Analog SFF, June 2007

by Dell Magazine Authors

  Suddenly I knew why Brittney had shut up when she was looking for an analogy. Because she'd been thinking about loving and losing ... and handholding in the face of death, rather than facing it alone.

  Somehow, despite every endeavor to avoid it, I'd found somebody to hold hands with. She just didn't have any hands. Instead, she offered vids.

  * * * *

  I suppose I should have gone back to the canister and started packing right away. But I continued to sit, partly feeling sorry for myself, partly prolonging the last moment of inactivity I was likely to live long enough to see.

  Below, a gust of wind tugged at the parachute, still attached to the canister. I flapped my hands in the sand, creating mini-avalanches and remembering the Kelso Dunes. Before I died, maybe I'd have to try to make these dunes boom, too. Brittney was right: one of the things I'd run away from was my own soul. Or maybe all those years ago, I'd left it, out on the sand.

  I tossed a handful into the air and watched it drift, thinking again that I ought to rise and start figuring out how to act as my own packhorse. But inertia held me. Sitting here, I wasn't using much oxygen. The self-pity was passing. What remained was the closest to peace I'd felt in a long time. There's something soothing about sand in a breeze.

  My dune was part of a ridge that ran as far as I could see, more or less in the direction of the research base. According to Brittney, the incessant breeze was caused by the sloshing of Titan's atmosphere due to tidal forces from Saturn. It wasn't much of a wind, but with the light gravity and dense air it was enough to build these dune fields of long, corduroy ridges—vast enough to stretch most of the way to the scientific base. Vast enough...

  An idea began to take shape.

  "Brittney,” I said. “What do you know about sandboarding?"

  * * * *

  Not much, it turned out, but she got the idea quickly enough. Still, it was nearly seventy-two hours before we were ready to depart, and we'd never have made it without the fusor and the supplies bestowed on us by the canister.

  The best construction materials proved to be the crates, which I cut into strips with an electric torch. Brittney worked out a “sand-dynamic” design, to which I added a tiller and a keel-like strip down the bottom that might allow us to tack—though she thought it might be easier just to sit tight and wait, if we got headwinds. “Mostly, the wind will be behind us or slightly to our starboard quarter,” she said, sounding very much the old salt. “I designed it for maximum efficiency at that point of sailing."

  Her main concern was abrasion. In theory, I should wax the base with something or other, but if there was a slippery concoction that could be made from reconstituted Cajun extract and key-lime concentrate, we didn't know it.

  "Use several thicknesses of plates,” Brittney said. “We've got a superabundance of sail, and we'll be mostly following ridges rather than climbing across them. The extra weight won't matter much."

  Next, I liberated a few clamps from the canister walls so I could equip our sled with cargo crates. I cut a hole in one crate to make a snorkel for the fusor, stuffed its remaining space with supplies, and set the fusor at a level where its waste heat would keep them from freezing. The other crates got oxygen, the distillation unit, tools, and anything else that might come in handy. I also tossed in the vid chips. The science base would have a viewer, and Brittney wouldn't be the only one to appreciate them.

  Then, using bands cut from someone else's very expensive skinsuit, I rigged a chairlike harness so I could nap while Brittney was at the helm.

  After that, it was just a matter of shrouds and servomotors, plus a lot of spare cables in case the power feeds from the fusor broke. I could trim the sail by hand if I had to, but then we'd have to stop when I needed to sleep.

  Finally, it was time to cast off. Attaching the sail, there was a tricky moment when I was afraid the sled would take off without me. Not that it mattered; Brittney had radio control over the servos, and the breeze was light. But still, the idea was disconcerting.

  The plan was for me to spend most of the time on the sled, resting and conserving oxygen, getting off to walk when I got too cramped or restless or if we needed to lighten the load to manhandle it up a big dune.

  We started off up a trough between dunes, then slowly climbed to catch the stronger wind on the crest. Looking back, I could see the silver hull of the canister, surrounded by castoff equipment and packing-crate scraps. Messy, human, home away from home, but overall, a place I was very happy to see the last of. I wondered how long it would take the sand to bury it.

  Then we were on the crest.

  "Whee!” Britney said after playing around with the servos. “Two klicks an hour. Unless we get another storm, that's about as fast as this baby will go."

  At that rate, it was going to take nearly two Titan days to cross the sand. Longer, if the wind changed. An entire Earth month. Plus several days of walking afterward. At least by then, I could abandon most of the gear. With the help of the torch, I might even be able to fashion a crude Santa's sack from pieces of the sail, so I could carry everything I needed in one load. But until then, Brittney and I were on a month-long sand voyage.

  I settled into my chair, watching the wind fill my sail. Would we make it? For the first time, the odds were in our favor, and there was nothing I could do to stack the deck any better. Not to mention that win or lose, we were doing something nobody had ever before attempted. How often do you get to make a claim like that?

  In full gravity, the seat would have been uncomfortable, but here the webbing absorbed the sled's bounces and wobbles with a gentle, almost hypnotic sway. It wasn't perfect, but it was definitely okay.

  At the crest of the dune, Brittney had changed course slightly to follow the terrain, rather than fighting it. Behind, the pancake dome was an orange-and-black mass, already receding. Ahead, dunes melted into the horizon.

  I leaned back, thinking about vast, spreading distances. About the difference between loneliness and open space, between solitude and being alone.

  "How many of those vids did you download from Ship?” I asked. “Pick one and show it to me.” I stretched, trying to make myself as comfortable as possible. “Make sure it's a good one.” Beneath us, the dune hummed.

  It didn't exactly sound like an oboe, but that was okay, too.

  Copyright ©2007 Richard A. Lovett

  [Back to Table of Contents]

  SCIENCE FACT: CRYOVOLCANOES, SWISS CHEESE, AND THE WALNUT MOON by RICHARD A. LOVETT

  What Cassini's first year taught us of the solar system.

  Only a few years ago, moons looked like some of the least interesting places in the Solar System. Our own was geologically dead, and others were presumed to be similar: airless balls of ice or meteor-scarred rock, primarily interesting as relics of the early Solar System.

  Then, in 1977, the Voyager spacecraft began their grand tour of the Outer System. First came Jupiter, where we discovered the ice-cracked surface of Europa—suddenly revealed as one of the most likely habitats for extraterrestrial life[1]—and the massive volcanism of Io, surprisingly found to be the most volcanically active place in the Solar System. A few years later came a high-speed flyby of Saturn, with quick glimpses of its even more enigmatic moons.

  [FOOTNOTE 1: See R. A. Lovett, “The Search for Extraterrestrial Oceans,” Analog, May 2003.]

  Now, we're back at Saturn, not just on another quick flyby, but for a prolonged visit. As I write this, the Cassini probe has been in orbit for more than two years on a mission scheduled to last for at least that much longer: until the maneuvering jets run out of propellant or some critical piece of equipment breaks.

  * * * *

  Cassini's images of Saturn's rings show never before seen details. Photo courtesy NASA/JPL-Caltech

  * * * *

  Each new report will be the stuff of headlines. But headlines are notoriously vague, so let's climb aboard Cassini for a more detailed examination of what's been learned to date. Alread
y, one thing is obvious: the Saturn system is anything but boring.[2]

  [FOOTNOTE 2: Much of the information in this article was drawn from the 2005 meeting of the Geological Society of America (GSA), Oct. 16-19 in Salt Lake City, and the December 2005 meeting of the American Geophysical Union, in San Francisco. This has been updated with information from a forty-page special supplement in the March 10, 2006 issue of Science, plus interviews and correspondence with some of the researchers.]

  * * * *

  Pan and Protoplanets

  The most spectacular elements of the Saturn system are the rings. Easily visible in small telescopes from Earth, they dominate the view from Cassini with an intricate beauty that becomes all the more complex the more closely you look at them.

  The rings are comprised of a vast number of tiny particles, ranging in size from marbles to chunks the size of small houses. There's also a lot of dust. All of these particles are in independent orbits, but they interact in ways that create incredibly intricate structures.

  One of the most useful things Cassini has done is to allow us to get a fairly precise spectrum of the particle size in each segment of the rings. That's done by observing what happens when the rings lie between the probe's radio antenna and a source of light or radio waves. Both are affected differently by particles of different sizes, allowing the Cassini scientists to map the distribution of marbles, basketballs, and larger rubble.

  That's a cute trick, and potentially useful to science-fictional ice miners, but for most people the big picture is more interesting: trying to figure out how the ring particles interact to create those intricate structures we see in photographs.

  From Earth, you can count three or four rings, separated by dark (particle-free) divisions called gaps. Voyager's photographs demonstrated that each ring contains numerous ringlets, some with odd, wavy patterns.[3] But the Voyager flyby was just a snapshot. Cassini will be there long enough to see how things change over the course of days, months, or even years.

  [FOOTNOTE 3: There are also spoke-like features radiating outward across multiple ringlets. They don't show up well, however, from the angles at which Cassini was viewing the rings in its first year, so there is, to date, no new information about them.]

  One of the things being watched is Pan, one of several tiny moons associated with the rings’ gaps. Pan is about 20 kilometers in diameter and inhabits the 300-kilometer-wide Encke Gap, in the outer portion of the A ring.[4]

  [FOOTNOTE 4: Saturn's rings are named alphabetically, in the order of discovery. Generally speaking, that means that the farther up the alphabet you get, the fainter they are. But there are so many ringlets within each ring that the divisions don't mean as much as people once thought they did, though they do remain useful as geographical markers.]

  At least two other such moons are known: 30-kilometer Atlas, and 7-kilometer Daphnis. One of Cassini's missions is to look for other moons in other gaps. Several candidates have been found, but the scientists aren't ready to announce the discovery until they're sure they are true moons and not just temporarily aggregations of ring particles.[5] One interesting aspect of these moons is that they tend to be shaped like flying saucers, but whether that's coincidence or a necessary result of their locations is unknown.

  [FOOTNOTE 5: Several other new moons have also been discovered. One is Pallene, which was observed by Voyager in 1981. It was then lost and has now been rediscovered. But others are new, bearing the names Methone and Polydeuces. “These may not be the most scientifically important results, but I find it very gratifying to be finding new real estate,” says Carolyn Porco, head of the Cassini imaging team at the Space Science Institute in Boulder, Colo. Updates on these and other Cassini discoveries can be found in Geotimes magazine (portions of which are available online at www.geot]

  One might expect that a moon like Pan would pull ring particles into the gap. Instead, it interacts with Saturn (and perhaps the planet's other moons) to kick out most of the particles that venture in. The exceptions are clumps of particles that appear to form within the heart of the gap. Two clumps are in gravitationally stable locations, in Pan's leading and trailing Lagrangian points, 60 degrees ahead or behind it, in the same orbit. Other clumps form at less stable locations, then slowly “march” around the gap until they get too close to Pan and are dispersed.

  "Pan is the master of this gap,” says Carolyn Porco, head of the Cassini imaging team at the Space Science Institute in Boulder, Colorado. “It is the creator of clumps and the destroyer of clumps."

  Pan also affects the edges of the rings adjacent to the gap, creating beautiful waves and spiral streamers of densely packed particles. Mathematical models had predicted that these waves should follow a simple sine-wave pattern, but they're anything but sinusoidal. “They're very complex,” says Porco. “We're having to expand our notions of what happens between a moon and a gap edge."

  More is at stake than simply understanding Saturn's rings, fascinating as they are. The interaction between Pan and the rings is a microcosm for the behavior of stars in galaxies. It's also a good model for testing theories about the accretion of planets from ring-like disks of dust and debris surrounding young stars.

  One important question for people attempting to model solar-system formation is what stops large worlds like Jupiter from gobbling up all of the available material, preventing other planets from forming. The answer seems to lie in moonlets like Pan and the gaps they create. Something similar, Porco says, might cause gas giant planets like Jupiter to truncate their own growth by opening gaps in the solar nebula.

  Equally exciting is the fact that at least one entire ringlet has changed brightness and shifted location since it was photographed by Voyager, twenty-three years earlier. The ringlet is a section of the diaphanous D ring, so faint it wasn't discovered until Voyager. Most of its bands are relatively unchanged, but one has shifted inward by about 200 kilometers. That's not a huge change, but it's an indication of just how dynamic the rings are—the type of information from which scientists might someday hazard a guess as to how old they are and how much longer they will last.

  "We think that in the days of the dinosaurs, Saturn was ringless,” says Porco. Current estimates, she adds, are that the rings can last at most a few hundred million years until collisions with micrometeorites erode them away.

  * * * *

  Propeller Blades

  The most recent find came in March 2006, when Porco's team found the first evidence of “missing link” moonlets, bigger than ring particles, but much smaller than Pan and Daphnis.

  In a paper published in the March 30 edition of Nature, Matthew Tiscareno of Cornell University found signs of four such moonlets in one small segment of the A ring. Tiscareno's group was examining the high-resolution photos Cassini had taken of the rings, back in 2004, looking for anything out of the ordinary. What they found were pairs of bright streaks shaped like two-bladed propellers. They weren't big, only extending a mile or so each way from the center, but they looked familiar: computer simulations had produced similar structures when the motions of ring particles were simulated in the presence of small, embedded moonlets. From their size, it appears that the moonlets that produced them are only about 100 meters in diameter—too small to be seen except via the effect of their gravity on nearby particles.

  The finding supports the theory that the rings are formed of debris from a larger object that broke into pieces. That's because it's hard to model the formation of 100-meter objects in the ring environment unless they began as shards from a breakup.

  The discovery also increases understanding of how Pan and Daphnis create their gaps. The propeller-like structures are wannabe gaps. If the moonlets creating them were larger, the blades would get longer and longer until eventually they would circle all the way around the ring. In the process, they would shift from being bright clusters of particles to dark gaps.

  Amazingly, the Cassini team found four moonlets, even though the photos covered only a ti
ny fraction of the ring. That means that there may be millions more in the A ring alone, Porco says. Bottom line: there are probably lots of other interesting things to be found within the rings. And, from a science fictional perspective, if you tried to hide a massive spaceship in there, as has been suggested by some writers, it might not be long before it gave away its location via its gravitational effect on neighboring particles. Though, of course, it might be hard to distinguish from one of those millions of natural moonlets.

  * * * *

  Tiger Stripes

  From the rings, let's turn our attention to Saturn's moons. There are a lot of them, ranging over a wide spectrum of sizes. In many cases, not much is known, but all of those that have been the subject of detailed study have proven to be extremely interesting.

  Saturn's brightest is the icy world of Enceladus, 504 kilometers in diameter. But it's not a uniform cue ball of ice. Some areas are heavily cratered—indicative of old surfaces that have been subjected to bombardment for a long time. Others are smoother, indicative of newer surfaces.

  How can a moon have surfaces that are both young and old? The same way the Earth does: via volcanic or tectonic processes that somehow destroy old surfaces or cover them with new material. In the case of Enceladus, it appears that most of the processes are tectonic rather than volcanic. That's because parts of the surfaces are chopped up in patterns that appear to be fault lines, where blocks have been shoved around like ice flows on the sea—or Earth's continents under the influence of continental drift.

  But that may not be the case at Enceladus's south pole, which shows a pattern of distinctive bands that reminded early observers of tiger stripes. The surrounding area is particularly young—so young that it has almost no impact craters. Given the rate of asteroid bombardment in the rest of the Saturn system, it appears that these smooth areas are probably less than four million years in age.