The Earth's atmosphere extends beyond the moon

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Diagram of the system of the moon of the earth. The Earth is surrounded by a cloud of gas that extends beyond the moon.

The outermost part of the Earth's atmosphere, called geocorona, extends outward almost twice as far as the orbit of the moon. Artist concept via ESA.

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On February 20, 2019, the European Space Agency (ESA) said that 20-year-old data from the SOHO space observatory had revealed an astonishing fact about the Earth. The data has shown that the outermost part of the Earth's atmosphere – called its geocorone – extends beyond the orbit of the moon.

This gaseous geocorone – a cloud of hydrogen atoms, faintly bright in the far ultraviolet through scattered sunlight – was known to exist. But nobody knew that he had reached so far into space. It extends almost twice as far as the orbit of the moon, nearly 630 000 km (50 000 km), or 50 times the diameter of the Earth.

Igor Baliukin from the Russian Space Research Institute led this research. He commented in a statement:

The moon crosses the earth's atmosphere.

SOHO stands for Solar and Heliospheric Observatory. The mission was launched in 1995 as a joint project of ESA and NASA, with an expected life of two years. Now, 24 years later, the craft is still in space and is still studying the sun and the sun-land environment. It revolves around the L-1 point of the Earth-Sun system.

SWAN, one of SOHO's instruments, provided data on the Earth's geocorone. The SWAN sensors plotted hydrogen in the geocorona and accurately detected where it was reduced to nothing.

A dark earth, surrounded by a ring of partial and luminous gas.

Apollo 16 astronauts on the moon acquired this ultraviolet image of Earth and its hydrogen envelope, or geocorone, in 1972. Image via ESA.

The evocative image above is a very interesting and historical image of the Earth's geocorone. It comes from the first telescope on the moon, placed by the Apollo 16 astronauts in 1972. The picture shows the geocorone that surrounds the Earth and shines brightly with ultraviolet light. Jean-Loup Bertaux is the former principal investigator of SWAN and co-author of the new journal. He commented:

At that time, astronauts on the lunar surface did not know that they were actually on the periphery of the geocorone.

By the way, we skywatchers sometimes see a similar crown on the moon or the sun. But it is a totally different phenomenon, with the glow provoked by the air of the Earth, and not by a prolonged lunar or solar atmosphere.

Learn more about this new ESA study

Orange sun with bright spots on it and a flare, and a spaceship with "wings" of solar panels.

Artist concept of ESA / NASA solar and heliospheric observatory (SOHO), superimposed on a real-life image of the sun as seen by SOHO's ultra-ultraviolet imaging telescope in 1999. Image via ESA.

In conclusion: scientists used the SWAN instrument data on the SOHO probe to learn that the outermost part of the earth's atmosphere – called geocorone – stretched almost twice as far as the orbit of the moon .

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