We were science fiction writers from everywhere in the United States. Over the years Jerry Pournelie had managed to establish a place for us at JPL: the SFWA members were a special case of "Press." Some of us had been here to watch the first pictures from the surface of Mars, and the featureless first close-up photos of Venus before JPL started playing with them, and the stunning pictures of Jupiter's moons, and Jupiter itself.

as if G.o.d had taken a tremendous spray-painter and had Himself a wonderful lime.

In the opening scenes of FOOTFALL Jerry and I captured some of the flavor of those wonderful few days. The probe fell past Saturn, past various moons, through the ring. We waited for some iceflake to smash it but it never happened. The F Ring was twisted. C'Haven't you ever seen three earthworms in love?") The panel of experts hadn't figured out why ("We're sure Saturn is doing everything right . . ."). . . ."). Perhaps the exhaust from a pa.s.sing interstellar s.p.a.cecraft had roiled Perhaps the exhaust from a pa.s.sing interstellar s.p.a.cecraft had roiled it? it? Europa had a huge crater ('Well, we've found the Death Star.") Europa had a huge crater ('Well, we've found the Death Star.") There was an orientation film for the Press. General laughter was heard when the narrator said, 'We expect to find at least six rings." He hadn't seen the pictures. We had. Thousands of ringsl In the Press Kit was a lecture about the atmosphere of litan. Astronomers have long known that t.i.tan has a cloudy atmosphere. They can also demonstrate that t.i.tan isn't ma.s.sive enough to hold an atmosphere. What's it doing there?

They call it the gas torus effect, and it works like this- litan isn't ma.s.sive enough, so molecules of atmosphere leak away. (Ii's happening to Earth's air, too, but much more slowly.) But the gas molecules are still bound by a strong gravitational field: Saturn's. They remain in orbit around Saturn.

The gas torus is of low density, and is shaped like an overinflated inner tube-or a smoke ring, if a smoke ring were spinning, with the inner part going somewhat faster than the outer. Some of the trapped gas escapes anyway. Most of it will end up back in t.i.tan's atmosphere, and leak away again, and return.

Wow!

I made notes all over my press kit, and presently transferred them to my computer. Those notes include an intermediate case. Ii's up for grabs: you can easily beat me into print.

We'll put a Mars-size moon in orbit about a Jupiter-size body, and move It to halfway between Mars and Earth.

The Jovian primary will radiate some heat. If we want Earthlike temperature we must put the system farther from the sun than Earth is. till still be warmer than Saturn's moon t.i.tan, so the warmer gas will escape faster unless we make the body more ma.s.sive than t.i.tan. Almost certainly it will be tidally locked, with one face turned toward the Jovian at all times; so days will be long. With all of that in mind. . . . . we now have a world with an Earthlike atmosphere and four-tenths of Earth's gravity. we now have a world with an Earthlike atmosphere and four-tenths of Earth's gravity.

Man-powered flight becomes easy. You need no more than bicycle gears and a propeller and a lot of wing. . . .say a hang glider or a short-winged Gossamer Albatross .say a hang glider or a short-winged Gossamer Albatross . . . . . . or even bird-wings, for a flyer with an injured leg. Notice that if I bring the moon closer to the Jovian (and move the Jovian farther from the sun, and make the sun a little bluer so it will put out more UV for plants, and so forth; don't forget that the moon will become gradually more egg-shaped) I can shrink the moon and thus the gravitational pull, until your arthritic Aunt Tanya can fly. or even bird-wings, for a flyer with an injured leg. Notice that if I bring the moon closer to the Jovian (and move the Jovian farther from the sun, and make the sun a little bluer so it will put out more UV for plants, and so forth; don't forget that the moon will become gradually more egg-shaped) I can shrink the moon and thus the gravitational pull, until your arthritic Aunt Tanya can fly.

But I became fascinated by an extreme case.

Forget the d.i.n.ky lilile Jovian. Let's put a neutron star at the center! That gives us a ferocious ferocious gravity gradient. We'll put a gas giant planet in close orbit around it gravity gradient. We'll put a gas giant planet in close orbit around it . . . . . . not necessarily something as big as Jupiter, but a world more like Neptune. The planet won't be habitable, not by a d.a.m.n sight. But the gas torus itself should have enough pressure to support life. If we give it enough time, if we let life develop, and green plants. not necessarily something as big as Jupiter, but a world more like Neptune. The planet won't be habitable, not by a d.a.m.n sight. But the gas torus itself should have enough pressure to support life. If we give it enough time, if we let life develop, and green plants.

We'll get a breathable Earthlike atmosphere in a doughnut-shape larger than a world, where everything is in free-fall except for tidal effects; where gravity is found only at the endpoint tufts of what I then called "spoke trees," that look like a free with Iwo tops and no bottom; where everything that lives can fly, except men.

Time must pa.s.s, not only for green life to produce raw avygen, but for the neutron star to spin down. Remember, that's the ashes of a supernova explosion. It carried the magnetic field of a murdered star into itself when it collapsed. A star like that spinning within a nebula-cloud that used to be the outer layer of that same murdered star, generates a signal powerful enough to shower Sal system with X-rays from hundreds of light-years away. That's why ii's called a pulsar. pulsar. We're describing enough radiation to fry any human. We're describing enough radiation to fry any human.

So give it time to spin down. A billion years may be enough. Two would be beffer. . . . . except that the Smoke Ring is not really very stable. It might be gone by the time we arrive. except that the Smoke Ring is not really very stable. It might be gone by the time we arrive.

This is the point at which I began to need hard numbers.

Dr. Robert Forward worked at Hughes Research in Malibu, California. His interests were and are wide-ranging. When I first met him he had a prototype ma.s.s detector on display; I described if in "The Hole Man." And he was about to publish a paper demonstrating that gravity-wave storms can result if ma.s.s spirals down into a black hole. . . . . when Jerry Pournelle's "He Fell Into a Dark Hole" appeared in when Jerry Pournelle's "He Fell Into a Dark Hole" appeared in a.n.a.log. a.n.a.log.

So Forward located this Jerry Pournelle's phone number and called him to acknowledge that Jerry had beaten him into print. And Jerry w.a.n.gled an interview. And invited me to go along.

Forward talked about everything under the sun. He described a new concept, Hawking's quantum black holes, quantum black holes, black holes of all sizes formed in the extreme conditions of the Big Bang. They're a natural for stories, and I told Jerry I'd beat him into print. (And did.) black holes of all sizes formed in the extreme conditions of the Big Bang. They're a natural for stories, and I told Jerry I'd beat him into print. (And did.) Forward must have liked science fiction writers. He became one himself with Dragon's Egg. Dragon's Egg. which involves natives of a neutron star as described by the astronomer Frank Drake. which involves natives of a neutron star as described by the astronomer Frank Drake.

So I had access to an expert on neutron stars and hypergravily.

Please understand: I had a two-lobed novel in mind, two intimately related stories taking place twenty years apart. One story would speak of simple survival; one would speak of the founding of civilization. I wrote a fairly detailed outline (calling it THE SPOKE TREES) to nail down what I was after.

Then I sent it to Robert Forward and asked for help. I sent it to Robert Forward and asked for help.

He gave if.

The numbers weren't too startling (to me). me). I'd get about one-twentieth of a gravity in a big tree. Bob did have some surprises for me. I'd get about one-twentieth of a gravity in a big tree. Bob did have some surprises for me.

First, I'd messed up some technical terms. Gas torus, plasma torus, flux tube Gas torus, plasma torus, flux tube are not interchangeable! are not interchangeable!

Second, I had not realized that the winds at the endpoints of the trees would be even more powerful than the tide! And so my spoke trees- pointing through the neutron star, like spokes in a wagon wheel-were shaped by the wind into long S-shapes, integral signs, integral trees, integral trees, and gained a good deal more detail. and gained a good deal more detail.

Details are where the fun is.

I had already decided to maroon a handful of human beings in the Smoke Ring, leave them alone for five hundred years, then see what they were up to. I needed oxygen, and therefore green plants. I needed normal sunlight so I made the neutron star (Levoy's Star, or Voy) part of a binary. That implied oxygen; oxygen implied green plants. What else did I know about life-forms in free-fall and breathable atmosphere?

Well- Water drops would come in all sizes, from fine mist through raindrops the size of your fist or your head up to blobs so big that the tide would pull them apart. (Call them ponds.) ponds.) Whatever their size, they could not be considered stable. Whatever lives in a pond (call it a Whatever their size, they could not be considered stable. Whatever lives in a pond (call it a fish) fish) might have to cross to another pond fairly frequently. might have to cross to another pond fairly frequently.

So they'll have lungs.

And they'll fly. In fact any Smoke Ring life form will find some way of getting about. Wings are the most obvious way, and most life forms will have wings. . . . . but they won't necessarily look like Earth's birds. but they won't necessarily look like Earth's birds.

After all, there's no gravity. In the Smoke Ring a bird with a broken wing can still fly! There's no unique down; down; no need for bilateral symmetry. What's required is thrust not lift. I gave most of the Smoke Ring's life forms trilateral symmetry, with plenty of room for evolution to fiddle around. no need for bilateral symmetry. What's required is thrust not lift. I gave most of the Smoke Ring's life forms trilateral symmetry, with plenty of room for evolution to fiddle around.

The birds look like fish and the fish fish act like birds. act like birds.

The integral trees are more mobile than I at first realized. When a free comes apart, both both segments will eventually return to the median (the region where the air is thickest.) They do it by sailing: the tree is accelerated by the wind in its remaining segments will eventually return to the median (the region where the air is thickest.) They do it by sailing: the tree is accelerated by the wind in its remaining tuft. tuft. (And when it reaches the median, where the fertilizer is adequate, it will not survive unless it can grow another tuft (And when it reaches the median, where the fertilizer is adequate, it will not survive unless it can grow another tuft fast) fast) There are other sailing plants, and plants that spray seeds, and seeds that spray compressed air. There are plants like rubber-band helicopters. Everything moves.

And how will humans adjust?

I'm dealing with savages here. (My choice.) They're environmentalists when they have to be: they keep their own region clean. Otherwise their philosophy may allow them to use their environment as they please.

Thanks to Bob Forward and the winds, my trees gained a way of gathering fertilizer: branchlets migrate forward along the branch, into the tree-mouth, carrying whatever they've sieved from the wind. And the treemouth is the key to a lot of things.

The treemouth is the tribe's toilet, and its funeral parlor, and its garbage pit. "Feed the tree" is a truly comprehensive insult.

I called the vegetation of the branch "the tuft." I made the foliage edible. The tribe will dig tunnels through it in the normal course of events. I left the branchlets springy enough to be woven into wickerwork "huts."

I had to design laundry and cooking techniques. . . . . and techniques of hunting and making war. and techniques of hunting and making war. . . . . and social hierarchies, different for every environment, including table manners and eating tools and social hierarchies, different for every environment, including table manners and eating tools . . . . and language. and language.

The details are where the fun is. I talked with friends about the Smoke Ring. Several got in a contest to suggest weapons; I took the footbow from that. Later, someone suggested making wings; I used Isaac Asimov's suggestion as to what they would look like.

The cover for THE THE INTEGRAL TREES, by Michael Whelan, was the best I'd ever had. It should have been, for the effort he put into ifi He read through the ma.n.u.script twice, then braced me at a world science fiction convention and held me prisoner for an hour while he asked questions. INTEGRAL TREES, by Michael Whelan, was the best I'd ever had. It should have been, for the effort he put into ifi He read through the ma.n.u.script twice, then braced me at a world science fiction convention and held me prisoner for an hour while he asked questions.

The SMOKE RING cover was just as good.

Authors can be nearly psychotic as regards the accuracy of a cover.

A stranger in a bookstore once looked at that cover and said, "Oh, a fantasy!" Nope. It's hard science fiction in a peculiar place.

Bob Gleason and Tom Doherly were my guests for a few days in May. They came parily to give me some help with the book you're reading now.

I'd already chosen excerpts from various of my novels. I couldn't decide what to take from THE THE INTEGRAL TREES and THE SMOKE RING. The books were relatively new; Tom and Bob had read them; let them give me some help. INTEGRAL TREES and THE SMOKE RING. The books were relatively new; Tom and Bob had read them; let them give me some help.

They spent most of a Friday rereading the books. Bob blames me for a blinding headache; Tom worked off the tension swimming back and forth in my pool, back and forth, like a d.a.m.n machine. Their conclusion: there was nothing they could tear out of either book without it bleeding all over their hands.

Heh heh heh. Jerry and I did that to Bob Gleason once before. We turned over to him a quarter-million words of LUCIFER'S HAMMER: too big a book to sell well, he thought. "I have this nightmare in which we sell millions of copies of LUCIFER'S HAMMER and lose a nickel on every book!" Bob sat down to cut it to size. . . . . and there wasn't one d.a.m.n word he could live without. and there wasn't one d.a.m.n word he could live without.

Serve him right. He's the man who taught us how to cut But Niven doesn't write excerpts; Niven writes novels!

On the other hand. . . . . they couldn't find an excerpt that would stand by itself. So they're demanding that I write a short story instead! they couldn't find an excerpt that would stand by itself. So they're demanding that I write a short story instead!

Thai's wprk.

Oh, well. I want to get back into the Smoke Ring universe anyway. There's a novel I want to write. . . . . involving really peculiar creatures who may have been shaped in the supernova explosion that began the Smoke Ring. involving really peculiar creatures who may have been shaped in the supernova explosion that began the Smoke Ring. And And I want to bring them home. I want to bring them home.

CHAPTER ONE.

YEAR 419 419 DAY 110 DAY 110.

The light filtering through the foliage had an ominous tinge: white with no blue in it, white like dry bone.

Aim crawled eastward through corridors that paralleled the branch. Slender branchlets grew airy, sweet stuff like green cotton candy, easy to brush aside. He ate the occasional handful of foliage without slowing. If n.o.body did that, the corridor would close completely.

Already it was uncomfortably narrow. The in tuft had been deserted these past two years.

Four boys crawled in Alin's wake. Their rolled-up kites caught in the foliage, slowing them. Alin knew how to keep his bundle pointed straight ahead through the branchlets.

The foliage thinned out, then ended in bare bark.

There was no sky. Brighton Tree was embedded in fog: one eightythree-klomter tree fading into an empty white universe.

The boys caught up. Stevn trailed, looking down into the bone-white sky. Stevn was Aim's oldest son, though the long, straight brown hair and the exaggerated frown were exactly his uncle David's.

Alin laughed at their disappointment. If Gilly or Stevn were relieved, Alin chose not to see that. He said, "Get out on the branch. This'll be gone by the time we're set up."

They crawled out along the bark, fingers and toes clinging. Mist streamed past them, blowing hard. In the point-oh-three tidal force of Brighton Tree, it was amazing how much water a tunic could hold.

Halfway to nothing, Aim called a halt. "No wings, citizens. Today it's kites. Frame them."

Each boy unwrapped what he had brought: two sheets of fabric, four brace poles almost as tall as himself, and fifty meters of lines. Bertam was the quickest. He had the bound kite strapped to his back at the waist, and the free kite a.s.sembled in his hands, while Gilly was still wrestling with fabric.

Aim had not touched his own kites yet. Today his students would do without their teacher's example.

The fog shredded and streamed away, and suddenly there was sky.

What had been fog could now be seen as a two-hundred-kiomter river of cloud streaming east and away through a universe of blue sky. The forward fringe of it roiled as it dipped into the chaotic currents of the Clump.

The Clump was an eternal sluggish storm a thousand kiomters across. Matter tended to gather in the tidal anomaly sixty degrees ahead of Goidbiatt's World in its...o...b..t around Levoy's Star. From here the Clump covered almost half the sky, lit from behind by a rising Sun: flamecolored, darkening toward the axis.

Other trees floated around Brighton Tree, all on a level, dark against the bright Clump. Their trunks were vertical lines bent into near-horizontal branches at the in and out ends.

A Navy spinner ship puffed toward the grove, too distant for detail, leaving a white thread of smoke.

The boys were ready. Aim looked them over and said, "Good. Bertam, jump."

Bertam rolled forward and dropped into the violet-white glare of Voy. Aim wondered if he had .closed his eyes. The wind gripped the kite on his back, the bound kite, and pulled him east.

"Stevn, go. Mario. Gilly, go. Go!"

Giiiy clutched the branch in terror.

They were calling Aim Newbry "Kitemaster" because he could fly with kites. "Kitemaster" instead of "Liftmaster's Apprentice"; but this was his first group of students. It had yet to be demonstrated that the Kitemaster could teach.

Every child took flying lessons with wings or jet pods, when he or she was old enough. Some were frightened. Some were reckless. Some were clumsy. Aim had watched, then chosen six, drilled them with their equipment for seven sleeps, taken them out onto the bare branch and drilled them there-and lost two more to their fear- And he was about to lose another, on their first real flight.

"Jump or don't jump, Gilly, but you know the choices." Aim a.s.sembled his kites rapidly. "Don't let me beat you into the sky."

Gilly jumped with no grace, like a rag doll tlung into the wind. A moment later the boy was using everything Aim had taught him. Left arm and leg reached out to turn him, then in again. Now he faced east, free kite clutched against his chest; the kite on his back blocked it from the wind. Now his hands and feet reached cautiously out, holding the running lines with fingers and toes. The free kite wafted east, and caught the wind.

Alin roiled into the sky.

Almost he felt Gilly's fear. Why would anyone jump out of a perfectly good tree? Wings Wings had been new to Brighton Tree when Aim was a baby, but had been new to Brighton Tree when Aim was a baby, but kites, kites, now . . . Aim Newbry was Brighton Tree's expert with kites. He'd seen his first pair of kites less than a year ago, and possessed them immediately thereafter. now . . . Aim Newbry was Brighton Tree's expert with kites. He'd seen his first pair of kites less than a year ago, and possessed them immediately thereafter.

The wind pulled him east. Voy blazed violet-white below him. The bound kite framed him, two spokes at right angles. Kites were more awkward than a good pair of wings bound to one's ankles; but kites didn't have to be flapped or pedaled. They pulled themselves.

Bertam was nicely under sail. His free kite (banded red and white) deployed east-and-inward, pulling him away from Brighton Tree. His arms bowed to the pull. Bertam hadn't grown to his full strength yet.

Mario was under sail too (yellow with a broad scarlet stripe). He seemed to be trying to join Bertam. Not a good idea. Collisions! But Bertram was laughing at Mario, sailing away, racing.

Stevn (orange swordbird on black) was all tangled up.

Gilly was slow. AIm thought he could see the boy's tongue between his teeth. Slow, but he wasn't making any mistakes. His free kite (black stars on scarlet) flapped and eased east, then east-and-in. Gilly moved after the others, sailing, flying without effort, wearing a wide white smile.

The laws of motion throughout the Smoke Ring were: East takes you out, out takes you west, west takes you in, in takes you east; north and south bring you back. East takes you out, out takes you west, west takes you in, in takes you east; north and south bring you back. Today's goal was to sail outward, then return to Brighton Tree's midpoint. Still, Aim wouldn't be too disappointed if a boy wound up somewhere else. Today's goal was to sail outward, then return to Brighton Tree's midpoint. Still, Aim wouldn't be too disappointed if a boy wound up somewhere else.

The East Grove was nineteen trees positioned far enough from the Clump to get decent tide. Any tree would send wingmen to rescue a lost boy. A mistake need not be dangerous. Capability Tree was an obvious target, east and a littie in .

And Natlee was hardly speaking to him, because he was trying to teach their oldest son to fly.

Alin was now moving almost with the wind's velocity. He deployed his free kite (a moby seen face-on, yellow on a scarlet background), but kept it on a short line. Was he going to have to rescue Stevn? Stevn was working more carefully now, getting himself untangled, glancing at Aim every few seconds while he tried to separate his running lines.

Stevn would overreact if his teacher-father began shouting instructions. Aim did too much of that anyway. Give him another few breaths.

One of the trees was getting longer.

Aim blinked. Capability Tree was separating into two halves.

There was no warning. There was only the numbing sight of a tree ripped in half at the midpoint, pulling ponderously apart, leaving a smoky trail of debris. One end fell into white Voylight, one toward the never-seen stars.

There were fifty to sixty people in Capability Tree, not counting children.

The Admiralty ship was still no more than a dot at the end of a vapor trail running through hazy blue-white. Aim watched the white curve as he worked his line.

Stevn had his line out now, east-and-in, as he'd been taught. He'd begun to accelerate.

Alin let his lines out gradually. The free kite pulled east-and-in, but he wrestled it horizontal. It went almost slack. Aim didn't stand a chance of catching any of the boys already in flight, not even Giily. He'd have to catch Stevn.

The white curve of the Navy ship's path remained almost straight. They hadn't seen.