"I'm the key figure in an ongoing government charade, a plot to conceal the truth about the existence of extraterrestrials. It's a global conspiracy actually, with key players at the highest levels of power that reaches down to the lives of every man, woman, and child on this planet. So of course no one believes me."—Agent Fox Mulder, The X-Files

This past weekend, I traveled to San Diego to visit relatives. Being the mass-transit fan that I am, I defied California's car culture and took the train down the coast from Los Angeles. It was a beautiful ride, with crashing surf and a spectacular sunset right out my window. At the end of the weekend, I boarded the return train to find it pretty packed, but after a bit of searching found an open seat next to a friendly and (very) talkative fellow traveler. We exchanged the usual small talk, the almost ritual greetings that pass between strangers briefly together inside rapidly moving aluminum cylinders. My neighbor was visibly excited to find that I'm an astronomer. "Oh, I love astronomy! Tell me, what are we learning from that spacecraft out at Saturn?" And I was happy to oblige him with a few tales of Cassini at Saturn, and its continuing discoveries: the exquisite fine structure of the ring system, polar methane seas on frigid yet "tropical" Titan, Enceladus's tiger stripes and vast ice geysers, and most recently the astounding closeups of the mottled black and white surface and baffling equatorial ridge of enigmatic Iapetus, utterly unique in the solar system. My interested neighbor asked a few followup questions, and we chatted a bit longer. So far so good. And then . . . the conversation took an unexpected turn

"Oh, but what do you think about aliens? They've gotta be out there, right?" I assured my fellow traveler that yes, I suspect the vastness of the cosmos probably holds many living worlds, but we don't yet have definitive proof. "Yes we do," my neighbor retorted, "they've been keeping it under wraps for years down in New Mexico. I saw all about it on TV." Oh boy, I thought to myself, a Roswell true believer. Here we go again.

You can probably imagine the next fifteen or twenty minutes of conversation fairly well without my giving the gory details. Never mind the historical record, which establishes without a doubt that the Roswell "UFO crash" story was an unintentional fabrication by a low-level officer, which the military brass subsequently played up to cover their true secret: an attempt to spy on Russian nuclear tests from sensor-laden high altitude balloons. Never mind the implausibility of a successful coverup lasting decades and involving probably thousands of conspirators. Never mind that the U.S. government is demonstrably incapable and incompetent at keeping any secrets whatsoever, from the XYZ Affair to the Teapot Dome Scandal to Watergate to Iran-Contra to Valerie Plame, on and on. Never mind the continued unmasking of essentially all UFO "sightings" as hoaxes, high altitude military aircraft, or the planet Venus. Despite all that, despite the careful work of UFO-story debunkers up to and including Carl Sagan, some people just cannot be convinced that the government doesn't have a bunker full of secrets and a couple of dead aliens on ice. "I want to believe," indeed.

But what would really happen, you may ask, if the government did stumble upon something momentous? Can we really be sure that some shadowy agency wouldn't try to keep it under wraps, futile though that might be? Can we really be sure they'd tell us their secrets from outer space? Luckily, we don't have to wonder. We can look to history instead, back four decades ago, when a tremendous secret from deepest space was known only to the most classified inner levels of the U.S. defense establishment. And they told the whole world.

Vela's Surprise

The setting: America, early nineteen sixties. The hippie movement is sweeping the nation. Martin Luther King, Jr.'s "Letter from a Birmingham Jail" prompts President Kennedy to call for a national civil rights bill. Philip K. Dick's The Man in the High Castle has just won the Hugo, as mankind takes its first fledgling steps to the stars. But all is not well: bare months after the Cuban Missile Crisis, the threat of nuclear Armageddon still hangs over the world. The first tentative steps towards détente are being taken, as the U.S., U.K., and Soviet Union sign the Partial Test Ban Treaty, forbidding all nuclear explosions above ground.

Twenty years before Reagan, "trust but verify" was already a keystone of America's Cold War strategy. And so the Air Force and aerospace contractor TRW prepared a top-secret monitoring satellite program, known by the code name Vela. The first two Vela satellites were launched into orbit just three days after the treaty was signed. Over the subsequent two decades, the Vela program lofted a dozen spacecraft capable of pinpointing a nuclear explosion anywhere on or around Earth using sensitive X-ray, gamma ray, and neutron detectors. Everyone knew you couldn't trust those dang Russians. For all we knew, they might try to test a bomb in outer space, maybe on the moon even—after all, we'd seriously considered testing nukes on the moon. So Vela's sensor network kept an eye on the planet, the moon, and everywhere else well into the 1980s. Had any nuclear explosions taken place, the detection of a simultaneous burst of X, gamma, and neutron radiation would have rung alarms around the world.

But of course, nothing happened. With the exception of one still-mysterious incident in 1979, Vela found no surprise nuclear explosions, and the Cold War gradually ground onwards towards its conclusion. The Vela program was a complete success, but a low-key, quiet, and unannounced one that just kept ticking away recording, well, mostly nothing much: the occasional cosmic ray, maybe some solar flares, and a bit of random static now and then. Amidst all this successful quiet, in 1972 a team of defense contractors at Los Alamos National Laboratory began carefully re-examining a decade's worth of recorded Vela data. Remember, the expected signal of a nuclear explosion was simultaneous bursts of X, gamma, and neutron radiation. With the limited computer power of the day, it wasn't until 1972 that the data was examined for any other sorts of bursts: by hand, painstakingly, line by line, page by page searching for any signals recorded by multiple satellites at once.

Shockingly, there were. Over a dozen bursts of gamma rays were found in the data, recorded almost simultaneously by multiple satellites and utterly unlike anything else known to science. By carefully comparing the time each satellite detected a given burst, and triangulating using the spacecrafts' known positions and the speed of light, an approximate direction for each burst could be determined. This only deepened the mystery: they did not come from the sun, nor the moon, nor any other known body. The bursts had no apparent relation to supernovae, or any other known astrophysical explosions. As far as could be determined, mysterious blasts of hard radiation, each lasting a few seconds, were coming from completely random directions in the sky at equally random times. Could we possibly be unwitting bystanders to some vast alien galactic war, with planets destroyed in cataclysmic explosions all around us?

Now, here we have perhaps the perfect ingredients for a government conspiracy. Data from classified sensors on a crucial piece of military hardware? Check. Inexplicable thing from outer space? Check. Potential military implications (if considered in an appropriately paranoid Cold War mindset interested in gamma ray weaponry)? Well, maybe check. So chances are you'd expect the bursts to be kept secret, the data carefully studied by nuclear weapons engineers. At the very best you might expect the data merely filed away as an interesting curiosity, to be stored in some vast cavernous government warehouse (you know, like the one with the Ark of the Covenant).

What you probably wouldn't expect is Drs. Klebesadel, Strong, and Olson, of the Los Alamos National Laboratory, standing in front of a packed room at a meeting of the American Astronomical Society in Columbus, Ohio in June 1973, announcing their inexplicable gamma ray bursts to the world. No conspiracy, no secrets kept. Even the technical details of the gamma ray sensors on the Vela spacecraft found their way into a research article printed in the Astrophysical Journal that month. Many in the audience were shocked, true, but not so much at the mere fact that weapons-lab spooks would come give a public talk, as at the astonishing discovery they reported.

The Search for an Explanation

Theories proliferated rapidly as to the cause of the bursts. With so little data to go on, and with the pulses having a wide range of brightnesses and durations, almost anything seemed plausible. (One of the first theories was, yes, the "alien nuclear war" idea I alluded to a few paragraphs above . . . published by the National Enquirer, which even back then sent reporters to astronomy conferences looking for good science to pillage for tabloid fodder.) The long list of theories contemplated includes some that seem more at home in science fiction than in serious scientific publications: collisions between matter and antimatter clouds, evaporating black holes, collapsing wormholes, or even white holes leaking energy from alternate dimensions. More serious contenders included stellar flares, collisions between neutron stars, a new kind of supernova, and perhaps radioactivity in comets in the outer solar system. The closer the bursts were, the smaller the amount of energy involved, making them easier to explain. But distinguishing between any of these theories required more precise positions than could be provided by the Vela spacecraft.

Over subsequent years, new instruments lifted off to address this need. Because gamma rays can't be observed from the ground, all measurements must be made from space. The early gamma ray detectors of those days didn't provide any directional information. Vela's triangulation method was limited primarily by the relatively close distances between the spacecraft, all in local Earth orbit, and could only localize bursts to within an area, oh, four or five times larger than the apparent size of the moon, containing tens of thousands of stars. The obvious route to improvement was to get larger baselines, and so, in a remarkable example of late-Cold-War international cooperation, half a dozen unrelated spacecraft headed to destinations around the solar system from the U.S., Russia, and Germany were outfitted with gamma ray detectors. As these spacecraft went about their various missions, they also recorded bursts. The data returned by this Interplanetary Network provided vastly better positions, leading to the first tentative reports that gamma ray bursts came from distant galaxies. This was dramatically confirmed in 1990 by the Compton Gamma Ray Observatory, the high-energy counterpart to the Hubble Space Telescope, whose sensitive detectors established unequivocally that gamma ray bursts originate in the far distant universe. And I do mean far: we now know that the average gamma ray burst comes from a galaxy seven or eight billion light years away, and its light has been traveling toward us for half the age of the universe. To be seen so brightly after that unimaginable distance, they must be among the most luminous objects in the entire cosmos.

Today, NASA's Swift spacecraft detects a new gamma ray burst typically every few days, measures its position precisely within seconds, and relays that measurement to the ground quickly enough for rapid followup of optical afterglows using the largest telescopes on Earth. The exact details of bursts' origin still remain somewhat mysterious, but scientists have identified two distinct kinds of bursts: "long" bursts, believed to be caused by jets of radiation emitted as massive dying stars collapse into black holes, and "short" bursts, probably caused by the collisions of pairs of neutron stars. The long bursts are believed to take the form of narrow, tightly focused jets of material and radiation; their narrow opening angles let them shine brightly across cosmic distances like gamma ray spotlights. Many questions remain, but the Swift spacecraft, and the horde of ground-based telescopes that rapidly follow up each burst it spies, have brought the pace of discovery to a fever pitch. (Many of my colleagues who work on gamma ray bursts carry pagers around at all times, to ensure they'll be alerted the instant each new burst occurs and can frantically rush to finagle telescope time from all the rest of us. Sometimes science truly is a race!) Now that gamma ray bursts are (partially) understood, some scientists have begun contemplating ways to use them as tools to study the far distant universe and its expansion with time, just as supernovae have served as crucial "standard candles" for measuring the properties of the relatively nearby universe. Along the way, the study of gamma ray bursts has helped launch a whole new subfield of astronomy: Time Domain Astronomy, studying gamma ray bursts along with cataclysmic variables, supernovae, hypernovae, pulsars, rotating radio transients, soft gamma repeaters, and a whole variety of other things that distantly go "boom" in the night. And just think, it all goes back to some spies deciding not to keep a secret.

The saga of gamma ray bursts' discovery is not the only such story of military applications leading to astrophysical discovery, either, though it is one of the more dramatic ones. Intercontinental missiles can be tracked from tens of thousands of kilometers away by their hot exhaust, radiating in the thermal infrared. But the infrared sky is awash in bright sources that could confuse sensors: dusty nebulae, star forming regions, massive dying stars. So the Air Force produced the first detailed maps of the infrared sky in the early 1980s, recording the positions and infrared brightnesses of thousands of sources into a catalog that could be used to tell launching nuclear missile from distant infrared nebula. That catalog, too, was promptly published, and is still used today by many astronomers, including me. Along the way, the military also developed most of the technology for digital infrared detectors that have since become the workhorse tools of the infrared astronomical community. That technology got released, too. Other Air Force officers led projects to spy upward on Russian and Chinese spacecraft, using telescopes outfitted with new techology to correct for the atmosphere's distorting effect. This time, the new "adaptive optics" technology was kept secret for a few years, until in the early 1990s civilian astronomers began reinventing it. At that point, the military declassified the vast majority of the adaptive optics technology in one fell swoop, to prevent the astronomy community from wasting time (and vast amounts of federal research money) reinventing the wheel. In all of these areas—gamma ray bursts, infrared sky mapping, digital detectors, and adaptive optics—astronomers have since taken the lead, and are now pushing the state of the art well beyond what the defense community achieved. But in all of those cases, the contribution of the military clearly advanced the state of science years beyond what it would otherwise have been.

So while I like The X-Files as much as any good geek, still think Men in Black remains a towering landmark in cinema, and am cautiously optimistic about Torchwood, I'd caution my seatmate on that train not to take Roswell quite so seriously. Not only is it highly improbable that the government has any alien secrets to keep, and exceptionally implausible they could successfully keep such news under wraps for long, the historical record suggests they wouldn't even try. The truth is out there, and most of the time it's in plain sight.