Earth's atmosphere consists of several layers: troposphere (upper boundary 20 km), stratosphere (boundary 50 km), mesosphere (boundary 85 km), thermosphere (boundary 690 km) and exosphere (boundary 10,000 km). For a long time, the so-called Karman line, located at an altitude of 100 kilometers, has been accepted as a conditional boundary between the Earth’s atmosphere and space. However, in the course of a new study, the results of which were published in the Journal of Geophysical Research: Space Physics, it was found that the atmosphere of our planet is much more complicated than it might seem at first glance. Scientists have found that its borders go far beyond the limits of the moon.
Space encompassing including the moon andbeing the outer part of the Earth’s highest atmosphere, the exosphere, the researchers call the geocorona. It is a cloud of hydrogen atoms, which begins to glow under the influence of ultraviolet radiation. Since this cloud is very thin, measuring its real boundaries has proven to be a daunting task. Thus, according to the results of previous studies, the upper limit of this space was determined by a distance of about 200,000 kilometers from the Earth, a point beyond which the pressure of the solar wind already blocks the force of the Earth’s gravity.
An international research team led byIgor Balyukin from the Space Research Institute of the Russian Academy of Sciences using data collected by the SOHO (Solar and Heliospheric Observatory) spacecraft, a joint project of the European Space Agency and the US Aerospace Agency NASA, found out that the previously established geocorona even didn’t closely correspond to the real state of affairs. The researchers found that the length of the geo-corona is actually at least 630,000 kilometers. In other words, this means that the boundaries of our atmosphere are far beyond the limits of the Moon, which, in turn, is only 384,000 kilometers away from our planet.
“The moon is inside the earth’s atmosphere. This was not known until the data collected by the SOHO space observatory were analyzed, ”says the lead author of the study, Igor Balyukin from the Space Research Institute of the Russian Academy of Sciences.
The blue color marks the boundary of the geocorona of the Earth (not to scale)
Even more interesting this discovery makes onethe fact that it was made on the basis of observational data taken from 1996 to 1998, that is, more than 20 years ago. All this time they were in the archive, waiting for analysis.
The data was obtained using a verySWAN sensitive instrument of a spacecraft designed to measure the far-ultraviolet radiation of hydrogen atoms, which are called Lyman-alpha photons. It is impossible to see them from the Earth - they are absorbed by the inner layers of the atmosphere, therefore, observations must be carried out directly in space. For example, the astronauts of the Apollo 16 mission were able to photograph the geocorona in 1972.
"At the time, being on the lunar surfaceastronauts did not even suspect that they were actually inside the geocorona, ”says co-author of a new study and former employee of the solar wind research program within the SOHO mission, Jean-Loup Berto of Versailles-Saint-Quentin-en-Yvelines (France).
A photograph of the Earth's geocorona, taken from the moon by the astronauts of the Apollo 16 mission
The advantage of the SWAN tool isthat he is capable of selectively measuring the radiation of the geocorona by filtering the Lyman-alpha radiation coming from deep space. This is what allowed scientists to create a more accurate map of this part of the earth's atmosphere.
New research not only helped to understandthe true size of the geocorona, but also showed that the pressure of sunlight increases the density of hydrogen atoms on the day side of the Earth and creates an area of increased density on the night side. Nevertheless, even on the day side, this density is rather low - at an altitude of about 60,000 kilometers above the surface of the planet, it is about 70 hydrogen atoms per cubic centimeter. On the night side, it is even lower and continues to drop down to 0.2 atoms per cubic centimeter as it approaches near-moon orbit.
“We usually call it a vacuum. Therefore, the presence of such a source of additional radiating ultraviolet hydrogen in this case can in no way facilitate the exploration of outer space, ”comments Balyukin.
The good news is, explain the authors of the study, that these particles will not create any additional threat to astronauts in the framework of future manned missions to the Moon.
"UV is also present in the geocoronradiation, because hydrogen atoms emit light in all directions, but its impact on astronauts in the lunar orbit will be insignificant compared to the main source of radiation, the Sun, ”explains Jean-Loup Berto.
The bad news is that geocorona may interfere with future astronomical observations that will be carried out near the moon.
"When using space telescopes,working ultraviolet wavelengths to study the chemical composition of stars and galaxies, will have to take into account the factor of the presence of Earth's geocorns, ”adds Berto.
The last can be noted one interesting fact. If these studies are correct, then from a technical point of view, even in the conditions of space launches, man never left the Earth’s atmosphere.
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