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It all began back in 1981. On the third day of August a Delta rocket lifted off from Vandenberg Air Force Base carrying a pair of NASA satellites, both known as Dynamics Explorer, into elliptical orbits. One of these satellites circles the poles of Earth at an altitude ranging from 350 miles to 14,500 miles. I was responsible for three of the instruments aboard the satellite, one of which is an ultraviolet camera, built and operated by my colleague John Craven.

This satellite was designed to examine Earth for certain light emissions that are invisible to the naked eye. I and other scientists hoped that these emissions would provide further insight into the nature of the auroral lights that occur in Earth’s polar atmosphere and detect any effects associated with them. I was particularly interested in getting the first global pictures of Earth’s aurora and I was not disappointed.

The pictures sent back from the ultraviolet camera on the satellite were spectacular. The remarkable auroral crowns encircle the poles of Earth, while the planet’s dayside looks like a bright ball illuminated by a flashlight. This bright feature is known as the dayglow. Dayglow is produced by the interaction of sunlight with the atomic oxygen present in Earth’s upper atmosphere. The ultraviolet light emitted by this dayglow is not visible to the naked eye but is within the range of the satellite’s specially-designed camera. The emissions it captures are transformed into a normal photograph.

But the images of Earth we obtained beginning in late 1981 contained an unexpected feature. The blanket of dayglow was not uniform. It was speckled with dark spots. The black spots on the images were like flies walking across a television set. They were annoying. They were there from the start, on the very first images. Strictly speaking, these spots were areas of greatly reduced brightness. In other words, there seemed to be holes in the dayglow. There is no question about who saw them first. Everybody saw them. We would give talks and the black spots were there on the images for everyone to see. And everyone assumed they were noise–those random fluctuations in data that are due to chance.

Life went on. During the summer of 1982, an undergraduate student named John Sigwarth began working for me. Sigwarth had come to the University of Iowa in 1979 and had taken his first physics class with me. He was very interested in space science and was very bright. I wanted him to take enlargements of the satellite images and scan them for signs of gravity waves, small scale ripples in the upper atmosphere that sometimes follow the brightening of auroras. These waves sweep across the face of Earth much like waves in the ocean. They have been detected on radar and I wanted to know whether these waves would show up as crests and valleys of light in the satellite images. I assigned to Sigwarth the task of processing the data to make the waves visible.

But he could not do it. He worked on the computer program, which was designed to extract subtle features from the original pictures and highlight them, but each time the computer stuttered and burped as it scanned those black holes in the atmosphere. The black spots kept getting in the way. Then one day in the fall of 1982 Sigwarth, quite exasperated, walked into my office on the second floor of Van Allen Hall and said: “How can we get rid of this stuff?”

Sigwarth, Craven, and I pondered the question and concluded there must be some disturbance in the camera’s electronics that would occasionally put these annoying little black spots in the image. Perhaps a transistor was fluky, or a computer was not functioning properly, or a problem arose as the pictures were being transmitted down to us from the satellite. It was possible. Each picture involves the transfer of an enormous amount of information. Like the image produced by a fax machine or by the display on a home computer, each of the satellite pictures is constructed of a large number of little dots called pixels. Each of these pixels is described by eight “bits,” actually a string of “0’s” and “1’s” that indicate the intensity or brightness of that pixel. So perhaps some of the image pixels were not being transmitted down properly from the spacecraft. Whatever the source of the noise, I did not relish spending my time tracking it down. Sigwarth got the job.

It was tempting to simply remove the spots from the images and get on with the search for gravity waves. But you cannot alter data on a mere assumption. You have to have a reason. We needed to show that the spots were either detector noise, or produced by electronics on the spacecraft, or generated by computers on the ground. Only once that was accomplished could we eliminate the spots from the processed images and get on with our work.

Sigwarth worked very hard trying to solve the mystery. From time to time he would come into my office and say he was not having much luck with it.The year 1982 drew to a close. Sigwarth kept working on it. But he was unable to trace how the holes appeared on the images. One possibility that we entertained was that one of the two light counters on the camera was failing. Every other pixel in the satellite images is produced by an entirely separate set of electronics. The counters, in other words, take turns producing the dots that comprise each image.So Sigwarth had separated the data produced by each counter. But when he examined the data he saw that both counters were observing spots in the same sequence and at the same rate. This told us the counters were not dropping bits, those meaningful strings of “0’s” and “l’s.” We knew that it was nearly impossible for two counters to malfunction in exactly the same way.

We also eliminated the possibility that these annoying little blackspots were caused by errors in radio transmission from the spacecraft. We checked the entire system from the time the data left the instrument, passed through the satellite itself, traveled down to the ground, and was relayed to us. Because the instrument regularly transmits fixed words, or fixed bit patterns, we could check to see if any transmission errors were occurring. We calculated that dark spots due to telemetry noise would appear once in every 200 images. But these spots appeared in the images almost a thousand times more often than expected.

All of the tests we performed on the data produced results that ran counter to our expectations. We really wanted to show that the holes were noise.But we were out of luck. So Sigwarth began to look at the pictures in great detail,trying to see if a spot that appeared in one frame could be seen in any of the subsequent frames. A very careful analysis showed that the spots could be followed in this way,although the spots in the subsequent exposures were not as dark as those in the initial exposures. This seemed to indicate that the black spots were moving and changing.

Sigwarth then programmed the camera so that instead of scanning the entire Earth, it would scan just a small portion of it. This allowed the camera to return to the same area more quickly. The series of pictures produced showed that a black spot would appear and disappear in a sequence of frames. The black spots seemed to be objects in motion. This was not characteristic of noise. Noise should appear at random all over the image. This indicated the presence of a real object.Sigwarth came down to the lab where I was working and showed me the data. He was very excited. I looked down at the pictures and congratulated him. I thought we were on to something.

Other clues convinced us that the spots were genuine. The spots,or holes in the atmosphere, appeared to move in the same direction across the face of Earth. If these holes were random events, due to malfunctioning equipment,for instance, you would expect to find half the spots going in one direction, and half going in the other direction. But this was not the case. Most of the holes appeared to move in the same direction across the face of Earth.

By February of 1983 we had come to the conclusion that something,some kind of object, was absorbing the ultraviolet radiation between the camera on the satellite and Earth and producing the apparent holes in the atmosphere. The more we looked the more it seemed that our images were actually snapshots of the movement of these objects above the atmosphere. We began to suspect that these objects were meteors of some unusual sort.

So we decided to compare the motion of our elusive black holes to the passage of meteoric dust and debris in our atmosphere. Much of this meteoric dust tends to orbit the Sun more rapidly than Earth. It essentially catches up to Earth, in other words, and approaches the atmosphere from the local evening face of the planet. Such motion relative to Earth is called prograde motion.Whatever the black spots represented, they showed the prograde motion that is characteristic of meteoric material. This not only implied that the spots were real but that the objects they represented were extraterrestrial. So we assumed, given the large number of spots that showed up in our images, that the holes were caused by a particularly large influx of meteors such as you would have with a meteor shower.

We went public with these results for the first time in May of 1983. Two weeks after receiving his undergraduate degree in physics, Sigwarth presented our findings in a paper entitled “Atmospheric Holes Possibly Associated with Meteors” at the spring meeting of the American Geophysical Union in Baltimore.I sponsored the paper and John Craven was listed as a co-author. People seemed interested and curious, nothing more. But over the next two-and-a-half years we presented three more papers on the topic at meetings of the American Geophysical Union and each time the audience grew.

Over this period of time Sigwarth and I analyzed over 10,000 images and learned a good deal about the black spots in the process. Our interpretation of the events continued to involve meteor impacts into Earth’s upper atmosphere.By counting the spots in our images we were able to estimate the rate at which these objects appeared. This was the simplest measurement to do. We saw ten holes per minute on the daylight side of Earth. So we doubled that figure to obtain the rate of these objects over the entire face of Earth. There had to be about twenty such objects entering the atmosphere every minute. That was an alarming number of objects.

We still needed to explain just how these objects, which we assumed to be meteors, could cause holes in the atmosphere’s screen of atomic oxygen. We entertained three possibilities. The first and simplest explanation had the meteors laying a blanket of material over the atmosphere, preventing the light from getting through, and creating a black spot in our images. Another possibility was that the atomic oxygen up there was being depleted by some special chemical process. But we could think of no chemical reaction that could get rid of the atomic oxygen quickly enough and none that allowed the atmosphere to restore itself as rapidly as we observed in our images. A third possibility involved a catalytic reaction of the sort that takes place in the catalytic converter in your car. Could some small amount of material,some catalyst, be converting the atomic oxygen in the atmosphere into molecular oxygen and producing the dark spots in our images? It was not likely, as we were never able to identify any such catalytic agent.

The knowledge that the spots actually moved across the face of Earth strongly pointed to the existence of some kind of an object that prevented light from passing through it. Whatever it was had to be big and blackening out the ultraviolet light at a certain wavelength. It could not be an atom. It could not be a rock. It could not be anything thrown up there from down here. It had to bea common molecule in the solar system that absorbs at the right wavelength. The only common molecule is water and water just happens to absorb at the wavelengths we were observing with our camera. There was no reason to look for anything exotic. Water,in the form of water vapor, fit the bill perfectly.

This explanation posed certain difficulties, all of which were more psychological than physical. When we calculated how much water we would need up there to produce a spot in our images, we came up with a figure of about a hundred tons. Anyone would tend to back off from such a large figure and initially we did too. Then we figured out how many such objects we needed to account for the holes in the images we observed over the course of the year. And it was not one, not a hundred, but ten million. There was the problem. One per year would not have been a problem. But ten million per year? Unfortunately, there was not much leeway in our numbers.

The size of the holes presented another problem. They were easy enough to measure. We knew the size of the area each pixel covered in our pictures and we knew the altitude of the spacecraft. But what looked like little dark spots on the images turned out, in reality, to be about thirty miles across. They could not be rocks because such large rocks would just smash the surface of Earth to pieces. These were clouds of water vapor.

Excerpted from ‘The Big Splash’ by Louis Frank and Patrick Huyghe