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Chapter 6: The Heptapus

Simba here. I get my wish at last, to take a sample of the mysterious life on planet Njord. The ocean below me is an unhealthy yellowish green color: by my Earth-trained standards it looks like a mixture of chlorophyll and rot, like the leaf of a houseplant that's been backed into a corner by the pressure of other leaves.

Willie: OK, Simba, you're getting close to 35 kilometers altitude. Let's take an air sample about here.

Me: That would be at 92000 meters geopotential. Just a sec... Got it, right at 35 kilometers. The next should be at twenty kilometers, right? 77000 coming up... Hold it, hold it, there, got it. Did you decide on the tropospheric one? I need to know the altitude.

Willie: Eight kilometers; that's in the troposphere but kind of at the top. Ten kilometers would be too high.

Me: Here it is. Got the sample. Now let's swoop down; Tiger, you want to keep an eye on me; after all, this is my first turn on the lander.

Tiger: You're doing fine. Watch the numbers; I doubt you can judge heights over the ocean until you're practically at the surface. Like now; I'd suggest... Right, slow it down. Keep your eyes on the weight at the end of the dip tube.

Me: There's its shadow. Splash, and I open valves four and five. We have the air sample but it's going to take some time to suck up the water. Jeez, what in hell is that?

Tiger: Up, up! It's a frigging tentacle!

Me: Max force, and it won't let go! There's another one! Jeez, I got away; I cut the force then slammed it, like in Indian wrestling.

Tiger: I don't think your skill helped. Look at the tube; it broke off when you jerked. You closed the valves, didn't you?

Me: Oops, thanks for reminding me. We didn't lose much sample.

Willie: What was it? If there are any like it on the land, we'd better get our samples up here before risking the lander over the jittery terrain.

Me: Wow, that gave me the willies! You're right; I'm bringing it up. Did my attention wander? Did you see it before it struck?

Wilma: Let me quickly look at the video... You can see it through the murk, just barely, about half a second before it broke the surface. The thing's body isn't visible at all. It's hard to tell the visibility in the water but I'd guess ten to twenty centimeters.

Me: So it's using sonar, not vision, and it's fast and aggressive. And large. We have to use sonar too. Tiger, what do you think? We have the zirconium.

Tiger: Jeez, I'd be shaking, not designing countermeasures. I am shaking.

Me: I'll shake when I get the lander docked. Talking helps me stay steady. You know that.

Tiger: Right; I'd better steady myself down too. We should use barium titanate for sonar transducers, not zirconate, and we have the barium. A sonar imager isn't going to be easy to build. I'm thinking of maybe twelve crystals in a phased array. When we get the samples up here let's have Simba start analyzing them. Willie, would you please look up a design for the sonar crystals, and I'll work on a set of oscillators to drive them, plus the detector amplifiers, and Simba, you and I will start on the program to turn the output into images when our initial jobs are finished. Wilma, would you please take over the lander once the sample bottles are cleaned out, and fly it down near the jittery terrain we planned to look at, but I'm the combat pilot and I'd like to take over at low altitude, in case the terrain fights back. I hope you're not too disappointed. I want you looking over my shoulder to interpret what we're going to see.

Wilma: I'm no expert at fending off tentacles.

I concentrate on flying the lander back to our ship. As a young lion I did adequately though not brilliantly in combat simulations in the gun range, and I tended to treat the flight simulation games as a chance to explore and to have fun in the three dimensional world, rather than as a socially approved opportunity to kill adversaries, as Charlie did. I did my part teaching our kittens combat skills, particularly in the years Tiger was recovering from her accident, though in truth Tiger is the better fighter in our family, though fortunately lacking Charlie's killer instinct. Even so, somehow the few actual combat situations we've run into have centered on me. Today's included. Even though the tentacles were 1e7 meters away, almost on the opposite side of the planet, as a teleoperator I felt as if their suckers were clutching and ripping off my own tail, and I have to struggle to keep myself calm and to concentrate on docking the lander safely with our ship containing my own nonteleoperational bod.

Me: Wilma, could you help with the gas samples? The sample port is supposedly connected to the mass spectrometer; here's a squirt of the 35 kilometers sample.

Wilma: It's coming through. Give me a full load of it. That's strange, mass twenty, a lot of neon? But there's a closely spaced molecular ion 0.014 AMU heavier... hydrogen fluoride, just a trace, but it shouldn't be there at all. That spectrum is downloaded; turn off the gas. Now let's have the twenty kilometers sample. Well, look at that! A little bit of something up at 135.90 AMU; I wonder what that is? And a bunch of neighboring peaks. There are little peaks all the way down to thirty AMU. This atmosphere has a very complicated chemistry, like Earth, but the trace molecule concentration is higher. One of my jobs today is going to be to identify these peaks and to figure out which one is the mystery absorber. Let's go to the next sample. Well, that's interesting; most of the trace items are gone, but the 135.90 complex is even a little stronger here. Now the sea level air: yes, 135.90 is even stronger, but there's stuff all over the spectrum, probably biogenic organics from the sea.

Me: OK, let's get the samples transferred to storage bottles, and bring the lander in. I really want to see what's in the water.

Wilma and I work together to store our air samples. Then I guide the lander gently into the airlock, as Tiger tries to not be seen keeping a sharp eye on my piloting. After the air pressure is equalized, popping our ears, Wilma lifts the aft panel and wrestles the lander past it into our tiny aft volume, displacing Willie temporarily from his work preparing a batch of barium titanate to be fired into sonar crystals.

The water really is interesting.

Me: Hey, people, check out the microscope camera feed. Come back here, you! See this little guy? It eats the algae cells, or the local equivalent.

Tiger: It looks like a little squid or something. I'm not surprised it has tentacles. Can you count them?

Me: No, they move too fast. Later I'll go over the video and maybe there will be a frame when it spreads them out. In the ocean we saw what's probably the top carnivore, and we're looking now at the primary producers and the herbivore level. The life forms in between, does anyone want to guess what they look like?

Tiger: Not until I've seen them. But supposing they're all squid types, remember how varied mammals are on Earth. Same for birds. Just because they're all squids doesn't mean they won't be diverse.

Me: That's a good point, and investigating it I'm afraid has to wait until we can deal with our adversary in that ocean, if only by getting out of its way. I'm going to analyze the water itself now. I can already tell it's extremely saline. And Wilma, when you have the sample bottles off the lander and the rock equipment installed, I'll help you get it out the airlock.

Yes, the water is very saline, resembling Utah's Great Salt Lake, except that trace elements are astonishingly abundant. For example, bromine is almost two grams per liter, and iodine is 0.1 gram per liter. More toxic elements like arsenic are also present, and on Earth the water would be devoid of life. But if an entire ocean had evaporated over thousands of years, life would have had time to evolve ways to exclude the toxic chemicals. The water is a soup of organics, some of which I suspect are as toxic as the arsenic. That water has body! Hmm, it looks like Tiger is taking over the lander controls. The jittery terrain made a lot of trouble for me and I really want to see what was causing it. I'm going to watch the video feed. I see Willie has also taken a break, or simply has to wait for the crystals to cook.

Tiger: I'm going to stay at about fifty meters, initially. The jittery terrain should start somewhere beyond these low hills... Well, I'll be dipped! They're trees! It's a forest of dead trees, about twenty meters high, and bushes along the dry river bed.

Me: Jeez, no wonder the radar altimeter went crazy, with the radar reflecting off the branches where they make angles with the trunk. Is there anything nasty living there? They all look pretty dead.

Tiger: I'm going to draw fire. Here's a kind of opening so I could go straight up if I need to.

Me: Spinning the lander makes me dizzy.

Tiger: I don't like it either, but that way I can keep an eye in all directions. We should have three cameras on this thing. I'll put that on the list of chips to be made. Well, no tentacles, or giant spiderwebs, so far. Wilma, I should land and do an APX scan, don't you think?

Wilma: Right. The trees probably died from drought, but there might be some clue in the soil. See the mounds? I wonder what they are.

Tiger: If I were a predator waiting for potential prey to land and become vulnerable, from which direction would I approach? From the nearest cover, so I'll face the little hill. Scanner extended. I wish we didn't have to stay put for two minutes to make a scan.

We wait nervously. No writhing mass heaves into view over the hill; it could just as well be sneaking up from the back, and we can't turn around to look without spoiling the scan.

Tiger: That's that. Up! And around... No tentacles. I'm going to investigate the nearest mound. It's about fifty meters long and it looks really straight when you look along its length, rather than from the side. Before we start the APX scan I'm going to grab a sample, just for laughs. Just shut up about tentacles, people, please. Got the sample.

Willie: You were the one talking about tentacles, Tiger.

Tiger: I was not! Well, maybe I was. OK, Wilma, is the scan done? I'm getting out of here unless anyone has a request.

Wilma: I do. Turn around to about 105 degrees; can you see my cursor? Two mounds cross here. I'd like to get a closer look. Stop there, please! Back it up.

Tiger: That's not where they cross.

Wilma: See, there's a kind of pit here, and the mound is wider at this end than the other. You can see that on several mounds; turn to about 170 or so and I think you can see another. Yes, it's even clearer. Think of a tree falling. It pulls up a clot of soil and leaves a pit, and the root ball plus the soil enlarges the remains of rotted wood. What I'm seeing is, you have moist forest with big trees, maybe not tropical rainforest but something towards that. The drought hits, the trees die, and they fall, but there's enough moisture that they rot, and among them younger trees, early successional species, spring up. They have fifty to a hundred years of limited water, and make it to the size we see here, and then dry out and die. There's still a little water in the center of the valley and the bushes take over the riverbed, but eventually they die too, leaving what we're looking at.

Willie: How depressing. It's a planet-scale ecological disaster. We saw similar signs all over the planet.

Me: It's a good warning for Earth. We're not going to evaporate our oceans like happened here, because the excess carbon dioxide cools the stratosphere while warming the ground, but even a subtle temperature shift could make a lot of trouble. For example, the Gulf Stream could stall.

Wilma: Shudder! Well, that's not our responsibility. The next site we're going to visit is a section of mid-ocean ridge near the eastern ocean. That sounds funny, doesn't it? Let's call it a plate separation ridge. When it was underwater there should have been a lot of hydrothermal activity and we might find some copper, and even if not, it will be interesting scientifically.

Tiger: Now I ease my way up... I don't want to hit my head on a branch. Now a brief suborbital hop. I was glad, frankly, that we didn't see any life, having gotten a taste of their style around here. Wilma, what did the scans show?

Wilma: Calcium, silicon, iron, aluminum, potassium. Nothing to tell what happened. Sorry.

Me: The surface temperature there was 280 kelvin, which is pretty hot for a place that high. Where we're going, how hot will it be?

Willie: I've got it; calculator... About 310. Jeez, it's a sauna!

Me: I thought a sauna had wet heat. Maybe there was an unusual atmospheric condition that let the forest heat up relative to the adiabatic average, but even so, this place is a lot hotter than Earth.

Wilma: I'll bet the air was very wet and there was a lot of cloud cover, that reflected sunlight. When the water was destroyed the planet couldn't cool itself. But why do we still have those two patches of ocean; why didn't they evaporate?

Me: They're so saline, I think, that they can hang onto the water, suck it out of the air.

Wilma: You're probably right, but they're not completely effective. In the air samples as well as the infrared we see some water. In the stratosphere there's much more than there should be. Also the oceans are clearly subduction trenches, and water will be pulled down with the bottom sediments. Willie and I will do some modeling and make an estimate how long the oceans will last.

Tiger: We're almost there. Here's a high altitude pass over the whole site; anyone see anything dangerous? No? Neither do I. Now I'll just turn around and buzz the first X, the hydrothermal vent.

Willie: There, got the frame. As soon as I get this picture projected flat, I'm going to put in another X. See my cursor; I thought I saw something there.

Tiger: Threatening?

Willie: A mound, that doesn't match the rest of the terrain. Here, I've indicated the frame and marked the item on it.

Tiger: It looks pretty inert, but you can be sure I'm going to approach really carefully. Did we look for hazards around our target, or were we all looking at Willie's mound? I'm going to make another pass. No, I don't see anything; did you? Coming in for a landing right next to the vent. OK, Wilma, start the APX machine.

Wilma: Just a second... There's the spectrum, and there's a lot of zinc sulfide, and some lead.

Tiger: Great! I'm filling two pockets with this stuff. Now let's move on to the next vent.

As we work our way along the vent complex the sulfide littering the ground changes in character, adding copper to the zinc, and by the time we get to the other end it has about fifteen percent copper sulfide plus twenty percent zinc sulfide, mixed with common dirt. It's well worth our while to fill another two rock pockets with the ore, and we'll return here several times, because we're very short of copper and the metal recovered here will give us a lot more freedom building our little gadgets. And with the zinc, we can make brass.

Tiger: Well, that's a good haul. I'm wondering, Willie, if we should bring this ore up now, and look at the mound next time.

Willie: Well, I suppose that would be prudent. But it's not as if anything shot at us.

Tiger: And you're curious. I'm curious too. Hell, we can't be nervous all the time, and we're going to be running ore all day, and we'll probably have trouble to come back to it tomorrow. Here goes. First an overflight at about fifty meters. Everyone watch really close. Now I'm coming back, and I'm just going to hover. Look at it frame by frame, both directions. Do you see anything at all?

Me: Jeez, will you look at that! About ten meters long, wouldn't you say? It gives the impression of lying on its side, with kind of feet on the north side. Look at my cursor; see this fan of material that cascaded into the, what do you call it, crack that it's lying in? In the little valley. The dirt is piled up against the carapace. The thing didn't move after it fell. It's dead.

Tiger: So what do you see in the way of threats? I don't like the shadows. Something could be lurking, and could get unhappy if we disturb its kill. Well, what do we have infrared for? The stupid thing blurs; I'll try to hold more still. Can you see anything?

Willie: Only that it's hotter where the sun hits it. I don't see any shapes in the shadows.

Tiger: Neither do I. We can't dither around forever; I'm going in. On the visible light image, it looks like it was trying to walk across the terrace and the soil collapsed under it, dumping it into this crack. When it fell it broke its back and its skin or carapace split open here. I have the camera right up to the split; can you make out anything useful inside?

Willie: Vague shapes. I wish we had a small lander that could fly inside.

Tiger: Hmm... That's a pretty good idea. Would you put a note on our list? That's enough on the crack. The feet seem worn, with frayed skin particularly around the edges. The thing wasn't in good condition, probably dehydrated and starving, as the ecosystem collapsed. It's significant, I think, that there are seven feet, but the inline arrangement isn't exactly Earthlike. It must have looked like a caterpillar when it walked. You know, we're just assuming that the carapace is hard. I'll push... it doesn't seem to press down. But a skin that was flexible in life could get rather rigid when it dries out and mummifies. Now let's check out the front; well, I can't see a mouth, so we don't know if it's the front.

Me: The mouth would be the more elaborate hole, I think.

Tiger: Humans would say a lion's anus is rather elaborate. But I'd expect teeth, or a trunk, or something. Let's check out the other end. Top of my head, I'd say the fall knocked the crap out of the thing: its digestive system split open and the content spilled out.

Willie: Look to the left. Back up, there it is, see the curved panel? I'll bet that's the carapace that split open, mostly buried under the pile from its intestines.

Tiger: I wish we could break off a sample, but it seems to have torn cleanly. Now look at the interior: I'd expect the guts to sag when deprived of support, but the bottom is rather flat, don't you think? And then there are regular ribs on what used to be the side, now the top.

Me: The biologist is really curious what that thing ate. Particularly given the condition of its feet; if it was starving it shouldn't have so much intestinal contents.

Tiger: Right. OK, Wilma, I'm sitting on the stuff; you can start the APX machine.

Wilma: Scan's coming in. Damn, it's a great time for the APX to go flaky.

Tiger: What's wrong?

Wilma: Look at this crap. There are energy bursts at 7.69 MeV. That's higher than the source at 5.46 MeV.

Me: What has an alpha decay energy of 7.69 MeV?

Wilma: You think it's not garbage?

Me: It looks like a line spectrum to me.

Wilma: OK, I'm looking in the database. Well, polonium-218 does.

Me: Follow the decays.

Wilma: Well, I'll be... Polonium-214 is there, and 210; radon-222, radium-226; this is the alpha decay chain for uranium-238! We're sitting on a pile of uranium ore. How did you guess?

Willie: A nuclear powered caterpillar?

Me: That's an interesting thought, but I'm coming to a different conclusion. Wilma, I didn't guess; I just believed the instrument. Next question: what life form eats uranium ore? I know the genus and species name of the Earth one.

Tiger: Spill it.

Me: Plaustrum macki, common name... the Mack truck. This is a damned vehicle!

Willie: What?! Aliens?

Tiger: Explain your reasoning. Not that I'm disagreeing, now that you point it out.

Me: I'll bet if we could get inside we'd find their bodies. Here are the facts: The feet are worn and frayed. A living creature's skin wears off more neatly and the soles are replaced continuously, like ours. Those feet are like a tire that's worn bald. Second, there were visible strands of reinforcing fiber where the carapace cracked open. Our bones are fibrous; I've had plenty of experience with that; but the fibers are much smaller. Those fibers are just too coarse to be biological. Third, as Tiger pointed out, the bed of the truck didn't sag. Think of hara kiri; you've seen samurai videos with gross special effects. And the ribs: no living creature could have ribs that straight and regular. And the rear carapace: Willie said it had split open, but it's not frayed while the other crack is. I think it was latched closed and the latch let go. And finally, a real animal would have no interest in eating uranium, while technological creatures might be avid for it.

Willie: It fits. So I have a couple of questions: Are these guys still around? Why did they just leave this truck lying here? How long has it been here? The trucks that made it through, where is the uranium now?

Tiger: I notice you didn't ask where the mine is. Unless anyone has more observations they want to make, I suggest we proceed like this: I'll bring up our load of copper and zinc. Next trip down we'll get one or two pockets full of the aliens' uranium ore; Wilma, can you tell what the mineral is?

Wilma: The APX is too confused. But in this setting autunite is a possibility, or maybe monazite.

Tiger: Whatever. Having a small amount of uranium and thorium may prove useful for some unforeseen purpose. Then we'll stick to our plan to mine the copper-zinc hydrothermal area we found, for the rest of today. Willie's questions are good, and I want people to think how to answer them. The task of investigating the ocean is important too, and I want to finish the ultrasonic array and its software before we start on any major new thing, but obviously we have to do something about our aliens, promptly. Simba, you figured it out, so would you write up a report that we can send to Earth?

Me: I'll do it now, in between helping smelt ore. I think the people back home aren't going to be bored with today's data feed.

Tiger: And Wilma, before you get tangled up with ore processing, or in between, could you please analyze the APX scan and find out how much uranium-235 is in that stuff?

Wilma: You're right, it probably isn't the same as on Earth. You know, that truck is too heavy to have been brought in from space; it had to have been built right here. But if we needed a truck, that's exactly what we would do: build it. Are the aliens residents or visitors? I don't know how we could tell.

Willie: We'd build a hover truck. We rejected a wheeled or tracked approach for the mining robot, remember, because CQMT pushers are so much simpler, and I doubt visitors could get here with primitive technology. Remember, the cosmic radiation would kill someone trying a three hundred year journey or longer, even if they missed the radiation channels.

Wilma: Technology fifteen years old is primitive, you say? So you think the owners developed on this planet. But why haven't we seen them? If we mapped Earth like we did Njord we'd have spotted a strip mall in the first five minutes.

Tiger: Well, it depends on the orbital track; it might take half an hour to see parking lots and stuff. But you're right, either these aliens are so different that we aren't recognizing their marks on the terrain, or they died out and the jungle has had time to cover them over, not likely since this truck was here when the sea was evaporated.

Me: How do we know that? It reminds me of a submarine on feet. On Earth, if we lost a vehicle like this on the seabed we might never find it.

Tiger: Good point. Wilma, would you make time to look at the images really closely and try to distinguish a dry from a wet accident? But now the lander is almost here and I'd like Willie and Wilma to unload it. Simba, the acoustic imaging software is on the critical path; that's a hint, though you can help on materials handling inside too. And I have nine more wave generators to wire up. Willie, I'm not pushing, but the furnace is being kept busy, isn't it, cooking barium titanate for the transducers?

Willie: Yes, continuously, except for a few hours before we woke. Wilma, could you move your butt away from the locker? Thanks; here's your suit and helmet.

I resume working on the imaging program. It's likely that something in the ocean will generate acoustic noise, which will bounce off silent targets. By correlating the incoming signals I can recognize, ambiguously, the noise source and the silent floaters, and if there are several sources, and given that we have twelve receiving crystals, the image can be reconstructed with a lot more certainty. And if the sea is inconveniently silent we can advertise our presence by sending out our own signal. It takes a lot of math on my part, and it will take a lot of computing power when we're operational, but I'm making progress and I think I'll at least have something to process the data when the crystals go into the water.

After helping Willie process the second batch of ore, coincidentally including the uranium, Wilma finishes a detailed analysis of the APX scan on the truck's load.

Wilma: This is wild! There's 3.5 percent U-235 in this stuff. It's more enriched than what goes into nuclear power plants. OK, calculator... Did you know that uranium on Earth started out being almost a quarter U-235? If Njord started out with the same ratio, which is likely given how heavy elements are produced in a supernova, it would take 2.69 billion years to reach the ratio I see. Could life evolve to the truck stage so quickly?

Me: What's that, sixty percent of our own age? Who knows? Life develops by lucky breaks, or unlucky ones that force the survivors to adapt. The truck is here.

Tiger: Willie asked where the uranium was going. I think it's obvious, that they were using it for nuclear fuel. What else is it good for? Now I think we ought to be looking for the reactor. Willie, give us some suggestions.

Willie: If we could measure the environmental radioactivity, we may be able to get an idea of how recently they were operating. The APX is no good; its own radioactive source obscures anything in the soil except when it's concentrated and potent, like that ore. However... I assume we want something fast, and a new radiation detector will have to wait in line for the chip maker. The solar X-ray instrument could be mounted on the lander in place of the APX, and it would make a good general purpose gamma detector. It's a one hour job. How about after I take care of the next batch of ore I dismount the thing and bring it inside.

Tiger: Good idea, and I'll put a replacement on the list, or if you think a different design would be better for gamma sensing, like thicker or with a different doping level, we can make that and put the X-ray sensor back outside when it's made.

Willie: Right, I'll check the design. As much as we can, we should take spot measurements of radioactivity. On Earth you wouldn't find much, even if you landed on top of a reactor, except around Chernobyl and Hanford and places like that. Even Three Mile Island; you'd never know what happened to it. But it's worth a try here; they might have been sloppy. Now one thing we ought to look for is atmospheric krypton-85. If they're still operating, it's almost impossible to keep that stuff out of the atmosphere. And another thing: we should measure our one sample of seawater. Today; I think there will be time. Any radioactive materials that got loose should wash into the sea eventually, and like Wilma did with the uranium, we can use the ratio of cesium-137 to 135 to estimate how old the contamination is.

Tiger: That would really tell us something; not the guesses we've had to make about when things happened. OK, the lander is just about down and I'd better pay attention to it.

I need a break, and I relieve Willie at the rolling mill, which we're using to draw newly smelted copper into wire. Willie and Wilma work together to interpret video frames around the truck, and they're almost certain that the ground was dry when the accident occurred, because of cracks and texturing that you wouldn't see underwater. Certainly that's a piece of the puzzle, but to me the pattern isn't obvious. Yet.

Wilma: Could you all take a look at the map frame where the truck is? My cursor is next to the truck. The map has 25 meter resolution, and the truck isn't even visible; it's less than half a pixel long. I think we ought to search for more trucks, but we're going to have to take new images to do it.

Tiger: At higher resolution, right, using one of the other eyepieces? We have a thirty centimeter mirror, and it's good but not diffraction limited; we can get half meter resolution if we're lucky. It's going to take half meter resolution to recognize pictures of trucks, and there's no way we can cover the whole planet: 2500 times longer, two hundred years. That's rather a long time.

Me: Then we'll cover what we can. Let's use this strategy: whenever a plate separation ridge is in view we image densely around it, up to half the images, but we put the other half of the effort into totally random coverage, of course not imaging the same patch twice. If we find that certain visible features are correlated with trucks, we can change the strategy to concentrate on them. But our best guess now is that recent hydrothermal areas have the ore the trucks want.

Wilma: I don't disagree, but plate motion carries the ore away from the ridge. The ore doesn't just disappear. Let's do one third along the ridge crests and two thirds random.

Me: Whatever. Who's going to do the image analysis program? If it's me, it will have to wait in line. And the smaller images will come in more frequently. Processing will have to be fast.

Wilma: Why don't I do that; we use similar image analysis to look for petroleum deposits. I'm thinking of a kind of computed holographic technique. And if we have other features we want to look for of about the same size, we can include them with essentially no extra processing cost. I'll work on that between ore deliveries. It won't be done today; it's about a twenty hour job, I think.

Tiger: Sounds good. We should be using both orbiters in addition to our own telescope, right?

Me: Well, maybe. Let's see how much computer time it takes to look for trucks in the images. We'll get eight images per second per orbiter; we may not be able to even process every one. Let's wait on converting the orbiters for higher magnification, until we know how fast the analysis program is.

Tiger: No, we can't go over the polar regions. If we want to find trucks there we have to convert at least one orbiter, and I think we should do that promptly. Willie, could you put that on your list, please? I'm bringing the lander up now. How many more loads do you think we should do?

Willie: Two more. I know that goes through the whole evening, but with all the stuff we're building we need a lot of copper.

While Willie brought the solar X-ray detector inside right away, it takes until the next day for him to have enough time to set it up for use on radioactive materials, and for Wilma to make the measurements. Over lunch she reports her results.

Wilma: You were right, Willie, about fission product releases. Our sample of seawater is small and there weren't many atoms in it, but there was a measurable amount of radioactive cesium that was produced between about two and four hundred years ago. I also measured the residue from ore smelting, and again the statistics are poor but the date comes out in the range of 300 to 550 years.

Tiger: So there may have been two different events?

Wilma: Yes, may have been. But the numbers are equally consistent with just one. Or, suppose the ocean dried up a few hundred years ago. Whatever was in it would soak the orebodies we mined, so naturally both would yield the same numbers, but there could have been any number of events putting cesium into the ocean.

Me: I wish we could just point a tricorder at it and say, the truck crashed so many years ago. The ocean dried up so many years before that. Extracting dates is so tough!

Wilma: Yeah. It took a lot of really delicate work to get the time scale nailed down on Earth, and even now some things aren't clear. We aren't going to be able to do anything near as detailed.

Willie: Can we draw any conclusions how the cesium got there? I can think of three possibilities: a big reactor accident, sloppy reprocessing of fuel, or nuclear war.

Wilma: Well, I did a calculation. You understand, I'm guessing the volume of the two oceans assuming they're standard subduction trenches, and substantial amounts of cesium may have been removed in crystallized salts or may never have gone into the ocean, but I'm estimating seeing the result of fissioning about two tons of uranium. The total disruption of one reactor would do that, or partial losses in several accidents. Really sloppy reprocessing could discharge that much, though they'd have to be really stupid not to realize that their people were dying; cesium isn't the only thing that would be released. And nuclear bombs use uranium very inefficiently; you could have a nice nuclear war while shooting off two tons of uranium, although the amount that was just vaporized would be a lot more. The facts I have don't tell much about how the cesium got there.

Tiger: How about other isotopes? How about americium-241, for example, or plutonium-239?

Wilma: Cesium is soluble; actinides aren't. But we should have seen something in our smelter residue. I'll get back to you on that, OK?

Tiger: OK. Ambiguous, yes, but you got a good result out of the facts we have available. Now, I have the last two wave generators to wire up. Then I have to make them all work together.

Wilma: And I really want to finish the image analysis program. It's not as easy as I thought.

Tiger: Nothing is. If a little help from me or Simba will give you a big boost, interrupt us.

Wilma: Thanks, but it seems to be mostly plugging through the algorithm, making sure everything is working with the same data, and finding a target pattern that doesn't miss simulated trucks and does miss non-simulated rocks. It's converging, but it just takes work.

The same is true of my project: quick, subtle inferences are easy for a lion's brain to make, but the computer doesn't think like us. Nonetheless, I'm able to produce pictures within my speed goal from crystal-clear simulated data from hard-edged scatterers. On the other hand, with vague shapes in the water and with high frequencies rolled off, as I think likely, the output looks nothing like the input. A little help from some image processing guru would give me a really big boost. But the nearest guru is 21.6 years away, for a round trip query at light speed.

But come to think of it, what do I do, really, when trying to see on low resolution passive infrared, or visually through fog or murk? When my brain judges that one voxel is filled, it adjusts the threshold so an ambiguous neighboring voxel would appear filled, while adjacent to a clearly empty voxel it would stay empty. Like a human I don't feel this happening explicitly, but I know how my designers programmed my brain to react to an ambiguous scene. What my program needs is to find the best voxels and finish them first, and then to use them as a framework to interpret the lower quality data. Rating the data won't be easy, particularly given the speed goal, but as with Wilma's project I think it will yield to patience and persistence.

By evening I have something usable, and so does Tiger.

Tiger: Well, then, let's fire it up and see if it works.

Wilma: (Yawn) Right now? It's kind of late.

Willie: Late, yes, but do you want those frames as your bed partner? I'm sick of trying to work around them. Let's test it and get it out of here.

Me: I agree. If you're sleepy let's take the frames down by the airlock and you and Willie can sleep up here tonight.

Wilma: I think I will. Sorry to be a party pooper, but I've kind of used up my energy on the truck finder program.

Tiger: Careful as you squeeze between the frames. I haven't run the wires through the conduits, in case we have to take a driver or crystal off and fix it. Sweet dreams. OK, Simba, I have the power on it; are you getting anything?

Me: Just a sec... Nothing. What did you feed the data into?

Tiger: Major device 45, minor 32 through 43.

Me: You used those channels? I thought you were going to use the good ADC. That one's too slow; we need the high frequency response. Put it on 39/16 through 27, like we discussed.

Tiger: Come on, you said 45 would work.

Me: I said it would barely work. Do we have to negotiate this?

Tiger: I'd like to see if anything's happening. I'll rewire it into major 39 tomorrow when we're not sleepy and snappish. I'll bet it's relatively simple to make the software read major 45.

Me: OK, OK, wait just a minute. I just have to delete the device files and rebuild them. There; is power still on? Evidently so: I can see my voice. And... Check it out! You can see the shape of the cabin, and us, even Wilma and Willie at the front end, just from the echoes of my voice. This thing is working! It's noisy as hell, and the resolution stinks, but what do you expect on the slow ADC? And actually this is a good test of the software, to be able to recover visible shapes with such crummy data.

Tiger: Great, great job! Now, do we need to do any extensive testing? I'd really like to get these frames out of here; I had only one set up last night and even so I had it poking in my back all night.

Willie: And the other three all day; they take up all the space in here. But we've got to think of safety. It's really late. I'm not sure I'd trust myself working with them in space, and Wilma, I think she's already in dreamland.

Tiger: Simba, you or me? Your tail is dragging; I think you were using your brain on the program, while I just had to cut tubes and attach wires.

Me: The ones you didn't stuff in the conduits...

Tiger: Can be done tomorrow, outside, and the same for replugging the ADC channels, which is why I left the wires hanging. Jeez, I can't get the door open to get my suit out. Just slide the frame forward; don't bump Wilma with it. You and Willie get out of the way while I suit up. Tomorrow we should all get some extra sleep, and then we'll finish up the assembly, and then send this thing down for a dip in the ocean.

A new day dawns in the rainforest... painted on our walls and lighted artificially, of course. We have the lander, with the four ultrasound imaging assemblies bolted together and hung underneath it, skimming the surface of the western ocean. This is the same spot where we had our previous encounter with the tentacled life form.

Me: Do you think it's still down there?

Tiger: Mean and hungry as ever, I'm sure. It's convenient to have the ultrasound running in air mode, for judging height above the sea. I wonder if we could have just one sonar crystal permanently mounted on the lander, as a short range altimeter when we land it. Here's the exact coordinates. Shift to water calibration. I'm going to dip in, stay for five seconds unless you say otherwise, then pull it out. No lingering this time. Here goes.

Me: There it is! Two of them. Stay in the water; it's an attack run, pincers pattern, but the water limits their speed. Now up! Four meters up, backward two, camera on the surface.

Willie: Jeez, look at those tentacles! They really want us!

Tiger: Mean and hungry.

Wilma: Do you think it's the same creature?

Me: Impossible to tell. They could be territorial, but in the open sea how do you define boundaries? And those two clearly cooperated in the attack. How long were we in the water? I have the time stamps: seven seconds. It's going to be hard to do anything in seven second snatches.

Tiger: That's right. Let's survey twenty or thirty sites, in this ocean and the other one, and get some statistics on population and attack latency.

We spend most of the day, the rest of the morning and early afternoon, executing that plan. Our shortest dip time is two seconds, when we come down practically on top of a creature. The longest is ninety seconds.

Wilma: That ocean is like a shopping mall on the day after Christmas. And the cooperation was uncanny. Whenever we could see multiple creatures, one seemed to take the point role and the others circled around to block our escape, assuming we had to swim for it.

Me: That's a real good observation. But what struck me was the prey density, or lack thereof. What are those things eating? In two cases we saw schools of smaller life forms rising generally vertically. Possibly, think of it like this: light is concentrated at the top, and so is plant growth. Top carnivores also stay at the top. Micro herbivores can safely graze among the algae, but midrange creatures concentrate at depth. They have to come up to snatch a bite, and then run away downward before the big guys eat them.

Willie: It's plausible. I wish we could investigate that without getting nailed by the monsters. How about a couple of dips in which we scan actively? We could see the population structure deeper in the ocean. It's not like we can hide from the things anyway.

Tiger: Good idea. We calculated that we can see about five hundred meters down, transmitting at full power. Let's try two places where we think we can see the bottom, and two in deeper water. That should take about an hour, and then we'll bring it up and start looking at the data in detail.

Wilma: While you're flying toward shore, I have something to report. First, the mysterious absorber wasn't in our atmospheric database because it isn't natural. It's trichloromonofluoromethane, Freon-11. Someone down there has a leaky air conditioner. Or rather, water conditioner, because the concentration is higher in the water than in the air. And something else: there's americium-241 in the smelter residue. That didn't get there by normal reactor operation; it was spread around on the land after one or more big explosions.

Willie: What kind of explosions?

Wilma: Impossible to tell, nor to estimate the age, but its half-life is 458 years, and it's plausible that it got there the same time the cesium-137 went into the water.

Tiger: That's something to think about, but I'd like to continue this later because we're at our next site. The bottom should be visible here. Eyes open; I'm going in.

Indeed there are schools of what look like fish, but coupled with larger individuals in what seems a continuous distribution of size. Our sonar transmissions seem to excite even more vigorous attack behavior by the large creatures, but we get one recording almost a minute long, which shows highly complex and fluid schooling behavior of the midrange prey in which the smaller ones both cooperate with yet stay somewhat separated from the larger prey. These are not Earth squid! And in many cases the big carnivores seem to be moving up or down through the prey layer, in holes vacated around them, possibly all the way to the bottom. Which, disappointingly, we can't see in any of the records due to high absorption and also scattering by the prey layer.

Wilma: These things are fascinating! I wish we could drop something on the bottom and watch continuously, but I kind of doubt those guys would leave it alone. The probe would have to be able to survive being chewed on, and a trip through whatever digestive acids the things have.

Willie: A titanium jacket: no problem. But as always, we're adding chip orders to our list faster than the chip maker can take them off.

Tiger: And I'm nervous about a political accident to our power supply. I really want to spend a full two months making a sundipper of our own. But that's off topic; let's get back to the wildlife. Look, we can't go around calling them ``things'' or ``creatures''.

Willie: Critters; let's call them that! Seriously, Simba, can you put up a good picture of one? They mostly seem like a pile of junk in the water; you can't see what shape they are.

Me: Actually, I remember one... Take a look at this frame, at the start of the second to last dip in the western ocean. See, the two of them are together and this one has its tentacles all stretched out.

Wilma: Mating behavior?

Me: Who knows? But you can count the tentacles: seven. You can sort of see that on the other one too. Let me flip through frames. Here's one with only six tentacles. But there's a stump; maybe one got bitten off in a fight. I think seven is the number around here, like five is on Earth. Remember the little herbivore we caught on the first day; it had seven tentacles too, I could see on a few freeze-frame images. They're good swimmers, but they don't look like squids. To me they look more like an octopus, though not very much. Like, the tentacles seem rooted around the equator while a squid or octopus has them at one end.

Willie: A heptapus. Let's call them that.

Me: Right, that's a good name for them.

Wilma: Yes, they're heptapi. Do they have any hard parts at all? That thing in the center seems to be about all they have. It could be jaws. I'm not sure I want to get close enough to find out.

Me: My sentiment exactly.

Tiger: Yeah. What really intrigues me is the cooperative behavior. Is there any sign how they handle that, like vocalization? If it's by electric fields we might have a problem detecting it.

Me: They do make sounds. That's something I mean to look at after dinner. That's a hint. And on the dinner topic, I have an announcement: I was up early this morning for the harvest, and we got eight kilos. That's in four days. That means we're self-supporting.

Tiger: Yay! Way to go! Let's make up a squash pie; there are two good squashes in storage.

Wilma: The flour...

Tiger: Is in storage too. I would have gotten awfully bored doing wiring for the entire day, yesterday.

Sure. My mate is the right one to be the commander. Attending to my reports and web postings about the food situation, she anticipated this announcement and diverted reserve grain so as to milk the biggest morale boost out of the event, whenever it would occur. And yesterday I was worried about processing speed for the ultrasonic images and I wondered if we could add another processor to the computer system, so I checked inventory. If needed, and if we wanted to take the time to make a motherboard for it, a spare CPU chip is sitting in the storage drawer, but my attention was drawn to the carefully recorded dates on the inventory database. Without bothering us with details, Tiger has been putting a steady ten percent of chip maker effort into key spare parts and generic chips we could use for a quick response; like, if we hadn't used all the camera chips, we have a small pusher chip, three actually, that we could use to make the mini-lander to look at the truck drivers' bodies. Everything is documented as it's done, either by us or by Tiger personally, and the reports are shipped back to Earth. Tiger doesn't have to do that; she (I should say we) paid for the ship and she can do what she damn well pleases, but keeping people informed is the right thing to do, and that's how Tiger operates.

Anyway, the squash pie is a big hit as dessert, and we decided to make Chinese onion cakes for the main dish, which we all like too. But after washing up I retreat to my console for a serious look at heptapus vocalizations. For example, the fairly long sequence that started with one heptapus all spread out in front of the other.

Now let's take it from the point of view of the heptapus that transmitted sonar first: speed of sound effects are significant. As our entry splash fades out the critter is emitting kind of frames of sound separated by short pauses, and the other one, with spread tentacles, inserts its own squawk into a gap left for it. Our splash sound reaches them, and two hundred milliseconds later it shuts up, then a hundred milliseconds after that it emits a powerful burst of sonar, then a lower level transmission presumably to the partner, which answers briefly, then another frame, and then they start the attack run. On the way they kind of alternate sonar and lower intensity communication until physically reaching our position about sixty seconds later, whereupon we depart. No question, they're coordinating their actions by sound.

There's something there to be seen, right in front of me. Let's dig a little in the data. First, how is their sonar organized? Intensity differences in the twelve sensors might reveal that. Yes, it does. First, it's a plowed field raster pattern: the beam moves across, with one pulse every half beam width, and then steps toward the sender's mouth end and moves back the other way, covering a rectangular area, not too badly centered on us, in about thirty rows. Second, the beam width is about three quarters meter, even at a range of 85 meters. That's very good resolution for a living creature, and we can do better, not that much, only because we have a big clumsy chassis and we're using a W32 processor to take advantage of multiple natural sound sources. I'd like to know how a heptapus works inside.

Those lower intensity frames of sound... 32 evenly spaced little glitches in the one after the sonar burst, interspersed with one or two clicks each. And that type of burst recurs, with varying numbers of segments, although some other frames have only four or five segments. If I were designing a heptapus I wouldn't have separate processors for sonar and communication; what happens if I plot various frames as if they were sonar echo returns? Well, there's a minor problem: how do you know which sonar click a returning click is a reflection of, since unlike in submarine videos, the heptapi have several pulses in transit at any one time. Hmm, if I do a Fourier transform... In the transmitted pulses the higher harmonics seem to be phase shifted in a repeating pattern of seven steps, and the communication clicks have a similar phase shift, so the timing of the originating click could be inferred; thus both the angle and distance of the represented object can be encoded compactly. Very neat! And while Doppler frequency shifts aren't evident in the two frames I've looked at in detail, a Doppler shift could encode motion.

Now, let's write a little program to decode communication frames as 3-D pictures. That should be simple, just a one hour job.

Yawn, one hour was a typical programmer's estimate, but I now have something to show before we get into our sleep webs.

Me: Hey, people, you want to see what we look like to a heptapus? My machine, top page.

Willie: There's our sensor frame! How did you do it?

Me: One heptapus scanned us with sonar and then told its friend what it saw. It sends simulated sonar echo returns, with not a lot of hashing up. It's a clean design; in fact, it's the kind of thing Dr. Franck would have put into a dolphin person.

Wilma: You think they're artificial, like lions?

Me: No, I'm not saying there's any evidence, but Earth life is usually so messy in design.

Tiger: That's wonderful progress. But I'm really interested in what they're communicating. Is it like cats meowing, twenty or so messages maybe with pictures? Or is it real speech? How could we tell? Are there any more pictures in the data stream?

Me: Yes, quite a number, plus non-picture frames; I can only guess they might be words. No, might be like terrestrial animals' vocalizations. We shouldn't jump to conclusions. Here's one from the start of the record. I had trouble to figure what it meant. You can see the spread out heptapus, but the compact one is right up against it, not like reality, and let me turn on color coding for Doppler shifts: the spread one is approaching fast.

Tiger: No, the other way; the compact one is crashing into the spread one. Maybe chewing it out: I'm going to kick your butt from here to Scranton.

Willie: Or propositioning it?

Me: Whatever. But they clearly communicate intentions or plans: here's the frame after the picture of us. The lines, see the Doppler shift on them, match pretty close to the paths they actually took, and about 35 seconds into the attack, here, the leader sends a different path picture so they split up in a pincers, approaching us from opposite ends of the chassis, and they actually do it. Wolves or Panthera leo make coordinated attacks, but not with that kind of detailed planning and coordination. My estimation of these guys is a little higher now than this morning.

Tiger: In other words, they're mean, hungry and intelligent. We'd better be even more careful in our interactions with them. I think it's worth a fair amount of effort to decode those words. Maybe we should think about what we have and make a plan for what to find out, before challenging the heptapi again. Random interactions like we were doing are risky.

Me: That's an understatement. I'll do my best. Tomorrow.

Wilma: Don't wait for me. I have just one more bug to fix, and then I'm going to let the truck finding program run overnight.

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