Turn Right At Orion (14 page)

Orion! As a child growing up in Montana, I had dreamed about going to Orion. It symbolized warmth, growth, and a nurturing environment to me, even before I knew why it should. This association has always seemed paradoxical, because Orion is quintessentially a winter sight at my home latitudes. Every autumn, I was torn between sadness at the loss of summer heat and excitement in welcoming the crystalline appearance of the constellation of Orion, complete with its opalescent centerpiece—the Nebula. It was only on those rare mid-August nights, when I was allowed to stay up well past midnight to watch the Perseid meteors, that I had my cake and ate it too: summer's warmth
and
Orion.

There had always seemed to be an effortless grandeur to the Orion Nebula. It was not just its presence smack in the middle of what was clearly the most sparkling and easily recognizable constellation, although this certainly helped. Orion's frame of brilliant stars—Betelgeuse at one corner, Rigel diagonally opposite, the other two corners known only by Greek letters but deserving better—set the nebula apart as a work of art. And this frame of stars in turn had a frame of glowing gas, in the form of deep red arcs that stretched a good 15 degrees over the December midnight sky: Barnard's Loop, 30 Moons across. Richly colored
photographs had burned its image into my imagination as indelibly as though I had seen it myself. My repeated efforts to detect its subliminal fluorescent glow were a fruitless project that had made its image even more vivid.

No such struggle was needed to see the nebula, though. With binoculars or my small telescope, the nebula filled the field of view and revealed the whole assembly to be. . . well, can think of no better way to describe it than as a kind of matriochka, a doll within a doll. For there amid the glowing clouds was a tiny pattern of four bright jewels, the cluster of stars known as the Trapezium, slightly lopsided, not so rectangular, but unmistakable in reiterating the stellar frame of the great constellation in miniature. As a child I had found this mysterious and had naively wondered whether, upon visiting the Trapezium, I might find a tiny model Orion Nebula hidden within this frame, and so forth.

Now the thought of visiting Orion seemed less of a scavenger hunt and more like a trip to see the neighbors. It had not escaped my attention that in each successive episode of my travels so far, I was venturing closer and closer to home. I found this reassuring, not just at the visual or visceral level, but also when I thought of what Orion really was. I knew that the Solar System was believed to lie near the inner edge of one of the Milky Way's spiral arms—not a major one, but a middling spur named, in fact, after Orion. These arms, as I had understood from my earlier travels, were self-perpetuating bottlenecks in the otherwise smooth flow of stars and gas clouds around the disk. They were the urban areas of this otherwise suburban Galaxy, the places where gas and stars mixed it up and things happened. All around the Sun, one could see evidence that new stars occasionally formed, mainly, it seems, through the jostling and bumping of molecular clouds that occurs in these Galactic traffic jams. The Sun had long since left its nursery, having survived nearly 5 billion years already, and was merely passing through the Orion arm. But some nearby stars were so bright that they were doomed to burn themselves out quickly and therefore could not
have existed for longer than an instant by the standards of a galaxy's life span. They had been born in the neighborhood. With some imagination, one could pick out an ill-defined belt of them surrounding the Sun at distances of 500 to 1500 light-years, as the astronomer Benjamin Gould first did in 1880. The Orion Nebula seemed to be the “buckle” of Gould's Belt, as the most spectacular of these nearby star-forming regions. I began to feel that Orion was part of the Sun's lifeline to the bustle of the Galaxy and that it could hold important lessons for me. Thus I rationalized, as adults often do, my innate desire to see the place for its own sake.

Orion's exact arrangement of stars and luminous mists, as viewed from Earth, is so elegant that I would like to have brought my craft back toward the Solar vicinity so that I could approach the nebula from the familiar direction. But this would have been a considerable detour, because Orion lay in the same general direction is the Crab Nebula (and Crab II), though merely 1500 light-years from Earth, compared to 6000. I was already near the Crab, so I reconciled myself to approaching Orion from “behind.”

This was slightly disconcerting at first, because I could not get my bearings. Orion's setting was not nearly so dramatic from this direction; in fact, it was virtually invisible. Rather, I should say that it was visible in the breach, by virtue of what it prevented me from seeing. From this direction, the Orion neighborhood presented a visual blockade, an array of impenetrable dust clouds that blotted out all view of the stars beyond. There was no bright nebula at all. The pattern of dark blotches on the sky reminded me of the rifts or “coalsacks” that had laced, split, and obscured my view of the Milky Way in the directions of Sagittarius and Scutum, frustrating my efforts to observe the Galaxy's central regions from Earth. I recognized these ragged shadows as the outlines of giant molecular clouds and tuned my radio receivers
to the frequencies of gyrating and jostling carbon monoxide molecules. An image of the clouds in glowing molecules lit up my display screen, and the nebular environment immediately seemed to reacquire shape and substance. Where there was carbon monoxide gas, there were also bound to be molecules of hydrogen—pairs of H atoms stuck together—and in this case lots of them. I estimated the complex of clouds to contain at least several hundred thousand solar masses of molecular gas, mixed with thousands of solar masses of dust. This was enough dirt to mold 10 billion Earths, although I knew that little of it would actually find its way into planets any time soon.

Looking out the window once again, I traced the clouds' silhouettes by the stars that peered around their edges. For the most part, these stars were fairly distant, some even not too far from the Sun. To one side, though, a modest cluster of medium-bright stars stood out. These were nearby, and from their temperatures and luminosities I could tell that they could not be much older than 10 or 12 million years. This was commonly thought to be the first association of bright stars that had condensed out of the Orion molecular clouds; in fact, their brightest members were already gone—burnt out. The present-day fireworks of the nebula surrounded even younger stars, and they were nowhere to be seen. The Trapezium cluster, the other hot and massive stars, the glowing sheets of gas—they all had to be on the far side, the side facing the Solar System. Of course I had modern navigational aids, so I knew where I was headed. The hidden stars were there, all right, their presence manifest in the blotches of infrared luminosity—patches of heated dust—that I now brought up on my screen. There, unmistakably, was the outline of the cavity blasted out by the Trapezium, the illuminated walls of which composed the Orion Nebula itself. A second warm glow, I knew, must be the cluster of newly formed stars that went by the utterly unromantic name BN-KL, after the initials of its discoverers. This grouping was obscured to the eye both from my present direction and from Earth's point of view, and I imagined it as occupying its own cozy niche completely
surrounded by the insulating and opaque molecular gas, a small cabin in dense woods.

Navigating by dead reckoning on the twin glows caused by the Trapezium and BN-KL, I plunged into the molecular cloud. My immediate gut feeling was to wish I hadn't. There is little so nerve-wracking as flying through a molecular cloud at high speed. As often as my technology performs flawlessly, there is always the slight doubt in the pit of my stomach that
Rocinante's
protective shielding will hold. Early airline passengers must have felt the same way. It's not the speed that bothers me; it's all that stuff coming at me at some tiny fraction less than the speed of light. I'm always aware how much of a punch it packs. I suppose the feeling is compounded by the fact that it is hardly possible to see anything because of all the dust.

To spare you from sharing my anxiety, let me tell you a little bit about how
Rocinante's
shielding works. It should come as no surprise that when I zip through interstellar matter at high speed, it doesn't see me coming. Of course, I don't mean “see” in the sense of perceiving my running lights. As fast as I can travel, light always travels faster and can run ahead. What I mean is that there is no mechanical warning of my proximity, no shove that tells the undisturbed gas to get out of the way before I arrive. My craft packs an incredible sonic boom, sweeping up everything in its path with a tremendous shock wave, A sheath of superheated, superpressurized gas is thrown up against
Rocinante's
skin, and it is against this that I need protection.

The pressure is not the main problem. It does increase stiffly as I approach the speed of light as measured by my Shangri-La factor, the ratio by which time passes more slowly in my craft than on Earth. For each doubling of this factor, the pressure quadruples. But interstellar matter is so sparse that even with these huge amplifications, the forces are easily parried, provided certain precautions are taken. When I traveled to the Milky Way's center, for example, I avoided all regions filled with more than one hydrogen atom in every cubic centimeter. At my peak Shangri-La factor of 13,000, I faced maximum pressures of barely 1 Earth
atmosphere—easily withstood. My trip to Orion was rather leisurely, by comparison, because I had only to move 5000 light-years or so, and my Shangri-La factor never exceeded a few thousand. By the time I entered the molecular cloud, my craft was well into its deceleration phase and the pressures encountered were truly negligible, even given that hydrogen concentrations as high as 1000 per cubic centimeter, or more, were unavoidable in this comparatively dense environment.

I am more worried about
Rocinante's
skin getting too hot. To particles hitting it at speeds within a hair of the speed of light, my vessel's skin is as porous as a sponge. Oncoming electrons and ions could penetrate to depths of many centimeters (meters, even!), which would not pose a problem (
Rocinante
has a thick skin) if only they didn't also deposit all their enormous energies subcutaneously. My main defense is a powerful magnetic barrier that deflects the oncoming particles before they hit. Unfortunately, no magnetic shield is perfect, and on numerous occasions I have watched anxiously as blobs of plasma pierced the force field and struck home. The shield is also helpless to keep out particles of dust, and these have presented a steady, though lighter, onslaught. The surface of my craft, warming until it could radiate away the frictional heat, would reach temperatures of tens of thousands of degrees. No hard material—not even the ceramic of which
Rocinante's
shell is constructed—can survive at such temperatures, and I have watched nervously as patches of
Rocinante's
skin vaporized. I have had nightmares of my entire craft being eaten away, turning into a metallic/silicate steam and being sloughed off into space. But as you see, I am still here. What has saved me is that the evaporated ceramic forms an insulating layer.
Rocinante's
shape, and the play of pressures across it, holds the hot vapor in place; the layer of vaporized spacecraft skin, in turn, bears the brunt of the frictional heating and returns most of it to space with a searing radiance.

Rocinante
continued to decelerate as we neared the Trapezium. I knew I was getting close to the cluster's illuminated cavity because conditions outside my craft had changed. Inside the
molecular cloud I had encountered a ubiquitous infrared glow—detectable only with the correct viewing apparatus—that was created by warmed dust. Like any radiation emitted by a solid material, the color of this radiation revealed the dust's temperature. Now I noticed that, after an interminable stretch of dull sameness, the temperatures were starting to increase, the glow tilting toward shorter wavelengths. I was nearing a source of heat. Off to one side I saw a much hotter area, a few hundred degrees above absolute zero—the temperature of ordinary objects on Earth. I was passing by the BN-KL cluster, still hidden by dust. Straight ahead the gas seemed to be thinning slightly and warming still more. The Trapezium lay there.

Some turbulence, and a few roller-coaster swells, told me that I was crossing into a new zone. This transition was not the sharp shock I had been expecting. I knew that the massive young stars of the Trapezium emitted winds that sped outward at 2000 kilometers per second and carried nearly as much power as the stars emitted in light. When these winds hit the wall of dense gas that lay between me and the star cluster, they pushed on it with uncompensated force, compacting the exposed layers into the cold substratum through which I was now passing. At the same time, the intense ultraviolet rays from the stars fried the cloud wall, destroying the molecules and increasing the temperature 100-fold. The evaporation of this heated layer would have increased the pressure at the cloud surface still further, helping the winds plow their way into the dusty cloud. These were classic conditions for a shock wave: a piston of gas pushed into unsuspecting, cold matter, setting it suddenly into motion with an accompanying increase of temperature, pressure, and density. Such transitions were usually so sharp that as ] had neared the expected location I had said to myself, “Don't blink”—I didn't want to miss it. I also gritted my teeth for a single, sharp jolt. But the transition turned out to be gradual, so gradual that I had time to analyze it and find out why.

The seemingly monolithic, gray medium I traversed had already revealed itself to be quite complex. All kinds of particles
were present, and all were in motion. The molecules, of course, dominated. They, and the occasional single atoms, danced from collision to collision in straight lines, changing direction at random only as they bumped against one another. Their encounters often seemed amusingly like a square dancer's do-si-do, as the molecules looped around one another and atoms sometimes exchanged electrons gratuitously as they passed. Grains of dust—a trillion times heavier than a molecule—executed gently curving paths, seemingly oblivious to the frenetic small-scale action of the molecules. As they passed, the grains tweaked my electromagnetic sensors ever so slightly, indicating that they carried a slight electric charge. It was the charged grains' motion in the weak magnetic field, which I also detected, that curved their trajectories.