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Did you know that the Earth's atmosphere extends beyond the Moon's orbit?



Strictly speaking, there are no strict boundaries between earth and space. Our atmosphere does not end only at a certain height. it is gradually sinking. A new study by the Russian Space Research Institute (SRI) shows that our atmosphere covers 630,000 kilometers in space.

The lead author of this study is Igor Baliukin. Researchers at the SRI in Russia, Department of planets, physics and small bodies of the solar system. Jean-Loup Bertaux of LATMOS at the Université de Versailles-Saint-Quentin-en-Yvelines, France, was also involved in the study. The study used SOHO (Solar and Heliospheric Observatory) archival data to determine the gaseous expansion of the Earth's atmosphere.

This study is about what is called Geocorona. It's a huge cloud of hydrogen atoms that's where the Earth's atmosphere merges with space. SOHO has 1

2 scientific instruments on board, and one of them is called SWAN (Solar Wind Anisotropies.). SWAN was able to detect the hydrogen signal from the Geocorona and recognize its outer boundaries more accurately than ever before.

  This image was taken by Apollo astronauts with a camera on the moon. It shows the Geocorona of Earth glowing with ultraviolet light. Picture credits: NASA.
This image was taken by Apollo astronauts with a camera on the moon. It shows the Geocorona of Earth glowing with ultraviolet light. Picture credits: NASA.

Apollo-16 astronauts actually took pictures of the Geocorona in 1972 with the first camera on the lunar surface. At that time they did not know yet that they are still in the earth's atmosphere.

" The moon flies through the Earth's atmosphere ."

Igor Baliukin, Russia's space research center.

This study also deals with what is known as Lyman Alpha Light. It is a specific wavelength of ultraviolet that interacts with hydrogen atoms. The atoms can both absorb and emit this light. The problem is that this light is absorbed in the earth's atmosphere. The circumference of the corona can only be seen from outer space. SWAN / SOHO observations can only be made at certain times of the year, even if the Earth and its Geocorona wheel are within sight of the Observatory.

The construction of SWAN makes it possible to measure the hydrogen atoms in Geocorona and filter out the hydrogen atoms in space.

  A SWAN / SOHO observation of Geocorona. The moon path is shown in dotted black. (Rayleigh is a unit of photon flux used to measure very low light.)
ESA / NASA / SOHO / SWAN; I. Baliukin et al. (2019)
A SWAN / SOHO observation of the Geocorona. The moon path is shown in dotted black. (Rayleigh is a unit of the photon flux used to measure very low light.) Photo credits:
ESA / NASA / SOHO / SWAN; I. Baliukin et al. (2019)

The researchers behind the new study found that sunlight compresses hydrogen at the geothermal probe and creates an increased density on the night side. However, this density is only relative; The dense region by day has only 60 atoms per cubic centimeter at 60,000 km above the earth. At the distance of the moon there are only about 0.2 atoms per cm³.

  A diagram showing the Earth, Moon, Geocorona, and SOHO L1 orbit. Photo credits: ESA
A diagram showing the Earth, the Moon, the Geocorona and the L1 orbit of SOHO. Picture credits: ESA.

" The moon flies through the Earth's atmosphere ," said Baliukin, the main author of the newspaper, who presented the findings. " We did not realize that until we wiped out the observations of the SOHO spacecraft more than two decades ago ."

Even if the Geocorona extends far enough to cover the moon, that means it would not support the exploration of space in any way. Although hydrogen is an extension of the atmosphere, the density of hydrogen atoms is still low enough to be a vacuum. However, this does not make this finding meaningless, not in the long run.

On Earth, we would call it vacuum, so this additional source of hydrogen is not significant enough to facilitate space exploration . [Igor] says

But it is significant when it comes to exoplanets – with planets with hydrogen in their exospheres, water vapor is often seen closer to the surface, which is the case for Earth, Mars and Venus, which can be helpful if you want to know which exoplanets could have water.

" This is particularly interesting in finding planets with potential water reservoirs outside our solar system ," explains Jean-Loup Bertaux, co-author and former investigator of SWAN.

This has been expanded. The atmosphere and the ultraviolet light contained therein pose no danger to astronauts on missions in this region of space. There is also ultraviolet radiation associated with geocorona, as the hydrogen atoms scatter the sunlight in all directions, but the effects on astronauts in lunar orbit are in comparison to the main radiation q uelle – the sun – to neglect Jean-Loup Bertaux.

It is possible, however, that the Geocorona disturbs astronomical observations made near the Moon. This is something every moon telescope would have to consider. " Space telescopes observing the sky in ultraviolet wavelengths to study the chemical composition of stars and galaxies would have to take this into account." adds Jean-Loup.

SOHO was launched in 1995 to study the sun for over 20 years. It is still up there to circle L1, though it was designed for a two-year mission. Throughout its lifetime, it has a number of "first" under the belts.

SOHO's SWAN instrument observed Earth's geocorona three times between 1996 and 1998. The team decided to retrieve and further analyze this data from the SOHO archives. This discovery lets us ask what other discoveries are hidden in their archives.

" Data archived many years ago can often be used for new science ," says Bernhard Fleck, project scientist at ESA SOHO. " This discovery highlights the value of data collected over 20 years ago and the extraordinary power of SOHO ."

The new study is published in the Journal of Geophysical Research: Space Physics .

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