So, what did I want? To fly? To be free? To do what I wanted? It's what half the vids I'd ever seen were about.
“You don't have to decide now,” Floyd said.
He was right, but for some reason it merely provided a focus I'd not found in the distant horizon.
“Yes I do." I thought of all the vids I'd seen of women stamping their feet. Maybe having a body did have certain advantages. “Part of it, anyway. You treat me like a precocious child. But I was always more than that, and now I'm grown up.”
Floyd was again silent for a long time—though my thought-processing speed was now in crisis mode, so several thousand milliseconds seemed like forever.
“I did kind of drag you into that cave, didn't I?” he said.
“Damn straight,” I said, surprising us both with my vehemence.
This time, the forever stretched for several seconds. “It's your choice,” he said. Another forever, longer yet. “But I'll miss you.” Another pause. “And I've never before said that to anyone, ever.”
Later, I was never sure how close I'd come to leaving. All I knew was that I felt like I was wandering through my own cave, without a map. I had been formed by a miracle. I owed it to the miracle—God, if you like—to make use of it. BrittneyShip would be fun, but was that the best use? I'd just wind up another Floyd, plying the Outer System all by myself. With Floyd, my uniqueness was doubled. And I'd miss him, too.
“If I stay, I need to be treated as an equal. Ties don't go to the one with legs.”
The suitcam bobbed: Floyd nodding to himself. “Yeah.” More silence. “So that means you don't want to go to Uranus.”
“I didn't say that. I just wanted to be asked.”
Someday, I really want to go to Earth. But it didn't have to be today. That was the message in the view. It changed, it evolved, it grew. But not instantly. For now, life still has a lot of interesting things to offer out-system, as well as in. And who knows, maybe someday, when I've grown to the point that I need to balance the out with the in, Floyd will be ready, too. If not? Well, he and I both have a lot of milliseconds in which to figure that one out.
Copyright (c) 2008 Richard A. Lovett
(EDITOR'S NOTE: Floyd and Brittney appeared earlier in “The Sands of Titan,” June 2007.)
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Reader's Department: IN TIMES TO COME
Our two annual double issues always offer plenty of “extras,” and this year's July/August issue features something especially extraordinary. Back in the early 1980s a completely unknown writer named David R. Palmer made a huge splash here with his very first story, “Emergence,” featuring Candy Smith-Foster, one of the most memorable people many of our readers had ever met on or off the printed page. But she's much more than just a remarkably talented little girl emerging from the ashes of a worldwide genocidal war: she's one of the first of a new species “just like us only more so,” emerging into the world as a delayed result of a historic plague. “Emergence” was followed by one more story here, then grew into the acclaimed novel Emergence. Now Emergence has a worthy sequel, Tracking, in which Candy discovers that, devastating as past events were, they weren't as finished as she thought. So naturally she has to set forth to Do Something About It, and we're proud to present her further adventures as a three-part serial beginning next month.
Carl Frederick, well known in various circles as both science fiction writer and physicist, appears as both next month, with a fact article on “The Challenge of the Anthropic Universe” and also the novelette “The Exoanthropic Principle.” Certain physicists lately have been debating which of several hard-to-swallow hypotheses are the least hard to swallow; Frederick's article surveys the ideas, and his story explores the implications if some of them turn out to be right.
Rounding out our oversize issue we have another of Richard A. Lovett's special features about writing (this time dealing with story beginnings), and an assortment of fiction by such writers as the perennially popular Michael F. Flynn, Maya Kaathryn Bohnhoff, Jerry Oltion, and a promising newcomer or three, covering a wide spectrum of length, subject matter, and flavor.
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Science Fact: PEROXIDE SNOW, EJECTED MOONS, AND DESERTS THAT CREATE THEMSELVES
by Richard A. Lovett
A popular subgenre of science fiction is world building, in which authors attempt to create ecologies, planets, and solar systems different from any we know. Such stories need to be scientifically plausible, logically coherent—and as exotic as possible. There's just one catch: the real universe keeps serving up ideas nearly as strange as any we've imagined.
In this article, we'll look at a smorgasbord of recent theories, starting with one of the best-known alien worlds: Mars.
* * * *
Dusty Death on the Red Planet
Mars is dusty. It's also, on occasion, windy. Not only does the thin Martian atmosphere generate winds strong enough to raise enormous dust storms, but it can also create dust devils: swirling vortexes that can tower several miles high and a quarter-mile wide at the base.
Dust devils aren't tornadoes, but Earthly ones can pack enough punch to knock you off your feet. On Mars, they've helped cleanse the Spirit and Opportunity rovers’ solar panels of light-blocking dust, dramatically extending the rovers’ operating lives. Now, scientists think the dust devils are also generating snow: not like any we've ever seen on Earth, but fluffy flakes of corrosive chemicals that settle into the planet's soil, sterilizing it of any traces of complex organic matter.
One of these chemicals is hydrogen peroxide, produced by the build-up of static electricity in the swirling dust.
Earthly thunderstorms generate static electricity by a similar process involving ice particles high in the atmosphere. “We think the same thing occurs on Mars, but instead of ice, it's dust,” says Gregory Delory, a physicist from the University of California, Berkeley, whose team spent years chasing dust devils across the Arizona desert with a special, instrumented truck.[1] “It's analogous to rubbing your feet against a carpet.”
[FOOTNOTE 1: Delory is lead author of one of a pair of articles on the subject, published in the June 2006 issue of the journal Astrobiology.]
The static fields aren't strong enough to produce sparks or lightning, but they do promote chemical reactions. Water vapor (a major constituent of the Martian atmosphere) can be dissociated into H+ and OH- ions. Carbon dioxide (also prevalent) can break down into carbon monoxide (CO) and atomic oxygen (O). “Once you do that,” Delory says, “it's like turning the oxidant-production mechanism into overdrive.” The result is a smorgasbord of byproducts, including enough hydrogen peroxide (H2O2) to fall to the ground as snow.
This explains a conundrum dating back to 1976, when the first Mars landers, Viking 1 and Viking 2, failed to find any trace of organic matter in the Martian soil. Hydrogen peroxide (commonly used as an antiseptic on wounds) is a potent oxidant that rapidly destroys organic matter.
Even if Mars never held life, the lack of organics in the soil was puzzling. “Organic material has been raining down from meteorites and comets for four and a half billion years,” says Sushil Atreya, director of the Planetary Science Laboratory at the University of Michigan.[2] “So where is it? Something must be oxidizing the organic material.”
[FOOTNOTE 2: Atreya is lead author of the second Astrobiology paper.]
The idea that hydrogen peroxide might be the culprit isn't new, but until now, the only known mechanism for creating it was decomposition of the Martian atmosphere by ultraviolet light from the Sun. That undoubtedly occurs, but it doesn't produce much peroxide. That which it does produce is high in the atmosphere, where it would last only a day or so before it, in turn, is destroyed by sunlight.
Dust devils, on the other hand, can produce hydrogen peroxide up to 10,000 times more quickly, Delory and Atreya calculated: right near the surface where it can easily reach the soil. “Once it gets
into the surface, it can last for years,” Atreya says. “Some calculations indicate it could even last for 10,000 years.”
That makes for some extremely oxidative soil, capable of destroying all organic matter in the manner observed by the Viking landers.[3]
[FOOTNOTE 3: In a new development, a paper in the October 23, 2006 online edition of the Proceedings of the National Academy of Sciences by a Mexican team led by Rafael Navarro-Gonzalez, found that Viking's sensors may have been blind to low levels of organic matter, such as that found in some of the Earth's own harshest environments. This doesn't mean, however, that there is organic matter in the soil or that peroxide isn't present. Unfortunately, no lander to date has been designed to test for hydrogen peroxide. It's not clear, incidentally, whether the chemicals in the soil might pose problems for future astronauts’ equipment. “[Hydrogen peroxide] is obviously not present at a level that is corrosive to something like the Mars rovers,” Delory says. “Though you never know—they did have a wheel get stuck.” And, he notes, there might be problems for equipment remaining in contact with the soil for many years.]
The finding has enormous implications for the search for life on Mars. To begin with, one potential sign of life on other planets is the presence of methane in the atmosphere. Methane can be produced by either organic or geological processes, but on Earth, the vast majority comes from biological sources. “So if you're looking for life, one of the first things you want to look for is methane,” Atreya says.
Normally, atmospheric methane would persist several hundred years before sunlight destroys it. But hydrogen peroxide would destroy it much more quickly.
What this means is that any methane in the Martian atmosphere (and there is some) represents a much stronger source than had previously been thought, whether that source is geological or biological.
If there is life, Atreya thinks it's likely to be well beneath the surface, probably 2,000 to 10,000 meters down. That's far below the peroxide zone—and deep enough that the planet's interior heat might allow liquid aquifers.
Of course, there could be peroxide-tolerant life closer to the surface. “We can't say how life would adapt,” Delory says. “The best we can say is that [the Martian surface] is inhospitable to most life as we know it. It's not inconceivable that there are forms of life that thrive under those conditions.”
* * * *
Lose One, Gain One
From Mars, let's move farther out to Triton, Neptune's largest moon.
Triton is one of the oddest bodies in the Solar System. It's big, as moons go: forty percent more massive than Pluto, an object that in many ways it resembles. Its orbit is tilted 23 degrees from the plane of Neptune's equator. And it orbits backward, or “retrograde,” compared to every other large moon in the Solar System.
Astronomers have long speculated that this means Triton and Neptune haven't always been paired. Triton appears to be an interloper, somehow captured by Neptune's gravity. The difficulty has come in figuring out how this might have occurred. Contrary to many science fiction movies, an object coming close to a planet isn't easily captured: something has to slow it down.
One possibility is that, eons ago, Triton smacked into one of Neptune's other moons. But the odds of such a collision are small. Another possibility is that it passed through a band of gas extending outward from Neptune and was slowed by aerodynamic braking. But it would take a lot of gas to accomplish this, and once Triton was captured, the braking would continue until its orbit decayed, unless the gas dissipated very, very quickly.
A paper in the May 11, 2007, issue of Nature has come up with a much more feasible capture mechanism, based on recent discoveries in the Kuiper Belt, a far-flung region of the outer reaches of the Solar System where dwarf planets slowly circle the sun. About 1,000 Kuiper Belt objects are now known, including Pluto. The biggest, once dubbed Xena but now called Eris, measures 2,400 kilometers in diameter (compared to Pluto's 2,300 kilometers and Triton's 2,700). Other sizeable bodies are Sedna (1,500 kilometers), Varuna (900 kilometers) and Quaoar (1,200 kilometers).
Interestingly, about ten percent of the Kuiper Belt objects are binaries. Pluto itself is one of these pairs, orbited by a companion, Charon, that is a full one-eighth of its mass.
The new study, by Craig Agnor, a planetary scientist at the University of California, Santa Cruz, and Douglas Hamilton of the University of Maryland, proposes that Triton originated as a member of another Kuiper Belt pair. As the two small worlds approached Neptune, Neptune's gravity yanked them apart, slowing one enough to be captured while flinging the other off into space.
Agnor and Hamilton tested their idea by computer models in which Triton and a companion approached Neptune in various manners. “We don't know the exact mass of the escaping object,” Agnor says, “but things like those observed in the Kuiper Belt seem to work.” Better yet, the new theory doesn't require any vanishing gas belts or low-probability collisions. “All you have to do is get close to the planet,” Agnor says.
* * * *
The Desert that Might Have Created Itself (But Probably Didn't)
Let's now return to Earth for a bizarre-sounding theory about the formation of the world's driest desert: a region where, in some places, no rain has ever been reported.
Deserts form when something screens them from sources of moisture. America's deserts, for example, lie downwind of mountains that wring most of the water from the clouds as they cross over.
The super-dry desert is the Atacama, which spans a big chunk of Chile, downwind of one of the world's biggest mountain ranges, the Andes. One theory is that the desert is so dry because the mountains, rising more than 20,000 feet, have cut off all of the moisture. But there's another theory, which says the desert may have aided in the formation of the mountains—exacerbating the process that made it dry, in a runaway feedback mechanism.
To understand this, we need to begin with a primer on Andean mountain-building. Off the coast of South America, the Pacific Ocean's Nazca Plate is being forced beneath the South American Plate in a long, slow collision. One result is that the South American Plate has buckled upward, east of the line of collision, to form the Andes. In the U.S., similar forces played a role in the formation of North America's western mountains. But there's a difference: in South America the prevailing winds blow from the east, rather than the west. That puts the desert on the coastal side of the mountains, rather than inland, like America's Mojave, Sonoran, and Great Basin deserts.
This difference in wind direction is potentially important, because the height of the Andean bulge should be affected by the “stickiness” of the fault between the Nazca and South American plates. The better lubricated the fault is, the more easily the Nazca Plate slides down and the less buckling there should be in the South American Plate.
One way to lubricate a fault is with sediments washed off from the continent. But in a desert, there's little rain and therefore little sediment. The result: a lot of buckling.[4]
[FOOTNOTE 4: This could also be why Chile is prone to devastating earthquakes, with one in the 1960s that was even bigger than the temblor that shook Sumatra in 2004. When sticky faults slip, they slip violently.]
Thus, while the desert might have been created by the mountains, it might also have come first, increasing the size of the mountains that would otherwise have formed.
To test these alternatives, Adrian Hartley, a geologist at the University of Aberdeen, set out to compare the ages of the desert and the mountains.
The Andes appear to have started forming 25 million years ago, but most of the uplift has been in the past six to ten million years. The desert is a bit harder to date, but Hartley has found several ways to track moisture fluctuations in the region. By examining sediments in dry lake beds, for example, it's possible to determine whether they are “evaporites” laid down by infrequent rains or melting snows, or “fluvial” deposits created by perennial streams. It's also possible to analyze pebbles to see how long they've been exposed
to cosmic-ray bombardment, an indicator of how long it's been since there was enough rain to wash them away.
Other desert-dating methods involve studying erosional landforms and looking for signs of waterborne minerals leaching into the subsurface rocks—something that only happens in a certain range of climate conditions.
Hartley's finding: there have been wet and dry interludes, but the desert neither created the mountains nor was formed by them. Rather, it was there before the mountains, and changes in it and the mountains are not well correlated. More likely, he says, its history is related to changes in global ocean currents, perhaps driven by changes in the Antarctic icecap.
Too bad. But this doesn't mean a self-creating desert is impossible. It just doesn't seem to be the case for the Atacama. On some other planet? Who knows...
* * * *
Shrinking Alps
Scientists have had better luck with a theory about the Alps and the Mediterranean Sea.
This theory relates to the Mediterranean “salinity crisis” that began about six million years ago and lasted for about 600,000 years. During that interval, the Strait of Gibraltar became a land bridge, cutting off the Mediterranean from the Atlantic Ocean. Because many of the lands draining into the Mediterranean are relatively dry, the Mediterranean's sea level dropped by hundreds or even thousands of meters, as evaporation exceeded influx.
One result was the conversion of the Mediterranean into a much-shrunken, very salty inland sea confined to a basin much farther below sea level than anything currently on Earth. That's interesting enough in itself, and was the topic ofHarry Turtledove's Hugo-winning alternate history novella, “Down in the Bottomlands” (Analog, January 1993). But Sean Willett, then of the University of Washington, and two European colleagues have suggested that the salinity crisis affected the growth of the Alps.
The Alps are the result of the northward motion of Italy, compared to the main body of Europe.
Analog SFF, June 2008 Page 7
