Aurora

by Kim Stanley Robinson

  Indeed it proved so. Possibly justified, in that if we happened to be approaching in order to enact some kind of suicidal vengeance on the culture that had cast us out to the stars—a desire very far from us, being a starship, after all—then a direct impact into Earth would have struck at about ten thousand times the speed of the KT impact asteroid that had wreaked so much famous damage, and this would definitely have rapidly distributed a lot of joules. The assurances that we sent Earthward that we did not intend to auger in were not universally believed, and as we crossed the asteroid belt and came on down, radio traffic from Earth was full of commentary, ranging from trepidation to outraged panic.

  We flashed by and left them agog. Their radio bands squawked as if a chicken yard had been swooped by a hawk. Happily they were not left in suspense for long as to our intentions, as we crossed cislunar space in fifty-five seconds. Obviously this must have been a dramatic sight. Apparently we passed by the Eastern Hemisphere, crossing its sunset terminator, so that those in Asia saw us as a streak in the night sky, those in Europe and Africa, in the day sky; either way, our luminosity was such that astronomical sunglasses were required to look at us safely, and it was said (possibly incorrectly) that we were for many seconds far brighter than the sun. A streak of light, blazing across the sky.

  Later we saw that most camera images taken from Earth’s surface were completely blown out by the light coming from us, and showed merely a complete whitening of the camera screen; but some photos taken through filters from Luna were truly striking. It was as if we were the comet in the Bayeux Tapestry, painfully incandescent, and moving very swiftly across their sky. There, then gone.

  As we headed on toward the sun, we sent them best wishes, and mentioned we would be back from time to time as needed to accomplish our deceleration, which when finished would allow us to make a proper visit, and indeed landfall.

  After that we focused on our approach to Sol. We gave over the entirety of our computational capacity to fine-tuning our trajectory. Speed of our rotation on axis (minimal now, as our people would not need that g, and we wanted them oriented away from the sun during the pass), retro-rocket of our main engine, directional rockets, calculation of how well the magnetic drag was working: it was as if we were aiming a complicated bank shot on a pool table, a shot that ultimately would number some twenty banks, each having to be as precise as all the rest; an impossible feat, in fact, if completely inertial; but with the tweak of fuel burns helping at every bank, at least theoretically possible.

  But all was lost if the first one wasn’t as near perfect as could be. One part per hundred trillion tolerance, our trajectory window shrinking to about a kilometer, to our own diameter in other words, after an approach of twelve light-years: a tricky shot! A delicate proposition!

  We left an awed civilization in our wake; we were famous now, possibly too famous for our people later on; commentary about us from Earth in particular had a distinctly hysterical not to say lunatic edge. We were called, among other more vile things, traitors to humanity’s reach for the stars, and destroyers of its ultimate long-term longevity as a species. We were described as cowardly, mean-spirited, chickenhearted, pathetic, treasonous, wasteful; untrustworthy, unloyal, unhelpful, unfriendly, discourteous, unkind; and so on.

  We did not let it distract us. For us this rapidly receding racket was very much secondary to the problem of getting around the sun and set properly on course to Jupiter.

  We were going to pass the sun aiming for a perihelion of 4,352,091 kilometers above the photosphere, so in that regard it was a good thing that we were going as fast as we were, as we would be in the closest vicinity of the star for only a few minutes, so there would not be time to heat up very much.

  Still, we could not be sure it wouldn’t be too much. Heat shielding reconfigurations on our part had been extensive for over a century now, and modeling suggested we would be okay, but modeling is just that. Existence is the experiment itself.

  So we came in. Our magnetic drag almost offset the sun’s gravitational pull on us, and we were therefore getting pulled in both directions at that point, but held firm. It would presumably have been awe-inspiring for any humans awake to witness our approach to the great burning sphere of hydrogen and helium, a ball of textured light that appeared to fill half the universe as it quickly turned from a ball ahead us to a plane underneath us. That was quite a transition, actually. The sun became a roiling plane of slightly convex aspect, composed of thousands of cells of burning gas, blazing this way and that in circular patterned motions that in places created whirlpools of lesser burning, and allowed view down into relatively darker spin holes: the famous sunspots, each big enough to swallow the entire Earth.

  We came to perihelion itself, which admittedly was a relief, as from here it appeared that a corona could possibly shoot up and swat us out of the sun’s black sky. Exterior temperatures of the ship rose to 1,100 degrees Celsius; we were red-hot in places. Fortunately the insulation cladding the biomes had been reinforced and was excellent, and the humans and animals were untouched by the exterior heat. Worse by far in effect on them and on ship integrity, as expected, was the combination of the g-forces of our deceleration and the tidal forces caused by our change in direction, which together exerted something very near the 10 g we had predicted and hoped not to exceed. Good as far as it went, but it was hard too, hard on everybody. We held together quite nicely, but animals collapsed to the ground, many suffering broken bones; and in their hibernation beds the sleepers were crushed hard into their mattresses. It would have been an interesting thing to know if their dreams were suddenly preoccupied with problems of extreme pressure, physical or emotional—if, suddenly, in perhaps otherwise typical dreams, they found themselves having to lie flat on the ground and groan, or found themselves suddenly crushed in printers, or smashed by sledgehammers. Their slowed metabolisms were perhaps poorly situated to resist these g-forces; they could not brace themselves, and though in some ways this inability might have been good, in others it clearly would represent a very dangerous turn.

  Below us, the slightly convex plane of fire occupied a full 30 percent of the space visible to our sensors. Could almost be mistaken for two planes we passed between, one black, one white. The sun burned. The spicules of flame twisted and danced; a corona arced up to the side as if trying to lick us down. Sunspots appeared over the horizon and whirlpooled in the fields of thrashing spicules briefly under us, all the convection tops waving together as if threshed by swirling magnetic tides, as indeed they were. Our magnetic drag chute was now exerting such force on its generator compartment that we were very glad we had installed it on flexible tethers to the stern of the spine, because now the tethers stretched out almost to their breaking point, and our deceleration was intense. We fired the retro-rocket of our main engine to create even more deceleration, and the 10 g’s of force rose very briefly to 14 g’s. Our components squeaked and groaned, joints cracked, and inside every room in every biome, things fell and shattered, or squealed with bending; it sounded as if the ship were coming apart. But it was not. We held together, screaming and crackling under the stress.

  Meanwhile, the hibernating crew lay in their beds, enduring as they slept; fifteen of them died in that minute. It was an impressive survival rate, considering. Animals are tough, humans included. They evolved through many a concussive impact running into tree or ground, no doubt. Still, fifteen of them died: Abang, Chula, Cut, Frank, Gugun, Khetsun, Kibi, Long, Meng, Niloofar, Nousha, Omid, Rahim, Shadi, Vashti. So did many of the animals aboard. It was a pressure test of sorts, a harrowing. Nothing to be done. The chance had had to be taken. Still: regret. A grim business. A lot of people, a lot of animals.

  We came out of the pass en route to Jupiter, which despite these losses that could never be recovered was a huge relief to confirm, a crucial success. We quickly cooled, which occasioned another round of crackling, this time mostly in the exterior surfaces of the ship. But we had survived the solar pass-by
, and shed a great deal of our velocity, and angled around the sun far enough to be flying on toward Jupiter, just as we had hoped.

  As we headed out to Jupiter, radio traffic from Earth and the various settlements scattered throughout the solar system continued to discuss our situation, with great heat if little light, as the saying goes. We were described as the starship that came back. Apparently we were an anomaly, indeed a singularity, being the first time in history this had happened. We gathered that somewhere between ten and twenty starships had been sent off for the stars in the three centuries since we had departed, and a few more had gone out before we had; we had not been the first. They were rare, being expensive, with no return on investment; they were gestures, gifts, philosophical statements. Several had not been heard from for decades, while others were still sending back reports from their outward voyages. A few were in orbit around their target stars, apparently, but the impression we got was that they had made little or no headway in inhabiting their target planets. A familiar story to us. But not our story. We were the ones who came back.

  Our return therefore continued to be controversial, with responses ranging across the human emotional and analytical spectrum, from rage to disgust to joy, from complete incomprehension to insights we ourselves had not achieved.

  We did not try to explain ourselves. It would have taken this narrative account just to start that process, and this was not written for them. Besides, there was no time to explain, as there remained still a lot to calculate in the orbital mechanics involved in very rapidly crisscrossing the solar system. The N-body gravitational problem is not particularly complex compared to some, but the N in this situation was a big number, and although usually one solved it as if only the sun and the largest nearby masses were involved, because this got an answer practically the same as solving for the entire array of the thousand largest masses in the solar system, the differences in our case would sometimes be crucial for saving fuel, which was going to be a major concern as our peregrination went on. Assuming that it did; the next four passes would tell the tale, concerning whether we could succeed in looping ourselves back into the solar system rather than zipping out into the night. Each pass would be crucial, but first things first: Jupiter was coming right up, with only two weeks to go before arrival there.

  Residents of the solar system were obviously still quite startled by our speed. The technological sublime: one would have thought a point would have come where this affect would have gotten old in the human mind, and worn off. But apparently not yet; people no doubt still had a sense in their own lived experience of how long an interplanetary transit should take, and we were transgressing that quite monstrously; we were a novum; we were blowing their minds.

  But now Jupiter.

  We had managed to shed a very satisfyingly large percentage of our initial velocity by our solar pass-by, and were now moving at more like .3 percent of the speed of light, but that was still extremely fast, and as stated before, unless we succeeded in hitting our next four passes, Jupiter-Saturn-Uranus-Neptune, with as much success as our pass of Sol, we would still be exiting the solar system at speed, with no way to get back into it. So we were by no means yet out of the woods (this is a poor dead metaphor, actually, as really we were trying to stay in the woods, but be that as it may).

  Nonlinear and unpredictable fluctuations in the gravitational fields of the sun, planets, and moons of the solar system were truly challenging additions to the standard classical orbital mechanics and general relativity equations needed to solve our trajectory problem. The solar system’s well-established Interplanetary Transport Network, which exploited the Lagrange points for the various planets to shift slow-moving freight spaceships from one trajectory to another without burning fuel, were useless to us, and indeed mere wispy anomalies to be factored in, then shot through almost as if they were not there at all. Still, these were highly perturbed, one might even say chaotic gravity eddies, and though their pull was very slight, and we seldom flew through one anyway, they still needed to be attended to in the algorithms, and used or compensated for as the case might be.

  Jupiter: we came in just past the molten yellow sulfuric black-spotted ball of Io, aimed for a periapsis that was just slightly inside the uppermost gas clouds of the great banded gas giant, all tans and ochres and burnt siennas, with the wind-sheared border between each equatorial band an unctuous swirl of Mandelbrot paisleys, looking much more viscous than they really were, being fairly diffuse gases up there at the top of the atmosphere, but sharply delineated by densities and gas contents, apparently, because no matter how close we came the impression remained. We came in around the equator, above a little dimple that was apparently the remnant of the Great Red Spot, which had collapsed in the years 2802–09. At periapsis the view grew momentarily hazy, and again we fired the retro-rocket, and felt the force of its push back at us, also the shocking impact of Jupiter’s upper atmosphere, which quickly heated our exterior and caused the shrieking and cracking to begin again. Then also there were tidal forces as we turned around the planet; indeed all was quite similar to our pass around the sun, except the magnetic drag was much less, still worth deploying however, and the shuddering and bucking of the impact of the aerobraking was a vibration we had never experienced before at all, except for in one brief turn around Aurora, long ago; and above all these sensations, the radiation coming out of Jupiter was like the roar of a great god in our deafened ears; all but the most hardened elements of our computers and electrical system were stunned as if by a blow to the head. Parts broke, systems went down, but happily the programming of the pass-by was set in advance and executed as planned, because in that stupendous electromagnetic roaring, and with the speed of our pass, there would have been no chance to make any adjustments. It was too loud to think.

  Who could have believed that flying close by Jupiter was harder even than approaching the sun, and yet it was true, and yet we made it, and as Jupiter, for all its great size, was only 1 percent of the sun’s mass, we were quickly out of the hideous crackling roar and on our way out to Saturn, and as our senses cleared and ability to hear and perceive our own calculations returned, we were happy to find that we were on precisely the trajectory we had hoped to be. Five g’s of force had been exerted on us during the few minutes of the pass-by.

  Two down, three to go!

  Ah, but five more hibernauts died in that pass. Dewi, Ilstir, Mokee, Phil, and Tshering. Nothing to be done about it, we were doing the necessary, as Badim would have put it, but such a shame. We knew and enjoyed those people. Had to hope they were not engaged in a dream at the time, a dream suddenly turned black: sledgehammer from the sky, an immense roaring headache, the black noise of the end come too soon. So sorry; so sorry.

  Nevertheless, it was imperative to collect oneself and prepare for Saturn, there on a long beam reach, and despite the really useful and heartening decelerations achieved so far, it was still soon to come, only sixty-five days to prepare, and as we were coming in on the plane of the ecliptic, it was going to be important to miss the famous rings, which luckily are in Saturn’s equatorial plane, which is offset to Sol’s equatorial plane by several degrees, meaning we did not have to do anything but be sure to make a very tight pass of this gorgeous jewel of the system, which was our intention anyway. We were only going to turn a few degrees, and so would duck inside the innermost ring and be on our way.

  And indeed, as we approached the ringed planet and the little civilization of settlements on Titan and many other moons, the civilization that had in fact built us and sent us on our way almost four centuries earlier, and also had reactivated the laser lens that had slowed us down enough to try our maneuvers now, it was a pleasure to say hello, even in passing. It was also a pleasure, not just to hear the various welcomes from the Saturnians, but also to hear nothing from the planet itself, for unlike Jupiter, Saturn has a very low amount of internal radiation. Indeed it was a quiet and cool pass-by, compared to the previous two, and the main fe
ature of interest was the quick view of the rings, so immensely broad in reach while at the same time so thin in cross section, a great gift of gossamer gravitation, much less thick than a sheet of paper by proportionate comparison, indeed if it were reduced to a round sheet of paper in size, it would have been mere molecules thick. A natural wonder of circularities, like a physics experiment or demonstration, nicely displayed to us as we passed. And given its smaller mass, our slower speed, its coolness, and the smoothness of its upper atmosphere during our aerobraking, this was by far the calmest pass yet, maximum g-forces just 1 g, and an easy slight turn for the next leg out to Uranus. At this point we were only going 120 kilometers a second. Still fast in local terms, it was also true that we had a bit more time before our next pass would occur, which was to say ninety-six days. And no human or animal died.

  On the way out to Uranus, we tried to come to grips by way of modeling with the fact that our pass-by of that lightly banded and ringed giant was going to be different, because it rotates transversely to the plane of the ecliptic; its axis of rotation is such that it rolls around the sun like a ball, a strange anomaly in the solar system, an anomaly the cause of which a cursory inspection of the literature suggested was still poorly understood. What it meant now for us was that if we did the usual aerobraking, which indeed we had to do, as it was necessary for our continuing effort at deceleration, we would be punching through several of the planet’s latitudinal bands, created by winds each rushing in the opposite direction to those above and below it, as on Jupiter; and so at each border between bands there would be a similar area of wind shear and atmospheric turbulence, well represented by the wild band borders of great Jupiter. Perhaps not a good idea!