technical and safety issues associated with the Search for Extraterrestrial Intelligence (SETI).