The disappearance of electrons in Earth's atmosphere that has puzzled scientists for the past 50 years may finally be understood after researchers at the Massachusetts Institute of Technology (MIT) discovered evidence of what could very well be the cause of this phenomenon.
During a presentation at the American Geophysical Union's (AGU) annual meeting last month, MIT atmospheric electrician Earle Williams and his colleagues explained how particles of meteor dust found high above Earth may be absorbing the electrons in the planet's atmosphere. This, in turn, creates what they describe as a "D-region ledge," where the concentration of electrons rapidly drops.
Williams said that physicists have long been baffled by the missing electrons, and had considered every possible explanation for the phenomenon they could come up with, from clouds of ice flying high above Earth to electrically charged clusters of water.
In their study, Williams described the location of the D-region ledge as "the most dramatic gradient" part of the ionosphere. He said it is highly conspicuous and it needs to be better understood.
Electrons in the atmosphere are produced when ultraviolet (UV) rays from the sun come into contact with atoms of nitric oxide. However, scientists have noticed that since the 1960s, there has been a significant drop in the concentration of electrons found in the atmosphere during nighttime.
This sudden decrease in electrons was discovered when rockets where sent into the upper atmosphere to measure its electron density, temperature and pressure. Researchers believe this "electron ledge" typically occurs within the D-layer of the ionosphere, which can be found between 37 miles and 56 miles above the surface of Earth.
The D-region ledge is often used as part of modern communication. While the portion of the ionosphere located above the ledge is known to conduct electricity, the electron-depleted area below the ledge does not allow the passage of electromagnetic waves.
Electron-depleted air found below the ledge serves as an insulator, which allows radio waves and electromagnetic waves between the ground and the atmosphere to circle the world.
Scientists have yet to determine why the D-region ledge is in the atmosphere, but they believe it is most visible at night and that it can be observed equally above the poles of Earth, the equator and even in other parts of the planet.
Cracking The Case Of The Missing Electrons
According to Williams and fellow researcher, Joanne Wu, of the National Cheng Kung University (NCKU) in Taiwan, they have considered various prevailing hypotheses that could help them understand the nature of the D-region ledge, but they were not able to find one they could use.
One of these hypotheses suggests that ice clouds could be the ones absorbing the electrons in the atmosphere. However, ice clouds are known to form mostly in high altitudes whereas the D-region ledge can be found equally prominent in different parts of Earth.
The researchers then came across an earlier study featured in the Journal of the Atmospheric Sciences that described another part of the atmosphere known as the sodium layer, which is formed from the fine dust particles of meteoroids.
The findings of the study point to how space rocks traveling through the upper atmosphere become heated when they interact with molecules of oxygen and nitrogen. These rocks then collide with other atoms as they continue to penetrate the atmosphere, causing them to become hot enough to reach boiling point. It is at this point in which atoms of sodium are detached from the meteoroid.
Williams and his colleagues considered these findings in their search for a possible explanation for the D-region ledge.
The team's new theory involves having minerals in meteoroids, such as silicon and iron, boil off in order to form a cloud of dust and smoke. The atoms of these minerals would then collide with the atoms of nitrogen and oxygen in Earth's atmosphere, causing free electrons from the atoms of silicon and iron to be knocked off. These electrons would then form glimmers of faint light too small to be visible to the naked eye.
The dust from the meteor would combine with the free electrons that came about after the UV rays from the sun interacted with Earth's atmosphere. It is believed that the D-region ledge is more prominent at night because the sun's UV radiation is 100 times more powerful during the day, causing the free electrons produced at daytime to minimize the effect of the ledge.
Williams said that if their theory is correct, these actions could form a thick layer of dust, which could then descend gradually to Earth as a result of gravity. The dust particles that end up on the planet's surface are so small that they are barely detectable.
The researchers' theory has it that the D-region ledge occurs 53 miles above Earth because the distance corresponds to the part of the atmosphere where meteoroids often burn up upon entry.
Ionospheric physicist Morris Cohen of the Georgia Institute of Technology, who is not involved in the current study, said the theory posited by Williams and his colleagues is plausible as there are numerous circumstantial evidence to support it.
Cohen, however, argued that it will be difficult to test the theory directly because the part of the atmosphere described in the MIT study is not easily accessible.
"It's too high to reach with balloons, and it's too low to hit with satellites," Cohen said.
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