* 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.
* One of the interesting small mysteries of science is that of the "booming dunes" -- sand dunes that make a startling variety of loud sounds, compared by witnesses to foghorns, thunder, low-flying propeller aircraft, pipe organs, and so on. While sand structures that make singing or squeaking sounds are fairly common, booming dunes are rare. Only about 30 such dunes have been identified around the world, and they are almost always isolated dunes deep in the desert or on "back beaches", remote from the shores.
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, and 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 usually if not always uniform in size and unusually smooth. It is generally true that booming dunes are very dry, and the booming of such dunes is reduced when they are relatively damp. Intermittent rainfall washes fine dust out of the sand matrix, allowing it to move more easily, 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
* Another one of the devious little mysteries of science are the strange stones of Death Valley in California. These stones sit on sun-baked, flat, cracked earth, and they have trails they have left as they have moved, for some baffling reason, across the wasteland. 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 Carey never really managed to link the movement of a rock to any event, and finally gave up. By that 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 and kept the place tidied up.
The puzzle was finally resolved in 2014, by a paper written by Richard Norris, an oceanographer at the Scripps Institution of Oceanography in La Jolla, California, and his cousin James Norris, an engineer at Interwoof in Santa Barbara, California. They placed 15 limestone rocks with GPS tracking units in the playa, and were able to catch them in motion. It turns out that when water freezes around the rocks, once it thaws and breaks up, the ice can pile up against the rocks, and shove them around. There may be other factors involved, but at least a validated mechanism had been found. It must have been fun to investigate, though the Norrises are unlikely to win the Nobel Prize for their work.BACK_TO_TOP
* It was a sunny, cloudless day in Spain in January 2000, when a football-sized lump of ice fell out of the sky and smashed through the windshield of a parked car in the village of Tocina. Jesus Martinez-Frias, a planetary geologist with the Center for Astrobiology in Madrid, went to Tocina to investigate the incident, as well as several other such iceball impacts in the region at that time. The phenomenon is not unique to that region; iceballs have fallen in other parts of the world, reportedly ranging in size up to 200 kilograms (440 pounds).
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. They are also 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 caused 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 the iceballs.
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
* One of the enduring small mysteries in science is that of ball lightning, glowing balls of light that exhibit bizarre behavior. They were known during World War II as "foo fighters" by bomber crew who observed them "in escort" off their wingtips. 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, sometimes with a pop or boom, after a few seconds, causing no serious damage. Witnesses in close contact with ball lightning report no sensation of heat, but it will melt holes in glass. There are tales of ball lightning 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. A video and an optical spectrum were obtained in 2014, but more data is required.BACK_TO_TOP
* Late in the 20th century, atmospheric scientists discovered an interesting mystery of science. Above the black hammerhead clouds of thunderstorms, hidden from view of the ground, aerial observers found strange geysers of light that shot up from the tops of the clouds into the dark skies above.
In 1989 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 -- sometimes collectively referred as "transient luminous events" -- 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 fact, there were reports of such phenomena going back to 1895.
* 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" since the energies of an electrical storm were nowhere near adequate to generate gamma rays. However, further research does seem to show that gamma rays may be spontaneously emitted from the Earth's upper atmosphere through what seems to be some sort of natural "particle accelerator" associated with atmospheric electrical activity.
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".
Some researchers believe that 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.
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 expands in a spherical fashion. In other words, the elves are a product of atmospheric heating, indirectly caused by an electrical discharge.
Studies continue on these phenomena, now collectively known by the bland designation of "transient luminous events (TLEs)". Microsatellites have been proposed to study TLEs. 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.
An instrument to observe TLEs was finally flown on the Taiwanese ROCSAT 2 spacecraft, launched on 20 May 2004. The instrument, named the "Imager of Sprites & Upper Atmosphere Lightning (ISUAL)", started obtaining images, spectra, and time histories of these events in the early summer of 2004. ISUAL was built by a collaboration of Taiwanese, Japanese, and University of California at Berkeley (UCB) researchers. It included an imaging camera that could take a burst of six images in six milliseconds to observe the evolution of the events; a six-band spectrophotometer to obtain spectral profiles; and an array photometer to observe the brightness distribution.
ISUAL was expected to obtain data on the events -- as well as auroral discharges -- for five years. It was followed by another smallsat, the "Sprite-Sat", built by Tohoku University in Japan and launched as a secondary payload on a Japanese H-2A booster on 22 January 2009.
The Danish Space Research Institute is now working on an instrument named the "Atmosphere-Space Interactions Monitor (ASIM)", an array of optical, X-ray, and gamma-ray sensors to observe TLEs; it will be flown to the International Space Station and mounted on the European Columbus station module for observations in 2016. The French CNES space agency is now working on a new smallsat named "Taranis" to study TLEs, with launch currently scheduled for 2017.BACK_TO_TOP
* I got interested in such freaks of nature back in the 1960s, which turned out to be an interesting study from several aspects -- not only exposing me to some fascinating science, but also teaching me to be wary of cranks, con games, and hoaxes, a caution which has grown over my lifetime.
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 glow 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.
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