by Ian Douglas
There’s a second set of tidal forces at work too—Europa’s resonances with both Io and Ganymede. Europa circles Jupiter once for every two orbits of Io, and twice for every one orbit of Ganymede. These Laplace resonances, as they are called, help pump up Europa’s interior temperature by ultimately stealing energy from Jupiter’s rotation through the tidal interactions between the planet and Io.
The combined effects are strong enough that even though the surface temperature is a frigid two hundred below zero, it turns out that there’s a liquid ocean between ice and the rocky mantle a hundred kilometers down.
And liquid water always means there’s a good potential for life.
During the last few hours of the approach, I watched the banded, slightly flattened disk of Jupiter swelling on the viewall in the mess bay. Three stars were visible to either side of the giant planet—two to the left and one on the right—three of the four classic Galilean satellites. First glimpsed through his primitive telescope by Galileo Galilei in 1610, those four moons shuttling around Jupiter rather than around a geocentric Earth had sounded the death knell of Aristotelian Cosmology. Four centuries later, the discovery of an induced magnetic field around one of those moons, Europa—a discovery made by a spacecraft named Galileo—had demonstrated for the first time that an actual liquid saltwater ocean existed somewhere other than on the planet Earth. In 2107, the Olympus Expedition to Jupiter had drilled down through the ice and discovered the Medusae. Three years later, exactly half a millennium after Galileo’s observations, the base beneath Conamara Chaos had been built, primarily to study them.
I was interested to see in the ephemeris data that “Jupiter II” is an alternate name for Europa. Until the mid-nineteenth century, only the four Galilean satellites were known. Europa was the second out from Jupiter after Io, and was followed by Ganymede and Callisto, Jupiter I through IV. Not counting Jupiter’s dark and mostly invisible ring system, though, we now know there are five moons closer to Jupiter than Europa; hence, “Jupiter f.”
The Haldane continued decelerating as we dropped deeper and deeper into Jupiter’s titanic gravity well. The missing moon of the quartet turned out to be Io, which eventually appeared as a tiny red disk visible against the backdrop of the Jovian cloud decks closely paced by the black dot of its own shadow. Hour by hour, the view slid off to the left as the turbulent colored bands of Jupiter’s upper atmosphere filled the viewall. The mess bay was filled now with Marines and off-duty naval personnel who’d wandered in to see the show.
Eventually, though, Jupiter drifted out of frame, and we were bearing down on the inner of the two stars to the left. Another hour, and Europa resolved as a gleaming blue-white sphere, as smooth faced as a billiard ball, and thickly webbed by darker, brownish streaks and lines. Those lines, properly called lineae, reminded me of the supposed “canals” once thought to have crisscrossed the deserts of Mars, thanks to a nineteenth-century English mistranslation of the Italian word for “channels,” canali.
One crater on that icy surface stood out more brightly than any other—a 26-kilometer-wide hole called Pwyll, looking like the starred impact of a hammer against a sphere of glass crystal. A thousand kilometers to the north, two particularly dark lineae crossed in a giant X, and just below was a tangle of broken and jumbled ice terrain darker than the surrounding areas. This was the Conamara Chaos, and the location of Humankind’s sole outpost within the vast Europan ocean.
It takes some getting used to . . . the idea of an ocean more than a hundred kilometers deep covering the entire Jovian satellite. Europa is slightly smaller than Earth’s moon, with a diameter of just over three thousand kilometers. Between its rocky, silicate mantle below and its shell of ice above lies that ocean of liquid water, but because of its depth, it’s an ocean that actually and surprisingly holds more than twice the volume of water of all of the oceans on Earth.
Europa’s ice varies considerably in thickness. South, where Pwyll Crater punched deep into the surface in the recent past, the crust is more than fifty kilometers thick. Elsewhere, though, as at Conamara Chaos, the ice is much thinner—in places only a few hundred meters thick. There’s evidence that the ice doesn’t rotate at the same speed, quite, as the moon’s central core . . . and even that the entire shell has shifted, rotating independently of that core by as much as eighty degrees, many times throughout its history.
The base itself was invisible from space. Europa’s disk filled the viewall, continuing to expand as the Haldane zeroed in on the navigation broadcasts from the colony’s surface facility.
The Conamara Chaos looks chaotic from above—a vast, sprawling tumble of ice blocks and floes, all frozen together now, but quite obviously the product of some major melting and jostling at some point in the not-so-distant past. We think there’s a collection of hot vents opening from the rocky core a hundred kilometers down, that major eruptions in the past actually broke through the ice cap at this point, and that continuing upwellings of hot water keep the ice at Conamara relatively thin. That’s what they were looking for when they began probing beneath Europa’s icy roof, of course—thin ice.
And they found it, here amid ten-kilometer floes and bergs that looked like they’d been jumbled together, spun about, and even flipped upside down before being refrozen, broken, and refrozen yet again. The dark reds and browns mixed in with the ice were organic chemicals from the sea below, organics that had worked their way up and onto the surface each time the ice cracked all the way through, a clue both to the presence of life and to the richness of that life down in that chill, lightless void.
Eventually, we were close enough to see a kind of navigational marker, a vast, twin plume or cloud hovering above its shadow. The Europan surface is cold—about minus 160 degrees Celsius near the equator, and much lower, minus 220ºC, at the poles. Conamara Base is heavily insulated to avoid damage to the local environment, and that means they need to dispose of excess heat as efficiently as possible, venting it as sterile plumes of steam from a pair of hundred-meter stacks north of the facility. The steam cools high above the surface, crystallizing as ice that eventually falls back across the chaotic terrain as a blanket of fresh, white snow.
The landing zone was well south of the plume, a flattened-out rectangle a kilometer across with a couple of other spacecraft resting there in the open. Nearby was a surface blockhouse, heavily insulated, and the array of dish antennas that maintained communications—through a satellite network orbiting Jupiter—with Earth.
Conamara Chaos is about a quarter of the way east around the moon from the sub-Jovian point; Jupiter at half-phase dominated the bleak, ice-block tumble of the western horizon, an enormous dome with pale red and pink, brown, white, gray, and salmon-hued stripes running up and down, with detail enough at this distance to see the swirls, eddies, and storm spots within the various fast-rotating cloud bands. I looked for the Great Red Spot, the south hemisphere superstorm two to three times as broad as Earth herself, but didn’t see it. I did see the small, flattened oval of Io’s shadow, though, close to the planet’s limb, and above, a tiny red disk that was Io itself.
We settled to ground, and the elevator tube rose up out of the ice to meet us. The expedition’s five Corpsmen, as technical staff, plus our two civilian passengers, the ship’s skipper, and Lieutenant Kemmerer would make the journey down to the base. Dr. Kirchner had been invited, I understood, but had opted to stay in his office on Haldane.
The radiation at Europa’s surface is fierce—about 540 rem per day, enough to kill an unprotected human in fairly short order. Haldane’s rad shielding had protected us down to the surface; from there on, the ice itself would keep us safe from being fried by Jupiter’s intense radiation belts.
I felt a spring in my step as I entered the elevator. We’d been accelerating at one gravity for a week, now, but the surface gravity on Europa was only a bit more than a tenth of that. Drop something and it will fall half a meter in the first second, so there is a clear up and down, unlike on
the tethered asteroid at Starport, but you need to watch your reflexes. Jump, and you could bang your noggin against the overhead.
“Welcome to Chaos,” a voice said from a hidden speaker as we gathered within the elevator. “We’re bringing you all the way down to Level Three. Please hang on to the handrails beside you. Enjoy the ride!”
The elevator ride was a long one—well over half a kilometer straight down. The warning about handrails was a good one. With a surface gravity of only 1.314 meters per second squared, our downward acceleration through that tunnel more than canceled our weight. I don’t know how fast we were going, but we were in zero-G for most of the descent. The trip was also boring, with nothing to see but the gray metal of the shaft sliding up around us through the clear transplas of the car.
But then the elevator emerged at the bottom level, we stepped out onto the main deck, and I gasped at the view.
Okay, so I’m easily impressed. But the others were speechless, too, even the usually unflappable Dubois, who said, “Fuck me,” the words spoken very, very softly. Nearby, Dr. Ortega muttered something that sounded like, “Sweet holy Mother of God.”
Conamara Base is upside down, as humans think of things, literally growing down from the underside of the ice ceiling overhead. Level One, with the hab quarters, is at the top, then Level Two with the lab spaces, with Level Three and the command center at the bottom, a broad, circular compartment fifty meters wide with instrument consoles and deck-to-overhead viewalls looking out into the abyss. The walls leaned out at a sharp angle, giving a clear view almost straight down.
Down . . .
The ocean here was just over a hundred kilometers deep. Lights on the outside of the base illuminated the water around us, as well as the eerily inverted icescape ceiling hanging above our heads. The light faded away swiftly with distance, however, and below, there yawned only a vast and empty night.
And yet, there were stars in that night. . . .
The year before, during the Bloodworld op, I’d spent some time on a gas giant moon—Niffelheim-e—my first experience with a hydrosubglacean world like Europa. On Niffelheim-e, the moon circling gas giant Gliese 581 VI, I’d linked in to a teleoperated submersible, cruising beneath the ice and encountering a variety of life forms there. Like abyssal forms in Earth’s oceans, many created their own light; one titanic species, the five-kilometer-wide Luciderm gigans, had looked like the night view of a city seen from the air.
There were lights here as well, clouds of soft-glowing phosphorescence speckled by thousands of harder points, like stars, shining yellow and green. All were in motion, the whole giving an irresistible impression of vibrant, thriving life.
We now suspect that the majority of life across the Galaxy may live in environments like this one, locked in the eternal darkness of an ocean between rock and ice. Life, it seems, appears anywhere the conditions are at all favorable—and that frequently means liquid water. There are far more ice-locked moons and worlds in the Galaxy, possibly on the order of thousands to every one, than there are temperate, habitable-zone planets like Earth. Humans and Brocs are the exceptions, not the rules.
“Welcome aboard, folks,” a civilian in white utilities said. “I’m Dr. Selby. I see you like the view.”
“Spectacular,” Lieutenant Kemmerer said. “And here I thought it would be boring, not having Jupiter in the sky all the time.”
“You do get used to it after a while. But we keep discovering new species out there, and that keeps us on our toes.”
“What’s the outside temperature here?” Dr. Montgomery wanted to know.
“About five Celsius. That’s actually pretty warm. We have some major convection currents rising beneath us at this point.”
“The warmest water is in the deeps, am I right?” Ortega said.
“Exactly. The interior of Europa’s core and deep mantle are still molten, and tidal interactions with Jupiter keep the mantle fairly plastic. The water near the mantle’s surface is close to five hundred degrees, most places, but the pressure a hundred kilometers down is so high the water stays liquid, and can’t turn to steam.”
“And convection currents heat the entire ocean, keep it liquid,” Ortega said, nodding.
“Correct. If Europa was a bit closer to Jupiter, she’d be like Io—kneaded and squeezed so hard by old Jove that the surface would be covered by volcanoes and flows of molten sulfur, and with all of the water driven off long ago. But out here the heating is just enough to maintain a liquid ocean.”
“And Ganymede’s mantle is all ice?” Ortega said.
“Right: ice, and a kind of warm ice slush down deep, above the inner silicate mantle. We have robots exploring Ganymede, looking for enclosed pockets of subsurface water like the deep lakes in Antarctica, and those might have evolved life as well, but so far at least, Europa is where all the biology is happening out here.”
“Well, Europa,” Montgomery said, “and the Jovian atmosphere.”
Selby grimaced, and looked uncomfortable. “Of course.”
We know precious little about life within Jupiter’s atmosphere, and that still made exobiologists like Selby uncomfortable. Collector robots skimming through Jupiter’s upper cloud layers have picked up organic molecules and what appear to be something like single-celled algae, the Jovian aeoleaprotistae. There was just a hint from these in their biochemistry that there might be more complex life existing deeper within the Jovian atmosphere, but at temperatures and pressures that made it unlikely that we’d be meeting it face to face anytime soon.
What it all added up to was the indisputable fact that life is incredibly resilient, amazingly adaptive, and as common as dirt throughout the cosmos.
“Europan life,” Lieutenant Kemmerer said, “they’re all heat eaters?”
Selby laughed. “Thermovores. Well, a lot of it is. We’ve been studying the Europan biome for almost a century and a half, and we’ve almost literally just scratched the surface. Most of the life forms we’ve catalogued so far appear to be thermovores, yes. We believe that there are chemovores in the great deeps, mainly because Europan life is based on sulfur, rather than carbon. We think they started off metabolizing chemical emissions around hot vents at the mantle, like the sulfur-metabolizing microbes around deep-ocean hydrothermal vents on Earth.”
“But the Medusae are different, aren’t they?” Dr. Montgomery said. “Not thermovores, but . . . what’s the word? Kymovores?”
“Exactly.”
“What the hell is a kymovore?” Garner wanted to know.
“They eat chemicals, of course,” McKean said, mistaking the pronunciation for chemovore.
“Uh-uh. Kymovores,” Selby said, stressing the y as more of an “oo” sound. “From kym, the Greek word for ‘waves.’ They get energy directly from the energy of waves in the water.”
McKean reddened slightly, but didn’t say anything. He didn’t like being caught in the wrong.
“Besides tidal flexing,” Selby went on, “there’s a second force acting on Europa’s ocean, keeping it warm. Europa has a very slight axial tilt—less than a tenth of a degree—but it’s enough to respond to Jupiter’s tide action and generate waves that pass through the ocean. They’re called Rossby waves. They travel quite slowly, only a few kilometers per day, but they release a lot of energy into the water—maybe two hundred times what Europa gets from tidal forces alone, and some species in the Europan ocean use that energy directly for metabolism. That includes the Medusae.”
As the conversation continued, I walked over to one of the big windows and looked down. The water was filled with small, drifting bits of white matter illuminated by the colony’s external lights. The underside of the ice cap was covered by branching, whitish growths called Europafitoformes—Europan plant forms—and debris from the stuff constantly drifted down into Europa’s ocean depths like snow. A lot of the biology down there depended on that organic rain.
I saw something rising out of the darkness.
It was l
arge, it was round—a kind of flattened umbrella shape—and it looked as though it was manufactured out of spun glass. I was reminded of certain terrestrial jellyfish, and recognized the Europan Medusa from downloads I’d taken on Earth a year ago.
At the translucent core of the thing’s body, there was a cluster of organic lights, and these were winking on and off in an obvious pattern as it rose. One light . . . two . . . four . . . eight . . . sixteen. Then they all winked off and the pattern began again: one, two, four, eight, sixteen. The Medusan Count, it was called, and it was the main reason xenosophontologists thought that the organism was intelligent.
“Dr. Selby?” I said. “Looks like you have someone trying to talk to you out here.”
Selby joined me at the window. “Hah! Looks like. They come up and blink at us every so often. I think they’re just saying ‘Hi, there.’ Or else they might just be reacting to our lights.”
I noticed from the light showing in the water above the window that the station was flashing something in response. “You have a bank of lights on the outside of the building, sir?” I asked.
“That’s right. We’ve been trying to respond to them.”
“Responding how?” Kemmerer asked.
“By continuing the series,” Selby replied. “We repeat the Medusa’s pattern, then add thirty-two, sixty-four, and one hundred twenty-eight.”
“Does it work?”
“Not really,” Selby explained. “Or rather, not yet. We try to respond every time they signal. Unfortunately, all either we or the Medusae can learn from the exchange is that the other guy knows how to count in geometric series. There’s no other exchange of information, no way to encode information. None that we’ve been able to discover, anyway.”
