With the laser power off, Prometheus had to make do with the weak red photons from Barnard. Although not powerful enough to have slowed the lightsail in its headlong relativistic flight, the light pressure was enough to swing the sail into a looping orbit that took Prometheus on a journey past the major planets in the system. By using the light from Barnard to add to their orbital speed, Jinjur and James could travel away from the star to the outer portions of the system, while tilting the sail the other way would slow their speed in orbit and allow Prometheus to drop in closer to the sun.
Tacking carefully, Prometheus rendezvoused with Gargantua and allowed itself to be captured into a trajectory that would take them past all of the moons in this miniature solar system. The nine larger moons of Gargantua had been detected at Earth by Caroline using Alan's large orbiting optical interferometer array. They had all been given proper names beginning with Z. In order of size they were Zapotec, Zouave, Zulu, Zuni, Zion, Zen, Zoroaster, Zwingli, and Zeus.
After the crew of Prometheus arrived, they found many smaller moonlets. According to the prearranged plan, these were to be treated in the same manner as the smaller asteroids in the solar system and given a Z-number in their order of discovery as soon as the complete orbital parameters of the moonlet had been calculated. The crew couldn't resist giving some of the more interesting ones Z-names, however, and soon there were moons named Zinc, Zoo, Zygote, and even Zipcode.
"What's our first stop, Sam?" asked Jinjur, as she started her work-shift and sat down in the central command post that George had just vacated.
"That would be Zapotec," said Sam. "Except for the smaller moons like Zeus, it's the farthest out and we'll reach it first on the inward portion of our flyby orbit. It's also the largest. It's a little bigger than Mercury and has a thin atmosphere not much different than that of Mars. I have some recommendations for the initial exploration probes for Zapotec."
"None for Zeus?" asked Jinjur.
"Maybe later," said Sam. "On our first pass we should only expend a few orbiters and landers on each of the larger moons to complement our remote sensing survey. Later, after visiting the rest of the planetary system, we can come back with probes that have been educated to extract the maximum amount of scientific information out of each moon."
"What gets dropped off here?" she asked.
"Since Zapotec is like Mars, we know pretty much what to expect in the way of dangers. I recommend using three probes on this one. Richard is ecstatic over the volcanic chain ringing the south pole. I especially want to investigate the equatorial rift valley that goes two hundred degrees around the planet. It's fifteen kilometers deep, and we ought to get a good cross-sectional view of the crust using a tether-connected dual crawler."
"I didn't know a creepy-crawler could climb cliffs," she said.
"They can't really," said Sam. "But for this moon we will replace the standard one-kilometer tether between the two crawlers with a fifteen-kilometer one. Then, instead of just rescuing each other from craters, cliffs, and oceans, one crawler can lower the other over the cliff to take samples as it descends."
"Sounds fine," said Jinjur. "What else besides the obligatory orbiter?"
"An airplane," said Sam.
"You're not using one of my dragonflys on a preliminary survey!" protested Jinjur. "It's too dangerous for the crew, and besides Zapotec has almost no atmosphere. You can't fly an airplane in a vacuum."
"I admit the air on Zapotec is thin by Earth standards, but it is actually thicker than the atmosphere of Mars. We'll send an unmanned probe that's a modified version of the dragonfly airplane. It has a huge wingspan and a light payload. With its VTOL jets it can land vertically, take up samples, then take off and fly a thousand kilometers to a new spot."
"OK. An airplane too," said Jinjur. "I think I'll come up with you and talk with it before it's launched."
Sam went to the bottom of the lift shaft. Instead of pushing himself upward in the low gravity, he asked his imp to call for the elevator. The doughnut-shaped platform swooped down from its parking spot in the starside science dome. Its progress was not smooth, for there were some humans traversing the long shaft. James, using the imps to monitor the positions of the humans, timed the drops of the elevator so that the meter-sized hole in the doughnut shaped plate passed around the humans at just the instant their bodies were at the middle of the shaft. Jinjur and Sam waited until the elevator came to a halt. They were joined by Richard and Shirley and the four stepped on the carpeted upper surface to be lifted back upshaft until they came to a painted number 42 on the shaft wall.
"An orbiter with two probe-racks," said Sam to Shirley. Shirley scanned around the wall at the four doors and palmed one open. Tucked in a triangular shaped room between the cylindrical shaft and the cylindrical bodies of the huge surface lander rockets was a spacecraft. A portion of the Christmas Bush was crawling over its surface, checking it out. Shirley reached in and slowly extracted the half-ton spacecraft. Its inertia was evident from the strain in her muscles. Richard stepped across the doughnut to help.
"I've got it just fine, Big Boy," said Shirley. "Thanks anyway."
"Is the orbiter ready to go, James?" Jinjur asked her imp.
"I'm in perfect condition and ready for my mission to Zapotec," replied Jinjur's imp in a strange computer voice with a sibilant overtone. It was the orbiter speaking.
"I didn't realize you could hear us," said Jinjur, apologizing to the orbiter, "I'm sorry... ahh..."
"I am called Carl," said the orbiter. "I have no mechanisms for hearing, or speaking for that matter, but James has me hooked up through your imps. Any last instructions?"
The lift headed starside as Sam talked to Carl.
"...start in an equatorial orbit, drop the airplane and creepy-crawler near the big equatorial rift valley, then stay with them until they are finished. Then switch to polar orbit while they head south and you can explore the volcanos. We'll be back in a few years to take up where you left off."
"Don't rush," said Carl. The more time my processor has to correlate images, the better will be the final batch of processed information."
They reached the top deck, and Shirley and Richard pushed the orbiter into the middle of the Christmas Bush's workroom. The Christmas Bush was busy weaving cloth using a bright green artificial thread that it had reconstituted from the lint fibers it had collected over the past years.
"Do you need any help?" asked the Christmas Bush.
"No thanks," said Shirley. "As long as you send a few imps down to unlatch the fasteners on a thin-atmosphere airplane and a creepy-crawler, we can do just fine. Besides, it's important you finish that shirt for Red. Her old one is getting kind of threadbare, and our eagle-eyed friend here is getting a bad case of google-eye."
Richard snorted and headed back to the central shaft. The lift took them down to get the airplane at level 33. Wrapped up in its protective aeroshell, the airplane looked like a clam. The aeroshell was three meters in diameter, but quite light for its size. They had to stand it on edge as they took it up to the workshop.
"It's hard to believe that has an airplane inside," said Jinjur.
"It's also hard to believe what hatches from an eagle egg," said Richard.
"Let me open it up and give you a peek," said Shirley. "I was involved in the design of the folding wings. We use somewhat the same principles in the wings of the dragonfly planes." She popped a few fasteners and lifted the top of the clam shell.
"Hi, Wilbur," she said, peering down to look at the video scanner in the stubby nose of the airplane buried under fold after fold of wing. "Do I look different than you thought I would?"
"I already had access to pictures of you taken through James's video cameras," said Wilbur through her imp. The computer voice was deep and matter-of-fact. "But since my scanner is designed to work in Barnard's illumination, which has a lot more infrared than Sol, you do indeed look different than I had expected. There seems to be a glow about you, especially in the chest section."
Shirley slammed the lid shut while Richard and Sam roared.
"Let's go get the creepy-crawler," said Shirley, heading for the lift. Soon they returned with Pushmi-Pullyou. The two crawlers were identical except that one had a reel on the front, while the other had a reel on the back. Between them ran a short length of high-strength line. When they entered the workshop, the Christmas Bush detached two of its arms and left the arms to continue the weaving tasks. It disappeared into a storage room and soon came back with a reel containing a much longer length of thinner line.
"Will it hold?" asked Sam. "It looks mighty thin."
"It has only a safety factor of three instead of ten," said the Christmas Bush, "But it should be more than adequate."
With the help of the Christmas Bush and Richard, Shirley assembled the orbiter and its two probes, then she and Richard suited up and took it through the upper cargo airlock and pushed it over the edge through a hole in the still-accelerating light sail and watched it drop toward the distant cousin of Mars.
"Goodby Carl," said Shirley. "Take good care of Wilbur and the Pushmi-Pullyou."
"I will, Miss Everett," said Carl. Shirley could almost hear a sibilant toothiness in the happy smile of Carl's voice as the orbiter gave a short burn of its rocket and headed off to carry out the lifetime job that it had been born and trained to do.
Now that they were in the gravitational pull of Gargantua, Jinjur tilted her sail for maximum deceleration and Prometheus dropped inward at a faster rate in an elliptical orbit that would take them past the other planets in the system. They passed by Zen and Zion, two tiny planetoids with orbits inside Zapotec, then dived in farther to catch the innermost of the larger moons, Zulu.
Zulu was not the innermost of all the moons of Gargantua. That honor was shared jointly by Zoroaster and Zwingli, two tiny moonlets that shared a common orbit. One was in a slightly lower orbit than the other. Since the differences in the orbital diameters was less than the moon diameters, it seemed that they would ultimately collide. But as the innermost one, traveling faster according to orbital law, would overtake the slower one, their joint gravitational interaction would slow the outer one even more, sending it outward, while the inner one's speed was increased, sending it inward, just enough so that the two avoided a collision. The gravitational attraction on the other side was reversed, restoring the two moons to their original orbits after their near collision. Zoroaster and Zwingli received little attention, except from Thomas, who was fascinated by their complex dynamics.
"Just two little orbiters, Jinjur," he said, protesting her decision. "They don't have to be very smart, all they have to do is transmit a carrier so I can get accurate doppler data. With that I can determine whether the system is absolutely stable or whether those two moons will turn into two projectiles or a Gargantuan ring system."
"You can have the orbiters in phase two," said Jinjur. "When we come back after the preliminary survey and do a thorough job on the whole system."
"But Jinjur," said Thomas. "For these stability equations you need to have the longest time-base possible, or else the error propagation makes the data meaningless."
"I'm sorry," said Jinjur. "I don't think we can waste two orbiters at this stage of the exploration."
"How about a lander with a transponder?" said Thomas.
"You need an orbiter to take the lander there and get it down safely," said Jinjur. "I'm afraid not."
Thomas whispered to his imp. Across the command deck Sam raised his head, listening to his imp. He ripped himself from his seat and came over to join the discussion.
"All you need is a transponder?" Sam asked Thomas. "No tracking, no data taking, no smarts?"
"That's all, just an omnidirectional transponder. I can interrogate it once a week with a high power beam, read out the velocity from the doppler shift in the signal, then go off on other business until the next interrogation."
"He could use two of my seismic harpoons," said Sam.
"We still have the problem of getting them there," said Jinjur, and that takes orbiters."
"Not the self-powered harpoons," said Sam. "You program them for the right trajectory look angle, send them off with a picture of what they are looking for, and they will trim course until they are on an impact trajectory. They aren't very smart, since most of what would have been brain is taken up with a tungsten carbide penetration spike. They are only designed to collect seismic and heat data and send it back upon interrogation, but if Thomas can get doppler out of the tracker carrier, I would be interested in the seismic and heat-flow data, especially during the period when the two moons are strongly interacting with each other."
"That'll do fine," said Thomas with alacrity. "How about it, Jinjur?"
"Sounds OK to me," said Jinjur. "Then if you find anything really interesting, we can back it up with orbiters when we come back. Why don't you two go get the 'harpoons' and send them off with detailed instructions."
Sam smiled. "Slam and Smash wouldn't know what to do with detailed instructions." He walked to the lift shaft, followed by Thomas, and the two of them jumped up the hollow column as Jinjur looked quizzically at Sam's departing back. She punched in some codes on her command console and started to read the technical descriptions for the seismic harpoons.
"Shouldn't we use the cargo lift?" said Thomas as he climbed after Sam to level 14. Sam stopped and palmed open a panel. There was a honeycomb rack containing many dozens of sharp pointed metal tips. Sam reached up to one of the larger diameter hexagons and pulled at the small pointed tip centered in the hole. At first all that came out was a meter long metal spike about two centimeters in diameter. As he continued to pull, the spike became thicker, then rapidly blossomed into a heavy exponentially tapered horn that was ten centimeters across. The tungsten carbide metal spike was faired into the nose of what looked like a missile. It was a missile, and it was looking for a target.
"Where is it?"
"Point me at it!"
"Let's go!"
A harsh, crude computer voice came from their imps. Thomas, who had stuck himself to the lift wall and had reached out a hand to help Sam with the harpoon, pulled his hand back as the harsh voice grated on his ear.
"I'll SLAM it good!"
"I'd like you to meet Slam," said the lanky geophysicist. "What it lacks in brainpower and courtesy it makes up for in purposefulness."
Sam spoke to his shoulder imp in the sideways voice that all the crew members had developed.
"Slam goes to Zoroaster," he said, and James instantly filled the miniature memory of the harpoon missile with the optimum trajectory information and a model of the surface features on the distant moonlet.
"I got it!" said Slam. "I'll find it! Let me go!"
"Just a minute," said Sam, handing the two-meter-long pointed bullet to Thomas, who took it gingerly. "You're going to have Smash as a traveling companion."
Slam ignored Sam's comments, its pea-sized brain intent only on hitting its target. Soon Smash was loaded with trajectory and surface feature information for Zwingli. Thomas and Sam took the two missiles up to the cargo lock in the top deck and sent the eager probes on their way to the do-si-do twins down below, each one eagerly bellowing through James's communication link.
"Where is it? I found it! I'm going! I'm gonna hit it! I'm gonna hit it with a SLAM!"
"I've got mine! I'm gonna SMASH it!"
"I sometimes think the persons who programmed those harpoons went out of their way to entertain us," said Sam.
As Prometheus approached Zulu in its elliptical dive into the gravity well of Gargantua, the resolution from their telescopes rapidly became better than the quick snapshots that had been made by the Barnard probe when it had sped through the system some fifty-three years ago. Jinjur got up from her command console at the center of the Control deck and wandered over to stand in back of Sam to look over his shoulder at the science screen. There were two pictures of Zulu on the screen, an old one from the probe and a new one fresh from the optical telescope in the science dome on starside. Jinjur stood up on tiptoes in her corridor boots, the weak acceleration making it easy to stay on point, and peered past Sam's imp at the screen. The imp, noticing her presence, scurried around to the other shoulder. Sam, feeling the motion of his imp, glanced around into curious brown eyes peering over his bony shoulder. He winked and turned back to the screen.
"There've been fewer changes in the past fifty years than I would've expected," said Sam. "Zulu is somewhat like Ganymede. Its surface is a thick layer of striated ice over a deep ocean. Unlike placid Ganymede, however, Zulu is as active as Io."
"Volcanos on a water planet?" said Jinjur.
"Not lava volcanos, but water geysers," said Sam. "There are hot spots all over the planet where there are periodic streams of steam and hot water shooting tens of kilometers up into the atmosphere. Here, let me superimpose an infrared map."
A false-color infrared image appeared on the screen. Zulu was a sphere of deep blue with red, yellow, and white spots on it.
"The yellow and white regions are the hottest points. They indicate the peaks of underwater volcanos. Let's watch this spot. It was yellow a few minutes ago and now it's white." Sam's finger pointed to the screen and his other hand turned off the infrared overlay to leave the optical image on the screen. Slowly, at a point just above where his finger was pointing there grew a small circle. It became larger and fatter until it was a brilliant white doughnut.
"Wow!" said Jinjur. "That was a big one."
Sam read off the numbers on the side of the screen as a computer generated cursor ring tracked the outer edge of the doughnut.
"Fifty kilometers in diameter and still growing," said Sam. "It's a large one, but not as big as Big Bertha's blasts on the other side. They go out to two hundred kilometers. The flyby probe caught one of Bertha's eruptions when it went by, so they must've been going on for at least fifty years."
"Where does all the heat come from?" asked Jinjur.
"There's a thick rocky core and there is probably plenty of heating from the decay of radioactive elements, like in the Earth's core, but in addition, there is tidal heating from Zouave and Zuni rocking the core about its normal tidally-locked orientation toward Gargantua. The core is probably liquid at the center and there is convection going on, because we are already starting to pick up evidence of a significant magnetic field. We can measure it better when we send down an orbiter and the two landers, but it's probably near fifty gauss, one hundred times stronger than the magnetic field of Earth."
"So you've already decided on the probes?" she asked.
"Yes," said Sam. "An orbiter and two amphibious landers with chemical analyzers. But instead of sending the orbiter directly to Zulu, I want to have it spiral inward slowly."
Sam got up from the console and walked to the lift shaft. Shirley saw him call the elevator and joined Sam and Jinjur as the elevator took them up the shaft to level 34. Shirley popped the panel and together they pulled an orbiter from the wall. The orbiter had two aeroshell landers, and as Sam talked to the robot, Shirley jumped up a few more levels and handed down two identical landers that looked like miniature amphibious tanks, with a boat-like enclosed hull, and a tread system that would act as tracks on the ice and as paddle wheels in the water. The landers had numbers, but someone had painted names in bright script on their sides, 'Splish' and 'Splash'.
"Now, Jacques," said Sam to the orbiter. "I want you to take your time orbiting in. Zulu must be losing water at a high rate because of all the steam it's making and its low gravity. I suspect that the water molecules that escape from the gravity of Zulu don't have the energy to escape from the gravity of Gargantua. They will stay in a torus centered at Zulu's orbit. If that is the case, Zulu will pick up the molecules again in a later revolution. I'd like a profile of the water density of that torus before you settle down to explore Zulu."
The imp on Sam's shoulder spoke in a strange nasal accent as James transmitted the orbiter's response.
"I will establish an orbit tilted to the orbit of Zulu. After some cycles I will have explored it not only radially, but out-of-plane," said Jacques.
Shirley was busily fastening Splash to the hold-downs inside the aeroshell. She paused as the nasal voice talked to her through her imp.
"Is there any objection to opening an aeroshell in space? The landers have much more sophisticated chemical sensors than I do. They could not only obtain data on the water vapor density, but could also identify the trace elements, isotopes, and compounds that might be missed by my particle analyzer."
Shirley thought for a moment.
"Splash and I can stand vacuum, Shirley," said a tiny voice through Shirley's imp.
"Yes," said a different tiny voice. "Besides, we want to get to work right away instead of being cooped up for months in that aeroshell."
"Unless James can think of some problem, it should be just fine," said Shirley. "Just remember to close the aeroshell long before you go into orbit about Zulu, Jacques. We don't want the aeroshell cap torn off by a gust of steam from a geyser."
"That and the remote possibility of a meteorite strike were the only dangers I could think of," said James.
"Good," said Sam. "I'm glad you thought of using the landers, Jacques. Are you all ready to go?"
"Goodby, Splish," said Shirley as she closed the cap on one aeroshell. "Goodby, Splash. You'd best be capped until we get Jacques launched and away from Prometheus." She closed the other cap and the elevator started to rise to the starside deck. Sam and Shirley put on suits and carried Jacques out the lock. They stood on the tiny platform imbedded in a three-hundred-kilometer sea of metallic foil and tossed the orbiter upward to the stars. There were a few short bursts of control rockets and the spacecraft drifted away. Sam and Shirley went back inside, took off their suits, and wandered into the science dome. A small portion of the Christmas Bush was busy operating the large optical/infrared telescope. Staying out of the way, the humans looked up and waited. There was a flare of a large rocket off in the distance, followed by three voices coming from both of their imps. Two were tiny and muffled while the other was strong and nasal.
"Goodbye!"
"Goodbye!"
"Au revoir!"
The elliptical trajectory of Prometheus took them zooming by Zulu. They got some excellent shots of Big Bertha in action. They also plotted some snow and rain storms that seemed to initiate near the point on Zulu that faced into its motion along its orbit. The storms weakened as they made their way around to the trailing side of the moon.
They left Zulu behind and closed in on Zouave. It was bigger than Zulu, but the optical and infrared telescopes showed a featureless disk.
Sam was sitting at the science console, but instead of telescope images he had a copy of Carmen's radar console on his screen. Carmen had activated the X-band detectors spaced around the three-hundred-kilometer periphery of the sail, and she was sending burst after burst of high-power chirped radar pulses out the X-band sender on the main body of Prometheus. The short radio waves penetrated the clouds that obscured the surface of Zouave, then bounced back to the detectors. James took each of the detector responses and synthesized a radar picture of the surface of the planet beneath the cloud layer.
"Looks pretty interesting," said Sam to Carmen through his imp. "In fact it seems to be all up and down, no flat areas to indicate seas."
"The thermal microwave radiation from the surface indicates a temperature of one-hundred-ten degrees absolute," said Carmen. "Looks like it's too balmy there for liquid nitrogen rain like we had back on Titan. Y'know, I never thought I would be saying this, but that orange ball of smog looks so much like Titan I'm beginning to feel homesick."
"It may be too hot for liquid nitrogen, but it sure is cold enough for frozen water and carbon dioxide," said Sam. "Where's all the snow?"
"They're dielectrics at that temperature," said Carmen. "The radar goes right through them until it hits the rock underneath. Here, let me adjust the threshold level so we can pick up the weak reflection at the surface of the snow layer."
Sam watched his screen as the computer shifted bits of information. Suddenly the rugged terrain turned into a smoothly rolling landscape. "What's the pressure?" he asked.
"I estimate nearly three atmospheres," said James.
"Gee, we'll be able to work down there with just heat-suits," said Richard.
"Over my dead body," said Jinjur. "Nobody is going no place under that pall of smog until we get a favorable report from a lander."
"Of course," said Richard. "I was just musing. I'm getting cramped living in this checker-stack. I want to get out and stretch my legs."
"That'll come soon enough," said Jinjur. "What landers and orbiters are you going to use?"
"No orbiter at all," said Richard. "Nothing to see but smog. And no landers in the usual sense. They'd probably get buried in snowdrifts."
"What then?" asked Jinjur.
"A couple more of the penetration probes to get down through the snow to bedrock, and some balloons. At that pressure level, they should be able to carry a big payload." He and Shirley took the elevator up the lift shaft and soon Punch and Poke were on their boisterous way, hauling aeroshells that would be released in the upper atmosphere of Zouave. Inside each aeroshell was a deflated high-pressure balloon and a sophisticated semi-intelligent payload. Tweedledum and Tweedledee would spend the next two years floating between the high cloud layer and the frozen surface below, landing occasionally when the winds were calm enough to take surface samples, then going on their way again when the winds rose. Slowly, the picture that they collected in their leisurely motion across the surface of the planet would be built up into a map of Zouave in James's distant memory.
The lightship continued its climb up the elliptical orbit. It began to close in on the multi-colored marble of Zuni. A little larger than the Earth's Moon, it shouldn't have been able to retain an atmosphere. But it did, and quite a spectacular one at that.
"It's like a miniature Earth," said Thomas, watching the screen over Richard's shoulder.
"Carmen — what's the radiometric temperature?" Richard asked of his imp. A voice across the control deck echoed the imp's reply.
"A balmy forty degrees centigrade at the surface," said Carmen. "And those clouds down near the surface are water, not ice crystals."
"It must be tidal heating from Zouave," said Richard. "For sure Barnard and Gargantua aren't hot enough to keep it that warm."
"How come it still has air and water when our Moon doesn't?" asked Thomas.
"I'm not positive," said Richard. "My guess is that like Zulu and Zouave, Zuni is losing air and water constantly, but most of it stays in orbit and is picked up again. In addition, I think that Zuni is capturing the leakage of water from Zulu and smog from Zouave. The strange mixture of chemicals and water raining down from the sky is probably what makes the different colors that we see."
"Is there any chance that there's plant life down there?" asked Jinjur.
"That was my first thought with those colored patches around the edges of the lakes, especially the big one in the southern hemisphere. Unfortunately, there's no sign of chlorophyll bands, but then chlorophyll wouldn't work well in the dim red light of Barnard. If there is life, it might use some other mechanism to collect energy than photosynthesis. Lots of work for the landers to do."
"What kind of landers are you going to use?" asked Jinjur, coming over.
"There are a lot of shallow lakes, and there may be some interesting things to be found if you muck around on the bottom. So, for sure, some submersible amphibious types. I was thinking about balloons too, but the pressure is only about a half-atmosphere and they couldn't carry much. Besides, they would probably get caught in one of those thunderstorms. I think I'll risk a flyer though. Orville can move fast enough to keep out of the way of the weather fronts, or land in a sheltered valley and fold up its wings if it gets too rough." Richard got up from his console and headed for the lift shaft. "Could you get Shirley for me, James?" he asked his imp. "I'm going to need help fitting an extra aeroshell on Bruce."
"I'm starside, Richard," came Shirley's voice through his imp. "Bruce is stored at level 37, see you there."
Richard, Thomas, and Jinjur stepped onto the lift, and as it slowly rose they looked up the tall shaft to see Shirley diving down toward them. Shirley slammed into the lift platform with a programmed response of her knee joints as the platform came to a halt at level 37. Soon the lander was pulled out and Burble and Bubble, the two amphibious landers, were installed in Bruce's two aeroshells.
"We've got one more for you to carry, Bruce," said Richard.
"I'm designed to hold up to four shells," reminded Bruce.
"Not the size of Orville's," replied Richard.
"You are, of course, correct," said Bruce through Richard's imp, its deep, matter-of-fact voice echoing somewhat in the long cylindrical shaft. Shirley had bounced upward again and soon returned holding a large aeroshell. She opened the lid and peeked in.
"Hi, Orville," she said. "Ready to go?"
"Quite ready," said Orville through her imp.
Shirley closed the lid, then looked at Bruce and the crowded lift shaft.
"I'll take Orville up starside, and you can bring Bruce up on the lift, it'll be easier to mate Orville's shell in the Christmas Bush's work area where I'll have more room." Holding the massive shell above her head, she bent her knees and leaped upward in the weak gravity, her legs working like pistons against the handholds along the walls of the shaft. The lift started upwards, more slowly this time, and took them starside.
Thomas hadn't been out in a while, so Richard stayed inside while Shirley and Thomas launched Bruce, Bubble, Burble, and Orville off on their exploration of Zuni. They could see the varicolored moon in the distance, and they both stood outside for a while after Bruce had shrunk into invisibility, to stare at the shining blue lakes and the curl of a weather front that extended over the terminator to the dark side. There was a tiny flash of light at the dark end of the arc of cloud.
"One-thousand one, one-thousand two, ..." murmured Thomas under his breath.
"What are you doing?" asked Shirley.
"I just saw a lightning stroke on the dark side and I'm counting. Every three seconds between the flash and the thunder is a kilometer."
"I'll give you some thunder," said Shirley, laughing and pounding the top of his helmet. Thomas ducked into the lock and cycled through. Shirley stayed outside to watch the lightning flashes on the dark side of the distant moon. Zuni was a prime candidate for a manned lander. They would be back.
Having taken a tour of the moons about Gargantua, Jinjur next set her sail for a close inspection of the giant planet itself. For a month she and James used the weak light from Barnard to drop the orbit of Prometheus closer and closer to the gigantic planet.
Four times more massive than Jupiter, Gargantua was close to being a sun itself. Like the larger planets in the solar system, it emitted more heat from its internal gravitational contraction and chemical phase changes than it received from Barnard. Its surface temperature was near the freezing point of water, which was cold, but it was still a lot warmer than the near-absolute-zero of the black sky, and its heat was a major contributor to the climatic patterns of its moons. Gargantua had a strong magnetic field, driven by the convection currents in its metallic hydrogen core, but its radiation belt was weaker than that of Jupiter, since the solar wind from the red dwarf Barnard wasn't too strong and the many moons kept the belts swept clean.
Jinjur and James were careful in their approach to Gargantua. Its gravitational well was deep and they didn't want to find themselves too far down in it while they were in the wrong type of orbit. Not that they were ever in any real danger of falling in, but the propulsion power for Prometheus was the light from Barnard. If they got into an orbit where they spent half their time with Gargantua blocking the sunlight, it would take forever to climb up out of the pull of the planet and escape.
Gargantua rotated only once a week, much more slowly than Jupiter. As a result, its weather patterns were not the multiplicity of belts and zones with occasional spots as on Jupiter, but instead it had a multiplicity of gigantic cyclones that were spawned near the equator and careened their way into the higher latitudes, where they dissipated into storm fronts. Except for the size, they looked quite similar to the weather patterns on Earth.
Gargantua had a larger rock core than Jupiter. Its density was nearly two grams per cubic centimeter, while Jupiter would nearly float if a big enough and salty enough ocean could be found to put it in. The core of Gargantua was not only evident from the density and the magnetic field, but showed up as permanent spots in the weather pattern. There were certain hot spots near the equator that seemed to be the seed spots for the hurricanes, and other colder spots that seemed to deplete the strength and deflect any cyclone pattern that wandered near it. The most amazing feature was not near the equator, but at a point near the south pole. The crew didn't notice it at first, for it was summer on Gargantua.
George and Arielle were sitting side-by-side on the control deck. Arielle was at the right science console studying Gargantua's gargantuan weather patterns while George was at the left.
"Look at this, George!" said Arielle. "She is cute!"
George cleared his screen.
"Ready!" he said.
Arielle punched some keys on her console and George's screen started a time-compressed video display of a huge weather pattern that had been spawned by the 22 S latitude, 22 E longitude hot spot and had headed south. A few weeks later it had passed over the southern terminator heading for the south pole hidden in the darkness. Instead of disappearing, however, the cloud pattern rebounded from the south pole blackness and broke into two smaller storms, both of which eventually made their way over the terminator on either side of the point that the storm had first entered.
"There must be something there," said George.
"Most certainly," said Arielle, turning serious. "I make doppler measurements on clouds there. They all move north."
"..and that's the only portion of Gargantua that we can't see," complained George.
"In two month we have summer at south pole. Then we have lots of light," said Arielle hopefully.
"In two months we should be through with our preliminary survey of Gargantua and on our way to Rocheworld," said George.
"You sound like you in a hurry, sky-jock," chided Arielle. "Like you do a quick job and get to go home."
George didn't answer, he was asking other questions of the radar pulses that were bouncing off the conductive clouds on the giant planet below.
"There's not only a north-flowing wind pattern, there's also a significant increase in cloud altitude at that point," he said.
"How many?" asked Arielle.
"One thousand kilometers," said George.
"This is impossible," said Arielle. "Things on Gargantua may be huge because the planet is so huge, but cloud altitude change of a thousand kilometers in just a few degrees is most impossible."
"You're right," said George. "But it's there. What we need is more light."
"I can give you that," said Jinjur's voice through George's imp. "I've been watching your displays on the command console. There is something strange going on in the nether regions. Next time around I will shed some light on the subject."
"We have searchlight?" asked Arielle.
"Unless you're a light-sailor, you don't think about it," said George. "But if you've ever been in a light-sail race and had to pay a fine for disturbing the darkness in some sleepy burg in Switzerland by flicking the full Sun at them during a tight tack, you quickly learn that a light sail makes a good searchlight, and we have one that is almost big enough for Gargantua."
"More than big enough," said Jinjur. "At our distance we can illuminate most of the south pole region by just tilting the sail a little. It'll shift our orbit slightly, but James can compensate later."
Some seventy minutes later, they finished their orbit of the northern polar regions of Gargantua and dipped down below the equator. James tilted the sail slightly and a beam of reddish photons from Barnard were reflected from the light sail down onto the darkened south pole of Gargantua.
"It's a tit!" said George, whose eyes had never missed one yet.
It did look like one. Not three degrees from the south pole of Gargantua was a large permanent mound half as big as Jupiter rising five thousand kilometers above the normal Gargantuan surface of ninety-eight thousand kilometers radius. In the center was a central peak—"A nipple!" George insisted. It was as big around as the Earth and reached upwards another thousand kilometers.
Jinjur had James curve the sail to concentrate the light on the central region as they orbited over the south pole region and looked down at the gigantic formation. It was a gigantic atmospheric volcano. A hot spot deep in the core was ejecting liquid metallic hydrogen in a continuous geyser that spurted upward at high pressure to climb for twenty thousand kilometers through the thick atmosphere until it burst into outer space. As it rose, the metallic hydrogen, released from its internal pressure that kept it in its relatively dense metallic form, converted back into hydrogen molecules, then atoms, then ionized plasma as the kinetic energy in the stream was converted into heat. The electric-blue "teat" of the atmospheric volcano gave off continuous lightning flashes as the flowing hydrogen atoms rose onto space, recombined back into hydrogen molecules, then fell in the strong gravitational field back into the upper cloud layers. Now a gas, the falling hydrogen built up into a permanent "high-pressure" area that slowly spread out in an atmospheric version of a lava shield and ultimately flowed back into the surrounding countryside.
The scientists had a field day with their instruments each time they passed over the "tit", slowly twirling once a week about the south polar axis. Behind them, trying not to get in the way, was Thomas, snapping shot after shot with his seventy millimeter electrocam. Whereas the scientists were interested in data, Thomas was interested in the rapidly varying light display, especially when they were right over the volcano and staring down into the blazing blue bowels of the gigantic planet. Six years later, it was one of his shots, not those of James and the planetary scientists, that made the cover of National Geographic.
They were on their twenty-fifth pass over the south pole of Gargantua. James had become expert at giving George and Arielle, the atmospheric experts, the illumination that they needed to study the strange atmospheric volcano near the south pole of Gargantua. George was analyzing some infrared images of the "tit" when he felt a strong black presence at his back.
"Are you and the beauty queen quite finished?" asked a deep voice. "I realize that I am merely the commander of this mission and my job is to make sure that you wizard types are kept happy and well fed, but I do have a few more planets to visit."
George looked at Arielle. Arielle looked at her nails. Two were chipped from the constant tapping of screen and pounding of keyboard during the last thirty-six hours. George turned to face Jinjur, and gave a weak smile. "I guess we're nearly done. Any time, General Jones."
Jinjur made her way back to her control seat. George could almost feel the 'stomp' in the corridor boots as they contacted the soft carpeting in the weak gravity. He turned back to his console to see if he could extract some more data before they had to leave. Jinjur punched her console and soon a display was on her screen. It came from the radar console that Thomas was using.
"How does it look, Thomas?" she asked. "Did those eggheads with the mammary gland fixation bollix our schedule so we'll have to chase the eggbeater?"
"James and I have the trajectory of Rocheworld pretty solid, but there is something going on that raises some questions," said Thomas off to her right. "We have old data from the flyby probe that we're still arguing about. James thinks it's too perfect. Either there has been absolutely no change in Rocheworld's orbit in fifty plus years, or else there has been a significant shift and things just happened to match up when we got here. I'm arguing that the second is implausible, but James seems to want to believe in the laws of entropy, that things must run down, and it is impossible for Rocheworld's dynamics not to have changed in fifty years."
"What's the problem?" asked Jinjur.
"James and I have tracked Rocheworld's two planetoids very carefully with radar while the rest of you have been peering at Gargantua's obscene bottom. Rocheworld is in a highly elliptical orbit with a period that James is sure is exactly one-third that of the orbital period of Gargantua. The elliptical orbit brings it close to Barnard at periapsis, then it swings out nearly to Gargantua's orbit. Once every three orbits the two periods match up and Rocheworld passes just outside Gargantua's moon system.
"That sounds awfully coincidental," said Jinjur.
"One of the lobes of Rocheworld must have been a moon of Gargantua," said Thomas. "With the other one being another moon in an elliptical orbit or an interloper from outer space. The only way we'll find out is to visit them."
"How's our pursuit trajectory? We are way behind in the science schedule. Can we make it up?"
"No way," said Thomas. "Rocheworld is on its way out and we're still down in Gargantua's gravity well with an undermasted sailboat instead of a diesel cruiser. There's no way we can meet it in time for its next close passage. We'll just have to catch it on the fly somewhere else in this system."
"OK," said Jinjur. She looked across the control deck at George and Arielle. "Had enough sightseeing, you two?" she said. "Don't forget, we'll be back after we've completed the preliminary survey."
George punched a few more keys on his console, and as James followed those commands to extract a few more pieces of information out of the images coming up from Gargantua, George turned and looked at Arielle. She shrugged her shoulders in resignation.
"All yours, Jinjur," he said. He got wearily up from the science console chair, and stumbling a bit on unused legs, he made his way to the lift shaft and his bed. Arielle went to bed too, but first she stopped off at the sick bay to get patches for her cracked fingernails, then the galley to get a bite to eat. She had a double helping of protocheese with real garlic from Nels's hydroponic gardens, two algae shakes with energy sticks mixed in for crunch, then still hungry, she finished with a desert consisting of a half-pound of white-meat sticks from "Chicken Little"— her real meat ration for a week—sliced into thin strips and hot-cooked with James's secret recipe of herbs and spices.