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Home » Mysteries Of Science
* In the last few centuries, scientific knowledge has been accumulating at such a rate that there were times when some scientists wondered if they might be facing a future where there was nothing new to discover. Of course their worries turned out to be unfounded, since the Universe is a big place and there's always going to be something new to learn about it. As it turns out, even though the four corners of the Earth have been thoroughly explored, there still remains some interesting mysteries on our own planet. This document provides a short survey of several of these modern mysteries of science. -------------------------------------------------------------------------------- --------------------------------------------------------------------------------
The phenomenon is clearly caused by an acoustic resonance of the sands shifting in the dunes, but the details remain unknown. Squeaking sands make high-pitched, harmonically pure sounds that last for a fraction of a second; booming dunes generate low-pitched, harmonically cluttered sounds that last for anywhere from a few seconds to many minutes. Unlike squeaking sands, large booming dunes can be deafeningly loud. Some can be heard 10 kilometers (6 miles) away. The first studies of booming dunes were performed late in the last century. The first comprehensive paper on the subject was published by British researcher R.A. Bagnold in 1966. Squeaking sands tend to be much quieter because the displacement that causes the sound is only caused by footsteps and the like. In a booming dune, the displacement is due to the avalanche that occurs when the dune grows too tall (with an angle of repose of more than about 35 degrees) and then collapses. In a big dune, this amounts to a lot of acoustic energy. But why don't all sand dunes create such sounds? One clue is that in many booming dunes, the sand grains are unusually uniform in size and unusually smooth, though this is not universally the case. It is generally true that booming dunes are unusually dry. Intermittent rainfall washes fine dust out of the sand matrix, allowing it to move more readily, and then long dry spells remove all the water, which dunes can retain with surprising efficiency. In such dunes, an avalanche collapse begins with the shearing movement of large "plates" of sand that eventually terminates with turbulent breakup. This action involves an up and down movement of masses of sand that apparently causes the loud booming sounds. Research on the subject has focused with varying degrees of success on reproducing the sound under experimental conditions. A complete explanation of the phenomenon remains for the moment out of reach. BACK_TO_TOP
The home of these mysterious stones is known, logically, as the "Racetrack Playa", a dry lakebed occasionally dampened by flash storms. The Racetrack measures 4.5 kilometers by 2.1 kilometers (2.8 by 1.3 miles), and is only about 5 centimeters (2 inches) higher at one end than the other. The trails left by the stones vary from a few meters to almost a kilometer in length. Some of the trails are straight, some zigzagged, some go in circles. In some cases the trails vary in width, meaning the stones must have rotated as they moved. 162 of the Racetrack's moving stones have been documented, and many of them have names, always female. They range from fist-sized to the size of an ice chest. In 1948, two US Geological Survey geologists suggested that the little desert whirlwinds known as "dust devils" might be responsible for moving the stones around. Then George Stanley, a geologist of Fresno State College in California, suggested the stones might become frozen in ice sheets during the winter and slide around with the sheets on an underlying slick of water. Between 1968 and 1975, two geologists, Robert Sharp of the California Institute of Technology and Dwight Carey of the University of California at Los Angeles, made careful measurements of the positions of 30 rocks in an attempt to answer the mystery of the drifting rocks once and for all. They tried to pound stakes around some of the rocks, on the principle that if the motion were caused by floating ice, the stakes would hold the ice in place. The mystery only seemed to deepen. In one case, a rock drifted out of the stakes while another remained where it was, and in other cases rocks moved near other rocks that remained stationary. Sharp and Reid never really managed to link the movement of a rock to any event and finally gave up. By this time, the US National Park Service was trying to protect the Racetrack, which was suffering from increasing numbers of intruders who were not always considerate of the special nature of the place. Rangers dug a trench to keep four-wheel drive vehicles out of the Racetrack and kept the place tidied up. Researchers still puzzle over the drifting rocks. John B. Reid JR of Hampshire College in Amherst, Massachusetts, is a partisan of the icefloe theory. Paula Messina, assistant professor of geology at San Jose State University in California, thinks they move in the wind over a slick of mud when the Racetrack is wet. Reid bases his conviction on studied performed by him and his students in the late 1980s and early 1990s, when they measured the force required to move some of the Racetrack's bigger rocks and determined that wind speeds of hundreds of kilometers per hour would be required to budge them. Sharp suggests that the measurements, taken in dry conditions, did not accurately reflect what would happen when the Racetrack was wet. Reid also observed that some separated rocks move in parallel, which would not be very likely if they were moved around by the wind. In response, Messina performed observations of many rocks using enhanced GPS location, and found that in general they moved in any direction they pleased, and parallel movements were the small exception rather than the rule. Research is somewhat limited by the fact that the Racetrack is now a protected Wilderness area. It is a unique place, with unique visitors. Sometimes park rangers find citizens dancing naked on the dried mud, apparently obtaining inspiration from the place's cosmic energies. Drug runners also occasionally use it as a landing strip, though ranger vigilance has largely eliminated this practice. Despite the obstacles, research continues. Possibly someday we may understand the mystery of the drifting rocks, though such a discovery is unlikely to win anyone the Nobel Prize. BACK_TO_TOP
Many researchers puzzling with the iceball mystery suggest they may have a simple explanation. Maybe they fell from aircraft passing overhead, or maybe they're simply a hoax, like crop circles, that publicity has spread around the world. Martinez-Frias claims that there were no aircraft overhead at the time of the better-recorded impacts, and that their structure and composition is not that of a simple block of ice that somebody could have created in a freezer. The water in the iceballs, which are formally known as "megacryometeors", matches the isotopic and chemical composition of rainwater, which incidentally rules out the idea that they fell from space, and they are full of air bubbles and have some degree of layering. In simpler terms, they seem to be huge hailstones. Martinez-Frias has constructed a theory that could account for them. Atmospheric observations of the region around Tocina during the time of the falls show that the ozone level was depressed, and that the lower levels of the atmosphere were very humid. Low ozone levels cause the lower atmosphere to cool, and Martinez-Frias and other suspect an ice particle, possibly created from the tenuous remains of a faded jet contrail, began to fall from high altitude, building up mass in the humid lower atmosphere until impact. He believes that global warming may be contributing to the conditions that create them. Some researchers are very skeptical about his theory, suspecting that the iceballs fell off aircraft whose passage was not recorded; and everybody remembers how crop circles were revealed to be hoax just about the time that some researchers were beginning to take them seriously. Martinez-Frias has been moving ahead cautiously, using the Internet to link up with and share data with iceball researchers in other countries. Given the rarity of such events, it may take a long time to prove that iceballs actually fall out of the clear blue sky -- or even longer to find conclusive proof that they don't. BACK_TO_TOP
There have plenty of sightings on the ground as well, going back at least two centuries. In recent times, a British housewife, for an example, saw a ball of violet light floating over her stove during a thunderstorm. Rattling faintly, the ball floated over to her, touched her, and disappeared with a boom, burning a hole in her dress but otherwise leaving her unharmed. In general, ball lighting will occur during thunderstorms. The ball will be about the size of a grapefruit, normally colored red to yellow, will meander around, unaffected by gravity or wind, and then vanish with a pop or boom after a few seconds, causing no serious damage. Witnesses in close contact with ball lightning report feeling no heat, but it will melt holes in glass. There are tales of them floating down the aisles of airliners. Nobody has any idea what ball lightning really is. It's clearly associated with electrical storms, but suggestions as to what it might be have ranged from a clump of antimatter to a ball of luminescent air. One of the more plausible theories is that it is just glowing plasma (ionized gas) generated by a lighting strike. This doesn't in itself explain why the ball would retain its form, or seem cool. In addition, the hot plasma would be expected to rise, not hug the ground. Further speculation along this line, however, shows that while the plasma would contain ions that quickly recombine to generate heat and light, it would also contain three relatively stable ions: positively charged hydrogen and negatively charged nitrites (NO2) and nitrates (NO3). As these ions diffuse out of the hot core into cooler air, they attract water molecules, which are electrically polarized due to their asymmetric organization, that condense to form water droplets. The condensation of the water, and the reaction of the nitrites with hydrogen to form nitrous acid, releases heat to keep the interior of the ball hot. At the same time, nitrites on the very exterior of the ball have accumulated so much water that it requires an input of energy to convert them into nitrous acid, making the skin cool. The nitrates keep accumulating water and make the skin watery, as well as make it heavy and keep it close to the ground. Nitrogen and oxygen migrating into the ball to sustain the reactions keep the ball spherical. The hydrogen ions provide a strong net positive charge that causes the ball to wander erratically, until it either loses enough energy to fade out or it is physically disrupted, resulting in an explosive reaction. Whatever the theories, in the absence of good observations they remain speculative. Researchers encourage would-be ball-lightning hunters to be keen-eyed and, if at all possible, see if they can get a good picture of it. Nobody has so far. BACK_TO_TOP
Such fireworks had been glimpsed from below the clouds for over a century, but it wasn't until 1989 that such "sprites", as they were named, were recorded on videotape while a University of Michigan researcher named Robert Franz was testing a low-light-intensity camera. In 1994, a research team from the University of Alaska at Fairbanks, searching for sprites by flying around thunderstorms over the midwestern US, managed to obtained the first high-quality color shots of them. The pictures showed that sprites were colorful (usually red); shaped like a carrot, turnip, or jellyfish; enormous (reaching up to 98 kilometers / 58 miles above the cloudtops and about 16 kilometers / 10 miles in diameter); and often had delicate structures, being made up of filaments with diameters of 100 meters (330 feet) or less. Sprites seemed to appear in groups above the cloud just as a lightning bolt, usually a really big one, struck the Earth below from the bottom of the cloud. Observations showed that when sprites occurred, they did so a few minutes apart, with each sprite lasting from a few milliseconds to a few hundred milliseconds. Researchers investigating the sprites soon found they weren't the only inhabitants of the domain above the clouds. High-altitude aircraft flights by the US National Aeronautics & Space Administration (NASA) to observe sprites also discovered "blue jets", cones of blue light that shot up from the tops of clouds at 300 times the speed of sound to altitudes of up to 40 kilometers (25 miles), below the altitudes of sprites. Later studies by a Japanese group and a Stanford group revealed yet another stratospheric electrical phenomenon -- halos of red light at altitudes of about 90 kilometers (56 miles) that seemed to propagate faster than the speed of light, which they named "elves". When the researchers began to publicize and discuss their findings, they were then a little embarrassed to find out that sprites, blue jets, and elves had been known outside their field for some time. Commercial airliner pilots, and no doubt military pilots, had been seeing them for decades and were perfectly familiar with them. * In the meantime, observations from space added to the mystery. In 1994, a satellite named "Alexis", which had been launched in 1993 to test technologies for monitoring nuclear blasts, detected microsecond radio pulses that were 10,000 times more intense than the radio noise generally produced by such storms. Adding to the mystery, in 1994 the orbiting Compton Gamma Ray Observatory picked up gamma-ray flashes from the upper atmosphere that also seemed to be synchronized to the storms, an observation one researcher called "jaw-dropping" as the energies of an electrical storm were nowhere near adequate to generate gamma rays. A number of plausible suggestions have been advanced to explain these creatures. Sprites appear to result from the electrostatic field that results above a thundercloud when it fires off a big lightning bolt. The field ionizes the atmosphere above the cloud and causes it to glow red, a color emitted by excited nitrogen atoms, a source confirmed by spectral analysis of the light from the sprites. They clearly involve electrical flows and basically have to be regarded as a form of low-energy, low-ionization lightning. They are sometimes referred to as "high altitude lightning". Blue jets may occur when a cosmic ray -- a fast-moving particle falling into the upper atmosphere from space -- creates a cascade of electrons that are accelerated by an atmospheric electrostatic field to generate the distinctive blue light. In other words, the blue jets may be an atmospheric electrical discharge triggered by a cosmic ray. Sprites may also have some relationship to cosmic rays, and in fact one blue jet was observed to trigger a sprite, creating an electrical cascade from the clouds to the top of the atmosphere. The cosmic rays are undoubtedly the source of the emissions picked up by the Compton observations. Elves appear to be a trickier challenge. The Stanford group managed to image ten of them with a ground-based photodetector array known as the "Fly's Eye", normally used for detecting the showers of particles generated by cosmic rays. The observations showed that elves also were synchronized to the emission of a bolt of lighting below the cloud, expanding into rings up to 300 kilometers (185 miles) in about a millisecond. The initial belief that they seemed to be propagating faster than light proved false, further studies showing that they were propagating at or near the speed of light. Researchers have constructed models of the elves that specify them as the result of an electromagnetic pulse generated by the lightning bolt. If the pulse is strong enough, it energizes ions at the border of the stratosphere and ionosphere and causes them to glow as the leading edge of the pulse emission expands in a spherical fashion. In other words, the elves are a product of atmospheric heating and are only indirectly caused by an electrical discharge. Studies continue on these newly-discovered phenomena. Microsatellites have been proposed to study sprites, along with lighting and other atmospheric discharge phenomena. Observations were made of sprites and elves by the crew of NASA space shuttle Columbia during a flight in the last half of January 2003 as part of an Israeli-designed experiment. Unfortunately, Columbia broke up on reentry and most of the data was lost along with the shuttle and its crew, though some imagery had been relayed to Earth while the spacecraft was still in orbit. It is unclear if these "demons above the clouds" are actually significant atmospheric processes, but they certainly have proven very interesting. BACK_TO_TOP
One of the little semi-mysteries of science that at least gets an honorable mention here are the "Wheels of Poseidon", a phenomenon that occurs in the Indian Ocean. Sailors on ships passing through some regions at night will suddenly see a wave of luminescence in the sea passing across them, followed by another and another, as if the ship was passing over a wheel with spokes made of light. There's no absolute mystery here. The tropical oceans are full of bioluminescent zooplankton that will emit light if disturbed. Sailors say that watching the bow of a ship passing over the ocean at night is one of the most beautiful sights they have ever seen. Clearly some disturbance of the sea, probably a seafloor earthquake, is creating the wheel-like pattern of light, though the exact details of how it happens remains unclear. * Sources include:
"Booming Sand" by Franco Nori, Paul Sholtz, & Michael Bretz, SCIENTIFIC AMERICAN, September 1997, 84:89. "Atmospheric Scientists Puzzle Over High-Altitude Flashes" by Richard A. Kerr, AAAS SCIENCE, 27 May 1994, 1250:1251. "Sprites & Elves" by W. Wayt Gibbs, from the SCIENTIFIC AMERICAN website, February 1997. "The Dancing Rocks" by Robert Evans, SMITHSONIAN, July 1999. "Global Warming Blamed For Ice Meteors", Reuters News Service, 27 September 2002. "On Sprites & Their Exotic Kin" by Torsten Neubert, AAAS
SCIENCE, 2 May 2003, 747:749. v1.0.0 / 01 jul 03 / gvg |
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